CDP Native VLAN Mismatch – How to Resolve

cdpcisco-3750cisco-ios-15

I am getting CDP NATIVE VLAN MISMATCH logs on my Cisco 3750x switch stack.
Gig 2/0/5 and Gig 4/0/6 are in no way physically connected to each other (neither is 1/0/44 and 2/0/13 as you'll see below). I interconnect each switch via Stackwise cabling. I haven't seen any performance issues regarding this. Possibly a bug? I'm running 15.2(4)E9 on all of the following switches

Dec  6 17:06:11: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50).
Dec  6 17:06:11: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50). (3750X_STACK-2)
Dec  6 17:07:07: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet4/0/6 (50), with 3750X_STACK GigabitEthernet2/0/5 (10).
Dec  6 17:07:07: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet4/0/6 (50), with 3750X_STACK GigabitEthernet2/0/5 (10). (3750X_STACK-4)
Dec  6 17:07:10: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50).
Dec  6 17:07:10: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50). (3750X_STACK-2)
Dec  6 17:07:59: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50).
Dec  6 17:07:59: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/0/5 (10), with 3750X_STACK GigabitEthernet4/0/6 (50). (3750X_STACK-2)
Dec  6 17:08:07: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet4/0/6 (50), with 3750X_STACK GigabitEthernet2/0/5 (10).
Dec  6 17:08:07: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet4/0/6 (50), with 3750X_STACK GigabitEthernet2/0/5 (10). (3750X_STACK-4)
3750X_STACK#show switch detail
Switch/Stack Mac Address : xxxx.xxxx.xxxx
                                           H/W   Current
Switch#  Role   Mac Address     Priority Version  State
----------------------------------------------------------
*1       Master xxxx.xxxx.xxxx     15     3       Ready
 2       Member xxxx.xxxx.xxxx     1      3       Ready
 3       Member xxxx.xxxx.xxxx     1      3       Ready
 4       Member xxxx.xxxx.xxxx     1      3       Ready



         Stack Port Status             Neighbors
Switch#  Port 1     Port 2           Port 1   Port 2
--------------------------------------------------------
  1        Ok         Ok                2        4
  2        Ok         Ok                3        1
  3        Ok         Ok                4        2
  4        Ok         Ok                1        3
3750X_STACK#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
3750X_STACK
                 Gig 2/0/5         171             R S I  WS-C3750X Gig 4/0/6
3750X_STACK
                 Gig 4/0/6         131             R S I  WS-C3750X Gig 2/0/5
3750X_STACK
                 Gig 2/0/13        150             R S I  WS-C3750X Gig 1/0/44
3750X_STACK
                 Gig 1/0/44        147             R S I  WS-C3750X Gig 2/0/13
Switch Ports Model                     SW Version            SW Image
------ ----- -----                     ----------            ----------
*    1 54    WS-C3750X-48P             15.2(4)E9             C3750E-UNIVERSALK9-M
     2 54    WS-C3750X-48P             15.2(4)E9             C3750E-UNIVERSALK9-M
     3 54    WS-C3750X-48P             15.2(4)E9             C3750E-UNIVERSALK9-M
     4 54    WS-C3750X-48P             15.2(4)E9             C3750E-UNIVERSALK9-M
3750X_STACK#show run interface gigabitEthernet 2/0/5
Building configuration...

Current configuration : 151 bytes
!
interface GigabitEthernet2/0/5
 switchport access vlan 10
 switchport trunk encapsulation dot1q
 switchport mode access
end

3750X_STACK#show run interface gigabitEthernet 4/0/6
Building configuration...

Current configuration : 106 bytes
!
interface GigabitEthernet4/0/6
 switchport access vlan 50
 switchport mode access
end

Best Answer

This happens when something downstream of the switch doesn't understand CDP and mishandles the traffic. So, something is connecting 2/0/5 to 4/0/6; chase the wiring and you'll find it. (someone has a dumb switch, or dumb VM leaking traffic)