HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 539

1 A source registers
with the RP
Multicast
Source of
Multicast
Group X
2
The RP joins SP tree
Source of
Multicast
Group X
Figure 11-3. Switching to an SP Tree (RP)
4. The RP forwards multicasts over both the RP tree and an SP tree as
needed.
When the RP created the (S, G) entry, it copied the outgoing interfaces
from the (*, G) entry. This means the RP can continue forwarding traffic
to routers that were downstream in the RP tree. As edge routers create
their own SP trees, they can, if these trees diverge from the shared tree,
send source-specific prunes towards the RP. These prunes indicate that
the downstream routers no longer need multicast traffic from the RP.
If all routers directly connected to the RP prune themselves in this way,
and if the RP is not itself an edge router for hosts in this multicast group,
the RP will prune itself from the SP tree.
Figure 11-4 shows an RP's multicast routing table immediately after all
routers in the PIM domain have switched to an SP tree that does not
include the RP.
Configuring Multicast Support with PIM-SM
Router A
DR
Router A
DR
Router B
RP for Group X
RP Tree
Router C
Intermediate
Router D
Edge router
Host Y
Router B
RP Tree
RP for Group X
Router C
Multicast
Intermediate
Router D
Edge Router
Overview
11-11