Switchport configured full duplex, but working on half

Unanswered Question
Sep 20th, 2010
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I have encountered a strange issue I have never seen before.

I have a 2811 router Fa0/0 interface connected directly to a C3750E gigabit switchport with a normal UTP patchcable.

Both sides are configured with speed 100, duplex full, but the switchport operational status is 100Mbps, Half-duplex.

Any ideas on what might cause this situation?

This is the switchport configuration:

0001#sh run int Gi1/0/44

Building configuration...


interface GigabitEthernet1/0/44

switchport access vlan 102

switchport mode access

speed 100

duplex full

no snmp trap link-status

spanning-tree bpduguard disable


This is the port operational status:
0001#sh int Gi1/0/44 status

Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/44                     connected    102          half    100 10/100/1000BaseTX
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Nagaraja Thanthry Mon, 09/20/2010 - 06:05
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  • Cisco Employee,


When both end hardware are different with different capabilities, it is better to set the speed/duplex to auto so that the two devices negotiate speed/duplex along with few other physical layer parameters.Here is a valid configuration table:


Here is a link that explains the reasons for enabling auto negotiation:


Hope this helps.




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