Kevin Dorrell Mon, 10/01/2007 - 06:43

Normally, if you are running Spanning Tree, it should not create a loop. Also, maybe it is not etherchannelling correctly.

The most likely explanation is that you have the fibres crossed. That is you have the TX of port 1 paired with the rx of port 2, and vice versa. If you enable UDLD on both switches, this would stop such a cabling problem becoming a loop. Best check the cables.

Kevin Dorrell


Anonymous (not verified) Mon, 10/01/2007 - 07:09

Anonymous (not verified) Mon, 10/01/2007 - 07:25

Anonymous (not verified) Mon, 10/01/2007 - 07:28

Sorry guys, this is new to me, thus i'm learning how to communicate.

I believe we have/had spanning tree portfast turned the major gi-ethernet interfaces.

My concern here is, if someone defines a trunked vlan on a major interface vs the portchannel interface will the etherchannel become unbundled. Its shouldn't right??

Kevin Dorrell Mon, 10/01/2007 - 07:47

So, welcome to the forum. BTW, how did you manage to get a blank username?

Just a tip: never put portfast on a trunk interface. Normally portfast will not even work on a trunk interface, but you can force it ... at your own peril.

Having said that, I think people sometime get too panicky about portfast. If you have portfast and you get a loop in your network, then you will get a broadcast storm. But only for a few seconds until one of the switches manages to process one of the BPDUs.

I'm not sure what happens if you configure one of the links of a bundle - I don't have my lab to hand to try it. But I do know that if the links are different, the box will not allow you to create the bundle in the first place.

However, that should not cause any problem, even if the links become unbundled. If two parallel links become unbundled, Spanning Tree will take care of it. What do you have? ... just an active link and a backup link.

But if you do have a broadcast storm, I think there is something more fundamental going on. Disconnect one of the links completely. Does the broadcast storm disappear? Ah, but you still have any connectivity at all?

Kevin Dorrell



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