[a-nsp] Terminating a Q-in-Q L3 interface?

[Bryan Holloway]

So in Cisco (IOSXR)-land, it's trivial to terminate double-tagged 
traffic on an SVI like so:

interface Bundle-Ether3.900
  ipv4 address 10.11.12.13 255.255.255.252
  encapsulation dot1q 900 second-dot1q 100

... where 900 is the outer-tag, and 100 is the inner-tag.

I've been trying to figure out a way to do this on Arista.

Since there's no built-in way to do it on standard SVIs, I thought I'd 
take a look at their double-tag VLAN translation feature, which looks 
like it'll do the trick.

So I created the following:

interface Ethernet49/1
    switchport trunk allowed vlan 900
    switchport mode trunk
    switchport vlan translation 900 inner 100 200

... which purports to dump double-tagged 900:100 traffic into the VLAN 
200 bridge domain.

To wit:

"On ingress, specified double-tagged packets are mapped to the bridging 
VLAN, and on egress packets with the ID of the bridging VLAN are double 
tagged as specified."

So I created VLAN 200 and an SVI:

interface Vlan200
    ip address 10.11.12.14/30

But it doesn't work. Notably, the SVI doesn't even come up because there 
are no interfaces using VLAN 200.

Fine ... so I added 200 to another unrelated trunk, which caused my 
VLAN200 interface to come up.

But still no joy. I know this is a bit kludge-y, but shouldn't it work 
as advertised?

Has anyone succeeded in something like this? I'm open to suggestions, 
thank you!

		- bryan

P.S.: Running 4.25.4M on the Arista, which is admittedly a little long 
in the tooth.