[c-nsp] ASR9K to ASR920 MPLS issue

[Lukas Tribus]

On Tue, 12 Jan 2021 at 18:02, James Bensley
<jwbensley+cisco-nsp at gmail.com> wrote:
> > Can I omit the "rewrite ..." on both sides?
>
> Why would you want to? I think that if you do that, a VLAN tagged
> frame coming into one end with VLAN 95, will be send over the
> pseudoiwre with the VLAN tag still present, at the other end it will
> have VLAN 95 push on egress, so it will leave the other end double
> tagged with an inner and outer VLAN tag of 95.

I don't believe this is what happens.

"rewrite ingress pop 1 symmetric" <-- the symmetric keyword means that
it pushes on egress and pops on ingress.

Without "rewrite *" it does neither afaik; therefore, if you have the
same configuration end-to-end, it works, because the tag is preserved
as-is and no vlan tags are pushed or popped anyware (just labels, of
course).

That's said I don't like the configuration without the rewrite keyword
at all, because it is confusing and redundant to have to include the
vlan tag, when all you need to transport is a single vlan. And it is
easier to get configuration mismatches when you do it this way.


Lukas