PIM DM pruning

PIM DM pruning
Grafting PIM DM is also ready to forward multicast data after 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. After this message is acknowledged, multicast data begins to be forwarded to the
router and on to the host. Figure 19.19 depicts the grafting process.
Sparse Mode Routing Protocols
Sparse mode protocols use shared tree distribution as their forwarding methods. This is done to
create a more efficient method of multicast distribution. Two sparse mode protocols are discussed
in this section:
 Core-based trees (CBT)
 Protocol Independent Multicast sparse mode (PIM SM)
Core-Based Trees
When we discussed shared trees, you learned that there were two types: unidirectional and bidirectional.
CBT utilizes the bidirectional method for its multicast data distribution. Because CBT
uses a shared tree system, it designates a core router that is used as the root of the tree, enabling
data to flow up or down the tree.
Data forwarding in a CBT multicast system is similar to the shared tree distribution we described
earlier. If a source to a multicast group sends multicast data to the CBT-enabled router, the router
then forwards the data out all interfaces that are included in the tree, not just the interface that leads
to the core router. In this manner, data flows up and down the tree. After the data gets to the core
router, the core router then forwards the information to the other routers that are in the tree.
Figure 19.20 depicts this process.
Host A
Host F
Host B Host C
Host D Host E
Source for
224.2.125.125
Member
224.2.125.125
Member
224.2.125.125
Member
224.2.125.125
Router 1
Router 2
Router 3
Host G