Installing and Administering PPP

Chapter 6 137
Troubleshooting pppd
Restart pppd with the novjcomp option. If this fixes the problem, then
the peer may be using a buggy IPCP option negotiation algorithm. Try
running pppd with the rfc1172-vj or the rfc1172-typo-vj option. If these
options do not work, go back to novjcomp and complain to the vendor of
the peer’s implementation of PPP.
Scenario: PPP connects and everything works, but it is slow and erratic.
Solution: Check if your Telebit modem is using the PEP protocol. PPP over PEP is
normally show and erratic.
Increase pppd’s debugging level to 2 (input framing errors). Make sure
that received frames are arriving undamaged and that you are not
getting an excessive number of FCS errors.
Make sure that the telephone lines are relatively clean. Noisy phone
lines can cause FCS or other transmission errors, or can cause V.42 or
MNP error correcting protocols to retransmit excessively, or can cause
the modems to retrain frequently, slowing the connection.
Make sure the serial port is not running faster than your computer can
handle.
Make sure that flow control is set up properly on the modem and on the
serial port to which it is connected. If you are using hardware flow
control, make sure the cable connects RTS and CTS (RS-232 pins 4 and
5).
Scenario: When the user uses telnet, ping, or some other program to attempt a
connection, the modem does not start dialing and nothing is written to
the log.
Solution: Increase pppd’s debugging level to 6 (IP message summary). If it now
shows the packets, but says ’dial failed,’ then PPP is waiting after a
failed call attempt until the call retry delay timer expires. Use SIGINT to
tell pppd to reset the timer, change the Systems file entry if it is set to
use too long a delay, or wait until the timer expires.
Scenario: To avoid using a separate subnet, you set up your network as described
in “ARP Table Manipulation” in the section “Connecting a Host to a
LAN.” The remote workstations can exchange packets with everything
on that LAN, but not with any hosts or networks that are reachable
through a particular router.