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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.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
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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:
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 |
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:
Router(config)# interface gigabitEehernet1/1/0.100 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 1/1/0.101 subinterface:
Router(config)# interface gigabitethernet1/1/0.101 Router(config-subif)# encapsulation dot1q 101 second-dot1q 2001-2100,3001-3100
Ambiguous subinterfaces can also use the anykeyword 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.
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.
Perform this optional task to verify the configuration of the IEEE 802.1Q-in-Q VLAN Tag Termination feature.
Step 1 | enable Enables privileged EXEC mode. Enter your password if prompted. Example:
Router> 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:
Router# 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 |
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 |
The following sections provide references related to the IEEE 802.1Q-in-Q VLAN Tag Termination feature.
Related Topic |
Document Title |
---|---|
Related commands |
Cisco IOS LAN Switching Command Reference |
Standards |
Title |
---|---|
IEEE 802.1Q |
-- |
MIBs |
MIBs Link |
---|---|
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs |
Title |
---|---|
No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature. |
-- |
Description |
Link |
---|---|
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. |
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 |
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