Understanding Redundant Virtual Tunnel Interfaces in MBGP MVPNs
In multiprotocol BGP (MBGP) multicast VPNs (MVPNs), VT interfaces are needed for multicast traffic on routing devices that function as combined provider edge (PE) and provider core (P) routers to optimize bandwidth usage on core links. VT interfaces prevent traffic replication when a P router also acts as a PE router (an exit point for multicast traffic).
Starting in Junos OS Release 12.3, you can configure up to eight VT interfaces in a routing instance, thus providing Tunnel PIC redundancy inside the same multicast VPN routing instance. When the active VT interface fails, the secondary one takes over, and you can continue managing multicast traffic with no duplication.
Redundant VT interfaces are supported with RSVP point-to-multipoint provider tunnels as well as multicast LDP provider tunnels. This feature also works for extranets.
You can configure one of the VT interfaces to be the primary interface. If a VT interface is configured as the primary, it becomes the next hop that is used for traffic coming in from the core on the label-switched path (LSP) into the routing instance. When a VT interface is configured to be primary and the VT interface is used for both unicast and multicast traffic, only the multicast traffic is affected.
If no VT interface is configured to be the primary or if the primary VT interface is unusable, one of the usable configured VT interfaces is chosen to be the next hop that is used for traffic coming in from the core on the LSP into the routing instance. If the VT interface in use goes down for any reason, another usable configured VT interface in the routing instance is chosen. When the VT interface in use changes, all multicast routes in the instance also switch their reverse-path forwarding (RPF) interface to the new VT interface to allow the traffic to be received.
To realize the full benefit of redundancy, we recommend that when you configure multiple VT interfaces, at least one of the VT interfaces be on a different Tunnel PIC from the other VT interfaces. However, Junos OS does not enforce this.
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