Dell M6220 User Configuration Manual page 1187

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Phase 3: Shortest Path Tree

Figure 43-4. PIM-SM SPT—Part 1

PIM-SM has the capability for last-hop routers (i.e., routers with directly

connected group members) to switch to the Shortest-Path Tree and bypass

the RP. This switchover is based upon an implementation-specific function

called SwitchToSptDesired(S,G) in the standard and generally takes a

number of seconds to switch to the SPT.

In the above example, the last-hop router (at the bottom of the drawing)

sends an (S, G) Join message toward the source to join the SPT and bypass

This (S, G) Join messages travels hop-by-hop to the first-hop router (i.e.,

the router connected directly to the source), thereby creating another

branch of the SPT. This also creates (S, G) state in all the routers along

this branch of the SPT.

Managing IPv4 and IPv6 Multicast

M8024 M6348 M8024-k