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System Administration Guide: Resource Management and Network Services

How to Diagnose and Fix Communications Problems

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

  2. Call the remote peer with debugging turned on.


    % 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: 

    1. The machine or modem might have faulty cabling.

    2. The modem configuration might have incorrect bit settings or have broken flow control.

    3. The chat script might have failed. In this situation, see Table 35-5.

    The pppd debug output shows that LCP comes up, 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 using 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. 

    1. Check the chat scripts to verify whether it has incorrect IP addresses.

    2. 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 and adjust accordingly.