Same dot1q on XR Platform

[Anuj Singhi]

Hi Members,

I wanted to know if I can configure same dot1q vlan on two different line card in CRS-3?

Regards,

Anuj

[Fredrik Lönnman]

Yes, you can.

[Anuj Singhi]

but what if both the vlans are dedicated for different services? Don't we have unwanted traffic to each of the ports in case broadcast domain being shared.

[Fredrik Lönnman]

dot1q tags are terminated on a per-interface basis, so they are per-interface significant. Sure if you use the same VLAN on two ports and combine them in a bridge-group they will be able to communicate with each other in the same broadcast domain.

[Anuj Singhi]

When you say "dot1q tags are terminated on a per-interface basis, so they are per-interface significant." that means I can have same dot1q on the same line card but on different interfaces? I thought we can only have it on different LC.

How does it work differently from any switch vlans where the broadcast will be received by all ports in that vlan? If we have same dot1q over two different interfaces, how does the traffic will differentiate where to go?

[tkarnani]

Hi Anuj,

i would recommend watching cisco live, its free to sign up and has a video that explains the evc framework

https://www.ciscolive.com/global/on-demand-library/?search=carrier#/session/1488328832026001rMeK

 at the 16 minute mark EFP presentation starts

[Fredrik Lönnman · Accepted solution]

VLANs on routers generally work different than VLANs on switches, where on a router it is almost always per-interface significant since it is generally terminated on a routed interface. It doesn't create a broadcast domain the same way it does in a switch. A bridge-domain could somewhat emulate the switch-behavior on a router, if that is preferred.