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Example: Configuring VPLS Multihoming (FEC 129)

VPLS Multihoming Overview

Virtual private LAN service (VPLS) multihoming enables you to connect a customer site to two or more PE routers to provide redundant connectivity. A redundant PE router can provide network service to the customer site as soon as a failure is detected. VPLS multihoming helps to maintain VPLS service and traffic forwarding to and from the multihomed site in the event of the following types of network failures:

  • PE router to CE device link failure

  • PE router failure

  • MPLS-reachability failure between the local PE router and a remote PE router

Figure 1: CE Device Multihomed to Two PE RoutersCE Device Multihomed to Two PE Routers

In the VPLS documentation, the word router in terms such as PE router is used to refer to any device that provides routing functions.

Figure 1 illustrates how a CE device could be multihomed to two PE routers. Device CE1 is multihomed to Routers PE1 and PE2. Device CE2 has two potential paths to reach Device CE1, but only one path is active at any one time. If Router PE1 were the designated VPLS edge (VE) device (also called a designated forwarder), BGP would signal a pseudowire from Router PE3 to Router PE1. If a failure occurred over this path, Router PE2 would be made the designated VE device, and BGP would re-signal the pseudowire from Router PE3 to Router PE2.

Multihomed PE routers advertise network layer reachability information (NLRI) for the multihomed site to the other PE routers in the VPLS network. The NLRI includes the site ID for the multihomed PE routers. For all of the PE routers multihomed to the same CE device, you need to configure the same site ID. The remote VPLS PE routers use the site ID to determine where to forward traffic addressed to the customer site. To avoid route collisions, the site ID shared by the multihomed PE routers must be different than the site IDs configured on the remote PE routers in the VPLS network.

Although you configure the same site ID for each of the PE routers multihomed to the same CE device, you can configure unique values for other parameters, such as the route distinguisher. These values help to determine which multihomed PE router is selected as the designated VE device to be used to reach the customer site.

Best Practice:

We recommend that you configure unique route distinguishers for each multihomed PE router. Configuring unique route distinguishers helps with faster convergence when the connection to a primary multihomed PE router goes down. If you configure unique route distinguishers, the other PE routers in the VPLS network must maintain additional state for the multihomed PE routers.

Remote PE routers in the VPLS network need to determine which of the multihomed PE routers should forward traffic to reach the CE device. To make this determination, remote PE routers use the VPLS path-selection process to select one of the multihomed PE routers based on its NLRI advertisement. Because remote PE routers pick only one of the NLRI advertisements, it establishes a pseudowire to only one of the multihomed PE routers, the PE router that originated the winning advertisement. This prevents multiple paths from being created between sites in the network, preventing the formation of Layer 2 loops. If the selected PE router fails, all PE routers in the network automatically switch to the backup PE router and establish new pseudowires to it.

Best Practice:

To prevent the formation of Layer 2 loops between the CE devices and the multihomed PE routers, we recommend that you employ the Spanning Tree Protocol (STP) on your CE devices. Layer 2 loops can form due to incorrect configuration. Temporary Layer 2 loops can also form during convergence after a change in the network topology.

The PE routers run the BGP path selection procedure on locally originated and received Layer 2 route advertisements to establish that the routes are suitable for advertisement to other peers, such as BGP route reflectors. If a PE router in a VPLS network is also a route reflector, the path selection process for the multihomed site has no effect on the path selection process performed by this PE router for the purpose of reflecting Layer 2 routes. Layer 2 prefixes that have different route distinguishers are considered to have different NLRIs for route reflection. The VPLS path selection process enables the route reflector to reflect all routes that have different route distinguishers to the route reflector clients, even though only one of these routes is used to create the VPLS pseudowire to the multihomed site.

Junos OS supports VPLS multihoming for both BGP VPLS and FEC129 VPLS. Support for FEC 129 is added in Junos OS Release 12.3.

Example: Configuring VPLS Multihoming (FEC 129)

This example shows how to configure virtual private LAN service (VPLS) multihoming. Multihoming allows a customer site to connect to multiple provider edge (PE) routers. A VPLS site multihomed to two or more PE routers provides redundant connectivity in the event of a PE router-to-CE device link failure or the failure of a PE router. The example demonstrates BGP-based multihoming support for FEC 129 VPLS (also known as LDP VPLS with BGP-based autodiscovery).


This example has the following hardware and software requirements:

  • One or more CE devices to represent a VPLS site.

  • Two or more PE devices.

  • Junos OS Release 12.3 or later running on the PE devices that are connected to the multihomed VPLS site.


BGP-based VPLS autodiscovery (FEC 129) enables each VPLS PE router to discover the other PE routers that are in the same VPLS domain. VPLS autodiscovery also automatically detects when PE routers are added or removed from the VPLS domain. You do not need to manually configure the VPLS and maintain the configuration when a PE router is added or deleted. VPLS autodiscovery uses BGP to discover the VPLS members and to set up and tear down pseudowires in the VPLS.

BGP multihoming enables you to connect a customer site to two or more PE routers to provide redundant connectivity while preventing the formation of Layer 2 loops in the service provider’s network. The redundant connectivity maintains the VPLS service and traffic forwarding to and from the multihomed site in the event of a PE router-to-CE device link failure, the failure of a PE router, or an MPLS reachability failure between the local PE router and a remote PE router. A redundant PE router can begin providing service to the customer site as soon as the failure is detected.

When a CE device connects to multiple PE routers, each of these routers advertises reachability for the multihomed site—routes that have the same site ID in the Layer 2 network layer reachability information (NLRI). The other PE routers in the network use a BGP path selection process to select only one of the advertising routers to which they send traffic destined for the CE device. This path selection process eliminates Layer 2 loops in the VPLS network.

Autodiscovery is not specifically related to multihoming. Autodiscovery is not required for multihoming to work. They are two separate features. That said, the meaning of FEC 129 is that VPLS does autodiscovery. So when you configure multihoming for FEC 129, you must also, by definition, configure autodiscovery (with the auto-discovery-only statement).

There are two places in the configuration where you can configure VPLS multihoming. One is for FEC 128, and the other is for FEC 129:

  • For FEC 128—routing-instances instance-name protocols vpls site site-name multi-homing

  • For FEC 129—routing-instances instance-name protocols vpls multi-homing

The following statements are used for configuring multihoming for FEC 129:

This example shows Device CE1 multihomed to Router PE1 and Router PE2. In addition, Device CE2 is single-homed to Router PE1. Device PE3 is the remote PE router, connected to Device CE3. Multihoming is not enabled on Device PE3. CLI Quick Configuration shows the configuration for all of the devices in Figure 2. The section Configuring Device PE1 has step-by-step instructions for configuring Device PE1.

Figure 2: Topology for FEC 129 MultihomingTopology for FEC 129 Multihoming


CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device PE1

Device PE2

Device PE3

Device CE1

Device CE2

Device CE3

Device P

Configuring Device PE1

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure Device PE1:

  1. Configure the interfaces.

    Configure family mpls on the provider-facing interfaces. Configure family vpls on the customer-facing interfaces.

  2. Configure the interior gateway protocol (IGP) and signaling protocols on the provider-facing interfaces.

    The traffic-engineering statement enables OSPF to advertise the label-switched path (LSP) metric in summary link-state advertisements (LSAs).

  3. Configure BGP.

    The auto-discovery-only statement notifies the routing process (rpd) to expect autodiscovery-related NLRI messages so that information can be deciphered and used by LDP and VPLS. The auto-discovery-only statement must be configured on all PE routers in a VPLS. If you configure route reflection, the auto-discovery-only statement is also required on provider (P) routers that act as the route reflector in supporting FEC 129-related updates.

    For interoperation scenarios in which a PE router must support both types of NLRI (FEC 128 and FEC 129), this example also includes the signaling statement.

  4. Configure the routing instance.

    Both CE-facing interfaces are included in the routing instance. Only the multihomed interface is included in the multihoming site.

    As a convention, the route distinguisher is composed of Device PE1’s loopback interface address and the multihoming site identifier.

  5. (Optional) Configure bidirectional forwarding detection (BFD) for FEC 129 VPLS.

  6. Configure the autonomous system (AS) number and router ID.


From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show routing-instances, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.


Confirm that the configuration is working properly.

Verifying That Multihoming Is Operational


Verify that multihoming is operational.


From operational mode, enter the show vpls connections extensive command.


The output shows the status of multihoming for routing instance green.

Checking the Multihoming Routes


Verify that the expected routes are identified as multihoming.


From operational mode, enter the show route table bgp.l2vpn.0 and show route table green.l2vpn.0 commands.


MH in the output indicates a multihoming route. AD indicates autodiscovery.

Checking the BFD Sessions


Verify that the BFD session status is operational.


From operational mode, enter the show bfd session command.


Up in the State field indicates that BFD is working.

Pinging the Remote PE Router in the VPLS Domain


Check the operability of the MPLS Layer 2 virtual private network (VPN) connection.


From operational mode, enter the ping mpls l2vpn command with the fec129 option.


The output shows that the ping operation is successful, meaning that the LSP for a FEC 129 Layer 2 VPN connection is reachable.