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Chapter 9
Multicast
Grafting
PIM DM is also ready to forward multicast data once a previously inactive
interface becomes active. This is done through the process of grafting. When
a host sends an IGMP group membership report to the router, the router
then sends a Graft message to the nearest upstream PIM neighbor. Once this
message is acknowledged, multicast data begins to be forwarded to the
router and on to the host. Figure 9.19 depicts the grafting process.
F I G U R E 9 . 1 9
PIM DM grafting
Sparse Mode Routing Protocols
Sparse mode protocols use shared tree distribution as their forwarding meth-
ods. This is done to create a more efficient method of multicast distribution.
There are two sparse mode protocols that will be discussed in this section:
Core-based trees (CBT)
Protocol Independent Multicast sparse mode (PIM SM)
HostA
HostF
HostB
HostC
HostD HostE
Source for
224.2.125.125
Member
Member
Member
New member of
224.2.125.125
Router1
Router2
Router3
HostG
Router5
Router4
Forward
multicast data
Graft
request
IGMP membership report
Forward multicast data
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