Stacked VLAN Processing
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Table Of Contents
Prerequisites for Stacked VLAN Processing
Information About Stacked VLAN Processing
Benefits of Using Stacked VLANs
Stacked VLAN Header Format in FastEthernet Packets
How to Configure Stacked VLAN Processing
Configuring a Subinterface for Stacked VLAN Processing
Configuration Examples for Stacked VLAN Processing
Configuring Stacked VLAN Processing on Subinterfaces: Examples
Displaying a Stacked VLAN Configuration: Example
Feature Information for Stacked VLAN Processing
Stacked VLAN Processing
First Published: May 7, 2004Last Updated: July 31, 2009The Stacked VLAN Processing feature supports the encapsulation of IEEE 802.1Q VLAN tags within a second layer of 802.1Q tag on provider edge (PE) routers to allow service providers to use a single VLAN to support customers who have multiple VLANs. The core service-provider network carries traffic with double-tagged, stacked VLAN (802.1Q-in-Q) headers of multiple customers while maintaining the VLAN and Layer 2 protocol configurations of each customer and without impacting the traffic of other customers. The Stacked VLAN Processing feature preserves VLAN IDs and keeps traffic in different customer VLANs segregated.
Finding Feature Information
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 for Stacked VLAN Processing" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
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Prerequisites for Stacked VLAN Processing
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Prerequisites for Stacked VLAN Processing
The PE-CLE device in each service-provider access network performs the stacked VLAN tag imposition and disposition. The Stacked VLAN Processing feature allows a router used as a PE router to process customer traffic with stacked VLAN headers and transmit the traffic across the service-provider network.
Information About Stacked VLAN Processing
To configure the Stacked VLAN Processing feature, you should understand the following concepts:
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Stacked VLANs
Business customers of service providers often have specific requirements for VLAN IDs and the number of VLANs to be supported. The VLAN ranges required by different customers in the same service-provider network might overlap, and traffic of customers through the infrastructure might be mixed. Assigning a unique range of VLAN IDs to each customer would restrict customer configurations and could easily exceed the VLAN limit of 4096 of the 802.1Q specification.
With stacked VLANs, service providers can use a unique VLAN (called a service-provider VLAN ID, or SP-VLAN ID) to support customers who have multiple VLANs. Customer VLAN IDs (CE-VLAN IDs) are preserved and traffic from different customers is segregated within the service-provider infrastructure even when they appear to be on the same VLAN.
Stacked VLANs expand the VLAN space by using a VLAN-in-VLAN hierarchy. Another layer of 802.1Q tag (SP-VLAN ID) is added to the 802.1Q-tagged (CE-VLAN ID) packets that enter the service-provider network.
The expanded VLAN space allows a service provider to provide certain services, such as Internet access on specific VLANs for specific customers, while providing other types of services to other customers on other VLANs.
Benefits of Using Stacked VLANs
<<Are all of these benefits OK for ASR 1000? Check the 3rd bullet especially.>>
The primary benefit for a service provider is a reduced number of VLANs supported for the same number of customers. Other benefits of this feature include:
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Using Stacked VLANs
Figure 1 shows an example of how to use stacked VLANs. Peer Ethernet subinterfaces are configured for the stacked VLAN processing of two customers' VLANs. Each customer is assigned a unique service-provider VLAN: SP-VLAN 50 for Customer A and SP-VLAN 100 for Customer B. The routers are configured as provider edge (PE) routers in two points of presence (POPs) in the service-provider network.
Customer traffic is received from aswitch in each service-provider access network. The switch functions as a provider edge (PE) device in customer location equipment (CLE) that encapsulates both 802.1Q-tagged VLAN and untagged packets for transmission over the service-provider network.
The PE-CLE switch interface does not strip the received customer edge 802.1Q tag from the header, but instead adds another layer of 802.1Q tag known as the SP-VLAN tag: SP-VLAN 50 for Customer A and SP-VLAN 100 for Customer B in Figure 1. The SP-VLAN tag is unique to each customer.
The original 802.1Q tag is preserved in the encapsulated packet. As shown in Figure 1, VLAN IDs from one customer (Customer A VLAN 10) can overlap with the VLAN IDs of another customer (Customer B VLAN 10).
Figure 1 Stacked VLAN Processing on Cisco ASR 1000 Series Aggregation Services Routers in a Service-Provider Network
You configure stacked VLAN processing on a per-subinterface basis. An IP interface in a service-provider network is defined by the uniqueness of two VLAN headers and the route underlying IP datagrams.
To keep traffic from different customers separate, you must configure traffic received from each customer on the PE-CLE device with a unique SP-VLAN tag that supports all of a customer's VLANs.
When a Cisco 12000 Series Internet Router configured for stacked VLAN processing in the PE-POP receives packets from a switch in the PE-CLE, packets in customer traffic may contain:
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When receiving double-tagged VLAN customer traffic, the ingress side of a subinterface examines packets to see what action to apply to a packet and how many VLAN tags to remove from a packet header. Packets can be transmitted for Layer 2 tunneling or Layer 3 forwarding as follows:
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When transmitting VLAN traffic, the egress side of an subinterface adds one 802.1Q VLAN tag, two 802.1Q-in-Q VLAN tags, or no tag to an Ethernet packet header as follows:
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Stacked VLAN Header Format in FastEthernet Packets
<<Should this section be removed or modified for ASR 1000? If modified, please provide further information--thanks>>
Figure 2 shows the double-tagged, stacked VLAN header used in FastEthernet packets processed by the Stacked VLAN Processing feature.
<<Is the following figure OK for ASR 1000? If not, should it be modified or removed?>>
Figure 2 Stacked VLAN Header Format in Fast Ethernet Packets
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For example, in Figure 1, Customer A uses VLANs 10 and 20; Customer B also uses VLAN 10. Packets entering the PE-CLE switch with 802.1Q tags are double-tagged for stacked VLAN processing and forwarded to the PE-POP router in the service-provider core network. An outer SP-VLAN tag is applied: 50 for Customer A and 100 for Customer B. The original inner CE-VLAN tag (for example, 10 or 20) is preserved in the encapsulation.
Although both Customers A and B have VLAN 10 in their networks, the traffic remains segregated within the service-provider network because the outer SP-VLAN tag is different. With stacked VLAN tunneling, each customer controls its own VLAN numbering space, which is independent of the VLAN numbering space used by other customers and the VLAN numbering space used by the service-provider network.
How to Configure Stacked VLAN Processing
This section contains the following procedure:
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Configuring a Subinterface for Stacked VLAN Processing
<<Steps OK for ASR 1000?>>
To configure and verify stacked VLAN processing on a subinterface, follow these steps:
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for Stacked VLAN Processing
<<PLease check the examples carefully to make sure they are OK for ASR 1000.>>
This section provides the following configuration examples:
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Configuring Stacked VLAN Processing on Subinterfaces: Examples
<<PLease check the example carefully to make sure they are OK for ASR 1000.>>
The following example shows how to configure 802.1Q-in-Q encapsulation for stacked VLAN processing on a FastEthernet subinterface configured for Layer 2 EoMPLS tunneling:
Router> enableRouter# configure terminalRouter(config)# interface fastethernet3/1/1Router(config-subif)# encapsulation dot1q 50 second-dot1q 10Router(config-subif)# xconnect 10.4.4.4 100 encapsulation mplsThe next example shows how to configure stacked VLAN processing on a FastEthernet subinterface that is not configured for Layer 2 tunneling and forwards Layer 3 data to a peer device without stacked VLAN headers:
Router(config)# interface fastethernet3/1/1Router(config-subif)# encapsulation dot1q 50 second-dot1q 20Router(config-subif)# ip address 10.5.5.5 255.255.255.0The following example shows how to configure stacked VLAN processing for all customer VLANs not already configured for stacked VLAN processing on other subinterfaces:
Router(config)# interface fastthernet3/0/0Router(config-subif)# encapsulation dot1q 50 second-dot1q anyRouter(config-subif)# xconnect 10.4.4.4 200 encapsulation mplsThe next example shows how to configure stacked VLAN processing and Layer 2 tunneling on another FastEthernet interface for a different customer, using a different service-provider VLAN ID:
Router(config)# interface gigabitethernet3/1/0Router(config-subif)# encapsulation dot1q 100 second-dot1q 10Router(config-subif)# xconnect 10.4.4.4 100 encapsulation mplsDisplaying a Stacked VLAN Configuration: Example
<<PLease check the examples carefully to make sure they are OK for ASR 1000.>>
The following example shows how to display statistics for a specified stacked VLAN (802.1Q-in-Q) configuration:
Router# show vlan dot1q 50 second-dot1q 10Total statistics for Outer/Inner VLAN 50/10:0 packets, 0 bytes input0 packets, 0 bytes outputAdditional References
The following sections provide references related to the Stacked VLAN Processing feature:
Related Documents
Interface commands: complete command syntax, command mode, defaults, usage guidelines, and examples
Cisco IOS Interface and Hardware Component Command Reference
Procedure for configuring VLANs for routing using 802.1Q VLAN encapsulation
Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation
Procedure for configuring 802.1Q double-tagged VLANs
Standards
MIBs
RFCs
Technical Assistance
Feature Information for Stacked VLAN Processing
Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note
Glossary
802.1Q—IEEE 802.1Q protocol used to interconnect multiple switches and routers, and for defining VLAN topologies.
802.1Q-in-Q—Support for double-tagged VLAN FastEthernet packets in which an 802.1Q tag from a customer VLAN (called a CE-VLAN ID) is encapsulated in a second 802.1Q tag from a service-provider network (called an SP-VLAN ID).
ARP—Address resolution protocol. ARP is a protocol for mapping IP address to physical addresses in the local network.
CE router—Customer edge router. A router that is part of a customer network and that interfaces to a provider edge (PE) router.
CE-VLAN—Customer edge VLAN.
encapsulation—Wrapping of data in a particular protocol header. For example, FastEthernet data is wrapped in a specific FastEthernet header before network transit. See also tunneling.
EoMPLS—Ethernet over Multiprotocol Label Switching (MPLS). A tunneling mechanism that allows a service provider to tunnel customer Layer 2 traffic though a Layer 3 MPLS network. EoMPLS is a point-to-point solution only. EoMPLS is also known Layer 2 tunneling.
Layer 2 Tunnel Protocol (L2TP)—An Internet Engineering Task Force (IETF) standards track protocol defined in RFC 2661 that provides tunneling of PPP. Based upon the best features of L2F and PPTP, L2TP provides an industry-wide interoperable method of implementing VPDN.
Layer 3 Switching—An Internet Engineering Task Force (IETF) standards track protocol defined in RFC 2661 that provides tunneling of PPP. Based upon the best features of L2F and PPTP, L2TP provides an industry-wide interoperable method of implementing VPDN.
MIB—Management Information Base. Database of network management information that is used and maintained by a network management protocol such as SNMP. The value of a MIB object can be changed or retrieved using SNMP commands, usually through a network management system (NMS). MIB objects are organized in a tree structure that includes public (standard) and private (proprietary) branches.
MPLS—Multiprotocol Label Switching. MPLS forwards IP traffic using a label. This label instructs the routers and switches in the network where to forward the packets based on pre-established IP routing information.
packet—Logical grouping of information that includes a header containing control information and (usually) user data. Packets most often are used to refer to network layer units of data.
PE router—Provider edge router. A router that is part of a service provider's network and is connected to a customer edge (CE) router.
POP—Point of presence. In an Operations Support System (OSS), a physical location where an interexchange carrier installed equipment to interconnect with a local exchange carrier (LEC).
SP-VLAN—Service-provider VLAN.
tunneling—Architecture that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme. See also encapsulation.
VLAN—Virtual LAN. Group of devices on one or more LANs that are configured (using management software) so that they can communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible.
VPN— Virtual Private Network. Enables IP traffic to travel securely over a public TCP/IP network by encrypting all traffic from one network to another. A VPN uses tunnels to encrypt all information at the IP level.
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