Technical Documentation

Option: Configuring VPLS Multihoming with BGP Signaling

With VPLS multihoming, you can connect multiple PE router interfaces to one customer site. This feature provides VPLS redundancy should a PE router or PE router interface fail.

To configure multihoming, you must configure the same site IDs on all PE routers and router interfaces that are connected to the same customer site, You must also specify on each PE router which interfaces are connected to the customer site. We recommend that you configure distinct route distinguishers for each multihomed router. Configuring distinct route distinguishers helps with faster convergence when the connection to a primary router goes down. It also requires that the other PE routers maintain additional state information.

To configure a route distinguisher, include the route-distinguisher statement at the [edit routing-instances instance-name] hierarchy level. To assign a site ID, include the site-identifier statement at the [edit routing-instances instance-name protocols vpls site name] hierarchy level. To specify the interfaces associated with a site, include the interface statement at the [edit routing-instances instance-name protocols vpls site name] hierarchy level.

To connect multiple PE routers to one customer site, you must configure multihoming on each PE router connected to that site. This will prevent routing loops should BGP connectivity fail. BGP automatically determines the primary and backup routers. Alternatively, you can statically configure a primary PE router and backup PE routers for a customer site by specifying the preference value. BGP uses preference values to determine routing paths.

Note: Multihoming relies on full BGP connectivity to all other PEs. Configure a dual router reflector topology to provide redundant PE-to-PE BGP connectivity.

To configure multihoming, include the multi-homing statement at the [edit routing-instances instance-name protocols vpls site name] hierarchy level. To configure preference value, include the preference-value statement at the [edit routing-instances instance-name protocols vpls site name] hierarchy level. You can configure the preference value as primary or backup, or you can specify a preference number. When specifying preference numbers, configure the primary interface with a preference value of 65,535 and any backup interfaces with a number from 1 to 65,534.

When multiple PE router interfaces on a single PE router are connected to one customer site, you must configure an active interface. All traffic will pass through the active interface unless this interface fails, in which case a backup interface will become the active interface.

To specify a multihomed interface as the primary interface for a site, include the active-interface statement at the [edit routing-instances instance-name protocols vpls site name] hierarchy level. The interface that you specify is called the primary interface. If the primary interface goes down, an alternate interface becomes the active interface. Once the primary interface comes back up, the primary interface becomes the active interface once again and the alternate interface becomes inactive.

If you do not want to specify a primary multihomed interface, you can use the any option. With the any option, the router dynamically chooses an active interface. If the active interface goes down, an alternate interface becomes the active interface. Once the down interface comes back up, it stays inactive.

If no active interfaces are configured at the site level, it is assumed that all traffic for a VPLS site travels through a single, nonmultihomed PE router.

Note: If you add a direct connection between CE devices that are multihomed to the same VPLS site on different PE routers, traffic loops and loss of connectivity might occur. We do not recommend this topology.

The following example shows a multihoming configuration with two PE routers that are connected to a single customer site. Note in the configuration that PE1 is the primary router and PE2 is the backup router.

Router PE1

[edit]routing-instances {green {instance-type vpls;interface fe-0/1/3.0;route-distinguisher 10.255.14.218:1;vrf-target target:11111:1;protocols {vpls {site-range 10;site green4 {site-identifier 4;multi-homing; # Ensures that BGP is established before forwarding on the
# site member interfaces.
preference value 65535;interface fe-1/1/3.0;}
}
}
}
}

Router PE2

[edit]routing-instances {green {instance-type vpls;interface fe-0/1/0.0;route-distinguisher 10.255.14.219:1;vrf-target target:11111:1;protocols {vpls {site-range 10;site green4 {site-identifier 4;multi-homing;preference value 1;interface fe-0/1/0.0;}}}}}

The following example shows a multihoming configuration with one PE router with multiple interfaces that are connected to a single customer site.

Router PE3

[edit]routing-instances {green {instance-type vpls;interface fe-1/1/0.0;interface fe-1/2/0.0;interface fe-1/3/0.0;route-distinguisher 10.255.14.218:1;vrf-target target:11111:1;protocols {vpls {site-range 10;site green4 {site-identifier 4;active-interface any;interface fe-1/1/0.0;interface fe-1/2/0.0;interface fe-1/3/0.0;}}}}}

For more information on VPLS multihoming, see the JUNOS VPNs Configuration Guide.


Published: 2010-04-15