flapping trunk port

[suthomas1]

Hi,

we have a 3750 connected via portchannel trunk to a 6500 switch.

the port channel goes into err disabled mode on the 6500, it comes back up after a manual no shut is done.

what could be the reason for its frequent flaps. we have arp inspection & dhcp snooping on certain vlans.

None of these have been put on the port channel interface. there are certain servers from these vlans operating on the 3750.

what could cause the portchannel to go down if arp inspection and dhcp snooping is enabled & how to fix this up.

Appreciate all inputs.

[Leo Laohoo]

the port channel goes into err disabled mode on the 6500

This is a related question, but what is the cause of the port going into error-disable?  Can you post the output (when it happens) to the command "sh interface status err"?

what could be the reason for its frequent flaps.

You should be able to see the related information in the "sh logs" of the chassis.

[suthomas1]

Thanks.we'll post the output once the subsidaries give it. But to get a fair idea, how can a server or node cause the link ti go down

With regards to arp inspection or snooping feature. 

[Leo Laohoo · Accepted solution]

Most common culprit why a link would go down/up erratically is when you've got a faulty cable or a faulty NIC. 

[mfurnival]

This document shows the possible reasons why a port will go into the err-disable state:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml#topic3