[c-nsp] ASR920 Service Instance - when to 'rewrite ingress'

Adam Vitkovsky Adam.Vitkovsky at gamma.co.uk
Sun Aug 30 05:41:06 EDT 2015

Hi Eric,

Thank you for bringing this "new" feature/EFP type to my attention,

Reading the doc this feature addresses a specific use case where the BD ID used to bundle two or more ports/EFPs together happens to match the VLAN ID on all these ports/EFPs.

So where we used to do:

interface gigabitethernet2/0/1
service instance 1 ethernet
encapsulation dot1q 1
bridge-domain 1
service instance 2 ethernet
encapsulation dot1q 2
bridge-domain 2
service instance 3 ethernet
encapsulation dot1q 3
bridge-domain 3

we can now do:

interface gigabitethernet2/0/1
service instance trunk 123 ethernet
rewrite ingress tag pop 1 symmetric
encapsulation dot1q 1 - 3
bridge-domain from-encapsulation

-and frames with dot1q tag 1 would be inserted into BD1 automatically and so forth for VLAN tags 2 and 3.
-though one would lose the COS markings in this setup
-anyways this is a specific use case as most of the times VLANs do not match in two separate access domains.



        Adam Vitkovsky
        IP Engineer

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-----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> Eric Van Tol
> Sent: 22 August 2015 13:50
> To: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] ASR920 Service Instance - when to 'rewrite ingress'
> > > not an ASR, which does not accept switchport configuration:
> > >
> > > ASR-1(config)#int gi0/0/15
> > > ASR-1(config-if)#swi?
> > > % Unrecognized command
> > > ASR-1(config-if)#swi?
> > > % Unrecognized command
> >
> >
> > Ok, I didn't know about that. So my particular example with the sniffer
> > on the core link "switchport" doesn't apply to the ASR920, but that
> > doesn't change anything about the EVC behavior and the point I'm trying
> > to make.
> It does, given the example you provided *and* the behavior you wanted me
> to observe (because it doesn't produce that behavior), but it doesn't matter
> because this whole discussion is pointless now.  My understanding of when
> to use rewrite was actually correct, yours is correct, and my entire issue
> stemmed from a missed line in the config docs that explicitly states rewrite is
> required on EFP trunks.  This was literally in the first bulltetpoint of the listed
> 'Restrictions'.
> I also think that another misunderstanding from your end is that I am trying
> to use core ports to transport C-Vlans (in the literal sense) when in reality,
> this is an S-Vlan.  The ASR was acting as a "distribution" layer router, in
> between non-MPLS capable edge switches and MPLS-capable hardware
> upstream.  It's all moot now, since we were able to migrate these edge-
> facing EFPs to MPLS xcons directly off the ASRs last night and the EFP trunks
> are now gone.
> Finally, I still argue that your point about not using EVC on core-facing links is
> incorrect *on the ASR*, because that's the only way to transport VLANs, as
> far as I know.  There is no other option but to use EFPs for core-facing links
> (no classic switchport config).  Again, if you or anyone else can provide
> alternative configs, I'm happy and appreciative to learn about it.
> Thanks for taking the time to help educate.
> -evt
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