Handling Of Multicast Packets; Table 9: Impact Of Igp Shortcut And Forwarding Adjacency On Unicast And Multicast Rtm - Alcatel-Lucent 7450 Manual

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Handling of Multicast Packets

This feature supports multicast Reverse-Path Check (RPF) in the presence of IGP shortcuts. When

the multicast source for a packet is reachable via an IGP shortcut, the RPF check fails since PIM

requires a bi-directional path to the source but IGP shortcuts are unidirectional.

The implementation of the IGP shortcut feature provides IGP with the capability to populate the

multicast RTM with the prefix IP next-hop when both the rsvp-shortcut option and the multicast-

import option are enabled in IGP.

This change is made possible with the enhancement introduced by which SPF keeps track of both

the direct first hop and the tunneled first hop of a node that is added to the Dijkstra tree.

Note that IGP will not pass LFA next-hop information to the mcast RTM in this case. Only ECMP

next-hops are passed. As a consequence, features such as PIM Multicast-Only FRR (MoFRR) will

only work with ECMP next-hops when IGP shortcuts are enabled.

Finally, note that the concurrent enabling of the advertise-tunnel-link option and the multicast-

import option will result a multicast RTM that is a copy of the unicast RTM and is thus populated

with mix of IP and tunnel NHs. RPF will succeed for a prefix resolved to a IP NH, but will fail for

a prefix resolved to a tunnel NH.

advertise-tunnel-link options with unicast and multicast RTMs.

rsvp-shortcut

rsvp-shortcut

1. Multicast RTM is different from unicast RTM as it is populated with IP NHs only,

2. Multicast RTM is a copy of the unicast RTM and is thus populated with mix of IP and

7450 ESS MPLS Guide

(Primary SPF)

including ECMP IP NHs. RPF check can be performed for all prefixes.

tunnel NHs. RPF will succeed for a prefix resolved to a IP NH but will fail for a prefix

resolved to a tunnel NH.

summarizes the interaction of the rsvp-shortcut and

Multicast RTM

(Primary SPF)

MPLS and RSVP

Multicast RTM