VLAN sub interfaces

Hi, I found this in the Cumulus documentation:

“A bridge cannot contain multiple subinterfaces of the same port. Attempting this configuration results in an error.”

On a linux software bridge you can have multiple subinterfaces, with different VLANs, as members of a (traditional) bridge.

I’m wondering why this is not possible with Cumulus - is this a hardware / asic limitation?

I would like to configure a bridge as follows:

auto br0
iface br0
bridge-ports swp2.10 swp2.11 swp2.12
bridge-vlan-aware no

Hi Swimgeek,

It would be possible in hardware, but it is not implemented at the moment. By default frames are not allowed to be forwarded on the same port they were received on.

However, could you explain how you are using this feature? Perhaps there are different solutions with the multiple vlan-aware bridge for example.

Hi, thanks for the quick response.

I’d like to use a Mellanox SN2010 to terminate a connection to a fibre to the home network - where the fibre network provides about 15 VLANs, one VLAN per geographic area. Ideally I want all the VLANs (and customer MACs) in one bridge where a DHCP server provides them with IPs from a single pool.

I have this working with a linux software router at the moment, but we’d like to change to a hardware solution.

I believe in Arista lingo this feature is called “Layer 2 Subinterfaces”:

“A Layer 2 subinterface is a logical bridging endpoint associated with traffic on an interface distinguished by 802.1Q tags, where each interface, 802.1q tag tuple is treated as a first-class bridging interface.”

We’re happy with this idea - currently we have nftables rules to isolate the vlans in the bridge - each vlan should only talk to the upstream router.

If they are 15 different VLANs (in your case for separating geographic areas), wouldn’t you want to start routing at that aggregation point? I have to assume the gateway for all VLANs exist on the 2010. With your suggestion you would be bridging the different VLANs which is typically not such a good idea.

If the sole purpose it to provide DHCP services, you can do that routed with a dhcp relay agent as well.

Thanks, I tested some routing ideas using the Cumulus VX Air lab - seems to work as expected. We’ll look into using dhcp relays and adding /32 routes for each customer.

Great, let us know if you need anything! AIR is a great resources to test this out.