Symptom

On an ASR920 router, the duplex mode of a GigabitEthernet interface with media-type SFP may get set to half-duplex and the following Syslog is generated : %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on (not full duplex), with (full duplex).

Conditions

The configuration "negotiation auto", which enables the auto-negotiation feature is configured on the GigabitEthernet interface on the ASR920 and on the connected interface on the peer. The routers are reloaded.

Workaround

There is no work-around. Configuring "no negotiation auto" and configuring "negotiation auto" to disable and re-enable the auto-negotiation feature may help recover from the problem.

Further Problem Description