Troubleshooting SLIP and PPP Links

Troubleshooting SLIP and PPP Links

If your SLIP or PPP link seems to be connecting, but you can't reach systems on the remote network, you might have a routing problem. Try to reach the remote system with ping:

% ping -c 10 dial-in.salad.com

If the connection is working, you should see output something like this:

PING dial-in.salad.com (192.26.79.52): 56 data bytes
64 bytes from 192.26.79.52: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 192.26.79.52: icmp_seq=1 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=2 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=3 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=4 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=5 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=6 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=7 ttl=255 time=1 ms
64 bytes from 192.26.79.52: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 192.26.79.52: icmp_seq=9 ttl=255 time=1 ms


----dial-in.salad.com PING Statistics----
10 packets transmitted, 10 packets received, 0% packet loss

If the connection is not working, you should see output like this:

PING dial-in.salad.com (192.26.79.52): 56 data bytes


----dial-in.salad.com PING Statistics----
10 packets transmitted, 0 packets received, 100% packet loss

If you can contact the remote host, but not other systems on the network, you probably have a routing problem. Check that your routing is set up as described in "SLIP and PPP Routing and Address Allocation".

If you aren't getting any connection at all, test the line with another utility. If you are familiar with uucp, you may want to establish a uucp link between the stations as a means of testing the connection. Most users will find cu an easier way to debug the link.

Note: cu requires a direct entry in the /etc/uucp/Devices file. Refer to "The Devices File" for more details. When debugging a SLIP connection, check each station separately. First check the port and modem on the local station by using a cu command like this:

cu -d -s speed -l port

For example, to test the port and modem installed on the station tuna.salad.com, you would use this cu command:

cu -d -s 38400 -l ttyf2

(It may be necessary to turn off the (uu)getty first by changing respawn to off on the line for the port in the file /etc/inittab.)

The modem should respond. Many modems respond by printing AT. If the modem does not respond as expected, review the SLIP configuration procedure for the local station and review the modem configuration and documentation. If the modem does respond as expected, disconnect from cu by typing a tilde followed by a dot:

~.

Connect the stations you want to link as you would for the SLIP link. On the local station, use cu to call the remote station through the port and connection you have already verified with cu.

Check the connection to the remote station with a cu command like this:

cu -d -sspeed telno

For example, to test the connection between tuna and dial-in.salad.com, you would call dial-in from tuna with this cu command:

cu -d -s38400 5552002

You should see the local station tell the modem to call the remote station. Eventually, you should see the login prompt. Type the send strings from the /etc/uucp/Systems file in response to the expect strings.