Native VLAN mismatch

[jplenbrook]

Hi all,

Just a quick question. To me, any mismatch sounds terrible and bad. Just wanted to ask about native vlans.

Let's say we have a router configured with vlan 30 on fa 0/0/0 (access port, no trunk) which is then connected to a switch fa 0/0/1 (access port, no trunk) which operates on default VLAN 1.

When you connect both ends, you get a message that there is native VLAN mismatch because router on this interface is running vlan 21 as a native VLAN, and switch is running vlan 1 as native VLAN. Communication still happens, however when you reload a switch or router you get this warning message.

I spoke to few people about it and they said: first of all, if it works - it works, and also I can't see any disadvantages of having native VLAN mismatch.

What do you guys think about it?

Best Regards,

[Reza Sharifi · Accepted solution]

Hi,

In you case since the ports are configured as access port, the vlan ids for both switch don't have to match.  So, you have vlan 30 on one switch that sends the CDP messages in vlan 30 and than the other switch receives the message in vlan 30 and has to put it in vlan 1 and so the switch complains about native vlan mismatch and fills up the logs. This works, but if you configure the same vlan on both sides you are not going to see this message.

HTH
 

[jplenbrook]

Reza, cheers for clarifying.

I was a bit confused about it at the beginning but then I thought this is what always happens when you connect unmanaged l2 switch to router access port, however you don't see log messages on a switch as it is unmanaged so there is no CLI access.

Anyway, thank you!

@edit

Let's say you have gigabitether0/0/1 configured with sub-interfaces 0/1.10 (vlan 10) amd 0/1.20 (vlan 20).
 Does it matter which vlan is a native VLAN if both interfaces are configured in a trunk mode?

[InayathUlla Sharieff]

@edit

Let's say you have gigabitether0/0/1 configured with sub-interfaces 0/1.10 (vlan 10) amd 0/1.20 (vlan 20).
 Does it matter which vlan is a native VLAN if both interfaces are configured in a trunk mode?

Answer:- Yes it does still matter. Simple terminalogy make sure if you are configuring/using the native vlan it should match both the ends to prevent VLAN Leaking.

Switch

int g0/1/0.1

encap dot1q native <vlan number>

HTH