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LAG from N7k to 5508 getting Duplex Mismatch errors


Has anyone seen Duplex MisMatch errors on a N7k with a LAG going to the 5508 WLC?  WLC code is

I found a BUG that is private to Cisco ( CSCth11041 ) that looks like it, but I want to make sure.

Any help would be appreciated.



6 Replies 6

Amjad Abdullah

Do you have your N7K ports configured as 1000 Mbps Full Duplex?

How did you find the bug if it is private?

I think only TAC can confirm you about the bug if it is private!



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Hunter I have exactly the same problem...

Saurav Lodh
Rising star
Rising star

A duplex mismatch is a situation where the switch  operates at full duplex and the connected device operates at half duplex  or vice versa. The results of a duplex mismatch are extremely slow  performance, intermittent connectivity, and loss of connection. Other  possible causes of data link errors at full duplex are bad cables,  faulty switch ports, or client software or hardware issues.

Resolution : Since for 5500s WLC , data rate is fixed 1k full duplex, please check the switch side data rate , make sure it is set to 1000 Mbps Full Duplex.

Jacob Snyder

The problem is not a speed/duplex issue. It is a compatibility issue between the 7k and 5508 CDP. You will get this error even if you use 1Gbps fiber where you cannot set speed and duplex.

You can disable CDP on the WLC and the errors go aways. I think some versions of code on the 7k support the "no CDP enable" under the interfaces to the controller which should resolve it as well.

Sent from Cisco Technical Support iPhone App


Yes i checked the port speed on both WLC and switch. Both are Set on 1000. full duplex. but still the same issue.



My WLC is connected to 5k , (5548 UP) not 7k, i have another  5500 WLC connected to differentnexus 5k. it is not throwing any duplex errors, so i dont think it is a compatibility issue,  any more ideas



I saw this problem between our WLC 8510 and our NX5596. The wireless lan controller default CDP version is version 1 and the default Nexus cdp version is 2.


The WLC has an option to change the cdp version to V2 after this change we no longer had the duplex mismatch in our logs.

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