L2VPN on A9K: Egress Dot1q tagging

[dfranjoso]

Hello A9K Olympus inhabitants,

I have some questions to you regarding the way the A9K deals with dot1q tag on the egress EFP:

First scenario:

• The frame arrives the ingress EFP (port-mode, with no encap, only l2transport config) with a dotq1 tag of 100;
• The ingress EFP doesn't do any rewrite before entering the VLL EVC;
• The egress EFP (vlan-mode subinterface, with dot1q encap) is configured with a dot1q tag of 300;
• The egress EFP doesn´t do any rewrite on the frame;

Which dot1q tag should arrive on the CE Switch ? Tag 100 or tag 300 ?

Second scenario:

• The frame arrives the ingress EFP (port-mode, with no encap, only l2transport config) with NO dotq1 tag;
• The ingress EFP doesn't do any rewrite before entering the VLL EVC;
• The egress EFP (vlan-mode subinterface, with dot1q encap) is configured with a dot1q tag of 300;
• The egress EFP doesn´t do any rewrite on the frame;

Which dot1q tag should arrive on the CE Switch ? Untagged frame or a framed tag with 300 ?

Thank you all!

David

[Alexei Kiritchenko · Accepted solution]

Hello David,

A9K  always uses VC type 5 (VLAN) for VPLS. For both VPLS and VPWS, it will try VC type 5 as default first.

With VC type 5 the frame is transported across the MPLS network as it looks like after the ingress VLAN manipulation.

So if there is either no VLAN tag, a single tag (C-TAG) or two or more tags (e.g. S-TAG/C-TAG), all get transparently transported to the other far end.

With VC type 4, ASR9k always add a dummy tag (tag 0)  which will get automatically removed by the egress ASR9K node when the packet is received on the MPLS interface.

So if we assume both ends are ASR9k and they use the default VC5, then:

Scenario 1 – we get tag 100 on the remote end

Scenario 2 – no tag on the remote end.

Regards,

/A

[dfranjoso]

Thanks Akiritch!