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14.2.5. Dialup Interfaces

If you are connecting to the Internet via a dialup connection, a configuration file is necessary for the interface.
PPP interface files are named using the following format:
ifcfg-ppp<X>
where <X> is a unique number corresponding to a specific interface.
The PPP interface configuration file is created automatically when wvdial, the Network Administration Tool or Kppp is used to create a dialup account. It is also possible to create and edit this file manually.
The following is a typical ifcfg-ppp0 file: 
DEVICE=ppp0 NAME=test WVDIALSECT=test MODEMPORT=/dev/modem LINESPEED=115200 PAPNAME=test USERCTL=true ONBOOT=no PERSIST=no DEFROUTE=yes PEERDNS=yes DEMAND=no IDLETIMEOUT=600
Serial Line Internet Protocol (SLIP) is another dialup interface, although it is used less frequently. SLIP files have interface configuration file names such as ifcfg-sl0.
Other options that may be used in these files include:
DEFROUTE=<answer>
where <answer> is one of the following:
  • yes — Set this interface as the default route.
  • no — Do not set this interface as the default route.
DEMAND=<answer>
where <answer> is one of the following:
  • yes — This interface allows pppd to initiate a connection when someone attempts to use it.
  • no — A connection must be manually established for this interface.
IDLETIMEOUT=<value>
where <value> is the number of seconds of idle activity before the interface disconnects itself.
INITSTRING=<string>
where <string> is the initialization string passed to the modem device. This option is primarily used in conjunction with SLIP interfaces.
LINESPEED=<value>
where <value> is the baud rate of the device. Possible standard values include 57600, 38400, 19200, and 9600.
MODEMPORT=<device>
where <device> is the name of the serial device that is used to establish the connection for the interface.
MTU=<value>
where <value> is the Maximum Transfer Unit (MTU) setting for the interface. The MTU refers to the largest number of bytes of data a frame can carry, not counting its header information. In some dialup situations, setting this to a value of 576 results in fewer packets dropped and a slight improvement to the throughput for a connection.
NAME=<name>
where <name> is the reference to the title given to a collection of dialup connection configurations.
PAPNAME=<name>
where <name> is the username given during the Password Authentication Protocol (PAP) exchange that occurs to allow connections to a remote system.
PERSIST=<answer>
where <answer> is one of the following:
  • yes — This interface should be kept active at all times, even if deactivated after a modem hang up.
  • no — This interface should not be kept active at all times.
REMIP=<address>
where <address> is the IP address of the remote system. This is usually left unspecified.
WVDIALSECT=<name>
where <name> associates this interface with a dialer configuration in /etc/wvdial.conf. This file contains the phone number to be dialed and other important information for the interface.