Routing

Answer

When a multicast source connects to two PE routers, the receiver PE router selects the upstream multicast PE router. By default, it selects the router whose upstream address is numerically highest.

In Junos OS 9.6 Release and later, it is possible to change the upstream PE router selection behavior, for example, if the primary sender PE router has a lower address than the backup sender PE router.

You can select the upstream multicast hop (UMH) based on the unicast route preference, using the unicast-umh-election statement as shown:

set routing-instances routing-instance name protocols mvpn unicast-umh-election

CAUTION: When using the unicast-umh-election statement:

• The unicast preference-based single forwarder election only works with the default deterministic path-selection algorithm in BGP. When a PE router is configured with the cisco-non-deterministic path selection algorithm in BGP, the unicast preference-based single forwarder election might fail. The unicast-umh-election statement can only be configured when cisco-non-deterministic path selection algorithm is not configured.
• All PE routers must prefer the same route to the upstream multicast hop. The unicast preferences for routes to the sources must not depend on any BGP path selection criteria (such as lowest IGP metric) that will cause one PE router to choose one UMH while another PE router chooses a different UMH.

 For more information, click Layer 3 VPNs Feature Guide.