8.2.5. Dialup Interfaces

If 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, not already discussed, 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 remote system's IP address. 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.