How does two different EVC communicate when using different encapsulation

In last post, ports are communicating with the same vlan encapsulation type. But how will the different encapsulation communicate with each other.

We know when we configure dot1q encapsulation on router’s port, it always remove the tag during ingress and add the tags during egress forwarding. If the router is configured with multiple sub-interfaces and every sub-interface is having different dot1q encapsulation; in that case the router always remove the vlan tags while ingress from one sub-interface and adds the tags during egress of that sub-interface. To perform this you must have router or layer 3 capable switch which could perform this. (Without Layer 3 device)

EVC architecture also works on the same mechanism, as per given configuration, both the service instances cannot communicate with each other as their encapsulation is different. One service instance is carrying 109 and other is carrying 110.  

Switch (config)# interface gigabitethernet0/10

Switch (config-if)# switchport mode trunk

Switch (config-if)# switchport trunk allowed vlan none

Switch (config-if)# service instance 101 Ethernet

Switch (config-if-srv)# encapsulation dot1q 109

Switch (config-if-srv)# bridge-domain 103

Switch (config)# interface gigabitethernet0/11

Switch (config-if)# switchport mode trunk

Switch (config-if)# switchport trunk allowed vlan none

Switch (config-if)# service instance 101 Ethernet

Switch (config-if-srv)# encapsulation dot1q 110

Switch (config-if-srv)# bridge-domain 103

Both the service instance can communicate if and only if they receive the same encapsulation type. To achieve this we must use the rewrite keyword in any of the service instance. Rewrite keyword performs the pop operation during ingress consequently vlan tag gets removed and symmetric keyword helps to perform the inverse function of adding vlans during egress.   

Switch (config)# interface gigabitethernet0/10

Switch (config-if)# switchport mode trunk

Switch (config-if)# switchport trunk allowed vlan none

Switch (config-if)# service instance 101 Ethernet

Switch (config-if-srv)# encapsulation dot1q 109

Switch (config-if-srv)# bridge-domain 103

Switch (config)# interface gigabitethernet0/11

Switch (config-if)# switchport mode trunk

Switch (config-if)# switchport trunk allowed vlan none

Switch (config-if)# service instance 101 Ethernet

Switch (config-if-srv)# encapsulation dot1q 110

Switch (config-if-srv)# rewrite ingress tag pop 1 symmetric

Switch (config-if-srv)# bridge-domain 103

People who read this post also read :