%CDP-4-NATIVE_VLAN_MISMATCH

[Ibrahim Jamil]

Hi Folks

what is the reason for below,output,How to trouleshoot?

45813: *Dec 26 01:02:51: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/49 (8), with CORE-2 GigabitEthernet1/8 (1).

645814: *Dec 26 01:03:51: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/49 (8), with CORE-2 GigabitEthernet1/8 (1).

645815: *Dec 26 01:04:51: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/49 (8), with CORE-2 GigabitEthernet1/8 (1).

645816: *Dec 26 01:05:51: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet1/0/49 (8), with CORE-2 GigabitEthernet1/8 (1).

[Rajeev Ranjan]

Hi Ibrahim,

When connecting Cisco switches through an 802.1Q trunk, make sure the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops might result.

So make sure that you have same native vlan on both switch(By default VLAN1 is the native VLAN). You can check by this command

SWITCH#Show Interface trunk.

Rajeev

[ranraju]

The switch interface gig1/0/49 has a native vlan as VLAN8, but on the other end of the link is of native vlan as VLAN1.

This can cause some serious trouble in terms of spanning tree on the network, when there is such a mismatch on the link, the packets from vlan8 and  vlan1 gets mixed. Which is not desirabled. How that happens is, this switch sends the frames untagged on VLAN8, and at the other end when frames are received untagged it would consider them as VLAN1 and then these frames are now in the VLAN1 instead of VLAN8.

So you need to make sure you have same native vlan on the  trunk on both ends of the link. The purpose of making it a native vlan  is to send frames in that vlan untagged across the link.

To change the native vlan on a link the command to use is "switchport trunk native vlan X".

To veiw what is the native vlan set on the link, you could always use the following commands, "show interface trunk" or "show int gigx/y switchport".

Hope this helps.

(kindly rate the helpful posts)

Regards,

ranraju

[glen.grant]

  Depends on what the link is , access or trunk .  If a trunk match the native vlans on each end and it will go away.  If its just a access port with a switch hung off the other end and that switch is configured in vlan 1 then it won't hurt anything other than you will get those continous cdp messages in your logg .  If you want to get rid of those then you would have to reconfigure that whole switch so everything is setup in vlan 8 and not vlan 1  and that will make it go away.

[Ibrahim Jamil]

Thanks

[milan.kulik]

Hi,

you don't have to reconfigure that whole switch  to get rid of those bothering messages.

As the native VLAN info is brought by CDP ver 2 only, I can also change CDP to ver 1 on the port or the whole switch.

BR,

Milan