H3C Technologies H3C SR8800 - Manual (Page 49)

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A physical link remains down
Symptom
A physical link remains down.
Analysis
A physical link is in the down state:
• The interface is not brought up.
• The interface is administratively shut down.
• LCP negotiation fails.
Solution
Execute the display interface serial command to check the state of the interface for the failure cause.
The following table describes the possible states of an interface.
Table 1 Description on the states of an interface and the corresponding output
Output Description
Serial2/1/9/1:0 current state: Administratively
DOWN
Line protocol current state: DOWN
The interface has been shut down by the
administrator.
Serial2/1/9/2:0 current state: DOWN
Line protocol current state: DOWN The interface has not been brought up yet or the
physical layer is down.
Serial2/1/9/2:0 current state: UP
Line protocol current state: UP
LCP negotiation has succeeded.
Serial2/1/9/2:0 current state: UP
Line protocol current state: DOWN The interface has been brought up but its LCP
negotiation failed.
A link remains down after IPv6CP negotiation fails
Symptom
Configure an IPv6 address on a PPP-encapsulated interface when IPv6 is disabled. The PPP link fails
IPv6CP negotiation and cannot go up. After enabling IPv6, the interface still cannot go up.
Analysis
IPv6CP negotiation cannot succeed when IPv6 is disabled. As IPv6CP does not support re-negotiation,
IPv6CP negotiation cannot succeed even if you enable IPv6 subsequently.
Solution
To resolve the problem, do the following:
• Enable IPv6 before configuring an IPv6 address on a PPP link.
• If IPv6CP negotiation fails, re-enable the interface with the shutdown command and the undo
shutdown command to re-enable IPv6CP negotiation.