Configuring the Point-to-Point Protocol (PPP)

Verifying the existence of a PPP network interface

Each PPP link must have a unique PPP network interface. For an outgoing link made from an automatic dialup or a dedicated serial endpoint, building this interface is the first action that the PPP daemon does after reading the endpoint configuration. If the network interface cannot be successfully built for these types of endpoint, no further progress toward establishing the PPP link is possible.

To verify the existence of a PPP network interface for your outgoing dedicated or automatic dialup endpoint:

ifconfig -a

ifconfig will display output similar to:

   net1: flags=4043<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
           inet 10.0.246.7 netmask ffffff00 broadcast 10.0.246.255
           ether 00:00:c0:06:95:18
   lo0: flags=4049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 8232
           inet 127.0.0.1 netmask ff000000
   ppp0: flags=4070<POINTOPOINT,WANTIOCTLS,RUNNING,MULTICAST> mtu 1500
           inet 10.0.246.6 --> 10.0.246.8 netmask ffffff00
   ppp1: flags=4070<POINTOPOINT,WANTIOCTLS,RUNNING,MULTICAST> mtu 1500
           inet 10.0.246.7 --> 10.0.246.9 netmask ffffff00
   ppp2: flags=4070<POINTOPOINT,WANTIOCTLS,RUNNING,MULTICAST> mtu 1500
           inet 10.0.246.10 --> 10.0.246.11 netmask ffffff00

The entries for ppp0, ppp1, and ppp2 are examples of what will appear for PPP network interfaces that exist. To determine which entry reflects the network interface for the PPP link you are troubleshooting, you must know the IP addresses specified in the PPP link configuration. In the entry for ppp2, for example, ``10.0.246.10'' is the IP address being used for the local host and ``10.0.246.11'' is the IP address being used for the remote host.

If a network interface entry is not displayed for the endpoint you are troubleshooting, PPP was unable to build an interface based on the interface parameters in the endpoint configuration. Perform the following steps:

Check that the source and destination addresses in the endpoint configuration in /etc/ppphosts are correct.
Force the PPP daemon to reread the /etc/ppphosts file:

kill -HUP `cat /etc/pppd.pid`

If a network interface still fails to appear for this endpoint, check the syslogd logging file for clues.

If a network interface entry does exist for the endpoint you are troubleshooting:

Check that the source and destination addresses are correct and have corresponding entries on the remote host.
Check the netmasks of both machines. An incorrect netmask can render a host or network unreachable.
Go to ``Verifying integrity of a dedicated serial line'' to continue troubleshooting a dedicated link.
Go to ``Testing automatic dialup connectivity'' to continue troubleshooting an outgoing link from an automatic dialup endpoint.

Next topic: Using ping to test reachability using host names
Previous topic: PPP troubleshooting flowchart

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003