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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:

And finally, going into Diald:

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:

##########################
# /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.
#          "Infovía 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-Telefónica) 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


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