How to Diagnose and Fix Serial-Line Speed Problems

1. Log in to the dial-in server. Call the peer with debugging enabled.

   If you need instructions, see How to Turn on PPP Debugging.

2. Display the resulting /var/log/pppdebug log.

   Check the output for the following message:

   LCP too many configure requests

   This message indicates that the speeds of serial lines that were configured for PPP might potentially be in conflict.

3. Check if PPP is invoked through a program such as /bin/login and the line speed that was set.

   In such a situation, pppd changes the originally configured line speed to the speed that is specified in /bin/login.

4. Check if a user started PPP from the mgetty command and accidentally specified a bit rate.

   This action also causes serial-line speeds to conflict.

5. Fix the conflicting serial-line speed problem as follows:

   1. Lock the DTE rate on the modem.

   2. Do not use autobaud.

   3. Do not change the line speed after configuration.