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

[Eric Van Tol]

> I always was under the impression that 'rewrite ingress tag' was used for
> either translation or termination of the VLAN on the local node, but
> unnecessary when transparently passing traffic between SIs on different
> interfaces.  Is this wrong?

Following up on this, I found that with the following configuration, I do not need to rewrite:

interface GigabitEthernet0/0/6
 mtu 9216
 no ip address
 load-interval 30
 negotiation auto !
 service instance 243 ethernet
  description SI243
  encapsulation dot1q 243
  bridge-domain 243
 !
end 
interface GigabitEthernet0/0/23
 mtu 9216
 no ip address
 load-interval 30
 negotiation auto
 service instance trunk 1 ethernet
  encapsulation dot1q 243
  bridge-domain 243

I tested this in the lab and rewriting is unnecessary - I can pass traffic just fine.  However, if I create the VLAN in a service instance trunk:

interface GigabitEthernet0/0/23
 mtu 9216
 no ip address
 load-interval 30
 negotiation auto
 service instance trunk 1 ethernet
  encapsulation dot1q 243,1958,1961,1969,1976,2305
  bridge-domain from-encapsulation

Then rewrite is required, for some reason, on both the 'local' interface (Gi0/0/6) and the core-facing interface (Gi0/0/23).

Can anyone tell me what is different about the SI trunk that would cause this behavior?  This is showing up in both 03.15.01.S and 03.16.00.S.

-evt