CDP Mismatch from CDP: Why?

[Chris Schroeder]

Switch A, Cisco 9300, VTP mode transparent

interface GigabitEthernet1/0/5
switchport access vlan 3
switchport mode access

Switch B, Cisco 3560, VTP mode transparent
interface GigabitEthernet1/0/1
switchport access vlan 3
switchport mode access

Vlan 3 (L2) vlan created on both switches
CDP is running on both switches

When I bring the ports up, I get these messages on the 9300:

Apr 25 14:33:17.240 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:18.240 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:19.239 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:20.241 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:21.241 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:22.244 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:33:23.247 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).
Apr 25 14:34:00.561 CDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/5 (3), with Switch GigabitEthernet1/0/1 (1).

I do not know why.  How do you have any protocol reporting a native vlan mismatch when there is not VTP communication and neither port is configured as a trunk?

[Ramblin Tech]

CDP itself sends its port's native VLAN as a TLV with type 0x000a.

https://learningnetwork.cisco.com/s/article/cisco-discovery-protocol-cdp-x

https://wiki.wireshark.org/CDP

You can verify which native VLAN each port is advertising with a packet capture and decode.

[Reza Sharifi]

Hi,

Can you post the output of "sh cdp nei deti" so we can see what Native vlan is configured on the switches?

HTH

[David Ruess]

Hello,

VTP doesn't send "Native VLAN" information, so regardless if you have it configured or not you will see those messages from CDP which is running between the switches.

Secondly you don't need a "trunk" link to have a native VLAN. By definition a Native VLAN is just an untagged VLAN on that interface. As a result any port in access mode with a vlan associated to it is running a "Native VLAN". For obvious reasons its not called a Native VLAN on an access port but just an access VLAN.

You could try configuring both interfaces as a trunk link to see if the error resolves. Any particular reason you're using access ports to connect network switches?

-David

[Richard Burts]

David makes a very good point that VTP does not have anything to do with native vlan mismatch. In addition to the show cdp neighbor detail requested by Reza it might be helpful to see the output of show interface status from both switches.

[MHM Cisco World]

the CDP send native VLAN in port which is trunk I check in Lab this point, and it dont send it if the port is access 

MHM

[MHM Cisco World]

show switchport interface 1/0/5 and 1/0/1

share this in from both SW

MHM

[Joseph W. Doherty]

As the others, and you, have already noted, this should not be happening between two access port configured with same VLAN number.  VTP mode should be irrelevant and VTP doesn't run on access ports.

So, either you've encountered some bug or the limited interface config information you've posted is incorrect.  Posting the information requested within the other replies would be very helpful.

BTW, two possibly errors that immediately jump to my mind are, first the config information you've posted is from a current show running-config?  Second, it's g1/0/5<>g1/0/1 not g1/0/1<>g1/0/5?  (I.e., you're sure you've identified the correct port per switch, as I suspect both switches have both those ports.)