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Summary

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shared tree. If there is another router with active members connected to the
router requesting the prune, it is removed from the outgoing interface list
and no additional Prune messages are sent to the RP. See Figure 9.21 for a
visual description.

F I G U R E 9 . 2 1

PIM SM pruning

Router5 receives an IGMP message requesting the removal of HostG

from the group. Because HostG was the last active member of the group, the
(*, G) entry is set to null 0 and a prune request is sent by Router5 to Router3.
When Router3 receives the request, it removes the link for interface S0 from
the forwarding table. Because HostF is a directly connected active member of the
group, the entry for (*, G) is not null 0, so no prune request is sent to Router2
(the RP for this example).

If HostF were not active, the entry for (*, G) would have been set to null

0 also and a prune request would have been sent to the RP.

Summary

n this chapter, we described the many different facets of IP multicast.

We started out with an overview of multicast and compared it with unicast

HostA

HostF

HostB

HostC

HostD HostE

Member
224.2.125.125

Router1

Router2

Router3

HostG

Router5

Router4

Prune
request

IGMP remove request

E0 removed from
forwarding cache

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