VLAN subinterfaces on a BVI Interface? (2821

[Justin Grote]

Hello,

I have a ISR 2821 at a branch office with the two integrated gigabit ethernet ports. The Gi0/0 is connected to a switch in another wiring closet and has three VLAN subinterfaces for data, video, and guest wifi.

The branch is adding a new switch for a new floor and it is being run back to the ISR, and it needs to be able to have ports on the same VLANs as the first switch.

I was thinking of just connecting the new switch to Gi0/1. Is it possible to bridge the gi0/0 and gi0/1 interfaces into a BVI, and then re-add the VLAN subinterfaces to the BVI? (e.g. BVI1.1, BVI1.5, etc.). I know the BVI is possible but I don't know about the VLAN subinterfaces and having the router still honor all the 802.1q tagged packets between the two switches.

If there's a better way of solving this problem outside of purchasing a switch HWIC, someone let me know. Otherwise I can just do that but I'd rather avoid the investment if its not necessary.

I don't have an option to just run the uplink from the existing switch and I don't have any rackspace to add a switch in the closet where the ISR is located.

Thanks for any assistance.

EDIT REVISION: After a bit more research I found I'm going about this slightly backwards. What it looks like I should do is configure the new interface with the same VLAN subinterfaces FIRST, and then create an individual BVI for each VLAN to bridge them together. This looks like it will work, just wanted to get confirmation.

[Peter Paluch · Accepted solution]

Justin,

The obvious solution would be to have the switches connected together via a trunk link. If both switches can reach your 2821, can't they reach themselves directly? Are they too far of each other for a single 100m cable span?

It is not possible to create subinterfaces on a BVI interface. However, you can create three independent bridge-groups and bridge the subinterfaces on Gi0/0 and Gi0/1 using these bridge-groups, i.e.:

bridge irb
!
interface GigabitEthernet0/0.11
 encapsulation dot1q 11
 bridge-group 1
!
interface GigabitEthernet0/0.12
 encapsulation dot1q 12
 bridge-group 2
!
interface GigabitEthernet0/0.13
 encapsulation dot1q 13
 bridge-group 3
!
interface GigabitEthernet0/1.11
 encapsulation dot1q 11
 bridge-group 1
!
interface GigabitEthernet0/1.12
 encapsulation dot1q 12
 bridge-group 2
!
interface GigabitEthernet0/1.13
 encapsulation dot1q 13
 bridge-group 3
!
bridge 1 protocol ieee
bridge 1 route ip
bridge 2 protocol ieee
bridge 2 route ip
bridge 3 protocol ieee
bridge 3 route ip

Would this make sense?

Best regards,
Peter

[Justin Grote]

As per my original post, I can't do the obvious solution. The switches are on different floors homerun back to the ISR via fiber, and building rules prevent us from running it between the switches instead. Building rules also only allow for 1U of rackspace for our equipment so we can't put a switch in the room in "front" of the ISR to solve the problem. Dumb I know.

Looks like you confirmed my edit, BVIs on VLAN subinterfaces is the way to go. Thanks for your assistance.