interface GigabitEthernet0/1
 port-type nni
 switchport trunk allowed vlan none
 switchport mode trunk
 !
 service instance 20 ethernet
  encapsulation dot1q 20
  rewrite ingress tag pop 1 symmetric
  bridge-domain 20 split-horizon group 0
 !
!
interface GigabitEthernet0/2
 port-type nni
 switchport trunk allowed vlan none
 switchport mode trunk
 !
 service instance 20 ethernet
  encapsulation dot1q 20
  rewrite ingress tag pop 1 symmetric
  bridge-domain 20 split-horizon group 0
 !
!
interface Vlan20
 ip address blahblah
!