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The Status of the LCP Cannot Change to Up

Publication Date:  2012-07-27 Views:  304 Downloads:  0
Issue Description

When PPP is configured, the link layer protocol cannot change to Up.

Alarm Information
Handling Process
  1. Enable the debugging by running the debugging ppp all [ interface interface-type interface-number ] command.
  2. If the LCP negotiation fails, check the LCP negotiation parameters.

    Run the display this interface command in the interface view to check the status of the LCP. If the status is opened, it indicates that the LCP negotiation succeeds; otherwise, it indicates that the LCP negotiation fails.

  3. If the LCP negotiation parameters are correct, check whether the authentication mode is correctly configured. Since the LCP negotiation involves negotiating the authentication mode, the failure to negotiate the authentication mode also results in the failure of the LCP negotiation.
  4. In the interface view, run the display this interface command to obtain the interface information. Check whether the configured parameters take effect. If not, in this interface view, run the shutdown command to close the interface, and then run the undo shutdown command to restart the interface.
Root Cause

The possible causes that the PPP authentication fails are as follows:

  • The PPP interface parameters are incorrectly configured.
  • Both ends are configured with different authentication modes.

The interfaces at both ends of the PPP link must be configured with the same parameters and authentication modes. In this manner, the LCP negotiation succeeds.