Specifications

Configuring Routing Between VLANs

How to Configure Routing Between VLANS

Router(config-subif)# ip access-group 1

Unambiguous and Ambiguous Subinterfaces

The encapsulation dot1q command is used to configure Q-in-Q termination on a subinterface. The

command accepts an Outer VLAN ID and one or more Inner VLAN IDs. The outer VLAN ID always

has a specific value, while inner VLAN ID can either be a specific value or a range of values.

A subinterface that is configured with a single Inner VLAN ID is called an unambiguous Q-in-Q

subinterface. In the following example, Q-in-Q traffic with an Outer VLAN ID of 101 and an Inner

VLAN ID of 1001 is mapped to the Gigabit Ethernet 1/0.100 subinterface:

Router(config)# interface gigabitEehernet1/0.100

Router(config-subif)# encapsulation dot1q 101 second-dot1q 1001

A subinterface that is configured with multiple Inner VLAN IDs is called an ambiguous Q-in-Q

subinterface. By allowing multiple Inner VLAN IDs to be grouped together, ambiguous Q-in-Q

subinterfaces allow for a smaller configuration, improved memory usage and better scalability.

In the following example, Q-in-Q traffic with an Outer VLAN ID of 101 and Inner VLAN IDs anywhere

in the 2001-2100 and 3001-3100 range is mapped to the Gigabit Ethernet 1/0.101 subinterface.:

Router(config)# interface gigabitethernet1/0.101

Router(config-subif)# encapsulation dot1q 101 second-dot1q 2001-2100,3001-3100

Ambiguous subinterfaces can also use the any keyword to specify the inner VLAN ID.

See the “Monitoring and Maintaining VLAN Subinterfaces” section on page 50 for an example of how

VLAN IDs are assigned to subinterfaces, and for a detailed example of how the any keyword is used on

ambiguous subinterfaces.

Only PPPoE is supported on ambiguous subinterfaces. Standard IP routing is not supported on

ambiguous subinterfaces.

Note On the Cisco 10000 series Internet router, Modular QoS services are only supported on unambiguous

subinterfaces.

Perform these tasks to configure the main interface used for the Q-in-Q double tagging and to configure

the subinterfaces.

• Configuring EtherType Field for Outer VLAN Tag Termination, page 45 (Optional)

• Configuring the Q-in-Q Subinterface, page 46 (Required)

• Verifying the IEEE 802.1Q-in-Q VLAN Tag Termination, page 47 (Optional)