Different physical interfaces with same Vlan ID

The VLAN ID specifies where 802.1Q tagged packets are sent and received on a specified subinterface. An 802.1Q VLAN subinterface must have a configured VLAN ID to send and receive traffic; without a VLAN ID, the subinterface remains in the down state. All VLAN IDs must be unique among all subinterfaces configured on the same physical interface. To change a VLAN ID, the new VLAN must not already be in use on the same physical interface. To exchange VLAN IDs, you must remove the configuration information and reconfigure the ID for each device.

NOTE: The subinterface does not pass traffic without an assigned VLAN ID.

/!\ Configuration of multiple subinterfaces of the same main interface with the same VID (1) is not permitted.

Sample Configuration and Verification:
XR Router:
vrf custA
address-family ipv4 unicast
!
vrf custB
address-family ipv4 unicast
!
interface GigabitEthernet0/0/0/0.3320
vrf custA
ipv4 address 1.1.1.1 255.255.255.252
encapsulation dot1q 3320
!
interface GigabitEthernet0/0/0/1.3320
vrf custB
ipv4 address 2.2.2.2 255.255.255.252
encapsulation dot1q 3320

R1 Router:
interface FastEthernet0/0.1
encapsulation dot1Q 3320
ip address 1.1.1.2 255.255.255.252

R1#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/28/40 ms

R2 Router:
interface FastEthernet0/0.3320
encapsulation dot1Q 3320
ip address 2.2.2.1 255.255.255.252

R2#ping 2.2.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

Note: VLAN IDs are only locally significant in your specific L3 interfaces, so no problem with or without vrf same encapsulation in different interface will work.

Reference: VLAN Subinterface Commandson the Cisco ASR 9000 Series Router

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