which config is correct, if either?

[russell maycock]

Hello,
I hav two 2910al 48 port layer 3 switches. I want to have one switch as one vlan and the other switch as another vlan. I'm trying to work out which is the best way to connect the switches together regarding vlans. I have setup a trunk between the switches on ports 47 and 48 on both switches. I have enabled ip routing on the first switch.


On the first switch which contains the default vlan 1 and a vlan called vlan 2. All ports are untagged as default vlan 1 expect 47 and 48 which are untagged as vlan 2.
On the second switch which should contain the second vlan vlan 2. However the way the switch has been configured all ports are untagged and part of default vlan 1. There is no other vlan on there.

Or is this correct

On the first switch which contains the default vlan 1 and a vlan called vlan 2. All ports are untagged as default vlan 1 expect 47 and 48 which are untagged as vlan 2.
On the second switch there are two vlans. The default vlan 1 and a vlan called vlan2 all ports are untagged and are part of vlan 2.

The second one makes sense to me but I was wondering if the first one was ok because all ports are part of the one vlan so when packets hit 47 and 48 on the first switch they would not get tagged so when it goes to the second switch it doesn't need to have vlan 2 on it and can instead use the orginal default vlan.

Thoughts pleaseeee

[Mohammed Faiz]

Hi,

The first scenario is definitely incorrect. What is happening is that switch 1 is "injecting" vlan 2 traffic into vlan 1 on the second switch. It would not cause you any issues in the first instance as you only have the one vlan on the second switch but I would highly recommend that you keep your vlan configuration consistent across your switches (i.e. vlan 2 should not equal vlan 1 on the second switch).

I would suggest you take the second option you have listed with a slight change. The rule that I follow is to always tag vlans on switch interlinks, this avoids any possible issues with vlan injection/leak and other configuration mistakes.

So in this case you would tag vlans 1 and 2 on ports 47 and 48 on both switches then untag the required vlan on the access ports.

HTH