What would course a port to go down..

[SoundsGood]

I am encountering an issue where on a Cisco 837 router, a device connected to one of the ports will cause another port to shutdown. For example on Fa0/1 there will be a Cisco 2950 switch, and on Fa0/4 there will be a single device for example a digital video recorder.

What occurs is that whilst port 4 is enabled on the router, no communication is possible between the router and the switch (nothing in cdp neighbours, nothing pingable, line protocol still shows as UP on both links). Whenever Fa0/4 is disabled, the switch immediately becomes visible again.

As this is being tested remotely I don't know exactly what device is on Fa0/4, my best guess is an misconfigured gateway causing a loop but I would appreciate any ideas from the wisdom that is OcUK?

 

[bigredshark]

sh span

are any of the links in a blocking state?

if so, you've created a loop, be glad the devices stopped you then fix it. It's going to be something like that and stp is enabled by default so it's a good bet...

 

[SoundsGood]

Ah good idea! thanks.

I will try that tomorrow.