CDP-4-DUPLEX_MISMATCH

[mvknl]

Last weekend we upgraded our Nexus 5K switches to run NX-OS 5.2(1). Since then we see the CDP-4-DUPLEX_MISMATCH messages on several ports while we didn't have these messages on 5.0.3.

We see these messages on several ports with different systems attached:

- WLC 5508

- MDS 9222i

- UCS

For example the MDS 9222i when viewing the configuration:

interface mgmt0

  ip address X.X.X.X 255.255.255.0

  switchport speed 100

  switchport duplex full

And on the nexus:

interface Ethernet108/1/10

  description SAN mgt

  switchport access vlan 851

  speed 100

  duplex full

However, when showing cdp neighbor detail we see the following:

----------------------------------------

Device ID:SAN(FOX1443GCR1)

System Name:SAN

Interface address(es):

    IPv4 Address: X.X.X.X

Platform: DS-C9222I-K9, Capabilities: Router Switch IGMP Filtering Supports-STP-Dispute

Interface: Ethernet108/1/10, Port ID (outgoing port): mgmt0

Holdtime: 147 sec

Version:

Cisco Nexus Operating System (NX-OS) Software, Version 5.0(1a)

Advertisement Version: 2

Duplex: half

Mgmt address(es):

    IPv4 Address: X.X.X.X

I don't get it. Why does the switch claim it's half duplex while all physical interfaces are configured full duplex?

[Rick Morris]

This is a weird issue that I have seen with servers in the past.  The issue we had was we would set the interfaces to AUTO and it would not negotiate at the correct speed and duplex.  To resolve the issue we had to specify the duplex and speed.  Have you tried to set the interace(s) as auto instead of specifying 100/full?

[mvknl]

Yes, we've had it configured every possible way. The interfaces also agree on the correct speed and duplex settings (also when configured auto/auto). But even then CDP will state that there's a duplex mismatch.