2

I am discovering MPLS configuration on Cisco ASR920, and for almost any "thing" that can be configured, there is often two or more ways to do it. For example, given this configuration:

interface pseudowire40
 encapsulation mpls
 signaling protocol ldp
 neighbor 193.47.70.66 40
!
interface GigabitEthernet0/0/1
 no ip address
 negotiation auto
 service instance 30 ethernet
  encapsulation dot1q 30
  rewrite ingress tag pop 1 symmetric
 !        
 service instance 40 ethernet
  encapsulation dot1q 40
  rewrite ingress tag pop 1 symmetric
 !        
 service instance 50 ethernet
  encapsulation dot1q 50
  rewrite ingress tag pop 1 symmetric
  xconnect 193.47.70.66 50 encapsulation mpls
 !
!
l2vpn xconnect context vlan-30
 member GigabitEthernet0/0/1 service-instance 30 
 member 193.47.70.66 30 encapsulation mpls
!         
l2vpn xconnect context vlan-40
 member GigabitEthernet0/0/1 service-instance 40
 member pseudowire40

There are three pseudowires configured, differently, and they all end up doing the exact same thing. I read most of the documentation regarding the ASR920 on Cisco's web site, and I am left with a feeling that I have no idea of the differences between those three configurations. And in the end, which I should go with, and why, so that we can kept all our configurations coherent, with the least exceptions possible.

3

vlan 50 method of configuration consolidates all related statements onto the PE-CE logical interface. This is the easiest to understand if you are configuring manually or doing any kind of troubleshooting.

Imagine each method as just fragments within a large router config. In that context, it's suddenly quite clear which option makes most sense.

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