Diald Howto

Table of Contents


  1. Introduction

     1.1 Objectives
     1.2 New versions
     1.3 Thanks

  2. Copyright and discharge of responsibility

  3. Quick Diald operation description

  4. Note about authentication

     4.1 Username and password - Login and password prompts.
     4.2 PAP - Password Authentication Protocol
     4.3 CHAP - Challenge Authentication Protocol

  5. Notes about DNS name resolution

  6. Connecting a standalone computer to an ISP using a modem and PPP

     6.1 /etc/diald/diald.options or diald.conf file
     6.2 Personal filters file
     6.3 Making the call
     6.4 Connection start script

  7. Conecting a computer to a group of different ISPs with a modem and PPP

     7.1 Note about sending mail using a relay host
     7.2 Scripts to automate multiple connections and changing from one to another
        7.2.1 Starting up
        7.2.2 New provider
        7.2.3 Changing from one to another

  8. Connecting a proxy/firewall to an ISP using a modem and PPP

     8.1 Example for Debian 2.1
     8.2 Example for Suse 6.1
     8.3 Example for Slackware 3.6

  9. Programs and versions used

  10. More information



  ______________________________________________________________________

  1.  Introduction



  1.1.  Objectives


  This document shows some typical scenarios for easy start using Diald.
  These scenarios include a connection from a standalone computer to an
  ISP using PPP over a modem without using pon/poff or ppp-on/ppp-off to
  a proxy/firewall server with different Internet connections through
  various ISPs.

  In the present document, the following scenarios will be treated:

  ·  Connecting a standalone computer to an ISP using a modem and PPP

  ·  Conecting a computer to a group of different ISPs with a modem and
     PPP

  ·  Connecting a proxy/firewall to an ISP using a modem and PPP

  In following versions of this document, other scenarios will be added,
  as multiple instances of Diald, ISDN lines and lines used to call and
  receive calls.

  Before this document, a Diald-mini-Howto exist, wrote by Harish Pillay
  h.pillay@ieee.org, that presented and example of connection to an ISP
  using a chat based authentication scheme (login and password previous
  to the pppd start, with no use of PAP or CHAP).

  Example configuration files will be included in this document to serve
  as starting point to get Diald up. To obtain maximum performance and
  all programs attributes, it is necesary you read all documentation
  from the programs and reconfigure the example configuration files
  included here.

  Finally, configuration files can be in different directories depending
  on what GNU/Linux distribution you are using. If you find a file
  commented here in other directory, please, write me.


  1.2.  New versions


  Latest version of this document can be found in my web page
  http://www.ctv.es/USERS/andressh/linux, in SMGL and HTML formats.
  Other versions and formats can be found in Spanish in the Insflug web
  site, http://www.insflug.org/documentos/Diald-Como/, and in other
  languages in the LDP - Linux Documentation Project,
  http://www.linuxdoc.org.


  1.3.  Thanks


  I want to be grateful to the people that help me to get my first Diald
  up and running with their example files (somebody who's name i forgot,
  Mr Cornish Rex, Hoo Kok Mun and John Dalbec), to the people that have
  wrote me to send corrections and suggestions for this document (Tim
  Coleman, Jacob Joseph, Paul Schmidt and Jordi Mallach), to the future
  translators of this document to other languages, and, of course, to
  all the people that have developed and develops Diald for us.

  This document was originally wrote in Spanish. The own author
  translated it, and some people made corrections.



  2.  Copyright and discharge of responsibility


  This document is Copyright © 2000 Andres Seco, and it's free. You can
  distribute it under the terms of the GNU General Public License, which
  you can get at http://www.gnu.org/copyleft/gpl.html. You can get
  unofficial translated issues somewhere in the Internet.

  Information and other contents in this document are the best of our
  knowledge. However, we may have made errors. So you should determine
  if you want to follow the instructions given in this document.

  Nobody is responsible for any damage to your computer and any other
  loss derived from the use of the information contained herein.

  THE AUTHOR AND MAINTAINERS ARE NOT RESPONSIBLE FOR ANY DAMAGE INCURRED
  DUE TO ACTIONS TAKEN BASED ON INFORMATION CONTAINED IN THIS DOCUMENT.

  Of course, i am open to all type of suggestions and corrections on the
  content of this document.


  3.  Quick Diald operation description


  In a few words, Diald creates a new network interface and sets it as
  the default gateway. This interface is not real (in the original
  documentation it is called proxy interface). Diald monitors this
  interface, and, when packets arrive, makes a ppp connection, waits for
  it to be stablished and changes the default gateway to this new ppp
  interface (usually ppp0).

  Diald monitors the interface to determine which packets have been
  received the interface and their types to decide if they are going to
  be considered to set the ppp connection up, maintain the link, drop it
  or do nothing, and how long the link should be help up after the
  packet is transmitted.

  Finally, if there is no more traffic and the last packet up time is
  over, Diald will close the link.

  You can control days and hours when the link can go up and when it
  cannot, so you can use the low cost hours/days or low trafic times.

  This previous description is valid for Diald versions from 0.16.5 to
  latest (0.99.3 when this document was finished), but latest versions
  also include aditional attributes such as user enabled list, advanced
  accounting, better support for ISDN lines, better performance using an
  ethertap device as proxy (this is like a network interface that
  read/writes over a socket instead of a real network adapter) in place
  of slip, backup connections and other functions.


  4.  Note about authentication


  When you connect to an Internet Services Provider, it is usually
  necesary that you send an username and a password. This can be
  accomplished using several methods; the exact method that you use is
  determined by your provider.

  Added to the three shown options, you can use a link without
  authentication, (generally when the remote end is also yours).



  4.1.  Username and password - Login and password prompts.


  Actually, this is not an usual authentication method to access the
  Internet through an ISP.

  Identification is made before pppd is started, and it is the dialer,
  usually chat, who sends the login name and the password. This data is
  sent in plaintext, so this method should not be considered secure.

  An example script for chat where you can see how to specify username
  and password to be sent before running pppd would look something like
  this:



       ABORT BUSY
       ABORT "NO CARRIER"
       ABORT VOICE
       ABORT "NO DIALTONE"
       ABORT "NO ANSWER"
       "" ATZ
       OK ATDT_TelephoneNumber_
       CONNECT \d\c
       ogin _Username_
       assword _Password_



  The last 2 lines define username and password, and when to send it
  (after receiving «ogin» and «assword» respectively.  The chat script
  only needs to see parts of the words «login» and «password» and so we
  don't check the first letter of each.  This is so that we don't need
  to worry about uppercase/lowercase characters.

  Suppose that this script is called provider, and it is saved into the
  /etc/chatscripts directory. Then, you can run it with:



       /usr/sbin/chat -v -f /etc/chatscripts/provider



  4.2.  PAP - Password Authentication Protocol


  If the provider you are using requires PAP as the authentication
  protocol, during the LCP negotiation in PPP this protocol will be
  asked to use this protocol. When the phone call is connected after
  using chat, pppd is started. In this scenario, pppd will send the
  username and the password, which it will look for in the /etc/ppp/pap-
  secrets file. This file must have read and write permissions only for
  root only, so that nobody else can read the passwords inside it.

  PAP is not very secure, as the password is sent in plaintext, so can
  be read by somebody that monitors your transmission line.

  Simple example of /etc/ppp/pap-secrets:



  _Username_ * _Password_



  4.3.  CHAP - Challenge Authentication Protocol


  If the provider you are using requires CHAP as the authentication
  protocol, during the LCP negotiation in PPP this protocol will be
  asked to use this protocol. When the phone call is connected after
  using chat, pppd is started. In this scenario, pppd will send the
  username and the password, which it will look for in the
  /etc/ppp/chap-secrets file. This file must have read and write
  permissions only for root only, so that nobody else can read the
  passwords inside it.

  CHAP is more secure than PAP, as the password is never sent through
  the transmission line in plaintext. The authentication server sends a
  random identifier (the challenge), that the client must encrypt with
  its password, and then send back to the server.

  Simple example of /etc/ppp/chap-secrets:



       _Username_ * _Password_



  Sometimes an ISP uses PAP and other times CHAP, so it is common to
  define your username and password in both files.


  5.  Notes about DNS name resolution


  Everytime you connect to an ISP, it is necesary to have configured DNS
  name resolution, so your computer can find IP addresses associated to
  a computer name.

  IP addresses of your DNS servers are placed into the /etc/resolv.conf
  file.

  In a standalone computer connecting to Internet, this file usually
  contains the IP addresses of your ISP's DNS servers:



       #/etc/resolv.conf file for ISPname
       nameserver 111.222.333.444
       nameserver 222.333.444.555



  In a proxy/firewall computer, this file usually contains its own IP
  address (or the loopback address, 127.0.0.1), and this computer
  includes a DNS server that translates DNS names to IP addresses by
  querying external DNS servers.



  #/etc/resolv.conf file for local DNS resolution
  nameserver 127.0.0.1



  Installation of a local DNS server is out of the scope of this
  document.  There is a lot of documentation about this, but a good and
  quick approach can be found in the DNS-Howto
  (http://www.linuxdoc.org/HOWTO/DNS-HOWTO.html).


  6.  Connecting a standalone computer to an ISP using a modem and PPP


  When configuring Diald to connect your computer to an ISP, the next
  steps will be necesary:

  ·  Getting the Diald package installed. The quickest way is to install
     the package that comes with your GNU/Linux distribution.

  ·  Configure DNS resolver (/etc/resolv.conf file).

  ·  Check that you can call an ISP. If your GNU/Linux distribution
     includes an utility to configure a connection, the quickest way
     will be to use it (pppconfig in Debian, kppp if you use KDE, etc).
     If you are having problems connecting to an ISP, the PPP-Howto
     (http://www.linuxdoc.org/HOWTO/PPP-HOWTO.html), Modem-Howto
     (http://www.linuxdoc.org/HOWTO/Modem-HOWTO.html) and Serial-Howto
     (http://www.linuxdoc.org/HOWTO/Serial-HOWTO.html) documents can
     help you.

  ·  Configure username and password in the /etc/ppp/pap-secrets and
     /etc/ppp/chap-secrets files, as mentioned in previous sections.

  And finally, going into Diald:


  ·  Prepare the Diald configuration file (/etc/diald/diald.options for
     version 0.16.5 and /etc/diald/diald.conf for later versions).

  ·  Prepare filters file /etc/diald/standard.filter, or better, leave
     that file as is, and modify a copy of it that you can call
     /etc/diald/personal.filter.

  ·  Prepare the script to make the call (/etc/diald/diald.connect with
     execute permissions for root) and instruction file for chat
     (/etc/chatscripts/provider), that will be used by the previous
     script.

  ·  Prepare scripts to be run when the link goes up and down
     (/etc/diald/ip-up and /etc/diald/ip-down) if you want to use it
     (both must have execute permissions for root).

  ·  Prepare script to set and delete routes (/etc/diald/addroute and
     /etc/diald/delroute) if you want (both must have execute
     permissions for root). This step is not necesary if you only use a
     single Diald instance.

  ·  Finally, start the diald daemon («/etc/init.d/diald start» in
     Debian, «/etc/rc.d/init.d/diald start» in RedHat).  Normally, Diald
     package installation process prepares the scripts to run Diald when
     the computer boot up in the /etc/rcX.d directories.

  If you make any change in the Diald config file when it is running, it
  is necesary to restart it («/etc/init.d/diald restart» in Debian,
  «/etc/rc.d/init.d/diald restart» in RedHat).


  6.1.  /etc/diald/diald.options or diald.conf file


  In this example file you must check for:

  ·  Comm port where your modem is connected. Option device.

  ·  Comm port speed to talk with modem. Option speed.

  ·  User name to be used in ppp. Option pppd-options.

  ·  Retry counters and timers.

  ·  Enabled connection hours. Options restrict.

  ·  Decide if you want to use the ip-up and ip-down scripts.  Options
     ip-up and ip-down.

  ·  Decide if you want to use the addroute and delroute scripts.
     Options addroute and delroute. Generally it is not needed to modify
     this scripts, but if you use more than one instance of Diald or
     have a complex configuration, you need it.

  ·  Decide if you use the standar or personal filter file. Options
     include.



  ##########################
  # /etc/diald/diald.options

  # Device where your modem is connected
  device /dev/ttyS0

  # Log file
  accounting-log /var/log/diald.log

  # Monitoring queue
  #fifo /var/run/diald/diald.fifo

  # Debug activation
  # Activating debug reduces performance
  #debug 31

  # We use PPP as encapsulator
  mode ppp

  # Local IP (when you connect this address is automatically modified
  # with the ip assigned by your ISP if you use the dinamic option).
  local 127.0.0.5

  # Remote IP (when you connect this address is automatically modified
  # with the ip of the remote server that receives our call).
  remote 127.0.0.4

  # Subnet mask for the wan link
  netmask 255.255.255.0

  # The IP addresses will be asigned when connection starts.
  dynamic

  # If link goes down by remote end, start it again only if there is
  # outgoing packets.
  two-way

  # When link is up, route directly to the real ppp interface, not the proxy
  # interface. Not to do this is a performance lost of about 20 per cent.
  # There are old kernels that do not support reroute. See diald manual for
  # more information
  reroute

  # Diald will set up the default route the the SLIP interface used as proxy
  defaultroute

  # Script to set up personalized routes
  #addroute "/etc/diald/addroute"
  #delroute "/etc/diald/delroute"

  # Scripts to execute when the link is up and ready or down and closed.
  # In Diald versions 0.9x there is another option called ip-goingdown that
  # can be used to run commands when the link is going to be down but is
  # still up.
  ip-up /etc/diald/ip-up
  #ip-down /etc/diald/ip-down

  # Scripts used to connect or disconnect the interface
  connect "/etc/diald/diald.connect"
  #disconnect "/etc/diald/diald.disconnect"

  # Use UUCP lock to signal the device is being used
  #lock

  # We connect over a modem. WARNING: Do not especify this options in the
  # ppp options file, because they will conflict with the diald options. To
  # see what ppp options that you can not use in the pppd-options option,
  # see the diald man page and search for pppd-options
  modem
  crtscts
  speed 115200

  # Some timers and retry options
  # See Diald man page for more information
  connect-timeout 120
  redial-timeout 60
  start-pppd-timeout 120
  died-retry-count 0
  redial-backoff-start 4
  redial-backoff-limit 300
  dial-fail-limit 10

  # Options to be passed to pppd
  # This options can be included in the /etc/ppp/options file, that are the
  # default options for pppd, but if you need to use different
  # configurations of diald for more than one instance, you must put it here
  # noauth - do not ask remote for authenticaion.
  #          "Infovнa Plus" (Spain) do not identify to our machine
  # user - our username and isp. Ask your isp for the sintaxis. Some isps,
  #        do not need the @isp
  pppd-options noauth user usuario@isp

  # Hour restriccions.
  # This section must be before filters.
  # The restrict command is experimental, and can change in other versions
  # of diald. Check the man page. (this example has been checked for 0.16,
  # but i think it runs in later versions).
  # Example: only use in the night from monday to friday, and all day in
  # saturday and sunday.
  restrict 8:00:00 18:00:00 1-5 * *
  down
  restrict * * * * *

  # No special tarificaion considerations
  # (first seconds included in the setup cost, tarify unit in seconds,
  # time in seconds to check if it is good to go down)
  #impulse 0,0,0
  # Bononet Noche (Spain-Telefуnica) is billed in seconds after the 160
  # first seconds
  impulse 160,0,0
  # if it would be billed in minuttes and the first 10 will be billed
  # always:
  #impulse 600,60,10

  # Standar filters
  #include /etc/diald/standard.filter
  # or personal filters
  include /etc/diald/personal.filter



  6.2.  Personal filters file


  Manipulation of this file must be done very carefully. This file is
  used to decide when and why to start up the line, maintain it, bring
  down the line or ignore a packet, depending on the traffic type.

  Generally, the Diald standar filter file is sufficient for most cases,
  but perhaps, it may be too restrictive or not restrictive enough in
  some situations. The personal.filter file that is shown has some
  corrections over the original from the 0.16 version.

  In next versions of this document, other commented more restrictive
  examples will be included.



  # /etc/diald/personal.filter
  # Filter rules shown are the same as in the standard.filter with the
  # following changes:
  #
  # Change 10 to 4 minuttes in "any other tcp conection".
  # Added "ignore tcp tcp.fin" to ignore the FIN ACK packets.
  # Ignore icmp packets (ping and traceroute don't fire up the interface).
  #

  # This is a pretty complicated set of filter rules.
  # (These are the rules I use myself.)
  #
  # I've divided the rules up into four sections.
  # TCP packets, UDP packets, ICMP packets and a general catch all rule
  # at the end.

  ignore icmp any

  #------------------------------------------------------------------------------
  # Rules for TCP packets.
  #------------------------------------------------------------------------------
  # General comments on the rule set:
  #
  # In general we would like to treat only data on a TCP link as significant
  # for timeouts. Therefore, we try to ignore packets with no data.
  # Since the shortest possible set of headers in a TCP/IP packet is 40 bytes,
  # any packet with length 40 must have no data riding in it.
  # We may miss some empty packets this way (optional routing information
  # and other extras may be present in the IP header), but we should get
  # most of them. Note that we don't want to filter out packets with
  # tcp.live clear, since we use them later to speedup disconnects
  # on some TCP links.
  #
  # We also want to make sure WWW packets live even if the TCP socket
  # is shut down. We do this because WWW doesn't keep connections open
  # once the data has been transfered, and it would be annoying to have the link
  # keep bouncing up and down every time you get a document.
  #
  # Outside of WWW the most common use of TCP is for long lived connections,
  # that once they are gone mean we no longer need the network connection.
  # We don't neccessarily want to wait 10 minutes for the connection
  # to go down when we don't have any telnet's or rlogin's running,
  # so we want to speed up the timeout on TCP connections that have
  # shutdown. We do this by catching packets that do not have the live flag set.

  # --- start of rule set proper ---

  # When initiating a connection we only give the link 15 seconds initially.
  # The idea here is to deal with possibility that the network on the opposite
  # end of the connection is unreachable. In this case you don't really
  # want to give the link 10 minutes up time. With the rule below
  # we only give the link 15 seconds initially. If the network is reachable
  # then we will normally get a response that actually contains some
  # data within 15 seconds. If this causes problems because you have a slow
  # response time at some site you want to regularly access, you can either
  # increase the timeout or remove this rule.
  accept tcp 15 tcp.syn

  # Keep named xfers from holding the link up
  ignore tcp tcp.dest=tcp.domain
  ignore tcp tcp.source=tcp.domain

  # (Ack! SCO telnet starts by sending empty SYNs and only opens the
  # connection if it gets a response. Sheesh..)
  accept tcp 5 ip.tot_len=40,tcp.syn

  # keep empty packets from holding the link up (other than empty SYN packets)
  ignore tcp ip.tot_len=40,tcp.live

  # Modification by Andres Seco to ignore the FIN ACK packets.
  ignore tcp tcp.fin

  # make sure http transfers hold the link for 2 minutes, even after they end.
  # NOTE: Your /etc/services may not define the tcp service www, in which
  # case you should comment out the following two lines or get a more
  # up to date /etc/services file. See the FAQ for information on obtaining
  # a new /etc/services file.
  accept tcp 120 tcp.dest=tcp.www
  accept tcp 120 tcp.source=tcp.www
  # Same for https
  accept tcp 120 tcp.dest=tcp.443
  accept tcp 120 tcp.source=tcp.443

  # Once the link is no longer live, we try to shut down the connection
  # quickly. Note that if the link is already down, a state change
  # will not bring it back up.
  keepup tcp 5 !tcp.live
  ignore tcp !tcp.live

  # an ftp-data or ftp connection can be expected to show reasonably frequent
  # traffic.
  accept tcp 120 tcp.dest=tcp.ftp
  accept tcp 120 tcp.source=tcp.ftp

  #NOTE: ftp-data is not defined in the /etc/services file provided with
  # the latest versions of NETKIT, so I've got this commented out here.
  # If you want to define it add the following line to your /etc/services:
  # ftp-data        20/tcp
  # and uncomment the following two rules.
  #accept tcp 120 tcp.dest=tcp.ftp-data
  #accept tcp 120 tcp.source=tcp.ftp-data

  # If we don't catch it above, give the link 10 minutes up time.
  #accept tcp 600 any
  # Modificacion de Andres Seco. Solo dejar 4 minutos mas.
  accept tcp 240 any

  # Rules for UDP packets
  #
  # We time out domain requests right away, we just want them to bring
  # the link up, not keep it around for very long.
  # This is because the network will usually come up on a call
  # from the resolver library (unless you have all your commonly
  # used addresses in /etc/hosts, in which case you will discover
  # other problems.)
  # Note that you should not make the timeout shorter than the time you
  # might expect your DNS server to take to respond. Otherwise
  # when the initial link gets established there might be a delay
  # greater than this between the initial series of packets before
  # any packets that keep the link up longer pass over the link.

  # Don't bring the link up for rwho.
  ignore udp udp.dest=udp.who
  ignore udp udp.source=udp.who
  # Don't bring the link up for RIP.
  ignore udp udp.dest=udp.route
  ignore udp udp.source=udp.route
  # Don't bring the link up for NTP or timed.
  ignore udp udp.dest=udp.ntp
  ignore udp udp.source=udp.ntp
  ignore udp udp.dest=udp.timed
  ignore udp udp.source=udp.timed
  # Don't bring up on domain name requests between two running nameds.
  ignore udp udp.dest=udp.domain,udp.source=udp.domain
  # Bring up the network whenever we make a domain request from someplace
  # other than named.
  accept udp 30 udp.dest=udp.domain
  accept udp 30 udp.source=udp.domain
  # Do the same for netbios-ns broadcasts
  # NOTE: your /etc/services file may not define the netbios-ns service
  # in which case you should comment out the next three lines.
  ignore udp udp.source=udp.netbios-ns,udp.dest=udp.netbios-ns
  accept udp 30 udp.dest=udp.netbios-ns
  accept udp 30 udp.source=udp.netbios-ns
  # keep routed and gated transfers from holding the link up
  ignore udp tcp.dest=udp.route
  ignore udp tcp.source=udp.route
  # Anything else gest 2 minutes.
  accept udp 120 any

  # Catch any packets that we didn't catch above and give the connection
  # 30 seconds of live time.
  accept any 30 any



  6.3.  Making the call


  /etc/diald/diald.connect file (it must have execute permission):



       /usr/sbin/chat -f /etc/chatscripts/provider



  /etc/chatscripts/provider file. In this example file you must check
  the destination phone number:



       ABORT BUSY
       ABORT "NO CARRIER"
       ABORT VOICE
       ABORT "NO DIALTONE"
       ABORT "NO ANSWER"
       "" ATZ
       OK ATDT123456789
       CONNECT \d\c



  6.4.  Connection start script


  It must have execute permission.

  This script can be used to many tasks (synchronize time, send the
  queued mail, get incoming mail, etc.).

  In the example, a message is sent to root with data passed to the
  script (interface, subnet mask, local ip address, remote ip address
  and cost for routing):



       #!/bin/sh

       iface=$1
       netmask=$2
       localip=$3
       remoteip=$4
       metric=$5

       # Set the time and date
       # netdate ntp.server.somecountry

       # Run the mail queue
       # runq

       echo `date` $1 $2 $3 $4 $5 | mail -s "diald - conecting" root@localhost



  7.  Conecting a computer to a group of different ISPs with a modem and
  PPP


  Many times, one standalone computer does not only connect to just one
  network. It is common to connect to different networks or to the
  Internet using some different service providers. In this case,
  changing configuration files each time you want to connect to a
  different site can be annoying.

  The solution i propose here consist in using different sets of
  configuration files for each different connection. You can find here
  some scripts to automate changing from one to another.


  7.1.  Note about sending mail using a relay host


  If your email client program uses a local Message Transfer Agent with
  a smtp relay host to send all messages, or if you use a email client
  program that sends the messages directly to your provider's smtp
  server, changing where you are connecting means you need to
  reconfigure this option for the smtp relay server. This is because the
  providers usually check if the receipt mailbox is local or to any
  domain directly maintained by this provider or if the origin ip
  address is from the range of ip addresses that this provider assigns,
  to avoid having an open relay server that can be used to send spam,
  anonymous message and so on.

  In the following examples, you will find how to change this parameter
  in the Smail configuration files in a simple configuration where all
  external messages are sent to a smtp relay server. If you use another
  Message Transfer Agent (MTA) in your system, you can send me what you
  must change in your MTA to include it here. If you use an email client
  program that directly sends to the external smtp server (Kmail,
  Netscape, etc.) send me your changes too.


  7.2.  Scripts to automate multiple connections and changing from one
  to another


  7.2.1.  Starting up


  First of all, create a subdirectory of /etc/diald called providers
  where you store your scripts to automatically change from one to
  another provider and the subdirectories with the set of files to
  configure each of the providers connections.

  With the next script this directory is created and filled with the
  current configuration files from Diald, chat, pppd and Smail, that
  will be treated as a template for the next configurations.



       #!/bin/sh
       #File /etc/diald/providers/setupdialdmultiprovider
       mkdir /etc/diald/providers
       mkdir /etc/diald/providers/setup
       cp /etc/ppp/pap-secrets /etc/diald/providers/setup
       cp /etc/ppp/chap-secrets /etc/diald/providers/setup
       cp /etc/resolv.conf /etc/diald/providers/setup
       cp /etc/diald/diald.options /etc/diald/providers/setup
       cp /etc/diald/standard.filter /etc/diald/providers/setup
       cp /etc/diald/personal.filter /etc/diald/providers/setup
       cp /etc/diald/diald.connect /etc/diald/providers/setup
       cp /etc/chatscripts/provider /etc/diald/providers/setup
       cp /etc/diald/ip-up /etc/diald/providers/setup
       cp /etc/diald/ip-down /etc/diald/providers/setup
       cp /etc/smail/routers /etc/diald/providers/setup



  7.2.2.  New provider


  With the next script the template configuration will be copied to a
  new directory to prepare it for a new provider connection or a new net
  connection. This script (/etc/diald/providers/newdialdprovider) will
  need a parameter with the provider or net name.



       #!/bin/sh
       #File /etc/diald/providers/newdialdprovider
       mkdir /etc/diald/providers/$1
       cp /etc/diald/providers/setup/* /etc/diald/providers/$1



  Now, you will modify as you need the new files in
  /etc/diald/providers/provdidername, being providername the parameter
  passed to newdialdprovider.


  7.2.3.  Changing from one to another


  At the end, with this script you will change all your configuration
  files related to Diald to connect to another provider or net. I use
  symbolic links to avoid using duplicate files. Using symbolic links,
  if you change any config file in its original location like
  /etc/resolv.conf, the change is really made in the
  /etc/diald/providers/providername/resolv.conf file.
       #!/bin/sh
       #File /etc/diald/providers/setdialdprovider
       /etc/init.d/diald stop
       #wait for Diald to stop.
       sleep 4
       ln -sf /etc/diald/providers/$1/pap-secrets /etc/ppp
       ln -sf /etc/diald/providers/$1/chap-secrets /etc/ppp
       ln -sf /etc/diald/providers/$1/resolv.conf /etc
       ln -sf /etc/diald/providers/$1/diald.options /etc/diald
       ln -sf /etc/diald/providers/$1/standard.filter /etc/diald
       ln -sf /etc/diald/providers/$1/personal.filter /etc/diald
       ln -sf /etc/diald/providers/$1/diald.connect /etc/diald
       ln -sf /etc/diald/providers/$1/provider /etc/chatscripts
       ln -sf /etc/diald/providers/$1/ip-up /etc/diald
       ln -sf /etc/diald/providers/$1/ip-down /etc/diald
       ln -sf /etc/diald/providers/$1/routers /etc/smail
       /etc/init.d/diald start



  8.  Connecting a proxy/firewall to an ISP using a modem and PPP


  Connecting a private net to the Internet with dedicated server which
  handles packet routing from the local network to the Internet along
  with proxy/caching services and security firewalling is a complex
  theme that is beyond the scope of this document. There are other
  «Howto» documents that handle these topics much more comprehensively.
  At the end of this document you can find a list of links and
  references to such documents.

  Here, we are only configuring Diald supposing that the computer
  already uses IP-Masquerading, has a web proxy like Squid or similar
  working, an ISP connection correctly configured and that access
  security to TCP/UDP ports have been revised (/etc/inetd.conf file and
  others like securetty, host.allow, etc).

  Basically, the only need is to reconfigure the rules for
  masquerading/filtering/accessing each time the set of interfaces
  change, that is, when the interface ppp0 is stablished and when it is
  deleted. A good location to do that are the ip-up and ip-down scripts
  from pppd.


  8.1.  Example for Debian 2.1


  With Debian, it is sufficient to install the ipmasq package answering
  that you want to change rules sinchronously with pppd when seting it
  up. Two scripts will be created inside /etc/ppp/ip-up.d and
  /etc/ppp/ip-down.d directories to call /sbin/ipmasq, a script that
  analizes existing interfaces and makes a simple configuration that is
  valid in many cases, but you can personalize it using rule files in
  /etc/ipmasq/rules.

  The only correction after installing this package is to change when
  the startup script for ipmasq is run, deleting the symbolic link from
  /etc/rcS.d and creating a new one in /etc/rc2.d to run it after
  S20diald. Now, when ipmasq is executed to analyze interfaces sl0
  already exist. S90ipmasq is a good name for this symbolic link to
  /etc/init.d/ipmasq.

  Using Debian there is no need to worry about the kernel version, as
  the /sbin/ipmasq script uses ipfwadm or ipchains as needed.
  8.2.  Example for Suse 6.1


  This example is from Mr Cornish Rex, troll@tnet.com.au.

  The following ip-masp and routing control commands are for use with
  version 2.2 kernels, using ipchains, but they are not valid for
  version 2.0 kernels.

  We are going to supose that the ethernet interface has the 192.168.1.1
  ip address with 16 bit netmask, that is, 255.255.0.0.

  This is the /etc/ppp/ip-up file:



       #!/bin/sh
       # $1 = Interface
       # $2 = Tty device
       # $3 = speed
       # $4 = local ip
       # $5 = remote ip
       # $6 = ipparam
       /sbin/ipchains -F input
       /sbin/ipchains -P input DENY
       /sbin/ipchains -A input -j ACCEPT -i eth0 -s 192.168.0.0/16 -d 0.0.0.0/0
       /sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 0:52 -l
       /sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 54:1023 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 0:112 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 114:1023 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6000:6010 -l
       /sbin/ipchains -A input -j DENY -p icmp --icmp-type echo-request \
       -i $1 -s 0.0.0.0/0 -l
       /sbin/ipchains -A input -j DENY -p icmp -f -i $1 -s 0.0.0.0/0 -l
       /sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 5555 -l
       /sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 8000 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 8000 -l
       /sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 6667 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6667 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4557 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4559 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4001 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 2005 -l
       /sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6711 -l
       /sbin/ipchains -A input -j DENY -i $1 -s 192.168.0.0/16 -d 0.0.0.0/0 -l
       /sbin/ipchains -A input -j ACCEPT -i $1 -s 0.0.0.0/0 -d $4/32
       /sbin/ipchains -A input -j ACCEPT -i lo -s 0.0.0.0/0 -d 0.0.0.0/0
       /sbin/ipchains -A input -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0 -l

       /sbin/ipchains -F output
       /sbin/ipchains -P output DENY
       /sbin/ipchains -A output -j ACCEPT -i eth0 -s 0.0.0.0/0 -d 192.168.0.0/16
       /sbin/ipchains -A output -j DENY -i $1 -s 192.168.0.0/16 -d 0.0.0.0/0 -l
       /sbin/ipchains -A output -j ACCEPT -i $1 -s $4/32 -d 0.0.0.0/0
       /sbin/ipchains -A output -j ACCEPT -i lo -s 0.0.0.0/0 -d 0.0.0.0/0
       /sbin/ipchains -A output -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0

       /sbin/ipchains -F forward
       /sbin/ipchains -P forward DENY
       /sbin/ipchains -M -S 120 120 120
       /sbin/ipchains -A forward -j MASQ -s 192.168.1.0/24
       /sbin/ipchains -A forward -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0

       exit 0


  This is the /etc/ppp/ip-down file:



       #!/bin/sh
       # $1 = Interface
       # $2 = Tty device
       # $3 = Speed
       # $4 = Local ip
       # $5 = Remote ip
       /sbin/ipchains -F input
       /sbin/ipchains -F output
       /sbin/ipchains -F forward
       /sbin/ipchains-restore < /etc/ppp/orig.chains



  Last file in last script, orig.chains, is the following file (original
  status of ipchains):



       # orig.chains
       # created with: ipchains-save > orig.chains
       :input ACCEPT
       :forward ACCEPT
       :output ACCEPT
       -A input -s 0.0.0.0/0.0.0.0 -d 192.168.1.1/255.255.255.255
       -A output -s 192.168.1.1/255.255.255.255 -d 0.0.0.0/0.0.0.0



  8.3.  Example for Slackware 3.6


  This example is from Hoo Kok Mun, hkmun@pacific.net.sg.

  This is the most simple example i have seen, but fully functional.
  From the beginning, this example configures masquerading, before the
  sl0 interface exists, and it does not change when the ppp0 interface
  appears. If you need advanced security considerations, it may be a
  little limited.



       #/etc/rc.d/rc.local
       /sbin/ipfwadm -F -p deny
       /sbin/ipfwadm  -F -a m -S 192.168.0.0/24 -D 0.0.0.0/0



  As you can see, it is for version 2.0 kernels.


  9.  Programs and versions used


  To write this document i have used the following diald versions:


  ·  Diald 0.16.5 - Last version maintained by the original diald autor.

  ·  Diald 0.99.3 - Last version until the first edition of this
     document.

  And the following pppd versions:


  ·  pppd 2.3.5

  Diald 0.16.5 version is perhaps the most extended, and the one that
  many Linux distributions include. It is suficient for many sites, and
  it is very reliable, but, of course, later versions have many
  interesting capabilites.


  10.  More information


  Original information from where this document has been obtained can be
  found in the man pages about diald, diald-examples, diald-control,
  diald-monitor, dctrl, pppd, chat, as well as from information in the
  /usr/doc directories and in web pages of this packages:


  ·  New Diald Official Home Page: http://diald.sourceforge.net/

  ·  Download of new versions: ftp://diald.sourceforge.net/pub/diald/

  ·  Previous Diald home page: http://diald.unix.ch

  ·  Old Diald home page until 0.16.5 version:
     http://www.loonie.net/~erics/diald.html

  ·  pppd FTP site: ftp://cs.anu.edu.au/pub/software/ppp/

  ·  Other site: http://www.p2sel.com/diald

  ·  One more: http://rufus.w3.org/linux/RPM/

  There is a mailing list for discussion about diald on David S.
  Miller's mailing list server at vger.rutgers.edu. To subscribe, send a
  message to Majordomo@vger.rutgers.edu with the text «subscribe linux-
  diald» IN THE MESSAGE BODY.

  An archive of the list can be found in http://www.geocrawler.com.

  There are also multiple RFC documents (Request For Comments) that
  define how the PPP encapsulated lines and its associated protocols
  (LCP, IPCP, PAP, CHAP, ...) must work. You can find these documents in
  the /usr/doc/doc-rfc directory and some World Wide Web sites, like
  http://metalab.unc.edu and http://nic.mil/RFC. You can ask for
  information about RFCs in RFC-INFO@ISI.EDU.

  The following «Howtos» can help you:


  ·  DNS-HOWTO - http://www.linuxdoc.org/HOWTO/DNS-HOWTO.html

  ·  Firewall-HOWTO - http://www.linuxdoc.org/HOWTO/Firewall-HOWTO.html

  ·  IP-Masquerade-HOWTO - http://www.linuxdoc.org/HOWTO/IP-Masquerade-
     HOWTO.html

  ·  IPCHAINS-HOWTO - http://www.linuxdoc.org/HOWTO/IPCHAINS-HOWTO.html

  ·  Modem-HOWTO - http://www.linuxdoc.org/HOWTO/Modem-HOWTO.html

  ·  NET3-4-HOWTO - http://www.linuxdoc.org/HOWTO/NET3-4-HOWTO.html

  ·  PPP-HOWTO - http://www.linuxdoc.org/HOWTO/PPP-HOWTO.html


  ·  Serial-HOWTO - http://www.linuxdoc.org/HOWTO/Serial-HOWTO.html