Native Vlan Mismatch error

Jan 20, 2008 2 Replies

I got two errors showing up on console:



(1) 4w5d: %LINK-4-ERROR: FastEthernet0/3 is experiencing errors


(2) 4w5d: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/16 (20), with Switch3 FastEthernet0/48 (1). Also, one port on one of the switch is flapping.



There are there switches on this rack connected by both fiber and crossover cable. How can I fix these problems. Thanks.


Change the native vlan on both switches to match. If its IOS based, I would think you need to do a switchport mode access, switchport access vlan . Then put your trunk statements back. On the catalyst side, set vlan , and then you again may need you put your trunking statements back. Its probably not a major issue, but you want your trunks in the same native vlan before configuring trunking.

if you are just passing traffic across a common vlan,no trunking, set each port to the same vlan and access mode.

If you are using 802.1q, though, you might want to define a native vlan for each dot1q trunk. The native vlan won't be tagged, and allow only the desired vlans to pass through. Don't use the native vlan number anywhere else in your net.

if 888 is the native vlan and you want to pass 5,6,7 then something like this works. add other i/f commands as suits your env.

IOS:

interface command:

switchport switchport trunk encapsulation dot1q switchport trunk native vlan 888 switchport trunk allowed vlan 5-7 switchport mode trunk etc.

catos:

set vlan 888 mod/port

set trunk mod/port dot1q 5-7

works well. the next dot1q tunnel you define might use 889 for the native vlan, etc. keep track, as always, of where vlans occur. keep as local as possible.

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