Bridge Domains And Vlan Encapsulation; Rewrite; Split Horizon - Cisco 3845 - Security Bundle Router Software Manual

Chapter 11 Configuring Ethernet Virtual Connections (EVCs)

Bridge Domains and VLAN Encapsulation

Unlike VLANs, the bridge-domain number does not need to match the VLAN encapsulation number.
Switch (config)# interface gigabitethernet0/1
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 10
Switch (config-if-srv)# bridge-domain 8000
Switch (config)# interface gigabitethernet0/2
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 10
Switch (config-if-srv)# bridge-domain 8000
However, when encapsulations do not match in the same bridge domain, traffic cannot be forwarded. In
this example, the service instances on Gigabit Ethernet 0/1 and 0/2 can not forward between each other,
since the encapsulations don't match (filtering criteria). However, you can use the rewrite command to
allow communication between these two.
Switch (config)# interface gigabitethernet0/1
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 10
Switch (config-if-srv)# bridge-domain 8000
Switch (config)# interface gigabitethernet0/2
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 99
Switch (config-if-srv)# bridge-domain 8000

Rewrite

In this example, a packet that matches the encapsulation will have one tag removed (popped off). The
symmetric keyword allows the reverse direction to have the inverse action: a packet that egresses out
this service instance will have the encapsulation (VLAN 10) added (pushed on).
Switch (config)# interface gigabitethernet0/1
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 10
Switch (config-if-srv)# rewrite ingress tag pop 1 symmetric
Switch (config-if-srv)# bridge-domain 8000

Split Horizon

In this example, service instances 1 and 2 cannot forward and receive packets from each other. Service
instance 3 can forward traffic to any service instance in bridge domain 8000 since no other service
instance in bridge domain 8000 is in split-horizon group 2. Service instance 4 can forward traffic to any
service instance in bridge domain 8000 since it has not joined any split-horizon groups.
Switch (config)# interface gigabitethernet0/1
Switch (config-if)# service instance 1 Ethernet
Switch (config-if-srv)# encapsulation dot1q 10
Switch (config-if-srv)# rewrite ingress pop 1 symmetric
Switch (config-if-srv)# bridge-domain 8000 split-horizon group 1
Switch (config-if-srv)# exit
Switch (config-if)# service instance 2 Ethernet
Switch (config-if-srv)# encapsulation dot1q 99
Switch (config-if-srv)# rewrite ingress pop 1 symmetric
Switch (config-if-srv)# bridge-domain 8000 split-horizon group 1
Switch (config)# interface gigabitethernet0/2
OL-23400-01
Cisco ME 3800X and 3600X Switch Software Configuration Guide
Configuring EFPs
11-11