[c-nsp] %CDP-4-DUPLEX_MISMATCH - But they aren't connected!

[Jay Hennigan]

Tuc at T-B-O-H.NET wrote:
> Hi,
> 
> 	I'm getting on a 3640 running (C3640-JK9S-M), Version 12.4(13a) :
> 
> Dec  1 13:07:26 EST: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on Ethernet0/0 (not full duplex), with c2924-1.house.tucs-beachin-obx-house.com FastEthernet0/15 (full duplex).
> 
> 	The problem is that E0/0 is 10/half and facing a transit provider,
> while E0/1 is part of a bridge group with E1/1, and E0/1 also at 10/half
>  connects to port FA0/24 on c2924-1.house.tucs-beachin-obx-house.com (At
> 10/half). Port FA0/15 is connected to a consumer Ethernet over Power extender....
> (And yea, THAT is 100 full).
> 
> 	Does CDP need EVERYTHING to be running the same speed/duplex even
> when not connected directly together?

You'll often see that problem when there are non-Cisco layer 2 devices 
between the neighbors.

Some non-Cisco gear relays CDP frames out all interfaces which results 
in CDP reporting direct connections which in reality are not.  The only 
workaround of which I am aware is to disable CDP on those interfaces or 
ignore the error reports.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV