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New Member

Problems with LateCollisions on AutoNeg-100FDX


I have Catalyst 6009 switches and servers connected to them. Both should autonegotiate to 100Mbps fullduplex. But sometimes the switch detects "late-collsions" and err-disables the server-port. This happens mostly at high network load on the server (data saving while night).

CatOS 6.3(3) / RJ21-connectors, on different Intel Pro100+Server adapters (newest drivers)

My question: Does the autonegotiation happen once at the Joining of the server or in regular intervals (eg. every minute, hour)? Could there be a duplex-problem which only happens on high load - maybe servers forgets "fullduplex"???

What could be the cause?




Re: Problems with LateCollisions on AutoNeg-100FDX

*Always* hard-code the speed and duplex, unless you''re looking for problems. :) Especially on servers.

Also, turn off trunking and channeling on these ports, and enable spanning tree portfast. The 'set host mod/port' (might be set port host mod/port) command sets all these for you in one step.

HTH, Erick

Cisco Employee

Re: Problems with LateCollisions on AutoNeg-100FDX

Ports only negotiate on link up or state change. Are you sure both ports are auto-negotiating to 100 Mbps, FD. Make sure you are using the latest NIC driver.

See for more details

New Member

Re: Problems with LateCollisions on AutoNeg-100FDX

We had problems with 3524XL switches getting collision fragments, alignment errors and late collisions from servers under high load. Changing from auto-negotiate to 100/full did not help. It was only after getting the vendor to re-write NIC drivers the problems were solved. Not an easy task.

New Member

Re: Problems with LateCollisions on AutoNeg-100FDX

I am not sure how to measure that the NIC-vendor made a mistake in the drivers. I have no tool to measure which part is wrong (switch or nic)?

Which nic card was it (Intel Pro 100+ Server) and what driver version?




Re: Problems with LateCollisions on AutoNeg-100FDX

Check your jumper cables between the switch and the servers. Bad cabling can give you all sorts of strange errors (especially if they're hand-made, and not up to specification).

Look for kinks, twists, stretched jacketing, and sharp bends (every bend should have at least a 2" radius, and not stretched around a corner).

The jacketing should be in good shape for the length of the cable, and secured at each end under the strain relief dimple on the top of the connectors.

Check your panels for loose punches, etc. If you have a good qualification-grade scanner, do an end-to-end with it to make sure your cables are up to spec.

You'd be surprised at home many problems like this come back to bad (usually hand-made) cabling.

Good Luck


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