Fixing General Communications Problems

Communications problems occur when the two peers cannot successfully establish a link. Sometimes these problems are actually negotiation problems that are caused by incorrectly configured chat scripts. This section contains information for clearing communications problems. For clearing negotiation problems that are caused by a faulty chat script, see Table 35–5.

How to Diagnose and Fix Communications Problems

1. Become superuser on the local machine. Then call the peer.

2. Call the remote peer. Then enable debugging features.

   % pppd debug call peer-name

   You might need to obtain debugging information from the peer in order to fix certain communications problems.

3. Check the resulting logs for the communications problems in the next table.

   Table 35–3 General Communications Problems That Affect PPP

   Symptom	Problem	Solution
   too many Configure-Requests	One peer cannot hear the other peer.	Check for the following problems:  The machine or modem might have faulty cabling. The modem configuration might have incorrect bit settings. Or, the configuration might have broken flow control. The chat script might have failed. In this situation, see Table 35–5.
   The pppd debug output shows that LCP starts, but higher-level protocols fail or show CRC errors.	The asynchronous control character map (ACCM) is incorrectly set.	Use the default-async option to set the ACCM to the standard default of FFFFFFFF. First try to use default-async as an option to pppd on the command line. If the problem clears, then add default-async to /etc/ppp/options or to /etc/ppp/peers/peer-name after the call option.
   The pppd debug output shows that IPCP comes up but terminates immediately.	IP addresses might be incorrectly configured.	Check the chat script to verify whether the script has incorrect IP addresses. If the chat script is okay, request debug logs for the peer, and check IP addresses in the peer logs.
   The link exhibits very poor performance.	The modem might be incorrectly configured, with flow-control configuration errors, modem setup errors, and incorrectly configured DTE rates.	Check the modem configuration. Adjust the configuration, if necessary.