Loss of Trunking

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Apr 9th, 2008
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I'm trying to find a possible cause for momentary loss of trunking on a Gig Interface. There's no apparent Layer 1 loss and the other end of the connection doesn't experience any impact to it's trunking. Here's the log entry.

Apr 8 15:25:13.413 EST: %DTP-5-NONTRUNKPORTON: Port Gi0/12 has become non-trunk

Apr 8 15:25:13.564 EST: %DTP-5-TRUNKPORTON: Port Gi0/12 has become dot1q trunk

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nambi_gct Wed, 04/09/2008 - 04:54
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Looks like your DTP packets are getting lost.Is the link very congested?

Else you can disable DTP by setting the trunk protocol explicitly.

lamav Wed, 04/09/2008 - 07:05
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Going on the missing DTP packets assumption....

...if you do care to keep trunk negotiation on and the utilization looks normal, you can try checking for line errors and collisions on the trunk ports on both ends of the trunk. Such errors can be caused by a degraded connection (bad hardware) or a duplex mismatch. The duplex mismatch will speciifically cause collisions.

Just a quick note...if you do determine that the speed and duplex settings are mismatched, just set both ends to auto-negotiate. Auto-negotiation sometimes causes a problem, depending on the manufacturer of the hardware and the default behavior of the hardware and drivers, but auto-negotiation for the gigebitethernet standard is pretty robust and defaults to 1000/full on all Catalyst switches anyway.



Kevin Dorrell Wed, 04/09/2008 - 07:38
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It's a long shot, but it reminds me when I had exactly this symptom. Are these 1000BaseSX GBICs? If so, just try replacing them at both ends of the link.

In my limited experience, 1000BaseSX lasers are about as reliable as the ones the build into domestic CD players. (Admittedly I am going on too small sample to be statistically significant.)

Kevin Dorrell



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