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New Member

Interesting Duplex/CDP Problem

I have a 3550 connected to a 3Com switch used to offload non-PoE devices and save ports on the 3550. Connected to the 3Com are 2 ATA 186s. The ATA's only run at half-duplex, and are working fine, but as the 3Com attaches to the 3550 on full-duplex, CDP thinks it sees a duplex mismatch where none exists. (CDP-4-DUPLEX_MISMATCH), and therefore constantly dumps messages to my syslog server. Now I can put "no cdp enable" on the interface, but in the future I won't be able to find those ATA's via CDP. I'm wondering if anyone has another possible solution to get CDP to ignore that error entirely or just on that interface.



Cisco Employee

Re: Interesting Duplex/CDP Problem

Hi Mark,

other than disabling CDP, the only other option is to lower your logging level to 3.



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Re: Interesting Duplex/CDP Problem

Get rid of your 3com switch. Not a option I suppose. This has alway been a issue with non cisco switches. They do not know what CDP is and do exactly what they are suppose to do with broadcast traffic and send it out.

I always thought it was funny that it would tell me I had a duplex mismatch between a 10/half port and a gig/full port. It didn't seem too concerned with the fact there was a speed mismatch.

Lately I have seen more vendor supporting CDP. HP and Juniper for example.

New Member

Re: Interesting Duplex/CDP Problem

Dependent on the os you can disable duplex mismatch errors under CDP in config:

"no cdp log mismatch duplex"


Re: Interesting Duplex/CDP Problem

I read somewhere they were supposed to working on a universal standard for device recognition but haven't seen anything else on it , would be nice if they could ratify something like that across all makers just like say trunking or other common protocols .