Multicast-Intact - Cisco ASR 9000 Series Configuration Manual

Multicast-Intact

6 By default, receipt of the first data packet prompts Router C to send a join message toward Source.
7 When Router C receives data on (S,G), it sends a prune message for Source up the shared tree.
8 RP deletes the link to Router C from outgoing interface of (S,G). RP triggers a prune message toward
Source.
Join and prune messages are sent for sources and RPs. They are sent hop by hop and are processed by each
PIM router along the path to the source or RP. Register and register-stop messages are not sent hop by hop.
They are exchanged using direct unicast communication between the designated router that is directly connected
to a source and the RP for the group.
The spt-threshold infinity command lets you configure the router so that it never switches to the shortest
Tip
path tree (SPT).
Multicast-Intact
The multicast-intact feature provides the ability to run multicast routing (PIM) when Interior Gateway Protocol
(IGP) shortcuts are configured and active on the router. Both Open Shortest Path First, version 2 (OSPFv2),
and Intermediate System-to-Intermediate System (IS-IS) support the multicast-intact feature. Multiprotocol
Label Switching Traffic Engineering (MPLS-TE) and IP multicast coexistence is supported in Cisco IOS XR
Software by using the mpls traffic-eng multicast-intact IS-IS or OSPF router command. See Cisco ASR 9000
Series Aggregation Services Router Routing Configuration Guide for information on configuring multicast
intact using IS-IS and OSPF commands.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP
shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGPs
route the IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel
(from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because reverse path
forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost next-hops
for use by PIM. These next-hops are called mcast-intact next-hops. The mcast-intact next-hops have the
following attributes:
• They are guaranteed not to contain any IGP shortcuts.
• They are not used for unicast routing but are used only by PIM to look up an IPv4 next hop to a PIM
• They are not published to the Forwarding Information Base (FIB).
• When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state
• In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together.
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 6.0.x
86
source.
advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute
applies even when the native next-hops have no IGP shortcuts.
(In OSPFv2, the behavior is slightly different.)
Implementing Layer-3 Multicast Routing on Cisco IOS XR Software