Core issue
A duplex mismatch is reported if the settings on two sides of a link are different.
Resolution
Issue the show interfaces command for Cisco IOS Software and the show port command for Catalyst OS (CatOS) commands, and check the duplex settings on both sides of the link. Make sure they match. If the settings on both devices match, check the reported values through Simple Network Management Protocol (SNMP).
For CatOS and Cisco IOS switches, refer to this output:
# snmpwalk -c public switch.cisco.com portDuplex
cisco.workgroup.ciscoStackMIB.portGrp.portTable.portEntry.portDuplex.1.1
: INTEGER: full
cisco.workgroup.ciscoStackMIB.portGrp.portTable.portEntry.portDuplex.1.2
: INTEGER: half
For Cat2900/3500, refer to this output:
# snmpwalk -c public c2900.cisco.com c2900PortDuplexStatus
cisco.ciscoMgmt.ciscoC2900MIB.c2900MIBObjects.c2900Port.c2900PortTable.c2900Port
Entry.c2900PortDuplexStatus.0.1 : INTEGER: halfduplex cisco.ciscoMgmt.ciscoC2900MIB.c2900MIBObjects.c2900Port.c2900PortTable.c2900Port
Entry.c2900PortDuplexStatus.0.2 : INTEGER: fullduplex
For Cisco IOS routers, refer to this output:
# snmpwalk -c public router.cisco.com dot3StatsDuplexStatus
transmission.dot3.dot3StatsTable.dot3StatsEntry.19.9 : INTEGER: halfDuplex
transmission.dot3.dot3StatsTable.dot3StatsEntry.19.10 : INTEGER: fullDuplex
If the device does not return the correct information through SNMP, upgrade the device to the latest image. Refer to LAN Switching Software.
If the device returns the correct information, install the latest Campus Manager Incremental Device Update (IDU). Refer to Software Download: Ciscoworks Campus Manager Patches.
