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Duplex Mismatch

I am getting the following error, "00:12:20 %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on Ethernet 0/0 (not full duplex) , with JAB050400 MH 5/40 (full duplex)"

This is a 2610 and I have changed from half to full and back again and I am still receiving this error. I have E0/0 plugged into a Cisco 4000 switch.

New Member

Re: Duplex Mismatch

Have you set both the switch and router to be full-duplex at the same time? Don't rely on auto-negotiation.

If so, are there any 3rd party switches between the router and the 4000 switch? There are issues with CDP and 3rd party switches incorrectly sensing duplex mismatches.


Re: Duplex Mismatch

Continuing on what Mick said...

You may see these errors also when you have an older device that speaks CDP v1 instead of CDP v2. Duplex info was added in CDP v2. You can turn off v2 support by doing 'no cdp advertise-v2' globally or just do a 'no cdp enable' on the interface going that this device is hanging off of. If you don't need CDP at all globally do 'no cdp run'

HTH, Erick

New Member

Re: Duplex Mismatch

Thank you guys- I finally had to use the "no cdp run" - we do have a 3rd party switch on the network, that might be the problem. What is wierd though is that this just started happening and this equiptment has not changed in over a year.

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