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

Eric Van Tol eric at atlantech.net
Wed Aug 19 09:09:24 EDT 2015

Hi all,
Ran into an issue we haven't seen before, primarily due to a misunderstanding of when to use 'rewrite ingress tag pop 1 symmetric'.  We turned up a new ASR920 and had some trouble getting traffic to pass between service instances on different interfaces.  Here's the config we had:

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
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

We had two issues here.  The first issue was that no traffic was coming in over Gi0/0/23 - no MAC addresses being learned on any of the VLANs.  Service instance 243 on Gi0/0/6 *was* learning MACs.  The MAC learning on the upstream port was resolved by adding 'rewrite ingress tag pop 1 symmetric', but then traffic wasn't passing from the SI on 0/0/23 to the downstream SIs until adding the same config line in each of the downstream service instances.

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?


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