Table of Contents

[2]About This Document
   1. [3]How can I help?
   2. [4]Introduction
        2.1. [5]Clients and Servers
        2.2. [6]Differences between Linux distributions
        2.3. [7]PPP configuration tools
   3. [8]IP Numbers
   4. [9]Aims of this Document
        4.1. [10]Setting up a PPP Client
        4.2. [11]Linking two LANs or a LAN to the Internet using PPP
        4.3. [12]Using intuitive configuration tools to set up PPP
        4.4. [13]Setting up a PPP server
        4.5. [14]Using PPP over a direct null modem connection
        4.6. [15]This document at present does NOT cover...
   5. [16]Software versions covered
   6. [17]Other Useful/Important Documents
        6.1. [18]Useful Linux Mailing Lists
   7. [19]Easy Configuration Utilities for PPP
        7.1. [20]KPPP - The KDE PPP Dialer
        7.2. [21]WvDial - A command-line pppd driver
        7.3. [22]rp3 - RedHat PPP dialer
        7.4. [23]Linuxconf - Universal (almost) Linux PPP dialer
   8. [24]Debugging
        8.1. [25]I have compiled PPP support into the kernel, but...
        8.2. [26]My modem connects but ppp never starts up
        8.3. [27]The syslog says "serial line is not 8 bit clean"
        8.4. [28]Default route not set
        8.5. [29]Other Problems
   9. [30]Overview of what has to be done to get PPP working as a client
        9.1. [31]Obtaining/Installing the software
        9.2. [32]Compiling PPP support into the kernel
        9.3. [33]Obtaining information from your ISP
        9.4. [34]Configuring your modem and serial port
        9.5. [35]Setting up Name to Address Resolution (DNS)
        9.6. [36]PPP and root Privileges
        9.7. [37]Checking your distribution PPP Files and setting up the
                PPP Options
        9.8. [38]If your PPP server uses PAP (Password Authentication
        9.9. [39]Connecting to the PPP server by hand
        9.10. [40]Automating your PPP Connection
        9.11. [41]Shutting down the link
        9.12. [42]If you have problems
        9.13. [43]After the link comes up
        9.14. [44]Problems with standard IP services on a Dynamic IP
                number PPP link
        9.15. [45]Maintaining a permanent connection to the net with
   10. [46]Configuring your Linux Kernel
        10.1. [47]Installing the Linux Kernel source
        10.2. [48]Knowing your hardware
        10.3. [49]Kernel compilation - the Linux 1.2.13 kernel
        10.4. [50]Kernel compilation - the Linux 1.3.x, 2.0.x, and 2.2.x
        10.5. [51]Note on PPP-2.x and /proc/net/dev
        10.6. [52]General kernel config considerations for PPP
   11. [53]Getting the Information you need about the PPP server
   12. [54]Configuring your modem and serial port
        12.1. [55]A note about serial ports and speed capabilities
        12.2. [56]Serial Port Names
        12.3. [57]Configuring your modem
        12.4. [58]Note on Serial Flow Control
        12.5. [59]Testing your modem for dial out
   13. [60]Setting up Name to Address Resolution (DNS)
        13.1. [61]The /etc/resolv.conf file
        13.2. [62]The /etc/host.conf file
   14. [63]Using PPP and root privileges
   15. [64]Setting up the PPP connection files
        15.1. [65]The supplied options.tpl file
        15.2. [66]What options should I use? (No PAP/CHAP)
        15.3. [67]Other options to consider adding
   16. [68]If your PPP server uses PAP (Password Authentication Protocol)
        16.1. [69]Using MSCHAP
        16.2. [70]The PAP/CHAP secrets file
        16.3. [71]The PAP secrets file
        16.4. [72]The CHAP secrets file
        16.5. [73]Handling multiple PAP-authenticated connections
   17. [74]Setting up the PPP connection manually
   18. [75]Automating your connections - Creating the connection scripts
        18.1. [76]Connection scripts for User name/Password
        18.2. [77]The ppp-on script
        18.3. [78]Editing the supplied PPP startup scripts
        18.4. [79]What a Chat script means...
        18.5. [80]A chat script for PAP/CHAP authenticated connections
        18.6. [81]The pppd debug and file option_file options
   19. [82]Testing your connection script
   20. [83]Shutting down the PPP link
   21. [84]Getting Help when totally stuck
   22. [85]Common Problems once the link is working
        22.1. [86]I can't see beyond the PPP server I connect to
        22.2. [87]I can send email, but not receive it
        22.3. [88]Why can't people finger, WWW, gopher, talk, etc. to my
   23. [89]Using Internet services with Dynamic IP numbers
        23.1. [90]Setting up email
        23.2. [91]Setting Up a local Name server
   24. [92]Linking two networks using PPP
        24.1. [93]Setting up the IP numbers
        24.2. [94]Setting up the routing
        24.3. [95]Network security
   25. [96]After the link comes up - the /etc/ppp/ip-up script
        25.1. [97]Special routing
        25.2. [98]Handling email queues
        25.3. [99]A sample /etc/ppp/ip-up script
        25.4. [100]Handling email
   26. [101]Using /etc/ppp/ip-down
   27. [102]Routing issues on a LAN
        27.1. [103]Note on Security
   28. [104]Setting up a PPP server
        28.1. [105]Kernel compilation
        28.2. [106]Overview of the server system
        28.3. [107]Getting the software together
        28.4. [108]Setting up standard (shell access) dialup.
        28.5. [109]Setting up the PPP options files
        28.6. [110]Setting pppd up to allow users to (successfully) run
        28.7. [111]Setting up the global alias for pppd
   29. [112]Using PPP across a null modem (direct serial) connection
   30. [113]PPPoE or PPP over Ethernet
About This Document

   This document was updated via assistance from the [114]Open Source
   Documentation Fund. This is a [115]LinuxPorts.Com Document for the
   [116]Linux Documentation Project
   This document shows how to connect your Linux PC to a PPP server, how
   to use PPP to link two LANs together and provides one method of
   setting up your Linux computer as a PPP server.The document also
   provides help in debugging non-functional PPP connections.
   This document is distributed under the terms of the GPL (GNU Public
Chapter 1. How can I help?

   We will try to provide comprehensive coverage for all Linux PPP
   implementations. However time is of the essence and this document is
   not a revenue maker. We provide this information in hopes that it will
   be useful to the Linux Community and newly converted Linux users. We
   are always interested in feedback and will implement every relevant
   topic possible to this HOWTO.
   If you would like to assist with this document, there are two primary
   avenues that are extremely helpful.
     * [117]Purchase an OpenBook! If you purchase OpenDocs books,
       OpenDocs Publishing will donate a portion of the proceeds back to
       the [118]Open Source Documentation Fund. This fund assists authors
       financially while they continue to write documentation for Open
       Source projects.
     * Provide a monetary contribution to the document. By doing so you
       can even request what you would like to have updated, written, or
       expanded with in the document. If it is a major revision (such as
       writing sections specifically for Mandrake or Caldera) please
       contact [119]Command Prompt, Inc.
     * If you have written something that you would like to contribute
       just email it to [120]
Chapter 2. Introduction

   PPP (the Point to Point Protocol) is a mechanism for creating and
   running IP (the Internet Protocol) and other network protocols over a
   serial link - be that a direct serial connection (using a null-modem
   cable), over a telnet established link, or a link made using modems
   and telephone lines (and of course using digital lines such as ISDN).
   Using PPP, you can connect your Linux PC to a PPP server and access
   the resources of the network to which the server is connected (almost)
   as if you were directly connected to that network.
   You can also set up your Linux PC as a PPP server, so that other
   computers can dial into your computer and access the resources on your
   local PC and/or network.
   As PPP is a peer-to-peer system, you can also use PPP on two Linux PCs
   to link together two networks (or a local network to the Internet),
   creating a Wide Area Network (WAN).
   One major difference between serial based PPP and an Ethernet
   connection is of course speed - a standard Ethernet connection
   operates at 10 Mbs (Mega - million bits per second) or 100 Mbs maximum
   theoretical throughput, whereas an analogue modem operates at speeds
   up to 56 kbps (kilo - thousand bits per second).
   Also, depending on the type of PPP connection, there may be some
   limitations in usage of some applications and services.
2.1. Clients and Servers

   PPP is strictly a peer to peer protocol; there is (technically) no
   difference between the machine that dials in and the machine that is
   dialed into. However, for clarity's sake, it is useful to think in
   terms of servers and clients.
   When you dial into a site to establish a PPP connection, you are a
   client. The machine to which you connect is the server.
   When you are setting up a Linux box to receive and handle dial-in PPP
   connections, you are setting up a PPP server.
   Any Linux PC can be both a PPP server and client - even simultaneously
   if you have more than one serial port (and modem if necessary). As
   stated above, there is no real difference between clients and servers
   as far as PPP is concerned, once the connection is made.
   This document refers to the machine that initiates the call (that
   dials in) as the CLIENT, whilst the machine that answers the
   telephone, checks the authentication of the dial in request (using
   user names, passwords and possibly other mechanisms) is referred to as
   the SERVER.
   The use of PPP as a client to link one or more machines at a location
   into the Internet is, probably, the one in which most people are
   interested - that is using their Linux PC as a client.
   The procedure described in this document will allow you to establish
   and automate your Internet connection.
   This document will also give you guidance in setting up your Linux PC
   as a PPP server and in linking two LANs together (with full routing)
   using PPP (this is frequently characterized as establishing a WAN -
   wide area network - link).
2.2. Differences between Linux distributions

   There are many different Linux distributions and they all have their
   own idiosyncrasies and ways of doing things.
   In particular, there are two different ways a Linux (and Unix)
   computer actually starts up, configures its interfaces, and so forth.
   These are BSD system initialization and System V system
   initialization. If you dip into some of the Unix news groups, you will
   find occasional religious wars between proponents of these two
   systems. If that sort of thing amuses you, have fun burning bandwidth
   and join in!
   Possibly the most widely used distributions are
     * Slackware which uses BSD style system initialization
     * Red Hat (and its former associate Caldera) which use SysV system
       initialization (although in a slightly modified form)
     * Debian which uses SysV system initialization
   BSD style initialization typically keeps its initialization files in
   /etc/... and these files are:-
                (and possibly other files)

   Of recent times, some BSD system initialization schemes use a
   /etc/rc.d... directory to hold the start up file rather than putting
   everything into /etc.
   System V initialization keeps its initialization files in directories
   under /etc/... or /etc/rc.d/... and a number of subdirectories under
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 init.d
-rwxr-xr-x   1 root     root         1776 Feb  9 05:01 rc
-rwxr-xr-x   1 root     root          820 Jan  2  1996 rc.local
-rwxr-xr-x   1 root     root         2567 Jul  5 20:30 rc.sysinit
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc0.d
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc1.d
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc2.d
drwxr-xr-x   2 root     root         1024 Jul 18 18:07 rc3.d
drwxr-xr-x   2 root     root         1024 May 27  1995 rc4.d
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc5.d
drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc6.d

   If you are trying to track down where your Ethernet interface and
   associated network routes are actually configured, you will need to
   track through these files to actually find where the commands are that
   do this.
2.3. PPP configuration tools

   There are many good tools available for configuring and using PPP on
   Linux. This document will try to cover some of the more popular ones,
     * kppp A PPP setup and dialer tool for KDE.
     * WvDial Another PPP driver for Linux, with an emphasis on
     * RP3...(short for RedHat PPP). It is a simple configuration program
       with a "wizard" interface- it asks a series of questions.
     * Linuxconf A generalized tool for configuring and managing your
       Linux machine, it has a section that helps configure PPP.
Chapter 3. IP Numbers

   Every device that connects to the Internet must have its own, unique
   IP number. These are assigned centrally by a designated authority for
   each country.
   If you are connecting a local area network (LAN) to the Internet, YOU
   MUST use an IP number from your own assigned network range for all the
   computers and devices you have on your LAN. You MUST NOT pick IP
   numbers out of the air and use these whilst connecting to another LAN
   (let alone the Internet). At worst this will simply not work at all
   and could cause total havoc as your 'stolen' IP number starts
   interfering with the communications of another computer that is
   already using the IP number you have picked out of the air.
   Please note that the IP numbers used throughout this document (with
   some exceptions) are from the 'unconnected network numbers' series
   that are reserved for use by networks that are not (ever) connected to
   the Internet.
   There are IP numbers that are specifically dedicated to LANs that do
   not connect to the Internet. The IP number sequences are:-
     * One A Class Network Address (netmask
     * 16 B Class Network Addresses - (netmask
     * 256 C Class Network Addresses - (netmask
   If you have a LAN for which you have not been allocated IP numbers by
   the responsible authority in your country, you should use one of the
   network numbers from the above sequences for your machines.
   These numbers should never be used on the Internet.
   However, they can be used for the local Ethernet on a machine that is
   connecting to the Internet. This is because IP numbers are actually
   allocated to a network interface, not to a computer. So whilst your
   Ethernet interface may use (for example), when you hook onto
   the Internet using PPP, your PPP interface will be given another (and
   valid) IP number by the server. Your PC will have Internet
   connectivity, but the other computers on your LAN will not.
   However, using Linux and the IP Masquerade (also known as NAT -
   Network address Translation) capabilities of the Linux and the ipfwadm
   software, you can connect your LAN to the Internet (with some
   restriction of services), even if you do not have valid IP numbers for
   the machines on your Ethernet.
   For more information on how to do this see the IP Masquerade
   mini-HOWTO at [121]Linux IP Masquerade mini HOWTO
   For most users, who are connecting a single machine to an Internet
   service provider via PPP, obtaining an IP number (or more accurately,
   a network number) will not be necessary.
   If you wish to connect a small LAN to the Internet, many Internet
   Service Providers (ISPs) can provide you with a dedicated subnet (a
   specific sequence of IP numbers) from their existing IP address space.
   Alternatively, use IP Masquerading.
   For users, who are connecting a single PC to the Internet via an ISP,
   most providers use dynamic IP number assignment. That is, as part of
   the connection process, the PPP service you contact will tell your
   machine what IP number to use for the PPP interface during the current
   session. This number will not be the same every time you connect to
   your ISP.
   With dynamic IP numbers, you are not necessarily given the same IP
   number each time you connect. This has implications for server type
   applications on your Linux machine such as sendmail, ftpd, httpd and
   so forth. These services are based on the premise that the computer
   offering the service is accessible at the same IP number all the time
   (or at least the same fully qualified domain name - FQDN - and that
   DNS resolution of the name to IP address is available).
   The limitations of service due to dynamic IP number assignment (and
   ways to work around these, where possible) are discussed later in the
Chapter 4. Aims of this Document

4.1. Setting up a PPP Client

   This document provides guidance to people who wish to use Linux and
   PPP to dial into a PPP server and set up an IP connection using PPP.
   It assumes that PPP has been compiled and installed on your Linux
   machine (but does briefly cover reconfiguring/recompiling your kernel
   to include PPP support).
   Whilst DIP (the standard way of creating a SLIP connection) can be
   used to set up a PPP connection, DIP scripts are generally quite
   complex. For this reason, this document does NOT cover using DIP to
   set up a PPP connection.
   Instead, this document describes the standard Linux PPP software
4.2. Linking two LANs or a LAN to the Internet using PPP

   This document provides (basic) information on linking two LANs or a
   LAN to the Internet using PPP.
4.3. Using intuitive configuration tools to set up PPP

   There are many tools used for configuring your PPP connection. This
   document will try to cover the most common and easiest to use of said
4.4. Setting up a PPP server

   This document provides guidance on how to configure your Linux PC as a
   PPP server (allowing other people to dial into your Linux PC and
   establish a PPP connection).
   You should note that there are a myriad of ways of setting up Linux as
   a PPP server. This document gives one method - that used by the author
   to set up several small PPP servers (each of 16 modems).
   This method is known to work well. However, it is not necessarily the
   best method.
4.5. Using PPP over a direct null modem connection

   This document provides a brief overview of using PPP to link two Linux
   PCs via a null modem cable. It is possible to link other OS's to Linux
   this way as well. To do so, you will need to consult the documentation
   for the operating system you are interested in.
4.6. This document at present does NOT cover...

     * Compiling the PPP daemon software See the documentation that comes
       with the version of pppd you are using.
     * Connecting and configuring a modem to Linux (in detail) See the
       Serial-HOWTO and for modem specific initialization, see [122]Modem
       Setup Information for information that may help you to configure
       your modem.
     * Using DIP to make PPP connections. Use chat instead...
     * Using socks or IP Masquerade. There are perfectly good documents
       already covering these two packages.
     * Using EQL to gang together two modems into a single PPP link. This
       is covered in the [123]Networking-HOWTO.
Chapter 5. Software versions covered

   This HOWTO assumes that you are using a Linux 1.2.x kernel with the
   PPP 2.1.2 software or 1.3.x/2.0.x/2.2.x kernel with the PPP 2.4.0
   This HOWTO will cover version 1.6.18 of KPPP.
   This HOWTO will cover version 1.41 of WvDial.
   This HOWTO will cover version 0.03 of PPPoE.
   This HOWTO will cover version 1.18 of Linuxconf.
   Please try to use the latest versions of software, as many bugs are
   fixed as time goes on.
Chapter 6. Other Useful/Important Documents

   Users are advised to read :-
     * The documentation that comes with the PPP package.
     * The pppd and chat man pages; (use man chat and man pppd to explore
     * The Linux Network Administration Guide (NAG); see [124]The Network
       Administrators' Guide.
     * The Net-2/3 HOWTO; see [125]Linux Networking-HOWTO.
     * Linux kernel documentation installed in
       /usr/src/linux/Documentation when you install the Linux source
     * The modem setup information page - see [126]Modem Setup
     * The excellent Unix/Linux books published by O'Reilly and
       Associates. See ([127]O'Reilly and Associates On-Line Catalogue).
       If you are new to Unix/Linux, run (don't walk) to your nearest
       computer book shop and invest in a number of these immediately!
     * The PPP-FAQ maintained by Al Longyear, available from [128]Linux
       PPP-FAQ. This contains a great deal of useful information in
       question/answer format that is very useful when working out why
       PPP is not working (properly).
     * The growing number of Linux books from various publishing houses
       and authors; You are actively encouraged to check the currency of
       these books. Linux development and distributions tend to evolve
       fairly rapidly, whilst the revision of books move (generally) much
       more slowly! Buying an excellent book (and there are many) that is
       now out of date will cause new users considerable confusion and
     * The documentation associated with the PPP tool(s) you are using
       The package specific documentation, usually easily available, is
       often the most useful when dealing with a specific tool.
   The best general starting point for Linux documentation is [129]The
   Linux Documentation Project Home Page. The HOWTO's tend to be revised
   reasonably regularly.
   Whilst you can use this document to create your PPP link without
   reading any of these documents, you will have a far better
   understanding of what is going on if you do so! You will also be able
   to address problems yourself (or at least ask more intelligent
   questions on the comp.os.linux... newsgroups or Linux mailing lists).
   These documents (as well as various others, including the relevant
   RFCs) provide additional and more detailed explanation than is
   possible in this HOWTO.
   If you are connecting a LAN to the Internet using PPP, you will need
   to know a reasonable amount about TCP/IP networking. In addition to
   the documents above, you will find the O'Reilly books "TCP/IP Network
   Administration" and "Building Internet Firewalls" of considerable
6.1. Useful Linux Mailing Lists

   There are many Linux mailing lists that operate as a means of
   communication between users of many levels of ability. By all means
   subscribe to those that interest you and contribute your expertise and
   A word to the wise: some lists are specifically aimed at "high
   powered" users and/or specific topics. Whilst no-one will complain if
   you 'lurk' (subscribe but don't post messages), you are likely to earn
   heated comments (if not outright flames) if you post 'newbie'
   questions to inappropriate lists.
   This is not because guru level users hate new users, but because these
   lists are there to handle the specific issues at particular levels of
   By all means join the lists that offer open subscription, but keep
   your comments relevant to the subject of the list!
   A good starting point for Linux mailing lists is [130]Linux Mailing
   List Directory
Chapter 7. Easy Configuration Utilities for PPP

7.1. KPPP - The KDE PPP Dialer
   KPPP is an easy tool for configuring your PPP links. It comes with the
   default installation of KDE, and is quite well integrated into that
   KPPP also has a good help system built in. If you just right click on
   the majority of the buttons in the application, a menu will pop up
   with an item called "Quickhelp". Clicking it will give a quick summary
   of whatever item you clicked on.
   The opening screen of kppp will list any available connections, and
   allow you to specify a Login ID and password for the connection. There
   is also a "Show Log Window" option. Selecting this will show a log
   window. This can be handy if you are trying to debug a connection.
   For now, click on the "Setup" button. This will bring up the setup
   window. It has a series of tabs across the top. Select the one called
   "Accounts". There will be a list of Accounts, if any.
   Select "New" from the right hand side. Another menu will pop up.
   First, specify a name for this connection in the "Connection Name"
   box. A good name would be the name of your ISP. Then enter the phone
   number. Select the type of authentication. If your ISP hasn't
   specified otherwise, leave it as "PAP". You can optionally store your
   password between sessions, but this may be a security risk.
   Click on the tab marked "IP". Here you have the option to configure
   your IP address, either a Dynamic or Static address. You should know
   what kind you want, specified by your ISP. You can also optionally
   specify that you wish to configure the hostname for this IP, which
   means that kppp will name your machine according to the name given to
   it by your ISP.
   Click on the tab marked "DNS". Here you can set up DNS. Fill in the
   appropriate fields with the information supplied from your ISP.
   Click on the "Gateway" tab. Here you can configure your gateway, or
   router address. If a gateway or router address was specified by your
   ISP, select "Static Gateway" and enter it in the box below. Otherwise
   leave this alone. The box marked "Assign the Default Route" should be
   The "Login Script" tag is only useful if you specified "Login Script"
   authentication under the "Dial" tab. If you need to use a Login
   Script, you can enter it here, as a series of commands. Select the
   type of command you wish to use, followed by the argument, then click
   "Add". Click "Remove" to remove a selected command.
   The "Accounting" tab allows you to track the number of bytes that you
   have sent and recieved for a given connection. This can be useful if
   your ISP tracks the amount of data that you use, and perhaps charges
   you based on that. If you wish to use accounting, click on the "Enable
   accounting" box. You can then select a country, if you live in a
   country that has taxes, tariffs, or other charges based on data
   transfer. Otherwise, just select either "Bytes in", "Bytes in and
   out", or "Bytes out". For more information, consult the KPPP manual.
   Click OK to finish the creation of this new account.
   Now we'll cover the other tabs in the kppp configuration window.
   The next one is "Device". It contains configuration information about
   your modem. You can select the device, flow control, line termination,
   and connection speed. It is recommended that you leave these alone
   unless otherwise specified by your ISP. You can also specify values
   for using a lock file for your modem device(recommended) and a modem
   timeout. Modem timeout refers to the amount of time that kppp will
   wait for your modem to respond.
   The "Modem" tab is mainly useful for debugging your modem. You can
   also adjust your modem volume. For more information on these commands,
   consult the kppp documentation.
   Next is the "PPP" tag. It contains many useful items for making kppp
   tailor fit to your needs. The "pppd Timeout" field specifies how long
   kppp should wait for pppd to bring up a connection. The "Dock" option
   states that kppp should recede into the KDE dock when it is connected.
   The "Automatic redial" specifies that kppp should redial if it is
   disconnected. The "show clock" option will display how time you have
   been connected. The "Disconnect on X-server shutdown" means that if
   you leave KDE, PPP should shut down. The "Quit on Disconnect" option
   will close kppp if you disconnect from your ISP. Finally, the
   "Minimize window on connect" option will minimize kppp when it
   The "Graph" tab is useful for kppp's throughput graphing. For more
   information on this feature, see kppp's documentation.
   Click Ok to leave this menu. Now ensure your connection is selected in
   the "Connect to:" box, and click "connect". You're all set!
7.2. WvDial - A command-line pppd driver

   The WvDial homepage is [131]here
   WvDial is a command-line pppd driver. It has two main components,
   wvdialconf and wvdial. Both must be run as root.
   First you must run wvdialconf. wvdialconf is generates a configuration
   file containing information on your modem and ISP information. Running
   wvdialconf will probe your comm ports, looking for a modem, and
   determine the capabilities of any modems it finds.
   wvdialconf is invoked with the name of your wvdial configuration file-
   which is always /etc/wvdial.conf. Here's what the output should look
[root@blah /root]# wvdialconf newconffile
Scanning your serial ports for a modem.

ttyS1<*1>: ATQ0 V1 E1 -- OK
ttyS1<*1>: ATQ0 V1 E1 Z -- OK
ttyS1<*1>: ATQ0 V1 E1 S0=0 -- OK
ttyS1<*1>: ATQ0 V1 E1 S0=0 &C1 -- OK
ttyS1<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 -- OK
ttyS1<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 S11=55 -- OK
ttyS1<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 S11=55 +FCLASS=0 -- OK
ttyS1<*1>: Modem Identifier: ATI -- 28800
ttyS1<*1>: Speed 2400: AT -- OK
ttyS1<*1>: Speed 4800: AT -- OK
ttyS1<*1>: Speed 9600: AT -- OK
ttyS1<*1>: Speed 19200: AT -- OK
ttyS1<*1>: Speed 38400: AT -- OK
ttyS1<*1>: Speed 57600: AT -- OK
ttyS1<*1>: Speed 115200: AT -- OK
ttyS1<*1>: Max speed is 115200; that should be safe.
ttyS1<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 S11=55 +FCLASS=0 -- OK
ttyS0<*1>: ATQ0 V1 E1 -- ATQ0 V1 E1 -- ATQ0 V1 E1 -- nothing.
Port Scan<*1>: S2   S3

Found a modem on /dev/ttyS1.

   If your output looks different, check that your modem is plugged in,
   turned on, and connected to a com port.
   Once you have run wvdialconf, you need to edit the /etc/wvdial.conf
   file to reflect the phone number to dial, and your username and
   password. Open up /etc/wvdial.conf in your favorite text editor. It
   should look something like this:
[Dialer Defaults]
Modem = /dev/ttyS1
Baud = 115200
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 S11=55 +FCLASS=0
; Phone = 555-1212
; Username = my_login_name
; Password = my_login_password

   Remove the ';' and fill in the appropriate fields- phone number, login
   name and password. Now you should be all set to run wvdial.
   Run wvdial. Assuming that you filled in your phone number, username,
   and password correctly, wvdial will now dial your ISP. wvdial will not
   exit until the connection is terminated- you can do a Ctrl-C to
   terminate it.
   wvdial is fairly new and untested software, so if you run into any
   problems along the way, you should contact the authors. You can find
   their contact info on the homepage listed above.
7.3. rp3 - RedHat PPP dialer

   A good page about rp3 is located [132]here.
   rp3 is available on any RedHat system running RedHat 6.2 or later. It
   is located on your GNOME menu under Internet- called "Dialup
   Configuration Tool". It is perhaps the simplest to use of the tools
   this HOWTO covers. When you start it up, it presents you with a screen
   that looks like this:
   Click "Next". If rp3 can't find a modem, it will try to confiugre one.
   Select your modem from the list and click next if this happens. You
   should see a screen asking for an "Account name" and a phone number.
   Enter your ISP's name and number in the appropriate fields. Click
   rp3 will then ask you for your username and password. Enter them in
   the appropriate fields and click "Next". Next rp3 will ask you if your
   ISP is named in a list. If it is, select it and click next. If not,
   select "Normal ISP" and click next.
   That's it! Click "Finish" to complete account creation.
   To initiate a connection, go to the GNOME menu again, and look under
   Internet for "RH PPP Dialer". Click on it. When asked for an
   interface, select "ppp0". This should bring up a small window. Right
   click on the window, then on "Connect to ppp0". Wait a few seconds,
   and you're online! To disconnect, right click on the window again, and
   then click "Disconnect". That's it.
7.4. Linuxconf - Universal (almost) Linux PPP dialer

   [133]Linuxconf homepage
   For help at any time while using Linuxconf, just hit the help key.
   Linuxconf has contextual help menus for most its functionality.
   Linuxconf's PPP section is fairly simple. First of all, open up
   Linuxconf. This must be done as root. Here's a shot of Linuxconf in
   Click on the box next to "Config", then the box on "Networking", then
   the box next to "Client tasks". You should see an entry called
   "PPP/SLIP/PLIP". Click on that. On the right hand side of Linuxconf,
   you should now see a box called "PPP/Slip/Plip configurations". There
   should be an area below that, listing existing PPP devices(if any) and
   three buttons below that.
   Click "Add" to add a new connection. It will then ask you to select a
   type of interface. Make sure "PPP" is selected, then press Accept.
   In this box, there are fields for phone number, modem, username and
   password. Enter the appropriate information into the appropriate
   fields, and you should be configured.
   To bring up the PPP link, open the "Control" tab on the left hand
   side, then go to "Control Panels", then "Control PPP/SLIP/PLIP Link".
   You should see a list of PPP devices. Click on the one you just made.
   A question will pop up, asking you if you wish to activate the
   connection. Click "Yes".
   There are also advanced configuration options, such as modem speed,
   connect scripts and etc. If you need to configure any of that, go back
   to the place where you originally configured the link, and click on
   the link you wish to customize. It should bring up a screen with four
   tabs: Hardware, Communication, Networking,and PAP.
   It is advisable to not change any of these options unless you are
   specifically told to do so by your ISP or modem vendor. Most of them
   will work just fine without any additional configuration.
   Linuxconf also has command line tools for use in bringing your PPP
   connection up and down:
     * netconf --connect pppsetup [--fore] This will bring the link up.
       The optional --fore means that it remains in the foreground.
       Otherwise it will terminate either if the connection is successful
       or if it fails. It will return 0 if successful, higher if
     * netconf --dialctl This will display all the available connections
       and their status.
     * netconf --disconnect pppsetup This will disconnect the link.
Chapter 8. Debugging

   There are any number of reasons that your connection does not work -
   chat has failed to complete correctly, you have a dirty line, etc. So
   check your syslog for indications.
8.1. I have compiled PPP support into the kernel, but...

   A very common problem is that people compile PPP support into the
   kernel and yet when they try to run pppd, the kernel complains that it
   does not support ppp! There are a variety of reasons this can occur.
8.1.1. Are you booting the right kernel?

   Whilst you have recompiled your kernel to support ppp, you are not
   booting the new kernel. This can happen if you do not update
   /etc/lilo.conf and rerun lilo.
   A good check on the kernel can be obtained by issuing the command
   uname -a, which should produce a line like:-
Linux archenland 2.0.28 #2 Thu Feb 13 12:31:37 EST 1997 i586

   This gives the kernel version and the date on which this kernel was
   compiled - which should give you a pretty good idea of what is going
8.1.2. Did you compile ppp kernel support as a module?

   If you compiled your kernel ppp support as a module, but did not make
   and install the modules, then you can get this error. Check the
   kernel-HOWTO and the README file in /usr/src/linux!
   Another module connected possibility is that you are expecting
   required modules to be automatically loaded, but are not running the
   kerneld daemon (which auto-loads and unloads modules on the fly).
   Check the kerneld mini-HOWTO for information on setting up kerneld.
8.1.3. Are you using the correct version of PPP for your kernel?

   You must use ppp-2.2 with kernel version 2.0.x. You can use ppp-2.2
   with kernel version 1.2.x (if you patch the kernel), otherwise you
   must use ppp-2.1.2.
8.1.4. Are you running pppd as root?

   If you are not running pppd as the root user (and pppd is not suid to
   root), you can receive this message.
8.2. My modem connects but ppp never starts up

   There are innumerable variations on this (take a look in
   A VERY common mistake is that you have mistyped something in your
   scripts. The only thing to do here is to make sure you are logging the
   chat conversation between you Linux PC and the server into your syslog
   (/var/log/messages) and then go through this line by line to make sure
   there are no mistakes.You may need to dial into the ppp server
   manually to check things out again.
   You need to check the log against the actual prompts very carefully -
   and bear in mind that we humans have a tendency to read what we THINK
   we have typed - not what is actually there!
8.3. The syslog says "serial line is not 8 bit clean"

   There are variations on this too - such as serial line looped back
   etc., and the cause can be one (or a sequence) of a number of things.
   To understand what is going on here, it is necessary to grasp a bit of
   what is going on behind the scenes in pppd itself.
   When pppd starts up, it sends LCP (link control protocol) packets to
   the remote machine. If it receives a valid response it then goes on to
   the next stage (using IPCP - IP control protocol packets) and only
   when this negotiation completes is the actual IP layer started so that
   you can use the PPP link.
   If there is no ppp server operating at the remote end when your PC
   sends lcp packets, these get reflected by the login process at the far
   end. As these packets use 8 bits, reflecting them strips the 8th bit
   (remember, ASCII is a 7 bit code). PPP sees this and complains
   There are several reasons this reflection can occur.
8.3.1. You are not correctly logging into the server

   When your chat script completes, pppd starts on your PC. However, if
   you have not completed the log in process to the server (including
   sending any command required to start PPP on the server), PPP will not
   So, the lcp packets are reflected and you receive this error.
   You need to carefully check and correct (if necessary) your chat
   script (see above).
8.3.2. You are not starting PPP on the server

   Some PPP servers require you to enter a command and/or a RETURN after
   completing the log in process before the remote end starts ppp.
   Check your chat script (see above).
   If you log in manually and find you need to send a RETURN after this
   to start PPP, simply add a blank expect/send pair to the end of your
   chat script (an empty send string actually sends a RETURN).
8.3.3. The remote PPP process is slow to start

   This one is a bit tricksy!
   By default, your Linux pppd is compiled to send a maximum of 10 lcp
   configuration requests. If the server is a bit slow to start up, all
   10 such requests can be sent before the remote PPP is ready to receive
   On your machine, pppd sees all 10 requests reflected back (with the
   8th bit stripped) and exits.
   There are two ways round this:-
   Add "lcp-max-configure 30" to your ppp options. This increases the
   maximum number of lcp configure packets pppd sends before giving up.
   For really slow server, you may need even more than this.
   Alternatively, you can get a bit tricksy in return. You may have
   noticed that when you logged in by hand to the PPP server and PPP
   started there, the first character of the ppp garbage that appears was
   always the tilde character (~).
   Using this knowledge we can add a new expect/send pair to the end of
   the chat script which expects a tilde and sends nothing. This would
   look like:-
\~      ''

   Note: as the tilde character has a special meaning in the shell, it
   must be escaped (and hence the leading backslash).
8.4. Default route not set

   If pppd refuses to set up a default route, it is because (quite
   correctly) it refuses to remove/replace an existing default route.
   The usual reason that this error occurs is that some distributions set
   up a default route via your Ethernet card as opposed to setting up a
   specific network route.
   See the Linux NAG and the Net2/3 HOWTOs for information on correctly
   setting up your Ethernet card and associated routes.
   An alternative to this is that your LAN uses a gateway/router already
   and your routing table has been set up to point the default route at
   Fixing up this last situation can require a fair bit of IP networking
   knowledge and is beyond the scope of this HOWTO. It is suggested you
   obtain some expert advice (via the news groups of from someone locally
   you can ask).
8.5. Other Problems

   There are many reasons apart from these that ppp fails to connect
   and/or operate properly.
   Look in the PPP FAQ (which is really a series of questions and
   answers). This is a very comprehensive document and the answers ARE
   there! From my own (sad) experience, if the answer to your problems is
   not there, the problem is NOT ppp's fault! In my case I was using an
   ELF kernel that I had not upgraded to the appropriate kernel modules.
   I only wasted about 2 days (and most of one night) cursing what had
   been a perfect PPP server before the light dawned!
Chapter 9. Overview of what has to be done to get PPP working as a client

   This document contains a great deal of information - and with each
   version it grows!
   As a consequence, this section aims to provide a concise overview of
   the actions you will need to take to get your Linux system connected
   as a client to a PPP server.
9.1. Obtaining/Installing the software

   If your Linux distribution does not include the PPP software, you will
   need to obtain this from [134]the Linux PPP daemon.
   Select the latest possible version(2.4.0 at the time of this writing.)
   The PPP package contains instructions on how to compile and install
   the software so this HOWTO does not!
9.2. Compiling PPP support into the kernel

   Linux PPP operations come in two parts
     * the PPP daemon mentioned above
     * kernel support for PPP
   Most distributions seem to provide PPP kernel support in their default
   installation kernels, but others do not.
   If at boot your kernel reports messages like
PPP Dynamic channel allocation code copyright 1995 Caldera, Inc.
PPP line discipline registered.

   your kernel does have PPP support compiled in.
   That said, you may want to compile your own kernel, whatever your
   distribution, to provide the most efficient use of system resources
   given your particular hardware configuration. It is worth remembering
   that the kernel cannot be swapped out of memory and so keeping the
   kernel as small as possible has advantages on a memory limited
   This document provides minimal kernel re-compilation instructions at
   section [135]Chapter 10.
   For greater detail, see the Kernel-HOWTO at [136]The Linux Kernel
9.3. Obtaining information from your ISP

   There are an almost infinite number of ways in which a PPP server can
   be set up. In order to connect to your ISP (or corporate PPP server to
   access your intranet), you will need to obtain information on how the
   PPP server operates.
   Because you are using Linux, you may have some difficulty with some
   ISP help desks (and work site based PPP intranet servers) which know
   only about MS Windows clients.
   However, a rapidly growing number of ISPs use Linux to provide their
   service - and Linux is also penetrating the corporate environment as
   well, so you may be lucky if you do strike problems.
   Section [137]Chapter 11 tells you what you need to know about the PPP
   server to which you are going to connect - and how to find out the
   information you need to know.
9.4. Configuring your modem and serial port

   In order to connect to a PPP server and to obtain the best possible
   data transfer rate, your modem needs to be configured correctly.
   Similarly, the serial ports on your modem and computer need to be set
   up correctly.
   Section [138]Chapter 12 provides information on this.
9.5. Setting up Name to Address Resolution (DNS)

   In addition to the files that run PPP and perform the automated log in
   to the PPP server, there are a number of text configuration files that
   have to be set up for your computer to be able to resolve names like to the IP address that is actually used to
   contact that computer. These are:-
     * /etc/resolv.conf
     * /etc/host.conf
   Section [139]Chapter 13 for details on setting this up.
   In particular, you do NOT need to run a name server on your Linux PC
   in order to connect to the Internet (although you may wish to). All
   you need is to know the IP number of at least one name server that you
   can use (preferably one at your ISPs site).
9.6. PPP and root Privileges

   As establishing a PPP link between you Linux computer and another PPP
   server requires manipulation of network devices (the PPP interface is
   a network interface) and the kernel routing table, pppd requires root
   For details on this, see section [140]Chapter 14.
9.7. Checking your distribution PPP Files and setting up the PPP Options

   There are a number of configuration and dialer files that need to be
   set up to get PPP operational. There are examples as part of the PPP
   distribution and this section shows what files you should have:-

   You may need to create some additional files depending on exactly what
   you are aiming to achieve with PPP:-

   In addition, the PPP daemon can use a large number of command line
   options and it is important to use the right ones; so this section
   takes you through the standard PPP options and helps you choose the
   options you should use.
   For details on this, see [141]Chapter 15.
9.8. If your PPP server uses PAP (Password Authentication Protocol)

   Many ISPs and corporate PPP servers use PAP. If your server does not
   require you to use PAP (if you can log in manually and receive the
   standard user name/password text based prompts it does not use PAP),
   you can safely ignore this section.
   Instead of logging into such a server using a user name and password
   when prompted to enter them by the server, a PPP server using PAP does
   not require a text based login.
   The user authentication information instead is exchanged as part of
   the link control protocol (LCP), which is the first part of
   establishing a PPP link.
   Section [142]Chapter 16 provides information on the files you need to
   set up to establish a PPP link using PAP.
9.9. Connecting to the PPP server by hand

   Having set up the basic files, it is a good idea to test these by
   connecting (using minicom or seyon) and starting pppd on your Linux PC
   by hand.
   See Section [143]Chapter 17 for full details of setting this up.
9.10. Automating your PPP Connection

   Once you are able to log in by hand, you can now move to setting up a
   set of scripts that will automate the establishment of the connection.
   Section [144]Chapter 18 covers setting up the necessary scripts, with
   considerable attention paid to chat and scripting the login process to
   the PPP server.
   This section discusses scripts for user name/password authentication
   as well as scripts for PAP/CHAP authenticating servers.
9.11. Shutting down the link

   Once your link is up and working, you need to be able to deactivate
   the link.
   This is covered in Section [145]Chapter 20.
9.12. If you have problems

   Many people have problems getting PPP to work straight away. The
   variation in PPP servers and how they require you to set up the
   connection is enormous. Similarly, there are many options to PPP - and
   some combinations of these just do not work together, ever.
   In addition to the problems of logging in and starting the PPP
   service, there are problems with the modems and the actual telephone
   lines as well!
   Section [146]Chapter 8 provides some basic information about common
   errors, how to isolate these and fix them.
   This is NOT intended to provide more than just the basics. Al Longyear
   maintains the PPP-FAQ which contains much more information on this
9.13. After the link comes up

   Once a PPP link is operational (specifically, once the IP layer is
   operational), Linux PPP can automatically run (as the root user), a
   script to perform any function you can write a script to accomplish.
   Section [147]Chapter 25 provides information on the /etc/ppp/ip-up
   script, the parameters it receives from PPP, and how to use it to do
   things like, acquire your email from your ISP account, send any queued
   email waiting transmission on your machine and such.
9.14. Problems with standard IP services on a Dynamic IP number PPP link

   As noted in the introduction, dynamic IP numbers affect the ability of
   your Linux PC to act as a server on the Internet.
   Section [148]Chapter 23 provides information on the (main) services
   affected and what you can do (if anything) to overcome this.
9.15. Maintaining a permanent connection to the net with pppd.

   If you are fortunate enough to have a semi permanent connection to the
   net and would like to have your machine automatically redial your PPP
   connection if it is lost then here is a simple trick to do so.
   Configure PPP such that it can be started by the root user by issuing
   the command:
# pppd

   Be sure that you have the `-detach' option configured in your
   /etc/ppp/options file. Then, insert the following line into your
   /etc/inittab file, down with the getty definitions:

   This will cause the init program to spawn and monitor the pppd program
   and automatically restart it if it dies.
Chapter 10. Configuring your Linux Kernel

   In order to use PPP, your Linux kernel must be compiled to include PPP
   support. Obtain the Linux source code for your kernel if you do not
   already have this - it belongs in /usr/src/linux on Linux's standard
   file system.
   Check out this directory - many Linux distributions install the source
   tree (the files and subdirectories) as part of their installation
   At bootup, your Linux kernel prints out a great deal of information.
   Amongst this is information about PPP support and if the kernel
   includes it. To view this information, look at your syslog file or use
dmesg | less

   to display the information to the screen. If your kernel includes PPP
   support, you will see lines like
PPP Dynamic channel allocation code copyright 1995 Caldera, Inc.
PPP line discipline registered.

   (this is for the Linux 2.x.x kernel series).
   Linux kernel sources can be obtained by ftp from or
   its mirror sites.
10.1. Installing the Linux Kernel source

   The following are brief instructions for obtaining and installing the
   Linux kernel sources. Full information can be obtained from [149]The
   Linux Kernel HOWTO.
   In order to install and compile the Linux kernel, you need to be
   logged in as root.
    1. Change directory to the /usr/src directory cd /usr/src.
    2. Check in /usr/src/linux to see if you already have the sources
    3. If you don't have the sources, get them from [150]Linux kernel
       source directory or your nearest mirror. Select the appropriate
       directory- v2.0 if you are running a 2.0.x kernel, or v2.2 if you
       are running a 2.2.x kernel. If you are looking for earlier
       versions of the kernel (such as 1.2.X), these are kept in [151]Old
       Linux kernel source directory.
    4. Choose the appropriate kernel - usually the most recent one
       available is what you are looking for. Retrieve this and put the
       source tar file in /usr/src. Note: a 'tar' file is an archive -
       possibly compressed (as are the Linux kernel source tar files)
       containing many files in a number of directories. It is the Linux
       equivalent of a DOS multi-directory zip file.
    5. If you already have the Linux sources installed but are upgrading
       to a new kernel, you must remove the old sources. Use the command
       rm -rf /usr/src/linux.
    6. Now uncompress and extract the sources using the command tar xzf
       linux-X.X.XX.tar.gz where "X.X.XX" is the version of the kernel
       you downloaded.
    7. Now, cd /usr/src/linux and read the README file. This contains an
       excellent explanation of how to go about configuring and compiling
       a new kernel. Read this file, (it's a good idea to print it out
       and have a copy handy whilst you are compiling until you have done
       this enough times to know your way around).
10.2. Knowing your hardware

   You MUST know what cards/devices you have inside your PC if you are
   going to recompile your kernel!!! For some devices (such as sound
   cards) you will also need to know various settings (such as IRQ's, I/O
   addresses and such).
10.3. Kernel compilation - the Linux 1.2.13 kernel

   To start the configuration process, follow the instructions in the
   README file to properly install the sources. You start the kernel
   configuration process with...
make config

   In order to use PPP, you must configure the kernel to include PPP
   support (PPP requires BOTH pppd AND kernel support for PPP).
  PPP (point-to-point) support (CONFIG_PPP) [n] y

   Answer the other make config questions according to the hardware in
   your PC and the features of the Linux operating system you want. Then
   continue to follow the README to compile and install your new kernel.
   The 1.2.13 kernel creates only 4 PPP devices. For multi- port serial
   cards, you will need to edit the kernel PPP sources to obtain more
   ports. (See the README.linux file that comes as part of the PPP-2.1.2
   distribution for full details of the simple edits you need to make).
   Note: the 1.2.13 configuration dialogue does NOT allow you to go
   backwards - so if you make a mistake in answering one of the questions
   in the make config dialogue, exit by typing CTRL C and start again.
10.4. Kernel compilation - the Linux 1.3.x, 2.0.x, and 2.2.x kernels

   For Linux 1.3.x, 2.0.x, and 2.2.x you can use a similar process as for
   Linux 1.2.13. Again, follow the instructions in the README file to
   properly install the sources. You start the kernel configuration
   process with...
make config

   However, you also have the choice of...
make menuconfig

   This provides a menu based configuration system with online help that
   allows you to move backwards and forwards in the configuration
   There is also a highly recommended X windows based configuration
make xconfig

   You can compile PPP support directly into your kernel or as a loadable
   If you only use PPP some of the time that your Linux machine is
   operating, then compiling PPP support as a loadable module is
   recommended. Using 'kerneld', your kernel will automatically load the
   module(s) required to provide PPP support when you start your PPP link
   process. This saves valuable memory space: no part of the kernel can
   be swapped out of memory, but loadable modules are automatically
   removed if they are not in use.
   To do this, you need to enable loadable module support:-
        Enable loadable module support (CONFIG_MODULES) [Y/n/?] y

   To add PPP kernel support, answer the following question:-
        PPP (point-to-point) support (CONFIG_PPP) [M/n/y/?]

   For a PPP loadable module, answer M, otherwise for PPP compiled in as
   part of the kernel, answer Y.
   Unlike kernel 1.2.13, kernel 2.0.x creates PPP devices on the fly as
   needed and it is not necessary to hack the sources to increase
   available PPP device numbers at all.
10.5. Note on PPP-2.x and /proc/net/dev

   If you are using PPP-2.x, you will find that a side effect of the 'on
   the fly' creation of the PPP devices is that no devices show up if you
   look in the /proc/net file system until a device is created by
   starting up pppd:-
[hartr@archenland hartr]$ cat /proc/net/dev
Inter-|   Receive                  |  Transmit
 face |packets errs drop fifo frame|packets errs drop fifo colls carrier
    lo:  92792    0    0    0    0    92792    0    0    0     0    0
  eth0: 621737   13   13    0   23   501621    0    0    0  1309    0

   Once you have one (or more) ppp services started, you will see entries
   such as this (from a ppp server):-
[root@kepler /root]# cat /proc/net/dev
Inter-|   Receive                  |  Transmit
 face |packets errs drop fifo frame|packets errs drop fifo colls carrier
    lo: 428021    0    0    0    0   428021    0    0    0     0    0
  eth0:4788257  648  648  319  650  1423836    0    0    0  4623    5
  ppp0:   2103    3    3    0    0     2017    0    0    0     0    0
  ppp1:  10008    0    0    0    0     8782    0    0    0     0    0
  ppp2:    305    0    0    0    0      297    0    0    0     0    0
  ppp3:   6720    7    7    0    0     7498    0    0    0     0    0
  ppp4: 118231  725  725    0    0   117791    0    0    0     0    0
  ppp5:  38915    5    5    0    0    28309    0    0    0     0    0
10.6. General kernel config considerations for PPP

   If you are setting up your Linux PC as a PPP server, you must compile
   in IP forwarding support. This is also necessary if you want to use
   Linux to link to LANs together or your LAN to the Internet.
   If you are linking a LAN to the Internet (or linking together two
   LANs), you should be concerned about security. Adding support for IP
   fire walls to the kernel is probably a MUST!
   You will also need this if you want to use IP masquerade to connect a
   LAN that uses any of the above mentioned 'unconnected' IP network
   To enable IP Masquerade and IP fire walling, you MUST answer yes to
   the first question in the make config process:-
Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL)?

   Whilst this may sound a bit off-putting to new users, many users are
   actively using the IP Masquerade and IP fire walling features of the
   Linux 2.0.x or 2.2.x kernels with no problems.
   Once you have installed and rebooted your new kernel, you can start
   configuring and testing your PPP link(s).
Chapter 11. Getting the Information you need about the PPP server

   Before you can establish a PPP connection with a server, you need to
   obtain the following information (from the sysadmin/user support
   people of the PPP server):-
     * The telephone number(s) to dial for the service If you are behind
       a PABX. You also need the PABX number that gives you an outside
       dial tone - this is frequently digit zero (0) or nine (9).
     * Does the server use DYNAMIC or STATIC IP numbers? If the server
       uses STATIC IP numbers, then you may need to know what IP number
       to use for your end of the PPP connection. If your ISP is
       providing you with a subnet of valid IP numbers, you will need to
       know the IP numbers you can use and the network mask (netmask).
       Most Internet Service Providers use DYNAMIC IP numbers. As
       mentioned above, this has some implications in terms of the
       services you can use. However, even if you are using STATIC IP
       numbers, most PPP servers will never (for security reasons) allow
       the client to specify an IP number as this is a security risk. You
       do still need to know this information!
     * What are the IP numbers of the ISPs Domain Name Servers? There
       should be at least two, although only one is needed. There could
       be a problem here. The MS Windows 95 PPP setup allows the DNS
       address to be passed to the client as part of its connection
       process. So your ISP (or corporate help desk) may well tell you
       you don't need the IP address of the DNS server(s). For Linux, you
       DO need the address of at least one DNS. The linux implementation
       of PPP does not allow the setting of the DNS IP number dynamically
       at connection time - and quite possibly will never do so. Note:
       whilst Linux (as a PPP client) cannot accept the DNS address from
       a server, it can, when acting as a server, pass this information
       to clients using the dns-addr pppd option.
     * Does the server require the use of PAP/CHAP? If this is the case
       you need to know the "id" and "secret" you are to use in
       connecting. (These are probably your user name and password at
       your ISP).
     * Does the server automatically start PPP, or do you need to issue
       any commands to start PPP on the server once you are logged in? If
       you must issue a command to start PPP, what is it?
     * Is the server a Microsoft Windows NT system and, if so, is it
       using the MS PAP/CHAP system? Many corporate LANs seem to use MS
       Windows NT this way for increased security.
   Carefully note down this information - you are going to use it!
Chapter 12. Configuring your modem and serial port

   You should make sure that your modem is correctly set up and that you
   know which serial port it is connected to.
     * DOS com1: = Linux /dev/cua0 (and /dev/ttyS0)
     * DOS com2: = Linux /dev/cua1 (and /dev/ttyS1) et cetera
   It is also worth remembering that if you have 4 serial ports, the
   standard PC set up is to have com1 and com3 share IRQ4 and com2 and
   com4 share IRQ3.
   If you have devices on standard serial ports that share an IRQ with
   your modem you are going to have problems. You need to make sure that
   your modem serial port is on its own, unique IRQ. Many modern serial
   cards (and better quality motherboard serial ports) allow you to move
   the IRQ of the serial ports around.
   If you are running Linux kernel 2, you can check the in-use IRQs using
   cat /proc/interrupts, which will produce output like
 0:    6766283   timer
 1:      91545   keyboard
 2:          0   cascade
 4:     156944 + serial
 7:     101764   WD8013
10:     134365 + BusLogic BT-958
13:          1   math error
15:    3671702 + serial

   This shows a serial port on IRQ4 (a mouse) and a serial port on IRQ15
   (the permanent modem based PPP link to the Internet. (There is also a
   serial port on com2, IRQ3 and com4 is on IRQ14, but as they are not in
   use, they do not show up).
   Be warned - you need to know what you are doing if you are going to
   play with your IRQs! Not only do you have to open up you computer,
   pull out cards and play with jumpers, but you need to know what is on
   which IRQ. In my case, this is a totally SCSI based PC, and so I can
   disable the "on motherboard" IDE interfaces that normally use IRQ14
   and 15!
   You should also remember that if your PC boots other operating
   systems, moving IRQs around may well mean that OS cannot boot properly
   - or at all!
   If you do move your serial ports to non-standard IRQs, then you need
   to tell Linux which IRQ each port is using. This is done using "
   setserial" and is best done as part of the boot process in rc.local or
   rc.serial which is called from rc.local or as part of the SysV
   initialization. For the machine illustrated above, the commands used
/bin/setserial -b /dev/ttyS2 IRQ 11
/bin/setserial -b /dev/ttyS3 IRQ 15

   However, if you are using serial modules dynamically loaded, when
   required by the kerneld process, you cannot set and forget the IRQs,
   (etc.) once at boot time. This is because if the serial module is
   unloaded, Linux forgets the special settings.
   So, if you are loading the serial module on demand, you will need to
   reconfigure the IRQs, (etc.) each time the module is loaded.
12.1. A note about serial ports and speed capabilities

   If you are using a high speed (external) modem (14,400 Baud or above),
   your serial port needs to be capable of handling the throughput that
   such a modem is capable of producing, particularly when the modems are
   compressing the data.
   This requires your serial port to use a modern UART (Universal
   Asynchronous Receiver Transmitter) such as a 16550(A). If you are
   using an old machine (or old serial card), it is quite possible that
   your serial port has only an 8250 UART, which will cause you
   considerable problems when used with a high speed modem.
   Use the command...
setserial -a /dev/ttySx

   to get Linux to report to you the type of UART you have. If you do not
   have a 16550A type UART, invest in a new serial card (available for
   under $50). When you purchase a new card, make sure you can move the
   IRQs around on it!
   Note: the first versions of the 16550 UART chip had an error. This was
   rapidly discovered and a revision of the chip was released - the
   16550A UART. A relatively small number of the faulty chips did however
   get into circulation. It is unlikely that you will encounter one of
   these but you should look for a response that says 16550A,
   particularly on serial cards of some vintage.
12.2. Serial Port Names

   Historically, Linux used cuaX devices for dial-out and ttySx devices
   for dial-in.
   The kernel code that required this was changed in kernel version 2.0.x
   and you should now use ttySx for both dial in and dial out. I
   understand that the cuaX device names may well disappear in future
   kernel versions.
12.3. Configuring your modem

   You will need to configure your modem correctly for PPP - to do this
   READ YOUR MODEM MANUAL! Most modems come with a factory default
   setting that selects the options required for PPP. The minimum
   configuration specifies:-
     * Hardware flow control (RTS/CTS) (&K3 on many Hayes modems)
   Other settings (in standard Hayes commands) you should investigate
     * E1 Command/usr/src/linux-2.0.27/include/linux/serial.h Echo ON
       (required for chat to operate).
     * Q0 Report result codes (required for chat to operate).
     * S0=0 Auto Answer OFF (unless you want your modem to answer the
     * &C1 Carrier Detect ON only after connect.
     * &S0 Data Set Ready (DSR) always ON.
     * (depends) Data Terminal Ready.
   There is a site offering modem setups for a growing variety of modems,
   makes and models at [152]Modem setup information which may assist you
   in this.
   It is also worth while investigating how the modem's serial interface
   between your computer and modem operates. Most modern modems allow you
   to run the serial interface at a FIXED speed whilst allowing the
   telephone line interface to change its speed to the highest speed it
   and the remote modem can both handle.
   This is known as split speed operation. If your modem supports this,
   lock the modem's serial interface to its highest available speed
   (usually 115,200 baud but maybe 38,400 baud for 14,400 baud modems).
   Use your communications software (e.g. minicom or seyon) to find out
   about your modem configuration and set it to what is required for PPP.
   Many modems report their current settings in response to AT&V, but you
   should consult your modem manual.
   If you completely mess up the settings, you can return to sanity
   (usually) by issuing an AT&F - return to factory settings. (For most
   modem modems I have encountered, the factory settings include all you
   need for PPP - but you should check).
   Once you have worked out the modem setup string required, write it
   down. You now have a decision: you can store these settings in your
   modem non-volatile memory so they can be recalled by issuing the
   appropriate AT command, or you can pass the correct settings to your
   modem as part of the PPP dialing process.
   If you only use your modem from Linux to call into your ISP or
   corporate server, the simplest set up will have you save your modem
   configuration in non-volatile RAM.
   If on the other hand, you modem is used by other applications and
   operating systems, it is safest to pass this information to the modem
   as each call is made so that the modem is guaranteed to be in the
   correct state for the call. (This has the added advantage also of
   recording the modem setup string in case the modem looses the contents
   of its NV-RAM, which can indeed happen).
12.4. Note on Serial Flow Control

   When data is traveling on serial communication lines, it can happen
   that data arrives faster than a computer can handle it (the computer
   may be busy doing something else - remember, Linux is a multi-user,
   multi- tasking operating system). In order to ensure that data is not
   lost (data does not over run in the input buffer and hence get lost),
   some method of controlling the flow of data is necessary.
   There are two ways of doing this on serial lines:-
     * Using hardware signals (Clear To Send/Request to Send - CTS/RTS).
     * Using software signals (control S and control Q, also known as
   Whilst the latter may be fine for a terminal (text) link, data on a
   PPP link uses all 8 bits - and it is quite probable that somewhere in
   the data there will be data bytes that translate as control S and
   control Q. So, if a modem is set up to use software flow control,
   things can rapidly go berserk!
   For high speed links using PPP (which uses 8 bits of data) hardware
   flow control is vital and it is for this reason that you must use
   hardware flow control.
12.5. Testing your modem for dial out

   Now that you have sorted out the serial port and modem settings it is
   a good idea to make sure that these setting do indeed work by dialing
   you ISP and seeing if you can connect.
   Using you terminal communications package (such as minicom), set up
   the modem initialisation required for PPP and dial into the PPP server
   you want to connect to with a PPP session.
   (Note: at this stage we are NOT trying to make a PPP connection - just
   establishing that we have the right phone number and also to find out
   exactly what the server sends to us in order to get logged in and
   start PPP).
   During this process, either capture (log to a file) the entire login
   process or carefully (very carefully) write down exactly what prompts
   the server gives to let you know it is time to enter your user name
   and password (and any other commands needed to establish the PPP
   If your server uses PAP, you should not see a login prompt, but should
   instead see the (text representation) of the link control protocol
   (which looks like garbage) starting on your screen.
   A few words of warning:-
     * some servers are quite intelligent: you can log in using text
       based user name/passwords OR using PAP. So if your ISP or
       corporate site uses PAP but you do not see the garbage start up
       immediately, this may not mean you have done something wrong.
     * some servers require you to enter some text initially and then
       start a standard PAP sequence.
     * Some PPP servers are passive - that is they simply sit there
       sending nothing until the client that is dialing in sends them a
       valid lcp packet. If the ppp server you are connecting to operates
       in passive mode, you will never see the garbage!
     * Some servers do not start PPP until you press ENTER - so it is
       worth trying this if you correctly log in and do not see the
   It is worth dialing in at least twice - some servers change their
   prompts (e.g. with the time!) every time you log in. The two critical
   prompts your Linux box needs to be able to identify every time you
   dial in are:-
     * the prompt that requests you to enter your user name;
     * the prompt that requests you to enter your password;
   If you have to issue a command to start PPP on the server, you will
   also need to find out the prompt the server gives you once you are
   logged in to tell you that you can now enter the command to start ppp.
   If your server automatically starts PPP, once you have logged in, you
   will start to see garbage on your screen - this is the PPP server
   sending your machine information to start up and configure the PPP
   This should look something like this :-
~y}#.!}!}!} }8}!}$}%U}"}&} } } } }%}& ...}'}"}(}"} .~~y}

   (and it just keeps on coming!)
   On some systems PPP must be explicitly started on the server. This is
   usually because the server has been set up to allow PPP logins and
   shell logins using the same user name/password pair. If this is the
   case, issue this command once you have logged in. Again, you will see
   the garbage as the server end of the PPP connection starts up.
   If you do not see this immediately after connecting (and logging in
   and starting the PPP server if required), press Enter to see if this
   starts the PPP server.
   At this point, you can hang up your modem (usually, type +++ quickly
   and then issue the ATHO command once your modem responds with OK).
   If you can't get your modem to work, read your modem manual, the man
   pages for your communications software and the Serial HOWTO! Once you
   have this sorted out, carry on as above.
Chapter 13. Setting up Name to Address Resolution (DNS)

   Whilst we humans like to give names to things, computers really like
   numbers. On a TCP/IP network (which is what the Internet is), we call
   machines by a particular name - and every machine lives in a
   particular domain. For example, my Linux workstation is called
   archenland and it resides in the domain. Its human
   readable address is thus (which is known
   as the FQDN - fully qualified domain name).
   However, for this machine to be found by other computers on the
   Internet, it is actually known by its IP number when computers are
   communicating across the Internet.
   Translating (resolving) machine (and domain) names into the numbers
   actually used on the Internet is the business of machines that offer
   the Domain Name Service.
   What happens is this:-
     * your machine needs to know the IP address of a particular
       computer. The application requiring this information asks the
       'resolver' on your Linux PC to provide this information;
     * the resolver queries the local host file (/etc/hosts and/or the
       domain name servers it knows about (the exact behaviour of the
       resolver is determined by /etc/host.conf);
     * if the answer is found in the host file, this answer is returned;
     * if a domain name server is specified, your PC queries this
     * if the DNS machine already knows the IP number for the required
       name, it returns it. If it does not, it queries other name servers
       across the Internet to find the information. The name server than
       passes this information back to the requesting resolver - which
       gives the information to the requesting application.
   When you make a PPP connection, you need to tell your Linux machine
   where it can get host name to IP number (address resolution)
   information so that you can use the machine names but your computer
   can translate these to the IP numbers it needs to do its work.
   One way is to enter every host that you want to talk to into the
   /etc/hosts file (which is in reality totally impossible if you are
   connecting to the Internet); another is to use the machine IP numbers
   as opposed to the names (an impossible memory task for all but the
   smallest LANs).
   The best way is to set up Linux so that it knows where to go to get
   this name to number information - automatically. This service is
   provided by the Domain Name Server (DNS) system. All that is necessary
   is to enter the IP number(s) for the domain name servers into your
   /etc/resolv.conf file.
13.1. The /etc/resolv.conf file

   Your PPP server sysadmin/user support people should provide you with
   two DNS IP numbers (only one is necessary - but two gives some
   redundancy in the event of failure).
   As previously mentioned, Linux cannot set its name server IP number in
   the way that MS Windows 95 does. So you must insist (politely) that
   your ISP provide you with this information!
   Your /etc/resolv.conf should look something like :-

   Edit this file (creating it if necessary) to represent the information
   that your ISP has provided. It should have ownership and permissions
   as follows :-
-rw-r--r--   1 root     root           73 Feb 19 01:46 /etc/resolv.conf

   If you have already set up a /etc/resolv.conf because you are on a
   LAN, simply add the IP numbers of the PPP DNS servers to your existing
13.2. The /etc/host.conf file

   You should also check that your /etc/host.conf file is correctly set
   up. This should look like
order hosts,bind
multi on

   This tells the resolver to use information in the host file before it
   sends queries to the DNS for resolution.
Chapter 14. Using PPP and root privileges

   Because PPP needs to set up networking devices, change the kernel
   routing table and so forth, it requires root privileges to do this.
   If users other than root are to set up PPP connections, the pppd
   program should be setuid root :-
-rwsr-xr-x   1 root     root        95225 Jul 11 00:27 /usr/sbin/pppd

   If /usr/sbin/pppd is not set up this way, then as root issue the
chmod u+s /usr/sbin/pppd

   What this does is make pppd run with root privileges even if the
   binary is run by an ordinary user. This allows a normal user to run
   pppd with the necessary privileges to set up the network interfaces
   and the kernel routing table.
   Programs that run 'set uid root' are potential security holes and you
   should be extremely cautious about making programs 'suid root'. A
   number of programs (including pppd) have been carefully written to
   minimise the danger of running suid root, so you should be safe with
   this one, (but no guarantees).
   Depending on how you want your system to operate - specifically if you
   want ANY user on your system to be able to initiate a PPP link, you
   should make your ppp-on/off scripts world read/execute. (This is
   probably fine if your PC is used ONLY by you).
   However, if you do NOT want just anyone to be able to start up a PPP
   connection (for example, your children have accounts on your Linux PC
   and you do not want them hooking into the Internet without your
   supervision), you will need to establish a PPP group (as root, edit
   /etc/group) and :-
     * Make pppd suid root, owned by user root and group PPP, with the
       'other' permissions on this file empty. It should then look like:-
-rwsr-x---   1 root     PPP        95225 Jul 11 00:27 /usr/sbin/pppd

     * Make the ppp-on/off scripts owned by user root and group PPP.
     * Make the ppp-on/off scripts read/executable by group PPP.
  -rwxr-x---   1 root     PPP           587 Mar 14  1995 /usr/sbin/ppp-on
  -rwxr-x---   1 root     PPP           631 Mar 14  1995 /usr/sbin/ppp-off

     * Make the other access rights for ppp-on/off nill.
     * add the users who will be firing up PPP to the PPP group in
   Even if you do this, ordinary users will STILL not be able to shut
   down the link under software control! Running the ppp-off script
   requires root privileges. However, any user can just turn off the
   modem (or disconnect the telephone line from an internal modem).
   An alternative (and better method) to this set up is to use the sudo
   program. This offers superior security and will allow you to set
   things up so that any (authorised) user can activate/deactivate the
   link using the scripts. Using sudo will allow an authorised user to
   activate/deactivate the PPP link cleanly and securely.
Chapter 15. Setting up the PPP connection files

   You now need to be logged in as root to create the directories and
   edit the files needed to set up PPP, even if you want PPP to be
   accessible to all users.
   PPP uses a number of files to connect and set up a PPP connection.
   These differ in name and location between PPP 2.1.2 and 2.2+.
   For PPP 2.1.2 the files are:-
/usr/sbin/pppd          # the PPP binary
/usr/sbin/ppp-on        # the dialer/connection script
/usr/sbin/ppp-off       # the disconnection script
/etc/ppp/options        # the options pppd uses for all connections
/etc/ppp/options.ttyXX  # the options specific to a connection on this port

   For PPP 2.2 the files are:-
/usr/sbin/pppd                  # the PPP binary
/etc/ppp/scripts/ppp-on         # the dialer/connection script
/etc/ppp/scripts/ppp-on-dialer  # part 1 of the dialer script
/etc/ppp/scripts/ppp-off        # the actual chat script itself
/etc/ppp/options                # the options pppd uses for all connections
/etc/ppp/options.ttyXX          # the options specific to a connection on this

   Red Hat Linux users should note that the standard Red Hat 4.X
   installation places these scripts in /usr/doc/ppp-2.2.0f-2/scripts.
   In your /etc directory there should be a ppp directory:-
drwxrwxr-x   2 root     root         1024 Oct  9 11:01 ppp

   If it does not exist - create it with these ownerships and
   If the directory already existed, it should contain a template options
   file called options.tpl. This file is included below in case it does
   Print it out as it contains an explanation of nearly all the PPP
   options (these are useful to read in conjunction with the pppd man
   pages). Whilst you can use this file as the basis of your
   /etc/ppp/options file, it is probably better to create your own
   options file that does not include all the comments in the template -
   it will be much shorter and easier to read/maintain.
   If you have multiple serial lines/modems, (typically the case for PPP
   servers), create a general /etc/ppp/options file containing the
   options that are common for all the serial ports on which you are
   supporting dial in/out and set up individual option files for each
   serial line on which you will be establishing a PPP connection with
   the individual settings required for each port.
   These port specific option files are named options.ttyx1,
   options.ttyx2 and so forth (where x is the appropriate letter for your
   serial ports).
   However, for a single PPP connection, you can happily use the
   /etc/ppp/options file. Alternatively, you can put all the options as
   arguments in the pppd command itself.
   It is easier to maintain a setup that uses /etc/ppp/options.ttySx
   files. If you use PPP to connect to a number of different sites, you
   can create option files for each site in /etc/ppp/ and
   then specify the option file as a parameter to the PPP command as you
   connect (using the file option-file pppd option to pppd on the command
15.1. The supplied options.tpl file

   Some distributions of PPP seem to have lost the options.tpl file, so
   here is the complete file. I suggest that you do NOT edit this file to
   create your /etc/ppp/options file(s). Rather, copy this to a new file
   and then edit that. If you mess up your edits, you can then go back to
   the original and start again.
# /etc/ppp/options -*- sh -*- general options for pppd
# created 13-Jul-1995 jmk
# autodate: 01-Aug-1995
# autotime: 19:45

# Use the executable or shell command specified to set up the serial
# line.  This script would typically use the "chat" program to dial the
# modem and start the remote ppp session.
#connect "echo You need to install a connect command."

# Run the executable or shell command specified after pppd has
# terminated the link.  This script could, for example, issue commands
# to the modem to cause it to hang up if hardware modem control signals
# were not available.
#disconnect "chat -- \d+++\d\c OK ath0 OK"

# async character map -- 32-bit hex; each bit is a character
# that needs to be escaped for pppd to receive it.  0x00000001
# represents '\x01', and 0x80000000 represents '\x1f'.
#asyncmap 0

# Require the peer to authenticate itself before allowing network
# packets to be sent or received.

# Use hardware flow control (i.e. RTS/CTS) to control the flow of data
# on the serial port.

# Use software flow control (i.e. XON/XOFF) to control the flow of data
# on the serial port.

# Add a default route to the system routing tables, using the peer as
# the gateway, when IPCP negotiation is successfully completed.  This
# entry is removed when the PPP connection is broken.

# Specifies that certain characters should be escaped on transmission
# (regardless of whether the peer requests them to be escaped with its
# async control character map).  The characters to be escaped are
# specified as a list of hex numbers separated by commas.  Note that
# almost any character can be specified for the escape option, unlike
# the asyncmap option which only allows control characters to be
# specified.  The characters which may not be escaped are those with hex
# values 0x20 - 0x3f or 0x5e.
#escape 11,13,ff

# Don't use the modem control lines.

# Specifies that pppd should use a UUCP-style lock on the serial device
# to ensure exclusive access to the device.

# Use the modem control lines.  On Ultrix, this option implies hardware
# flow control, as for the crtscts option.  (This option is not fully
# implemented.)

# Set the MRU [Maximum Receive Unit] value to <n> for negotiation.  pppd
# will ask the peer to send packets of no more than <n> bytes. The
# minimum MRU value is 128.  The default MRU value is 1500.  A value of
# 296 is recommended for slow links (40 bytes for TCP/IP header + 256
# bytes of data).
#mru 542

# Set the interface netmask to <n>, a 32 bit netmask in "decimal dot"
# notation (e.g.

# Disables the default behaviour when no local IP address is specified,
# which is to determine (if possible) the local IP address from the
# hostname. With this option, the peer will have to supply the local IP
# address during IPCP negotiation (unless it specified explicitly on the
# command line or in an options file).

# Enables the "passive" option in the LCP.  With this option, pppd will
# attempt to initiate a connection; if no reply is received from the
# peer, pppd will then just wait passively for a valid LCP packet from
# the peer (instead of exiting, as it does without this option).

# With this option, pppd will not transmit LCP packets to initiate a
# connection until a valid LCP packet is received from the peer (as for
# the "passive" option with old versions of pppd).

# Don't request or allow negotiation of any options for LCP and IPCP
# (use default values).

# Disable Address/Control compression negotiation (use default, i.e.
# address/control field disabled).

# Disable asyncmap negotiation (use the default asyncmap, i.e. escape
# all control characters).

# Don't fork to become a background process (otherwise pppd will do so
# if a serial device is specified).

# Disable IP address negotiation (with this option, the remote IP
# address must be specified with an option on the command line or in an
# options file).

# Disable magic number negotiation.  With this option, pppd cannot
# detect a looped-back line.

# Disable MRU [Maximum Receive Unit] negotiation (use default, i.e.
# 1500).

# Disable protocol field compression negotiation (use default, i.e.
# protocol field compression disabled).

# Require the peer to authenticate itself using PAP.
# This requires TWO WAY authentication - do NOT use this for a standard
# PAP authenticated link to an ISP as this will require the ISP machine
# to authenticate itself to your machine (and it will not be able to).

# Don't agree to authenticate using PAP.

# Require the peer to authenticate itself using CHAP [Cryptographic
# Handshake Authentication Protocol] authentication.
# This requires TWO WAY authentication - do NOT use this for a standard
# CHAP authenticated link to an ISP as this will require the ISP machine
# to authenticate itself to your machine (and it will not be able to).

# Don't agree to authenticate using CHAP.

# Disable negotiation of Van Jacobson style IP header compression (use
# default, i.e. no compression).

# Increase debugging level (same as -d).  If this option is given, pppd
# will log the contents of all control packets sent or received in a
# readable form.  The packets are logged through syslog with facility
# daemon and level debug. This information can be directed to a file by
# setting up /etc/syslog.conf appropriately (see syslog.conf(5)).  (If
# pppd is compiled with extra debugging enabled, it will log messages
# using facility local2 instead of daemon).

# Append the domain name <d> to the local host name for authentication
# purposes.  For example, if gethostname() returns the name porsche,
# but the fully qualified domain name is porsche.Quotron.COM, you would
# use the domain option to set the domain name to Quotron.COM.
#domain <d>

# Enable debugging code in the kernel-level PPP driver.  The argument n
# is a number which is the sum of the following values: 1 to enable
# general debug messages, 2 to request that the contents of received
# packets be printed, and 4 to request that the contents of transmitted
# packets be printed.
#kdebug n

# Set the MTU [Maximum Transmit Unit] value to <n>. Unless the peer
# requests a smaller value via MRU negotiation, pppd will request that
# the kernel networking code send data packets of no more than n bytes
# through the PPP network interface.
#mtu <n>

# Set the name of the local system for authentication purposes to <n>.
# This will probably have to be set to your ISP user name if you are
# using PAP/CHAP.
#name <n>

# Set the user name to use for authenticating this machine with the peer
# using PAP to <u>.
# Do NOT use this if you are using 'name' above!
#user <u>

# Enforce the use of the host name as the name of the local system for
# authentication purposes (overrides the name option).

# Set the assumed name of the remote system for authentication purposes
# to <n>.
#remotename <n>

# Add an entry to this system's ARP [Address Resolution Protocol]
# table with the IP address of the peer and the Ethernet address of this
# system.

# Use the system password database for authenticating the peer using
# PAP.

# If this option is given, pppd will send an LCP echo-request frame to
# the peer every n seconds. Under Linux, the echo-request is sent when
# no packets have been received from the peer for n seconds. Normally
# the peer should respond to the echo-request by sending an echo-reply.
# This option can be used with the lcp-echo-failure option to detect
# that the peer is no longer connected.
#lcp-echo-interval <n>

# If this option is given, pppd will presume the peer to be dead if n
# LCP echo-requests are sent without receiving a valid LCP echo-reply.
# If this happens, pppd will terminate the connection.  Use of this
# option requires a non-zero value for the lcp-echo-interval parameter.
# This option can be used to enable pppd to terminate after the physical
# connection has been broken (e.g., the modem has hung up) in
# situations where no hardware modem control lines are available.
#lcp-echo-failure <n>

# Set the LCP restart interval (retransmission timeout) to <n> seconds
# (default 3).
#lcp-restart <n>

# Set the maximum number of LCP terminate-request transmissions to <n>
# (default 3).
#lcp-max-terminate <n>

# Set the maximum number of LCP configure-request transmissions to <n>
# (default 10).
# Some PPP servers are slow to start up. You may need to increase this
# if you keep getting 'serial line looped back' errors and your are SURE
# that you have logged in correctly and PPP should be starting on the server.
#lcp-max-configure <n>

# Set the maximum number of LCP configure-NAKs returned before starting
# to send configure-Rejects instead to <n> (default 10).
#lcp-max-failure <n>

# Set the IPCP restart interval (retransmission timeout) to <n>
# seconds (default 3).
#ipcp-restart <n>

# Set the maximum number of IPCP terminate-request transmissions to <n>
# (default 3).
#ipcp-max-terminate <n>

# Set the maximum number of IPCP configure-request transmissions to <n>
# (default 10).
#ipcp-max-configure <n>

# Set the maximum number of IPCP configure-NAKs returned before starting
# to send configure-Rejects instead to <n> (default 10).
#ipcp-max-failure <n>

# Set the PAP restart interval (retransmission timeout) to <n> seconds
# (default 3).
#pap-restart <n>

# Set the maximum number of PAP authenticate-request transmissions to
# <n> (default 10).
#pap-max-authreq <n>

# Set the CHAP restart interval (retransmission timeout for
# challenges) to <n> seconds (default 3).
#chap-restart <n>

# Set the maximum number of CHAP challenge transmissions to <n>
# (default 10).

# If this option is given, pppd will re-challenge the peer every <n>
# seconds.
#chap-interval <n>

# With this option, pppd will accept the peer's idea of our local IP
# address, even if the local IP address was specified in an option.

# With this option, pppd will accept the peer's idea of its (remote) IP
# address, even if the remote IP address was specified in an option.
15.2. What options should I use? (No PAP/CHAP)

   Well, as in all things, that depends, (sigh). The options specified
   here should work with most servers.
   However, if it does NOT work, READ THE TEMPLATE FILE
   (/etc/ppp/options.tpl) and the pppd man pages and speak to the
   sysadmin/user support people who run the server to which you are
   You should also note that the connect scripts presented here also use
   some command line options to pppd to make things a bit easier to
# /etc/ppp/options (NO PAP/CHAP)
# Prevent pppd from forking into the background
# use the modem control lines
# use uucp style locks to ensure exclusive access to the serial device
# use hardware flow control
# create a default route for this connection in the routing table
# do NOT set up any "escaped" control sequences
asyncmap 0
# use a maximum transmission packet size of 552 bytes
mtu 552
# use a maximum receive packet size of 552 bytes
mru 552
#-------END OF SAMPLE /etc/ppp/options (no PAP/CHAP)
15.3. Other options to consider adding

   There are a couple useful things you might want to add to the
   /etc/ppp/options file.
   One is an idle time. Pppd can terminate the connection if it has been
   idle for too long. This could be nice if your isp charges by time, or
   if you don't want to keep your phone line tied up. To use this
   feature, simply add the line:
# Idle after X seconds
idle X

   Replace 'X' with the number of seconds you wish the connection to
   terminate after.
   The next feature is "dial on demand". This means that every time you
   attempt to open an interent connection, pppd will try to open a PPP
   connection to your ISP. In order to do this, add the following lines
   to /etc/ppp/options
# dial on demand

   This should make pppd dial out when necessary.
Chapter 16. If your PPP server uses PAP (Password Authentication Protocol)

   If the server to which you are connecting requires PAP or CHAP
   authentication, you have a little bit more work.
   To the above options file, add the following lines
# force pppd to use your ISP user name as your 'host name' during the
# authentication process
name <your ISP user name>       # you need to edit this line
# If you are running a PPP *server* and need to force PAP or CHAP
# uncomment the appropriate one of the following lines. Do NOT use
# these is you are a client connecting to a PPP server (even if it uses PAP
# or CHAP) as this tells the SERVER to authenticate itself to your
# machine (which almost certainly can't do - and the link will fail).
# If you are using ENCRYPTED secrets in the /etc/ppp/pap-secrets
# file, then uncomment the following line.
# Note: this is NOT the same as using MS encrypted passwords as can be
# set up in MS RAS on Windows NT.
16.1. Using MSCHAP

   Microsoft Windows NT RAS can be set up to use a variation on CHAP
   (Challenge/Handshake Authentication Protocol). In your PPP sources tar
   ball, you will find a file called README.MSCHAP80 that discusses this.
   You can determine if the server is requesting authentication using
   this protocol by enabling debugging for pppd. If the server is
   requesting MS CHAP authentication, you will see lines like:-
rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <auth chap 80> <magic 0x46a3>]

   The critical information here is auth chap 80.
   In order to use MS CHAP, you will need to recompile pppd to support
   this. Please see the instructions in the README.MSCHAP80 file in the
   PPP source file for instructions on how to compile and use this
   You should note that at present this code supports only Linux PPP
   clients connecting to an MS Windows NT server. It does NOT support
   setting up a Linux PPP server to use MSCHAP80 authentication from
16.2. The PAP/CHAP secrets file

   If you are using pap or chap authentication, then you also need to
   create the secrets file. These are:

   They must be owned by user root, group root and have file permissions
   740 for security.
   The first point to note about PAP and CHAP is that they are designed
   to authenticate computer systems not users.
   Huh? What's the difference? I hear you ask.
   Well now, once your computer has made its PPP connection to the
   server, ANY user on your system can use that connection - not just
   you. This is why you can set up a WAN (wide area network) link that
   joins two LANs (local area networks) using PPP.
   PAP can (and for CHAP DOES) require bidirectional authentication -
   that is a valid name and secret is required on each computer for the
   other computer involved. However, this is NOT the way most PPP servers
   offering dial-up PPP PAP-authenticated connections operate.
   That being said, your ISP will probably have given you a user name and
   password to allow you to connect to their system and thence the
   Internet. Your ISP is not interested in your computer's name at all,
   so you will probably need to use the user name at your ISP as the name
   for your computer.
   This is done using the name user name option to pppd. So, if you are
   to use the user name given you by your ISP, add the line
name your_user name_at_your_ISP

   to your /etc/ppp/options file.
   Technically, you should really use user our_user name_at_your_ISP for
   PAP, but pppd is sufficiently intelligent to interpret name as user if
   it is required to use PAP. The advantage of using the name option is
   that this is also valid for CHAP.
   As PAP is for authenticating computers, technically you need also to
   specify a remote computer name. However, as most people only have one
   ISP, you can use a wild card (*) for the remote host name in the
   secrets file.
   It is also worth noting that many ISPs operate multiple modem banks
   connected to different terminal servers - each with a different name,
   but ACCESSED from a single (rotary) dial in number. It can therefore
   be quite difficult in some circumstances to know ahead of time what
   the name of the remote computer is, as this depends on which terminal
   server you connect to!
16.3. The PAP secrets file

   The /etc/ppp/pap-secrets file looks like
# Secrets for authentication using PAP
# client        server       secret     acceptable_local_IP_addresses

   The four fields are white space delimited and the last one can be
   blank (which is what you want for a dynamic and probably static IP
   allocation from your ISP).
   Suppose your ISP gave you a user name of fred and a password of
   flintstone you would set the name fred option in
   /etc/ppp/options[.ttySx] and set up your /etc/ppp/pap-secrets file as
# Secrets for authentication using PAP
# client        server  secret          acceptable local IP addresses
fred            *       flintstone

   This says for the local machine name fred (which we have told pppd to
   use even though it is not our local machine name) and for ANY server,
   use the password (secret) of flintstone.
   Note that we do not need to specify a local IP address, unless we are
   required to FORCE a particular local, static IP address. Even if you
   try this, it is unlikely to work as most PPP servers (for security
   reasons) do not allow the remote system to set the IP number they are
   to be given.
16.4. The CHAP secrets file

   This requires that you have mutual authentication methods - that is
   you must allow for both your machine to authenticate the remote server
   AND the remote server to authenticate your machine.
   So, if your machine is fred and the remote is barney, your machine
   would set name fred remotename barney and the remote machine would set
   name barney remotename fred in their respective /etc/ppp/options.ttySx
   The /etc/chap-secrets file for fred would look like
# Secrets for authentication using CHAP
# client        server  secret            acceptable local IP addresses
fred            barney  flintstone
barney          fred    wilma

   and for barney
# Secrets for authentication using CHAP
# client        server  secret            acceptable local IP addresses
barney          fred    flintstone
fred            barney  wilma

   Note in particular that both machines must have entries for
   bidirectional authentication. This allows the local machine to
   authenticate itself to the remote AND the remote machine to
   authenticate itself to the local machine.
16.5. Handling multiple PAP-authenticated connections

   Some users have more than one server to which they connect that use
   PAP. Provided that your user name is different on each machine to
   which you want to connect, this is not a problem.
   However, many users have the same user name on two (or more - even
   all) systems to which they connect. This then presents a problem in
   correctly selecting the appropriate line from /etc/ppp/pap-secrets.
   As you might expect, PPP provides a mechanism for overcoming this. PPP
   allows you to set an 'assumed name' for the remote (server) end of the
   connection using the remotename option to pppd.
   Let us suppose that you connect to two PPP servers using the username
   fred. You set up your /etc/ppp/pap-secrets something like
fred    pppserver1      barney
fred    pppserver2      wilma

   Now, to set connect to pppserver1 you would use name fred remotename
   pppserver1 in your ppp-options and for pppserver2 name fred remotename
   As you can select the ppp options file to use with pppd using the file
   filename option, you can set up a script to connect to each of your
   PPP servers, correctly picking the options file to use and hence
   selecting the right remotename option.
Chapter 17. Setting up the PPP connection manually

   Now that you have created your /etc/ppp/options and /etc/resolv.conf
   files (and, if necessary, the /etc/ppp/pap|chap-secrets file), you can
   test the settings by manually establishing a PPP connection. (Once we
   have the manual connection working, we will automate the process).
   To do this, your communications software must be capable of quitting
   WITHOUT resetting the modem. Minicom can do this - ALT Q (or in older
   version of minicom CTRL A Q)
   Make sure you are logged in as root.
   Fire up you communications software, (such as minicom), dial into the
   PPP server and log in as normal. If you need to issue a command to
   start up PPP on the server, do so. You will now see the garbage you
   saw before.
   If you are using pap or chap, then merely connecting to the remote
   system should start ppp on the remote and you will see the garbage
   without logging in, (although this may not happen for some servers -
   try pressing Enter and see if the garbage starts up).
   Now quit the communications software without resetting the modem (ALT
   Q or CTL A Q in minicom) and at the Linux prompt (as root) type...
pppd -d -detach /dev/ttySx 38400 &

   The -d option turns on debugging - the ppp connection start up
   conversation will be logged to your system log - which is useful if
   you are having trouble.
   Your modem lights should now flash as the PPP connection is
   established. It will take a short while for the PPP connection to be
   At this point you can look at the PPP interface, by issuing the

   In addition to any Ethernet and loop back devices you have, you should
   see something like :-
ppp0     Link encap:Point-Point Protocol
         inet addr:  P-t-P: Mask:
         UP POINTOPOINT RUNNING  MTU:552  Metric:1
         RX packets:0 errors:0 dropped:0 overruns:0
         TX packets:0 errors:0 dropped:0 overruns:0

     * inet addr: is the IP number of your end of the link.
     * P-t-P: is the SERVER's IP number.
   (Naturally, ifconfig will not report these IP numbers, but the ones
   used by your PPP server.)
   Note: ifconfig also tells you that the link is UP and RUNNING!
   If you get no ppp device listed or something like:-
ppp0     Link encap:Point-Point Protocol
         inet addr:  P-t-P:  Mask:
         POINTOPOINT  MTU:1500  Metric:1
         RX packets:0 errors:0 dropped:0 overruns:0
         TX packets:0 errors:0 dropped:0 overruns:0

   Your PPP connection has not been made...see the later section on
   You should also be able to see a route to the the remote host (and
   beyond). To do this, issue the command
route -n

   You should se something like:-
Kernel routing table
Destination     Gateway         Genmask         Flags MSS    Window Use Iface    *      UH    1500   0        1 ppp0       *            U     3584   0       11 lo        *            U     1500   0       35 eth0
default    *               UG    1500   0        5 ppp0

   Of particular importance here, notice we have TWO entries pointing to
   our ppp interface.
   The first is a HOST route, (indicated by the H flag) and that allows
   us to see the host to which we are connected to - but no further.
   The second is the default route, (established by giving pppd the
   option defaultroute. This is the route that tells our Linux PC to send
   any packets NOT destined for the local Ethernet(s) - to which we have
   specific network routes - to the PPP server itself. The PPP server
   then is responsible for routing our packets out onto the Internet and
   routing the return packets back to us.
   If you do not see a routing table with two entries, something is
   wrong. In particular if your syslog shows a message telling you pppd
   is not replacing an existing default route, then you have a default
   route pointing at your Ethernet interface - which MUST be replaced by
   a specific network route: YOU CAN ONLY HAVE ONE DEFAULT ROUTE!!!
   You will need to explore your system initialization files to find out
   where this default route is being set up (it will use a route add
   default... command). Change this command to something like route add
   Now test the link by 'pinging' the server at its IP number as reported
   by the ifconfig output, i.e.

   You should receive output like
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=255 time=328.3 ms
64 bytes from icmp_seq=1 ttl=255 time=190.5 ms
64 bytes from icmp_seq=2 ttl=255 time=187.5 ms
64 bytes from icmp_seq=3 ttl=255 time=170.7 ms

   This listing will go on for ever - to stop it press CTRL C, at which
   point you will receive some more information :-
--- ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 170.7/219.2/328.3 ms

   So far so good.
   Now try pinging a host by name (not the name of the PPP server itself)
   but a host at another site that you KNOW is probably going to be up
   and running...). For example

   This time there will be a bit of a pause as Linux obtains the IP
   number for the fully qualified host name you have 'ping'ed from the
   DNS you specified in /etc/resolv.conf - so don't worry (but you will
   see your modem lights flash). Shortly you will receive output like
 PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=254 time=190.1 ms
64 bytes from icmp_seq=1 ttl=254 time=180.6 ms
64 bytes from icmp_seq=2 ttl=254 time=169.8 ms
64 bytes from icmp_seq=3 ttl=254 time=170.6 ms
64 bytes from icmp_seq=4 ttl=254 time=170.6 ms

   Again, stop the output by pressing CTRL C and get the statistics...
--- ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 169.8/176.3/190.1 ms

   If you don't get any response, try pinging the IP address of the DNS
   server at your ISP's site. If you get a result from this, then it
   looks like you have a problem with /etc/resolv.conf.
   If this doesn't work, you have a routing problem, or your ISP has a
   problem routing packets back to you. Check your routing table as shown
   above and if that is OK, contact your ISP. A good test of the ISP is
   to use another operating system to connect. If you can get beyond your
   ISP with that, then the problem is at your end.
   If everything works, shut down the connection by typing:-

   After a short pause, the modem should hang itself up.
   If that does not work, either turn off your modem or fire up your
   communications software and interrupt the modem with +++ and then hang
   up with ATH0 when you receive the modem's OK prompt.
   You may also need to clean up the lock file created by pppd.
rm -f /var/lock/LCK..ttySx
Chapter 18. Automating your connections - Creating the connection scripts

   Whilst you can continue to log in by hand as shown above, it is much
   neater to set up some scripts to do this automatically for you.
   A set of scripts automates the log in and PPP start up so all you have
   to do (as root or as a member of the PPP group) is issue a single
   command to fire up your connection.
18.1. Connection scripts for User name/Password Authentication

   If your ISP does NOT require the use of PAP/CHAP, these are the
   scripts for you!
   If the ppp package installed correctly, you should have two example
   files. For PPP 2.1.2 they are in /usr/sbin and for PPP 2.2 they are in
   /etc/ppp/scripts. They are called
   for PPP-2.1.2

   and for PPP-2.2

   Now, if you are using PPP 2.1.2, I strongly urge you to delete the
   sample files. There are potential problems with these - and don't tell
   me they work fine - I used them for ages too (and recommended them in
   the first version of this HOWTO)!
   For the benefit of PPP 2.1.2 users, here are BETTER template versions,
   taken from the PPP 2.2 distribution. I suggest you copy and use these
   scripts instead of the old PPP-2.1.2 scripts.
18.2. The ppp-on script

   This is the first of a PAIR of scripts that actually fire up the
# Script to initiate a PPP connection. This is the first part of the
# pair of scripts. This is not a secure pair of scripts as the codes
# are visible with the 'ps' command.  However, it is simple.
# These are the parameters. Change as needed.
TELEPHONE=555-1212      # The telephone number for the connection
ACCOUNT=george          # The account name for logon (as in 'George Burns')
PASSWORD=gracie         # The password for this account (and 'Gracie Allen')
LOCAL_IP=        # Local IP address if known. Dynamic =
REMOTE_IP=       # Remote IP address if desired. Normally
NETMASK=   # The proper netmask if needed
# Export them so that they will be available to 'ppp-on-dialer'
# This is the location of the script which dials the phone and logs
# in.  Please use the absolute file name as the $PATH variable is not
# used on the connect option.  (To do so on a 'root' account would be
# a security hole so don't ask.)
# Initiate the connection
exec /usr/sbin/pppd debug /dev/ttySx 38400 \
        $LOCAL_IP:$REMOTE_IP \
        connect $DIALER_SCRIPT

   Here is the ppp-on-dialer script:-
# This is part 2 of the ppp-on script. It will perform the connection
# protocol for the desired connection.
/usr/sbin/chat -v                                                 \
        TIMEOUT         3                               \
        ABORT           '\nBUSY\r'                      \
        ABORT           '\nNO ANSWER\r'                 \
        ABORT           '\nRINGING\r\n\r\nRINGING\r'    \
        ''              \rAT                            \
        'OK-+++\c-OK'   ATH0                            \
        TIMEOUT         30                              \
        OK              ATDT$TELEPHONE                  \
        CONNECT         ''                              \
        ogin:--ogin:    $ACCOUNT                        \
        assword:        $PASSWORD

   For PPP-2.2, the ppp-off script looks like:-
# Determine the device to be terminated.
if [ "$1" = "" ]; then

# If the ppp0 pid file is present then the program is running. Stop it.
if [ -r /var/run/$ ]; then
        kill -INT `cat /var/run/$`
# If the kill did not work then there is no process running for this
# pid. It may also mean that the lock file will be left. You may wish
# to delete the lock file at the same time.
        if [ ! "$?" = "0" ]; then
                rm -f /var/run/$
                echo "ERROR: Removed stale pid file"
                exit 1
# Success. Let pppd clean up its own junk.
        echo "PPP link to $DEVICE terminated."
        exit 0
# The ppp process is not running for ppp0
echo "ERROR: PPP link is not active on $DEVICE"
exit 1
18.3. Editing the supplied PPP startup scripts

   As the new scripts come in two parts, we will edit them in turn.
18.3.1. The ppp-on script

   You will need to edit the script to reflect YOUR user name at your
   ISP, YOUR password at your ISP, and the telephone number of your ISP.
   Each of the lines like "TELEPHONE=" actually set up shell variables
   that contain the information to the right of the '=' (excluding the
   comments of course). So edit each of these lines so it is correct for
   your ISP and connection.
   Also, as you are setting the IP number (if you need to) in the
   /etc/ppp/options file, DELETE the line that says

   Also, make sure that the shell variable DIALER_SCRIPT points at the
   full path and name of the dialer script that you are actually going to
   use. So, if you have moved this or renamed the script, make sure you
   edit this line correctly in the ppp-on script!
18.3.2. The ppp-on-dialer script

   This is the second of the scripts that actually brings up our ppp
   Note: a chat script is normally all on one line. the backslashes are
   used to allow line continuations across several physical lines (for
   human readability) and do not form part of the script itself.
   However, it is very useful to look at it in detail so that we
   understand what it is actually (supposed) to be doing!
18.4. What a Chat script means...

   A chat script is a sequence of expect string, send string pairs. In
   particular, note that we ALWAYS expect something before we send
   If we are to send something WITHOUT receiving anything first, we must
   use an empty expect string (indicated by " ") and similarly for
   expecting something without sending anything! Also, if a string
   consists of several words, (e.g. NO CARRIER), you must quote the
   string so that it is seen as a single entity by chat.
   The chat line in our template is:-
exec /usr/sbin/chat -v

   Invoke chat, the -v tells chat to copy ALL its I/O into the system log
   (usually /var/log/messages). Once you are happy that the chat script
   is working reliably, edit this line to remove the -v to save
   unnecessary clutter in your syslog.
TIMEOUT         3

   This sets the timeout for the receipt of expected input to three
   seconds. You may need to increase this to say 5 or 10 seconds if you
   are using a really slow modem!
ABORT           '\nBUSY\r'

   If the string BUSY is received, abort the operation.
ABORT           '\nNO ANSWER\r'

   If the string NO ANSWER is received, abort the operation
ABORT           '\nRINGING\r\n\r\nRINGING\r'

   If the (repeated) string RINGING is received, abort the operation.
   This is because someone is ringing your phone line!

   Expect nothing from the modem and send the string AT.
OK-+++\c-OK   ATH0

   This one is a bit more complicated as it uses some of chat's error
   recovery capabilities.
   What is says is...Expect OK, if it is NOT received (because the modem
   is not in command mode) then send +++ (the standard Hayes-compatible
   modem string that returns the modem to command mode) and expect OK.
   Then send ATH0 (the modem hang up string). This allows your script to
   cope with the situation of your modem being stuck on-line!
TIMEOUT         30

   Set the timeout to 30 seconds for the remainder of the script. If you
   experience trouble with the chat script aborting due to timeouts,
   increase this to 45 seconds or more.
OK              ATDT$TELEPHONE

   Expect OK (the modem's response to the ATH0 command) and dial the
   number we want to call.
CONNECT         ''

   Expect CONNECT (which our modem sends when the remote modem answers)
   and send nothing in reply.
ogin:--ogin:    $ACCOUNT

   Again, we have some error recovery built in here. Expect the login
   prompt (...ogin:) but if we don't receive it by the timeout, send a
   return and then look for the login prompt again. When the prompt is
   received, send the username (stored in the shell variable $ACCOUNT).
assword:        $PASSWORD

   Expect the password prompt and send our password (again, stored in a
   shell variable).
   This chat script has reasonable error recovery capability. Chat has
   considerably more features than demonstrated here. For more
   information consult the chat manual page (man 8 chat).
18.4.1. Starting PPP at the server end

   Whilst the ppp-on-dialer script is fine for servers that automatically
   start pppd at the server end once you have logged in, some servers
   require that you explicitly start PPP on the server.
   If you need to issue a command to start up PPP on the server, you DO
   need to edit the ppp-on-dialer script.
   At the END of the script (after the password line) add an additional
   expect send pair - this one would look for your login prompt (beware
   of characters that have a special meaning in the Bourne shell - such
   as $ and [ or ] (open and close square brackets).
   Once chat has found the shell prompt, chat must issue the ppp start up
   command required for your ISPs PPP server.
   In my case, my PPP server uses the standard Linux Bash prompt
[hartr@kepler hartr]$

   and requires that I type

   to start up PPP on the server.
   It is a good idea to allow for a bit of error recovery here, so in my
   case I use
        hartr--hartr    ppp

   This says, if we don't receive the prompt within the timeout, send a
   carriage return and looks for the prompt again.
   Once the prompt is received, then send the string ppp.
   Note: don't forget to add a \ to the end of the previous line so chat
   still thinks the entire chat script is on one line!
   Unfortunately, some servers produce a very variable set of prompts!
   You may need to log in several times using minicom to understand what
   is going on and pick the stable "expect" strings.
18.5. A chat script for PAP/CHAP authenticated connections

   If your ISP is using PAP/CHAP, then your chat script is much simpler.
   All your chat script needs to do is dial the telephone, wait for a
   connect and then let pppd handle the logging in!
# This is part 2 of the ppp-on script. It will perform the connection
# protocol for the desired connection.
exec /usr/sbin/chat -v                                  \
        TIMEOUT         3                               \
        ABORT           '\nBUSY\r'                      \
        ABORT           '\nNO ANSWER\r'                 \
        ABORT           '\nRINGING\r\n\r\nRINGING\r'    \
        ''              \rAT                            \
        'OK-+++\c-OK'   ATH0                            \
        TIMEOUT         30                              \
        OK              ATDT$TELEPHONE                  \
        CONNECT         ''                              \
18.6. The pppd debug and file option_file options

   As we have already seen, you can turn on debug information logging
   with the -d option to pppd. The 'debug' option is equivalent to this.
   As we are establishing a new connection with a new script, leave in
   the debug option for now. (Warning: if your disk space is tight,
   logging pppd exchanges can rapidly extend your syslog file and run you
   into trouble - but to do this you must fail to connect and keep on
   trying for quite a few minutes).
   Once you are happy that all is working properly, then you can remove
   this option.
   If you have called your ppp options file anything other than
   /etc/ppp/options or /etc/ppp/options.ttySx, specify the file name with
   the file option to pppd - e.g.
exec /usr/sbin/pppd debug file options.myserver /dev/ttyS0 38400 \
Chapter 19. Testing your connection script

   Open a new root Xterm (if you are in X) or open a new virtual console
   and log in as root.
   In this new session, issue the command
tail -f /var/log/messages

   (or whatever your system log file is).
   In the first window (or virtual console) issue the command
ppp-on &

   (or whatever name you have called your edited version of
   /usr/sbin/ppp- on). If you do not put the script into the background
   by specifying & at the end of the command, you will not get your
   terminal prompt back until ppp exits (when the link terminates).
   Now switch back to the window that is tracking your system log.
   You will see something like the following (provided you specified -v
   to chat and -d to pppd)....this is the chat script and responses being
   logged to the system log file followed by the start up information for
   pppd :-
Oct 21 16:09:58 hwin chat[19868]: abort on (NO CARRIER)
Oct 21 16:09:59 hwin chat[19868]: abort on (BUSY)
Oct 21 16:09:59 hwin chat[19868]: send (ATZ^M)
Oct 21 16:09:59 hwin chat[19868]: expect (OK)
Oct 21 16:10:00 hwin chat[19868]: ATZ^M^M
Oct 21 16:10:00 hwin chat[19868]: OK -- got it
Oct 21 16:10:00 hwin chat[19868]: send (ATDT722298^M)
Oct 21 16:10:00 hwin chat[19868]: expect (CONNECT)
Oct 21 16:10:00 hwin chat[19868]: ^M
Oct 21 16:10:22 hwin chat[19868]: ATDT722298^M^M
Oct 21 16:10:22 hwin chat[19868]: CONNECT -- got it
Oct 21 16:10:22 hwin chat[19868]: send (^M)
Oct 21 16:10:22 hwin chat[19868]: expect (ogin:)
Oct 21 16:10:23 hwin chat[19868]: kepler login: -- got it
Oct 21 16:10:23 hwin chat[19868]: send (hartr^M)
Oct 21 16:10:23 hwin chat[19868]: expect (ssword:)
Oct 21 16:10:23 hwin chat[19868]:  hartr^M
Oct 21 16:10:23 hwin chat[19868]: Password: -- got it
Oct 21 16:10:23 hwin chat[19868]: send (??????^M)
Oct 21 16:10:23 hwin chat[19868]: expect (hartr)
Oct 21 16:10:24 hwin chat[19868]: [hartr -- got it
Oct 21 16:10:24 hwin chat[19868]: send (ppp^M)
Oct 21 16:10:27 hwin pppd[19872]: pppd 2.1.2 started by root, uid 0
Oct 21 16:10:27 hwin pppd[19873]: Using interface ppp0
Oct 21 16:10:27 hwin pppd[19873]: Connect: ppp0 <--> /dev/cua1
Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(LCP): Sent code 1, id 1.
Oct 21 16:10:27 hwin pppd[19873]: LCP: sending Configure-Request, id 1
Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfreq(LCP): Rcvd id 1.
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd MRU
Oct 21 16:10:27 hwin pppd[19873]: (1500)
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd ASYNCMAP
Oct 21 16:10:27 hwin pppd[19873]: (0)
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd MAGICNUMBER
Oct 21 16:10:27 hwin pppd[19873]: (a098b898)
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd PCOMPRESSION
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd ACCOMPRESSION
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: returning CONFACK.
Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(LCP): Sent code 2, id 1.
Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfack(LCP): Rcvd id 1.
Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 1, id 1.
Oct 21 16:10:27 hwin pppd[19873]: IPCP: sending Configure-Request, id 1
Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfreq(IPCP): Rcvd id 1.
Oct 21 16:10:27 hwin pppd[19873]: ipcp: received ADDR
Oct 21 16:10:27 hwin pppd[19873]: (
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: ipcp: received COMPRESSTYPE
Oct 21 16:10:27 hwin pppd[19873]: (45)
Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
Oct 21 16:10:27 hwin pppd[19873]: ipcp: returning Configure-ACK
Oct 21 16:10:28 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 2, id 1.
Oct 21 16:10:30 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 1, id 1.
Oct 21 16:10:30 hwin pppd[19873]: IPCP: sending Configure-Request, id 1
Oct 21 16:10:30 hwin pppd[19873]: fsm_rconfreq(IPCP): Rcvd id 255.
Oct 21 16:10:31 hwin pppd[19873]: ipcp: received ADDR
Oct 21 16:10:31 hwin pppd[19873]: (
Oct 21 16:10:31 hwin pppd[19873]:  (ACK)
Oct 21 16:10:31 hwin pppd[19873]: ipcp: received COMPRESSTYPE
Oct 21 16:10:31 hwin pppd[19873]: (45)
Oct 21 16:10:31 hwin pppd[19873]:  (ACK)
Oct 21 16:10:31 hwin pppd[19873]: ipcp: returning Configure-ACK
Oct 21 16:10:31 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 2, id 255.
Oct 21 16:10:31 hwin pppd[19873]: fsm_rconfack(IPCP): Rcvd id 1.
Oct 21 16:10:31 hwin pppd[19873]: ipcp: up
Oct 21 16:10:31 hwin pppd[19873]: local  IP address
Oct 21 16:10:31 hwin pppd[19873]: remote IP address

   (Note - I am using STATIC IP numbers - hence my machine sent that to
   the PPP server - you won't see this if you are using DYNAMIC IP
   numbers.) Also, this server requires a specific command to start ppp
   at its end.
   This looks OK - so test it out as before with pings to IP numbers and
   host names.
   Fire up you web browser or whatever and go surfing - you are
Chapter 20. Shutting down the PPP link

   When you have finished with the PPP link, use the standard ppp-off
   command to shut it down (remember - you need to be root or a member of
   the PPP group!).
   In your system log you will see something like:-
Oct 21 16:10:45 hwin pppd[19873]: Interrupt received: terminating link
Oct 21 16:10:45 hwin pppd[19873]: ipcp: down
Oct 21 16:10:45 hwin pppd[19873]: default route ioctl(SIOCDELRT): Bad address
Oct 21 16:10:45 hwin pppd[19873]: fsm_sdata(LCP): Sent code 5, id 2.
Oct 21 16:10:46 hwin pppd[19873]: fsm_rtermack(LCP).
Oct 21 16:10:46 hwin pppd[19873]: Connection terminated.
Oct 21 16:10:46 hwin pppd[19873]: Exit.

   Don't worry about the SIOCDELRT - this is just pppd noting that it is
   terminating and is nothing to worry about.
Chapter 21. Getting Help when totally stuck

   If you can't get your PPP link to work, go back through this document
   and check everything - in conjunction with the output created by
   "chat-v..." and "pppd -d" in you system log.
   Also consult the PPP documentation and FAQ plus the other documents
   mention herein!
   If you are still stuck, try the comp.os.linux.misc and
   comp.os.linux.networking newsgroups are reasonably regularly scanned
   by people that can help you with PPP as is comp.protocols.ppp
   You can try sending me personal email, but I do have a day job (and a
   life) and I do not guarantee to respond quickly (if at all) as this
   depends on my current work load and the state of my private life!
   GROUPS NOR SEND IT TO ME BY EMAIL - the former wastes huge amounts of
   network bandwidth and the latter will be consigned to /dev/null
   (unless I have specifically requested it).
Chapter 22. Common Problems once the link is working

   One problem you will find is that many service providers will only
   support the connection software package that they distribute to new
   accounts. This is (typically) for Microsoft Windows :-( - and many
   service provider help desks seem to know nothing about Unix (or
   Linux). So, be prepared for limited assistance from them!
   You could of course do the individual a favour and educate then about
   Linux (any ISP help desk person should be reasonably 'with it' in
   Internet terms and that means they should have a home Linux box - of
   course it does)!
22.1. I can't see beyond the PPP server I connect to

   OK - your PPP connection is up and running and you can ping the PPP
   server by IP number (the second or "remote" IP number shown by
   ifconfig ppp0), but you can't reach anything beyond this.
   First of all, try pinging the IP numbers you have specified in
   /etc/resolv.conf as name servers. If this works, you can see beyond
   your PPP server (unless this has the same IP number as the "remote" IP
   number of your connection). So now try pinging the full Internet name
   of your service provider - eg

   If this does NOT work, you have a problem with the name resolution.
   This is probably because of a typo in your /etc/resolv.conf file.
   Check this carefully against the information you acquired by ringing
   your service provider. If all looks OK, ring your service provider and
   check that you wrote down the IP numbers correctly.
   If it STILL doesn't work (and your service provider confirms that his
   name servers are up and running), you have a problem somewhere else -
   and I suggest you check carefully through your Linux installation
   (looking particularly for file permissions).
   If you STILL can't ping your service provider's IP name servers by IP
   number, either they are down (give them a voice call and check) or
   there is a routing problem at your service provider's end. Again, ring
   them and check this out.
   One possibility is that the "remote end" is a Linux PPP server where
   the IP forwarding option has not been specified in the kernel!
   A good general test is to try connecting to your service provider
   using the software that most supply for (gulp) Microsoft Windows. If
   everything works from another operating system to exactly the same
   account, then the problem is with your Linux system and NOT your
   service provider.
22.2. I can send email, but not receive it

   If you are using dynamic IP numbers, this is perfectly normal. See
   "Setting up Services" below.
22.3. Why can't people finger, WWW, gopher, talk, etc. to my machine?

   Again, if you are using dynamic IP numbers, this is perfectly normal.
   See "Setting up Services" below.
Chapter 23. Using Internet services with Dynamic IP numbers

   If you are using dynamic IP numbers (and many service providers will
   only give you a dynamic IP number unless you pay significantly more
   for your connection), then you have to recognize the limitations this
   First of all, outbound service requests will work just fine. That is,
   you can send email using sendmail (provided you have correctly set up
   sendmail), ftp files from remote sites, finger users on other
   machines, browse the web etc.
   In particular, you can answer email that you have brought down to your
   machine whilst you are off line. Mail will simply sit in your mail
   queue until you dial back into your ISP.
   However, your machine is NOT connected to the Internet 24 hours a day,
   nor does it have the same IP number every time it is connected. So it
   is impossible for you to receive email directed to your machine, and
   very difficult to set up a web or ftp server that your friends can
   access! As far as the Internet is concerned your machine does not
   exist as a unique, permanently contactable machine as it does not have
   a unique IP number (remember - other machines will be using the IP
   number when they are allocated it on dial-in).
   If you set up a WWW, (or any other server), it is totally unknown by
   any user on the Internet UNLESS they know that your machine is
   connected AND its actual (current) IP number. There are a number of
   ways they can get this info, ranging from you ringing them, sending
   them email to tell them or cunning use of ".plan" files on a shell
   account at your service provider (assuming that your provider allows
   shell and finger access).
   Now, for most users, this is not a problem - all that most people want
   is to send and receive email (using your account on your service
   provider) and make outbound connections to WWW, ftp and other servers
   on the Internet. If you MUST have inbound connections to your server,
   you should really get a static IP number. Alternatively you can
   explore the methods hinted at above...
23.1. Setting up email

   Even for dynamic IP numbers, you can certainly configure sendmail on
   your machine to send out any email that you compose locally.
   Configuration of sendmail can be obscure and difficult - so this
   document does not attempt to tell you how to do this. However, you
   should probably configure sendmail so that your Internet service
   provider is designated as your "smart relay" host (the DS
   option). (For more sendmail configuration info, see the sendmail
   documents - and look at the m4 configurations that come with sendmail.
   There is almost certain to be one there that will meet your needs).
   There are also excellent books on Sendmail (notably the 'bible' from
   O'Reilly and Associates), but these are almost certainly overkill for
   most users!
   Once you have sendmail configured, you will probably want to have
   sendmail dispatch any messages that have been sitting in the outbound
   mail queue as soon as the PPP connection comes up. To do this, add the
sendmail -q &

   to your /etc/ppp/ip-up script (see below).
   Inbound email is a problem for dynamic IP numbers. The way to handle
   this is to:-
     * configure your mail user agent so that all mail is sent out with a
       "reply to" header giving your email address at your Internet
       Service provider. If you can, you should also set your FROM
       address to be your email address at your ISP as well.
     * use the popclient, fetchmail programs to retrieve your email from
       your service provider. Alternatively, if your ISP is using IMAP,
       use an IMAP enabled mail user agent, (such as pine).
   You can automate this process at dial up time by putting the necessary
   commands in the /etc/ppp/ip-up script (see below).
23.2. Setting Up a local Name server

   Whilst you can quite happily use the domain name servers located at
   your ISP, you can also set up a local caching only (secondary) name
   server that is brought up by the ip-up script. The advantage of
   running a local (caching only) name server is that it will save you
   time (and bandwidth) if you frequently contact the same sites during a
   long on-line session.
   DNS configuration for a caching only nameserver (that uses a
   "forwarders' line in the named.boot file pointing at your ISPs DNS) is
   relatively simple. The O'Reilly book (DNS and Bind) explains all you
   want to know about this.
   There is also a DNS-HOWTO available.
   If you are running a small LAN that can access the Internet through
   you Linux PC (using IP Masquerade for example), it is probably a good
   idea to run a local name server (with a forwarders directive) whilst
   the link is up as this will minimise the bandwidth and delays
   associated with name resolution.
   One point of Nettiquette: ask permission from your ISP before you
   start using a secondary, caching only name server in your ISP's
   domain. Properly configured, your DNS will not cause any problems to
   your ISP at all, but if you get things wrong, it can cause problems.
Chapter 24. Linking two networks using PPP

   There is basically no difference between linking a single Linux PC to
   a PPP server and linking two LANs using PPP on a machine on each LAN.
   Remember, PPP is a peer to peer protocol.
   However, you DEFINITELY need to understand about how routing is
   established. Read the NET-2 howto and the Linux Network Administrator
   Guide (NAG). You will also find TCP/IP Network Administration
   (published by O'Reilly and Assoc - ISBN 0-937175-82-X) to be of
   invaluable assistance.
   If you are going to be sub networking an IP network number on either
   side of the link, you will also find the Linux (draft) sub networking
   mini-howto) to be of use. This is available at [153]Linux Sub
   networking mini-HOWTO.
   In order to link two LANs, you must be using different IP network
   numbers (or subnets of the same network number) and you will need to
   use static IP numbers - or use IP masquerade. If you want to use IP
   masquerade, see the IP masquerade mini-howto for instructions on
   setting that up.
24.1. Setting up the IP numbers

   Arrange with the network administrator of the other LAN the IP numbers
   that will be used for each end of the PPP interface. If you are using
   static IP numbers, this will also probably require you to dial into a
   specific telephone number.
   Now edit the appropriate /etc/ppp/options[.ttyXX] file - it's a good
   idea to have a specific modem and port at your end for this
   connection. This may well require you to change your /etc/ppp/options
   file - and create appropriate options.ttyXX files for any other
   Specify the IP numbers for your end of the PPP link in the appropriate
   options file exactly as shown above for static IP numbers.
24.2. Setting up the routing

   You must arrange that packets on your local LAN are routed across the
   interface that the PPP link establishes. This is a two stage process.
   First of all, you need to establish a route from the machine running
   the PPP link to the network(s) at the far end of the link. If the link
   is to the Internet, this can be handled by a default route established
   by pppd itself at your end of the connection using the 'defaultroute'
   option to pppd.
   If however, the link is only linking two LANs, then a specific network
   route must be added for each network that is accessible across the
   link. This is done using a 'route' command for each network in the
   /etc/ppp/ip-up script (see "After the link comes up"...) for
   instructions on doing this.
   The second thing you need to do is to tell the other computers on your
   LAN that your Linux computer is actually the 'gateway' for the
   network(s) at the far end of the ppp link.
   Of course, the network administrator at the other end of the link has
   to do all this too! However, as s/he will be routing packets to your
   specific networks, a specific network route will be required, not a
   default route (unless the LANs at the far and of the link are linking
   into you to access the Internet across your connection).
24.3. Network security

   If you are linking you LAN to the Internet using PPP - or even just to
   a "foreign" LAN, you need to think about security issues. I strongly
   urge you to think about setting up a firewall!
   You should also speak to the LAN administrator at your site BEFORE you
   start linking to foreign LANs or the Internet this way. Failure to do
   so could earn you anything from no reaction to really serious trouble!
Chapter 25. After the link comes up - the /etc/ppp/ip-up script

   Once the PPP link is established, pppd looks for /etc/ppp/ip-up. If
   this script exists and is executable, the PPP daemon executes the
   script. This allows you to automate any special routing commands that
   may be necessary and any other actions that you want to occur every
   time the PPP link is activated.
   This is just a shell script and can do anything that a shell script
   can do (i.e. virtually anything you want).
   For example, you can get sendmail to dispatch any waiting outbound
   messages in the mail queue.
   Similarly, you can insert the commands into ip-up to collect (using
   pop) any email waiting for you at your ISP.
   There are restrictions on /etc/ppp/ip-up:-
     * It runs in a deliberately restricted environment to enhance
       security. This means you must give a full path to binaries etc.
     * Technically, /etc/ppp/ip-up is a program not a script. This means
       it can be directly executed - and hence it requires the standard
       file magic (#!/bin/bash) at the start of the first line and must
       be readable and executable by root.
25.1. Special routing

   If you are linking two LANs, you will need to set up specific routes
   to the 'foreign' LANs. This is easily done using the /etc/ppp/ip-up
   script. The only difficulty arises if your machine handles multiple
   PPP links.
   This is because the /etc/ppp/ip-up is executed for EVERY ppp
   connection that comes up, so you need to carefully execute the correct
   routing commands for the particular link that comes up - and not when
   any other link comes up!
25.2. Handling email queues

   When the link between two LANs comes up, you may well want to make
   sure that email that is queued at either end is flushed - sent out to
   its destination. This is done by adding the appropriate sendmail
   Using the bash 'case' statement on an appropriate parameter that pppd
   passes into the script accomplishes this. For example, this is the
   /etc/ppp/ip-up script I use to handle our WAN links and the link to my
   home Ethernet (also handled on the same ppp server).
25.3. A sample /etc/ppp/ip-up script

   The example below provides a variety of example uses.
# Script which handles the routing issues as necessary for pppd
# Only the link to Newman requires this handling.
# When the ppp link comes up, this script is called with the following
# parameters
#       $1      the interface name used by pppd (e.g. ppp3)
#       $2      the tty device name
#       $3      the tty device speed
#       $4      the local IP address for the interface
#       $5      the remote IP address
#       $6      the parameter specified by the 'ipparam' option to pppd
case "$5" in
# Handle the routing to the Newman Campus server
                /sbin/route add -net gw
# and flush the mail queue to get their email there asap!
                /usr/sbin/sendmail -q &
# Our Internet link
# When the link comes up, start the time server and synchronise to the world
# provided it is not already running
                if [ ! -f /var/lock/subsys/xntpd ]; then
                        /etc/rc.d/init.d/xntpd.init start &
# Start the news server (if not already running)
                if [ ! -f /var/lock/subsys/news ]; then
                        /etc/rc.d/init.d/news start &
# Get the email down to my home machine as soon as the link comes up
# No routing is required as my home Ethernet is handled by IP
# masquerade and proxyarp routing.
                /usr/sbin/sendmail -q &
exit 0

   As a result of bringing up the ppp link to our Newman campus and this
   script, we end up with the following routing table entries (this
   machine also is our general dial up PPP server AND handles our
   Internet link). I have interspersed comments in the output to help
   explain what each entry is) :-
[root@kepler /root]# route -n
Kernel routing table
Destination     Gateway         Genmask         Flags MSS    Window Use Iface
# the HOST route to our remote internet gateway   *      UH    1500   0      134 ppp4
# the HOST route to our Newman campus server    *      UH    1500   0       82 ppp5
# the HOST route to my home ethernet    *      UH    1500   0       74 ppp3
# two of our general dial up PPP lines     *      UH    552    0        0 ppp2     *      UH    552    0        1 ppp1
# the specific network route to the Newman campus LAN   UG    1500   0        0 ppp5
# the route to our local Ethernet (super-netting two adjacent C classes)      *        U     1500   0     1683 eth0
# the route to the loop back device       *            U     3584   0      483 lo
# the default route to the Internet
default   *               UG    1500   0     3633 ppp4
25.4. Handling email

   The previous section shows how to handle the outgoing mail - simply by
   flushing the mail queue once the link is up.
   If you are running a WAN link, you can arrange with the network
   administrator of the remote LAN to do exactly the same thing. For
   example, at the Newman Campus end of our WAN link, the /etc/ppp/ip-up
   script looks like :-
# Script which handles the routing issues as necessary for pppd
# Only the link to Hedland requires this handling.
# When the ppp link comes up, this script is called with the following
# parameters
#       $1      the interface name used by pppd (e.g. ppp3)
#       $2      the tty device name
#       $3      the tty device speed
#       $4      the local IP address for the interface
#       $5      the remote IP address
#       $6      the parameter specified by the 'ipparam' option to pppd
case "$5" in
                /usr/sbin/sendmail -q
exit 0

   If however you have only a dynamic IP PPP link to your ISP, you need
   to get your email from the account on your ISPs machine. This is
   usually done using the POP (Post Office Protocol). This process can be
   handled using the 'popclient' program - and the ip-up script can
   automate this process for you too!
   Simply create a /etc/ppp/ip-up script that contains the appropriate
   invocation of popclient. For my laptop that runs Red Hat Linux (which
   I take on any travels), this is...
popclient -3 -c -u hartr -p <password> |formail -s procma

   You could use slurp or whatever to do the same for news, and so forth.
   Remember, the ip-up script is just a standard bash script and so can
   be used to automate ANY function that needs to be accomplished every
   time the appropriate PPP link comes up.
Chapter 26. Using /etc/ppp/ip-down

   You can create a script that will be executed once the link has been
   terminated. This is stored in /etc/ppp/ip-down. It can be used to undo
   anything special that you did in the corresponding /etc/ppp/ip-up
Chapter 27. Routing issues on a LAN

   If you are connected to a LAN but still want to use PPP on your
   personal Linux machine , you need to address some issues of the routes
   packets need to take from your machine to reach your LAN (through your
   Ethernet interface) and also to the remote PPP server and beyond.
   This section does NOT attempt to teach you about routing - it deals
   only with a simple, special case of (static) routing!
   I strongly urge you to read the Linux Network Administrator Guide
   (NAG) if you are NOT familiar with routing. Also the O'Reilly book
   "TCP/IP Network Administration" covers this topic in a very
   understandable form.
   The basic rule of static routing is that the DEFAULT route should be
   the one that points to the MOST number of network addresses. For other
   networks, enter specific routes to the routing table.
   The ONLY situation I am going to cover here is where your Linux box is
   on a LAN that is not connected to the Internet - and you want to dial
   out to the Internet for personal use whilst still connected to the
   First of all, make sure that your Ethernet route is set up to the
   specific network addresses available across your LAN - NOT set to the
   default route!
   Check this by issuing a route command, you should see something like
   the following:-
[root@hwin /root]# route -n
Kernel routing table
Destination     Gateway         Genmask         Flags MSS    Window Use Iface
loopback        *        U     1936   0       50 lo        *        U     1436   0      565 eth0

   If your Ethernet interface (eth0) is pointing at the default route,
   (the first column will show "default" in the eth0 line) you need to
   change your Ethernet initialization scripts to make it point at the
   specific network numbers rather than the default route (consult the
   Net2 HOWTO and NAG).
   This will allow pppd to set up your default route as shown below:-
[root@hwin /root]# route -n
Kernel routing table

Destination     Gateway         Genmask         Flags MSS    Window Use Iface   *      UH    488    0        0 ppp0       *        U     1936   0       50 lo        *        U     1436   0      569 eth0
default   *               UG    488    0        3 ppp0

   As you can see, we have a host route to the PPP server ( via ppp0 and also a default network route that uses the
   PPP server as its gateway.
   If your set up needs to be more complex than this - read the routing
   documents already mentioned and consult an expert at your site!
   If your LAN already has routers on it, you will already have gateways
   established to the wider networks available at your site. You should
   STILL point your default route at the PPP interface - and make the
   other routes specific to the networks they serve.
27.1. Note on Security

   When you set up a Linux box on an existing LAN to link into the
   Internet, you are potentially opening your entire LAN to the Internet
   - and the hackers that reside there. Before you do this, I strongly
   urge you to consult your network administrator and site security
   policy. If your PPP connection to the Internet is used to successfully
   attack your site, you will at the very least earn the intense anger of
   your fellow users, network and system administrators. You may also
   find yourself in very much more serious trouble!
   Before you connect a LAN to the Internet, you should consider the
   security implications of even a DYNAMIC connection - hence the earlier
   reference to the O'Reilly "Building Internet Firewalls"!
Chapter 28. Setting up a PPP server

   As already mentioned, there are many ways to do this. What I present
   here is the way I do it, (using a Cyclades multi-port serial card),
   and a rotary dial in set of telephone lines.
   If you don't like the method I present here, please feel free to go
   your own way. I would however, be pleased to include additional
   methods in future versions of the HOWTO. So, please send me your
   comments and methods!
   Please note, this section only concerns setting up Linux as a PPP
   server. I do not (ever) intend to include information on setting up
   special terminal servers and such.
   Also, I have yet to experiment with shadow passwords (but will be
   doing so sometime). Information currently presented does NOT therefore
   include any bells and whistles that are required by the shadow suite.
28.1. Kernel compilation

   All the earlier comments regarding kernel compilation and kernel
   versions versus pppd versions apply. This section assumes that you
   have read the earlier sections of this document!
   For a PPP server, you MUST include IP forwarding in your kernel. You
   may also wish to include other capabilities (such as IP fire walls,
   accounting etc etc).
   If you are using a multi-port serial card, then you must obviously
   include the necessary drivers in your kernel too!
28.2. Overview of the server system

   We offer dial up PPP (and SLIP) accounts and shell accounts using the
   same user name/password pair. This has the advantages (for us) that a
   user requires only one account and can use it for all types of
   As we are an educational organization, we do not charge our staff and
   students for access, and so do not have to worry about accounting and
   charging issues.
   We operate a firewall between our site and the Internet, and this
   restricts some user access as the dial up lines are inside our
   (Internet) firewall (for fairly obvious reasons, details of our other
   internal fire walls are not presented here and are irrelevant in any
   The process a user goes through to establish a PPP link to our site
   (once they have a valid account of course) is :-
     * Dial into our rotary dialer (this is a single phone number that
       connects to a bank of modems - the first free modem is then used).
     * Log in using a valid user name and password pair.
     * At the shell prompt, issue the command ppp to start PPP on the
     * Start PPP on their PC (be it running Windows, DOS, Linux MAC OS or
       whatever - that is their problem).
   The server uses individual /etc/ppp/options.ttyXX files for each dial
   in port that set the remote IP number for dynamic IP allocation. The
   server users proxyarp routing for the remote clients (set via the
   appropriate option to pppd). This obviates the need for routed or
   When the user hangs up at their end, pppd detects this and tells the
   modem to hang up, bringing down the PPP link at the same time.
28.3. Getting the software together

   You will need the following software:-
     * Linux, properly compiled to include the necessary options.
     * The appropriate version of pppd for your kernel.
     * A 'getty' program that intelligently handles modem communications.
       We use getty_ps2.0.7h, but mgetty is highly thought of. I
       understand that mgetty can detect a call that is using pap/chap
       (pap is the standard for Windows95) and invoke pppd automatically,
       but I have yet to explore this.
     * An operational domain name server (DNS) that is accessible to your
       dial up users. You should really be running your own DNS if
28.4. Setting up standard (shell access) dialup.

   Before you can set up your PPP server, your Linux box must be capable
   of handling standard dial up access.
   This howto does NOT cover setting this up. Please see the
   documentation of the getty of your choice and serial HOWTO for
   information on this.
28.5. Setting up the PPP options files

   You will need to set up the overall /etc/ppp/options with the common
   options for all dial up ports. The options we use are:-
asyncmap 0

   Note - we do NOT use any (obvious) routing - and in particular there
   is no defaultroute option. The reason for this is that all you (as a
   PPP server) are required to do is to route packets from the ppp client
   out across your LAN/Internet and route packets to the client from your
   LAN and beyond.
   All that is necessary for this is a host route to the client machine
   and the use of the 'proxyarp' option to pppd.
   The 'proxyarp' option sets up (surprise) a proxy ARP entry in the PPP
   server's ARP table that basically says 'send all packets destined for
   the PPP client to me'. This is the easiest way to set up routing to a
   single PPP client - but you cannot use this if you are routing between
   two LANs - you must add proper network routes which can't use proxy
   You will almost certainly wish to provide dynamic IP number allocation
   to your dial up users. You can accomplish this by allocating an IP
   number to each dial up port. Now, create a /etc/ppp/options.ttyXX for
   each dial up port.
   In this, simply put the local (server) IP number and the IP number
   that is to be used for that port. For example

   In particular, note that you can use valid host names in this file (I
   find that I only remember the IP numbers of critical machines and
   devices on my networks - names are more meaningful)!
28.6. Setting pppd up to allow users to (successfully) run it

   As starting a ppp link implies configuring a kernel device (a network
   interface) and manipulating the kernel routing tables, special
   privileges are required - in fact full root privileges.
   Fortunately, pppd has been designed to be 'safe' to run set uid to
   root. So you will need to...
chmod u+s /usr/sbin/pppd

   When you list the file, it should then appear as...
-rwsr-xr-x   1 root     root        74224 Apr 28 07:17 /usr/sbin/pppd

   If you do not do this, users will be unable to set up their ppp link.
28.7. Setting up the global alias for pppd

   In order to simplify things for our dial up PPP users, we create a
   global alias (in /etc/bashrc) so that one simple command will start
   ppp on the server once they are logged in.
   This looks like...
alias ppp="exec /usr/sbin/pppd -detach"

   What this does is
     * exec : this means replace the running program (in this case the
       shell) with the program that is run.
     * pppd -detach : start up pppd and do NOT fork into the background.
       This ensures that when pppd exits there is no process hanging
   When a user logs in like this, they will appear in the output of 'w'
  6:24pm  up 3 days,  7:00,  4 users,  load average: 0.05, 0.03, 0.00
User     tty       login@  idle   JCPU   PCPU  what
hartr    ttyC0     3:05am  9:14                -

   And that is it...I told you this was a simple, basic PPP server
Chapter 29. Using PPP across a null modem (direct serial) connection

   This is very simple - there is no modem in the way so things are much
   First of all, choose one of the machines as a 'server', setting up a
   getty on the serial port so you can test that you do have connectivity
   using minicom to access the serial port on the 'client'.
   Once you have this functioning, you can remove the getty UNLESS you
   want to make sure that the connection is validated using user
   name/password pairs as for a dial up connection. As you have 'physical
   control' of both machines, I will presume that you do NOT want to do
   Now, on the server, remove the getty and make sure that you have the
   serial ports on both machines configured correctly using 'setserial'.
   All you need to do now is to start pppd on both systems. I will assume
   that the connection uses /dev/ttyS34 on both machines. So, on both
   machines execute the command:-
pppd -detach crtscts lock <local IP>:<remote IP> /dev/ttyS3 38400 &

   This will bring up the link - but as yet you have no routing
   specified. You can test the link by pinging to and fro to each
   machine. If this works, bring down the link by killing one of the pppd
   The routing you need will of course depend on exactly what you are
   trying to do. Generally, one of the machines will be connected to an
   Ethernet (and beyond) and so the routing required is exactly the same
   as for a PPP server and client.
   So on the Ethernet equipped machine, the pppd command would be...
pppd -detach crtscts lock proxyarp <local IP>:<remote IP> /dev/ttyS3 38400 &

   and on the other machine ...
pppd -detach crtscts lock defaultroute <local IP>:<remote IP> /dev/ttyS3 38400

   If you are linking two networks (using a serial link!) or have more
   complex routing requirements, you can use /etc/ppp/ip-up in exactly
   the same way as mentioned earlier in this document.
Chapter 30. PPPoE or PPP over Ethernet

   This document does not currently cover PPoE as it appears to NOT (for
   Linux anyway) be under active development. For those who have interest
   or need of PPPoE we do include the following links.
   We have heard rumors that the 2.4 series of kernels will have PPoE but
   we are unable to confirm this at this time. If you know differently
   please [154]contact us.
     * [155]pppoe: a PPP-over-Ethernet redirector for pppd
       This program can be used to enable PPPoE support using the pppd
       daemon. PPPoE is a technique for the encapsulation of PPP streams
       inside of Ethernet frames. This technology is being deployed by
       high-speed Internet access providers (cable modems, xDSL, etc.) in
       order to decouple the supply of bandwidth from ISP services. In
       particular, in Canada, the Bell Sympatico ADSL service is moving
       from DHCP-based access control to PPPoE. Further details on PPPoE
       can be found in RFC2516.
     * [156]Roaring Penguin PPoE Client.
       The client is a user-mode program and does not require any kernel
       modifications. It is fully compliant with RFC 2516, the official
       PPPoE specification.
     * [157]A PPoE FAQ Page. This page includes comprehensive information
       on what PPoE is, what it is used for, and implementations of the
       protocol. If you are looking for a good all around resource on
       PPoE this is an excellent page to start with.
     * [158]The actual RFC. This is for the technically minded only and
       usually only of help to those wishing to program with or for the


   2. ppp/PPP-HOWTO.html#AEN20
   3. ppp/PPP-HOWTO.html#AEN28
   4. ppp/PPP-HOWTO.html#AEN44
   5. ppp/PPP-HOWTO.html#AEN52
   6. ppp/PPP-HOWTO.html#AEN71
   7. ppp/PPP-HOWTO.html#AEN100
   8. ppp/PPP-HOWTO.html#AEN112
   9. ppp/PPP-HOWTO.html#AEN143
  10. ppp/PPP-HOWTO.html#AEN145
  11. ppp/PPP-HOWTO.html#AEN150
  12. ppp/PPP-HOWTO.html#AEN153
  13. ppp/PPP-HOWTO.html#AEN156
  14. ppp/PPP-HOWTO.html#AEN161
  15. ppp/PPP-HOWTO.html#AEN164
  16. ppp/PPP-HOWTO.html#AEN180
  17. ppp/PPP-HOWTO.html#AEN189
  18. ppp/PPP-HOWTO.html#AEN227
  19. ppp/PPP-HOWTO.html#TOOLS
  20. ppp/PPP-HOWTO.html#AEN238
  21. ppp/PPP-HOWTO.html#AEN314
  22. ppp/PPP-HOWTO.html#AEN328
  23. ppp/PPP-HOWTO.html#AEN342
  24. ppp/PPP-HOWTO.html#PROBLEMS
  25. ppp/PPP-HOWTO.html#AEN386
  26. ppp/PPP-HOWTO.html#AEN412
  27. ppp/PPP-HOWTO.html#AEN419
  28. ppp/PPP-HOWTO.html#AEN452
  29. ppp/PPP-HOWTO.html#AEN459
  30. ppp/PPP-HOWTO.html#AEN463
  31. ppp/PPP-HOWTO.html#AEN467
  32. ppp/PPP-HOWTO.html#AEN474
  33. ppp/PPP-HOWTO.html#AEN492
  34. ppp/PPP-HOWTO.html#AEN499
  35. ppp/PPP-HOWTO.html#AEN505
  36. ppp/PPP-HOWTO.html#AEN521
  37. ppp/PPP-HOWTO.html#AEN526
  38. ppp/PPP-HOWTO.html#AEN537
  39. ppp/PPP-HOWTO.html#AEN545
  40. ppp/PPP-HOWTO.html#AEN550
  41. ppp/PPP-HOWTO.html#AEN557
  42. ppp/PPP-HOWTO.html#AEN562
  43. ppp/PPP-HOWTO.html#AEN570
  44. ppp/PPP-HOWTO.html#AEN577
  45. ppp/PPP-HOWTO.html#AEN582
  47. ppp/PPP-HOWTO.html#AEN609
  48. ppp/PPP-HOWTO.html#AEN640
  49. ppp/PPP-HOWTO.html#AEN644
  50. ppp/PPP-HOWTO.html#AEN656
  51. ppp/PPP-HOWTO.html#AEN676
  52. ppp/PPP-HOWTO.html#AEN686
  53. ppp/PPP-HOWTO.html#SERVER-INFO
  54. ppp/PPP-HOWTO.html#MODEM
  55. ppp/PPP-HOWTO.html#AEN745
  56. ppp/PPP-HOWTO.html#AEN753
  57. ppp/PPP-HOWTO.html#AEN761
  58. ppp/PPP-HOWTO.html#AEN797
  59. ppp/PPP-HOWTO.html#AEN808
  60. ppp/PPP-HOWTO.html#DNS
  61. ppp/PPP-HOWTO.html#AEN877
  62. ppp/PPP-HOWTO.html#AEN892
  63. ppp/PPP-HOWTO.html#ROOT
  64. ppp/PPP-HOWTO.html#OPTIONS
  65. ppp/PPP-HOWTO.html#AEN964
  66. ppp/PPP-HOWTO.html#AEN970
  67. ppp/PPP-HOWTO.html#AEN980
  68. ppp/PPP-HOWTO.html#PAP
  69. ppp/PPP-HOWTO.html#AEN994
  70. ppp/PPP-HOWTO.html#AEN1005
  71. ppp/PPP-HOWTO.html#AEN1034
  72. ppp/PPP-HOWTO.html#AEN1053
  73. ppp/PPP-HOWTO.html#AEN1071
  74. ppp/PPP-HOWTO.html#MANUAL
  75. ppp/PPP-HOWTO.html#AUTOMATE
  76. ppp/PPP-HOWTO.html#AEN1173
  77. ppp/PPP-HOWTO.html#AEN1188
  78. ppp/PPP-HOWTO.html#AEN1200
  79. ppp/PPP-HOWTO.html#AEN1219
  80. ppp/PPP-HOWTO.html#AEN1285
  81. ppp/PPP-HOWTO.html#AEN1290
  82. ppp/PPP-HOWTO.html#AEN1303
  83. ppp/PPP-HOWTO.html#OFF
  84. ppp/PPP-HOWTO.html#AEN1329
  85. ppp/PPP-HOWTO.html#AEN1337
  86. ppp/PPP-HOWTO.html#AEN1341
  87. ppp/PPP-HOWTO.html#AEN1354
  88. ppp/PPP-HOWTO.html#AEN1357
  90. ppp/PPP-HOWTO.html#AEN1368
  91. ppp/PPP-HOWTO.html#AEN1386
  92. ppp/PPP-HOWTO.html#WAN
  93. ppp/PPP-HOWTO.html#AEN1403
  94. ppp/PPP-HOWTO.html#AEN1410
  95. ppp/PPP-HOWTO.html#AEN1418
  96. ppp/PPP-HOWTO.html#IP-UP
  97. ppp/PPP-HOWTO.html#AEN1442
  98. ppp/PPP-HOWTO.html#AEN1448
  99. ppp/PPP-HOWTO.html#AEN1455
 100. ppp/PPP-HOWTO.html#AEN1464
 101. ppp/PPP-HOWTO.html#AEN1477
 102. ppp/PPP-HOWTO.html#AEN1482
 103. ppp/PPP-HOWTO.html#AEN1500
 104. ppp/PPP-HOWTO.html#PPP-SERVER
 105. ppp/PPP-HOWTO.html#AEN1510
 106. ppp/PPP-HOWTO.html#AEN1516
 107. ppp/PPP-HOWTO.html#AEN1535
 108. ppp/PPP-HOWTO.html#AEN1547
 109. ppp/PPP-HOWTO.html#AEN1552
 110. ppp/PPP-HOWTO.html#AEN1569
 111. ppp/PPP-HOWTO.html#AEN1577
 112. ppp/PPP-HOWTO.html#DIRECT
 113. ppp/PPP-HOWTO.html#AEN1609
 137. ppp/PPP-HOWTO.html#SERVER-INFO
 138. ppp/PPP-HOWTO.html#MODEM
 139. ppp/PPP-HOWTO.html#DNS
 140. ppp/PPP-HOWTO.html#ROOT
 141. ppp/PPP-HOWTO.html#OPTIONS
 142. ppp/PPP-HOWTO.html#PAP
 143. ppp/PPP-HOWTO.html#MANUAL
 144. ppp/PPP-HOWTO.html#AUTOMATE
 145. ppp/PPP-HOWTO.html#OFF
 146. ppp/PPP-HOWTO.html#PROBLEMS
 147. ppp/PPP-HOWTO.html#IP-UP

Комментариев нет:

Отправить комментарий