c871 - VLAN1 is self-looped

Unanswered Question
Sep 19th, 2008

Does anyone know why spanning-tree would place the Fa0 interface on a c871 in to a self-looped state?

When we connect a PC to the interface everything works fine and the PC can ping the vlan1 interface on the router. As soon as we place a switch on the same port 'sh spanning-tree' shows:

Port 1 (FastEthernet0) of VLAN1 is self-looped

The router is on a customers site and they are connecting a Linksys SRW248G4, it is only connecting to the one port on the 871 router and the switch connects to nothing else.

Spanning-tree indicates that the router is root for vlan1.

Any ideas? The router is running c870-advipservicesk9-mz.124-4.T1



I have this problem too.
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Giuseppe Larosa Fri, 09/19/2008 - 04:34

Hello Mel,

a cross-over RJ-45 cable could help in connecting to another switch port.

or you need to enable negotiation of MDXI

Hope to help


Mel Popple Fri, 09/19/2008 - 05:46

Thanks for the response.

The interface shows Up & Up so I am presuming that the link is OK. it's set to 100 full.

How do you enable negotiation of MDX on these routers I can't see anything under the interface settings for change this.


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