0

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
  • 2
    Is it possible that someone connected two switch connections on a wall plate? Did someone connect two interfaces of a PC that are bridged? Somehow, you have those switch interfaces connected as CDP reports. – Ron Maupin Dec 6 '19 at 22:36
  • 3
    What I do not see in your configuration are portfast and bpduguard. You should enable those. You can do it globally (recommended) or per interface. You are not getting a broadcast storm because those are different VLANs, but enabling those will shut down switch interfaces that see BPDUs from another switch, and that can really save you in the event of a spanning tree loop. Also, you now have created a larger broadcast domain (at least with VLAN 10 and 50) by combining the VLANs. – Ron Maupin Dec 6 '19 at 22:42
5

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)

| improve this answer | |
  • 1
    I've seen some really odd results from CDP in mixed vendor environments. – Ricky Beam Dec 6 '19 at 22:59
  • 2
    Confirming this answer. CDP frames can be forwarded/flooded by switches which do not speak the CDP protocol. Worth understanding what is physically out these ports. If you use per vlan spanning tree it may be worth verifying that the vlans are not “merged” into one spanning tree instance (look for the root bridge on each vlan). – Darrell Root Dec 7 '19 at 1:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.