Check that the interface is included into the bridge domain:
PE1# sh interfaces bridge
Bridges Interfaces
---------- --------------------------------------------------------------
bridge 1 gi1/0/4
PE1# sh interfaces status bridge 1
Interface 'bridge 1' status information:
Description: --
Operational state: Up
Administrative state: Up
Supports broadcast: Yes
Supports multicast: Yes
MTU: 1500
MAC address: a8:f9:4b:ac:4d:15
Last change: 4 minutes and 22 seconds
Mode: Routerport
PE2:
PE2(config)# bridge 1
PE2(config-bridge)# enable
PE2(config-bridge)# exit
PE2(config)# interface gigabitethernet 1/0/4
PE2(config-if-gi)# mode switchport
PE2(config-if-gi)# bridge-group 1
PE2# sh interfaces bridge 1
Bridges Interfaces
---------- --------------------------------------------------------------
bridge 1 gi1/0/4
PE2# sh interfaces status bridge 1
Interface 'bridge 1' status information:
Description: --
Operational state: Up
Administrative state: Up
Supports broadcast: Yes
Supports multicast: Yes
MTU: 1500
MAC address: a8:f9:4b:ad:f2:45
Last change: 10 seconds
Mode: routerport
PE3: