%CDP-4-NATIVE_VLAN_MISMATCH

[Georg Pauwen]

Hello,

I have a Cisco 2950 connected to a 3550 through a cross-cable on FastEthernet0/1 and FastEthernet0/4, respectively.

On the 2950, I get the following error message:

%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/1 (0), with switch FastEthernet0/4 (1).

I cannot really figure out how to get rid of this error message, both interfaces are in VLAN1. Also, would this mismatch have any impact on the connectivity between these two devices ?

Thanks for your input in advance.

Regards,

Georg

[frejac]

Both are in vlan 1 and none of them are configured for trunking? (using "switchport mode access" to disable trunking)

Cant see that this errormsg could mean any impact on connectivity then. You might want to turn CDP off on those ports to precent it, but I havent seen any issue where that would be needed before.

[konigl]

Georg,

I agree with Fredrik. If both ports are set to switchport mode access and the access VLAN on each port is VLAN 1, then native VLAN mismatch really should have no impact on connectivity.

You may have an unnecessary "switchport trunk native vlan x" command in the configuration of one or both ports, left over from when it may have been configured as a switchport mode trunk. Double-check your config for this. It is not uncommon to have several switchport trunk-related commands remain in the config when the port mode is changed from trunk to access.

Even though the ports are set up for access mode, CDP will communicate any relevant information about the port configurations to other Cisco devices which may be attached to them. If this message is really annoying, you can turn off CDP on just those ports, as Fredrik suggests; but then you would lose the benefit of having CDP exchange other important information between the two switches.

Hope this helps.

[milan.kulik]

I agree.

Just additional suggestions:

Try sh cdp nei details to see what native VLAN number is advertised from the opposite side.

If you were not able to fix the problem by removing config trunk commands, you don't have to disable CDP on the port. You can just degrade it to CDP ver 1 (not sending native VLAN info) by no cdp advertise-v2 (an disadvantage is that this is a global command).

Regards,

Milan

[andrew.butterworth]

Are the 3550 ports configured as routed ports (i.e. no switchport)? I have seen the exact same thing with Catalyst 6500's running Native IOS connected to 3500XL switches. I think CDP is trying to be too clever in reading the VLAN ID from the CDP messages it receives; I think there is no VLAN ID in the CDP messages from the routed ports. I am sure everything will work fine but the messages are damn annoying. I suggest turn CDP off the 2950s?

Andy

[ahmed.yacoob]

You can degrade it to CDP ver 1 by no cdp advertise-v2  under that interface.