IEEE 802.1Q-in-Q VLAN Tag Termination

Encapsulating IEEE 802.1Q VLAN tags within 802.1Q enables service providers to use a single VLAN to support customers who have multiple VLANs. The IEEE 802.1Q-in-Q VLAN Tag Termination feature on the subinterface level preserves VLAN IDs and keeps traffic in different customer VLANs segregated.

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Information About IEEE 802.1Q-in-Q VLAN Tag Termination

IEEE 802.1Q-in-Q VLAN Tag Termination on Subinterfaces

IEEE 802.1Q-in-Q VLAN Tag Termination simply adds another layer of IEEE 802.1Q tag (called “metro tag” or “PE-VLAN”) to the 802.1Q tagged packets that enter the network. The purpose is to expand the VLAN space by tagging the tagged packets, thus producing a “double-tagged” frame. The expanded VLAN space allows the service provider to provide certain services, such as Internet access on specific VLANs for specific customers, and yet still allows the service provider to provide other types of services for their other customers on other VLANs.

Generally the service provider’s customers require a range of VLANs to handle multiple applications. Service providers can allow their customers to use this feature to safely assign their own VLAN IDs on subinterfaces because these subinterface VLAN IDs are encapsulated within a service-provider designated VLAN ID for that customer. Therefore there is no overlap of VLAN IDs among customers, nor does traffic from different customers become mixed. The double-tagged frame is “terminated” or assigned on a subinterface with an expanded encapsulation dot1q command that specifies the two VLAN ID tags (outer VLAN ID and inner VLAN ID) terminated on the subinterface (see the figure below).

IEEE 802.1Q-in-Q VLAN Tag Termination is generally supported on whichever Cisco IOS XE features or protocols are supported on the subinterface. The only restriction is whether you assign ambiguous or unambiguous subinterfaces for the inner VLAN ID. See the Unambiguous and Ambiguous Subinterfaces section.

The primary benefit for the service provider is reduced number of VLANs supported for the same number of customers. Other benefits of this feature include:

  • PPPoE scalability. By expanding the available VLAN space from 4096 to approximately 16.8 million (4096 times 4096), the number of PPPoE sessions that can be terminated on a given interface is multiplied.

  • When deploying Gigabyte Ethernet DSL Access Multiplexer (DSLAM) in wholesale model, you can assign the inner VLAN ID to represent the end-customer virtual circuit (VC) and assign the outer VLAN ID to represent the service provider ID.

Whereas switches require IEEE 802.1Q tunnels on interfaces to carry double-tagged traffic, routers need only encapsulate Q-in-Q VLAN tags within another level of 802.1Q tags in order for the packets to arrive at the correct destination.

Figure 1. Untagged, 802.1Q-Tagged, and Double-Tagged Ethernet Frames

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 1/1/0.100 subinterface: 


Device(config)# interface gigabitEehernet1/1/0.100
Device(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 1/1/0.101 subinterface: 


Device(config)# interface gigabitethernet1/1/0.101
Device(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 Configuration Examples for IEEE 802.1Q-in-Q VLAN Tag Termination section 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.

How to Configure IEEE 802.1Q-in-Q VLAN Tag Termination

Configuring the Interfaces for IEEE 802.1Q-in-Q VLAN Tag Termination

Perform this task to configure the main interface used for the Q-in-Q double tagging and to configure the subinterfaces. An optional step in this task shows you how to configure the EtherType field to be 0x9100 for the outer VLAN tag, if that is required. After the subinterface is defined, the 802.1Q encapsulation is configured to use the double tagging.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. dot1q tunneling ethertype ethertype
  5. interface type number . subinterface-number
  6. encapsulation dot1q vlan-id second-dot1q {any | vlan-id | vlan-id - vlan-id [ vlan-id - vlan-id ]}
  7. pppoe enable [group group-name ] [max-sessions max-sessions-number ]
  8. exit
  9. Repeat Step 5 to configure another subinterface.
  10. Repeat Step 6 and Step 7 to specify the VLAN tags to be terminated on the subinterface.
  11. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:


Device(config)# interface gigabitethernet 1/0/0

Configures an interface and enters interface configuration mode.

Step 4

dot1q tunneling ethertype ethertype

Example:


Device(config-if)# dot1q tunneling ethertype 0x9100

(Optional) Defines the Ethertype field type used by peer devices when implementing Q-in-Q VLAN tagging.

Step 5

interface type number . subinterface-number

Example:


Device(config-if)# interface gigabitethernet 1/0/0.1

Configures a subinterface and enters subinterface configuration mode.

Step 6

encapsulation dot1q vlan-id second-dot1q {any | vlan-id | vlan-id - vlan-id [ vlan-id - vlan-id ]}

Example:


Device(config-subif)# encapsulation dot1q 100 second-dot1q 200

(Required) Enables the 802.1Q encapsulation of traffic on a specified subinterface in a VLAN.

  • Use the second-dot1q keyword and the vlan-id argument to specify the VLAN tags to be terminated on the subinterface.

  • In this example, an unambiguous Q-in-Q subinterface is configured because only one inner VLAN ID is specified.

  • Q-in-Q frames with an outer VLAN ID of 100 and an inner VLAN ID of 200 will be terminated.

Step 7

pppoe enable [group group-name ] [max-sessions max-sessions-number ]

Example:


Device(config-subif)# pppoe enable group vpn1

Enables PPPoE sessions on a subinterface.

The example specifies that the PPPoE profile, vpn1, will be used by PPPoE sessions on the subinterface.

Step 8

exit

Example:


Device(config-subif)# exit

Exits subinterface configuration mode and returns to interface configuration mode.

  • Repeat this step one more time to exit interface configuration mode.

Step 9

Repeat Step 5 to configure another subinterface.

Example:


Device(config-if)# interface gigabitethernet 1/0/0.2

(Optional) Configures a subinterface and enters subinterface configuration mode.

Step 10

Repeat Step 6 and Step 7 to specify the VLAN tags to be terminated on the subinterface.

Example:


Device(config-subif)# encapsulation dot1q 100 second-dot1q 100-199,201-600

Example:


Device(config-subif)# pppoe enable group vpn1

Step 6 enables the 802.1Q encapsulation of traffic on a specified subinterface in a VLAN.

  • Use the second-dot1q keyword and the vlan-id argument to specify the VLAN tags to be terminated on the subinterface.

  • In the example, an ambiguous Q-in-Q subinterface is configured because a range of inner VLAN IDs is specified.

  • Q-in-Q frames with an outer VLAN ID of 100 and an inner VLAN ID in the range of 100 to 199 or 201 to 600 will be terminated.

Step 7 enables PPPoE sessions on the subinterface. The example specifies that the PPPoE profile, vpn1, will be used by PPPoE sessions on the subinterface.

Step 11

end

Example:


Device(config-subif)# end

Exits subinterface configuration mode and returns to privileged EXEC mode.

Verifying the IEEE 802.1Q-in-Q VLAN Tag Termination

Perform this optional task to verify the configuration of the IEEE 802.1Q-in-Q VLAN Tag Termination feature.

SUMMARY STEPS

  1. enable
  2. show running-config
  3. show vlans dot1q [internal interface-type interface-number . subinterface-number [detail ] | second-dot1q inner-id any ]] [detail]

DETAILED STEPS

Step 1

enable

Enables privileged EXEC mode. Enter your password if prompted.

Example:


Device> enable
Step 2

show running-config

Use this command to show the currently running configuration on the device. You can use delimiting characters to display only the relevant parts of the configuration.

Example:


Device# show running-config
Step 3

show vlans dot1q [internal interface-type interface-number . subinterface-number [detail ] | second-dot1q inner-id any ]] [detail]

Use this command to show the statistics for all the 802.1Q VLAN IDs. In this example, only the outer VLAN ID is displayed.

Example:


Router# show vlans dot1q

Total statistics for 802.1Q VLAN 1:
   441 packets, 85825 bytes input
   1028 packets, 69082 bytes output
Total statistics for 802.1Q VLAN 101:
   5173 packets, 510384 bytes input
   3042 packets, 369567 bytes output
Total statistics for 802.1Q VLAN 201:
   1012 packets, 119254 bytes input
   1018 packets, 120393 bytes output
Total statistics for 802.1Q VLAN 301:
   3163 packets, 265272 bytes input
   1011 packets, 120750 bytes output
Total statistics for 802.1Q VLAN 401:
   1012 packets, 119254 bytes input
   1010 packets, 119108 bytes output

Configuration Examples for IEEE 802.1Q-in-Q VLAN Tag Termination

Configuring any Keyword on Subinterfaces for IEEE 802.1Q-in-Q VLAN Tag Termination Example

Some ambiguous subinterfaces can use the any keyword for the inner VLAN ID specification. The any keyword represents any inner VLAN ID that is not explicitly configured on any other interface. In the following example, seven subinterfaces are configured with various outer and inner VLAN IDs.


Note

The any keyword can be configured on only one subinterface of a specified physical interface and outer VLAN ID. 


interface GigabitEthernet1/0/0.1
 encapsulation dot1q 100 second-dot1q 100
interface GigabitEthernet1/0/0.2
 encapsulation dot1q 100 second-dot1q 200
interface GigabitEthernet1/0/0.3
 encapsulation dot1q 100 second-dot1q 300-400,500-600
interface GigabitEthernet1/0/0.4
 encapsulation dot1q 100 second-dot1q any
interface GigabitEthernet1/0/0.5
 encapsulation dot1q 200 second-dot1q 50
interface GigabitEthernet1/0/0.6
 encapsulation dot1q 200 second-dot1q 1000-2000,3000-4000
interface GigabitEthernet1/0/0.7
 encapsulation dot1q 200 second-dot1q any

The table below shows which subinterfaces are mapped to different values of the outer and inner VLAN ID on Q-in-Q frames that come in on Gigabit Ethernet interface 1/0/0.

Table 1. Subinterfaces Mapped to Outer and Inner VLAN IDs for GE Interface 1/0/0

Outer VLAN ID

Inner VLAN ID

Subinterface mapped to

100

1 through 99

GigabitEthernet1/0/0.4

100

100

GigabitEthernet1/0/0.1

100

101 through 199

GigabitEthernet1/0/0.4

100

200

GigabitEthernet1/0/0.2

100

201 through 299

GigabitEthernet1/0/0.4

100

300 through 400

GigabitEthernet1/0/0.3

100

401 through 499

GigabitEthernet1/0/0.4

100

500 through 600

GigabitEthernet1/0/0.3

100

601 through 4095

GigabitEthernet1/0/0.4

200

1 through 49

GigabitEthernet1/0/0.7

200

50

GigabitEthernet1/0/0.5

200

51 through 999

GigabitEthernet1/0/0.7

200

1000 through 2000

GigabitEthernet1/0/0.6

200

2001 through 2999

GigabitEthernet1/0/0.7

200

3000 through 4000

GigabitEthernet1/0/0.6

200

4001 through 4095

GigabitEthernet1/0/0.7

A new subinterface is now configured: 


interface GigabitEthernet1/0/0.8
 encapsulation dot1q 200 second-dot1q 200-600,900-999

The table below shows the changes made to the table for the outer VLAN ID of 200. Notice that subinterface 1/0/0.7 configured with the any keyword now has new inner VLAN ID mappings.

Table 2. Subinterfaces Mapped to Outer and Inner VLAN IDs for GE Interface 1/0/0--Changes Resulting from Configuring GE Subinterface 1/0/0.8

Outer VLAN ID

Inner VLAN ID

Subinterface mapped to

200

1 through 49

GigabitEthernet1/0/0.7

200

50

GigabitEthernet1/0/0.5

200

51 through 199

GigabitEthernet1/0/0.7

200

200 through 600

GigabitEthernet1/0/0.8

200

601 through 899

GigabitEthernet1/0/0.7

200

900 through 999

GigabitEthernet1/0/0.8

200

1000 through 2000

GigabitEthernet1/0/0.6

200

2001 through 2999

GigabitEthernet1/0/0.7

200

3000 through 4000

GigabitEthernet1/0/0.6

200

4001 through 4095

GigabitEthernet1/0/0.7

Additional References

The following sections provide references related to the IEEE 802.1Q-in-Q VLAN Tag Termination feature.

Related Documents

Related Topic

Document Title

Related commands

Cisco IOS LAN Switching Command Reference

Standards

Standards

Title

IEEE 802.1Q

--

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Feature Information for IEEE 802.1Q-in-Q VLAN Tag Termination

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 3. Feature Information for IEEE 802.1Q-in-Q VLAN Tag Termination

Feature Name

Releases

Feature Information

IEEE 802.1Q-in-Q VLAN Tag Termination

Cisco IOS XE Release 2.1

This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

The following commands have been modified for this feature: dot1q tunneling ethertype , encapsulation dot1q , and show vlans dot1q