HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 552

Configuring Multicast Support with PIM-SM
Overview
Event
The router receives multicast traffic
on its SP tree.
The last outgoing interface is
deleted from a (S, G) entry (RP-bit
set).
A change in the unicast routing table
or in the subnet's DR changes the
best connection to the RP.
A change in the unicast routing table
or in the subnet's DR changes the
best connection to a multicast
source.
11-24
Action
If the SP incoming interface is
different from the RP incoming
interface, the router sets the STP-
bit for the (S, G) entry.
In this case, the router starts to
use the SP tree exclusively, and
so it prunes itself from the RP tree.
The router remains in the RP tree,
but refuses traffic from that
specific source because all of its
neighbors are using an SP tree for
that source.
The router's RP tree changes.
After a randomized interval, the
router sends a join to the new
neighbor.
The router's SP tree changes.
After a randomized interval, the
router sends a join to the new
neighbor.
Sending Periodic Join/Prune Packets. Routers also send join/prune
packets at the close of every join/prune interval. (See "Changing PIM-SM
Timers" on page 11-37 to set this interval.)
The router transmits these packets out the interfaces that connect to any
upstream RP neighbor or upstream SP neighbor. In each packet, the router
includes only the joins or prunes relevant to the neighbor receiving the packet.
To the upstream RP neighbor for a group, the router sends a periodic join/
prune packet that can include:
a join for a (*, G) entry with at least one outgoing interface
a prune for a (*, G) entry with no outgoing interfaces
a prune for an (S, G) entry with its RP-bit set and no outgoing interfaces
a prune for an (S, G) entry with the STP-bit set, if the RP neighbor is
different from the source-specific neighbor
To the upstream neighbor for a specific source, the router sends a periodic
join/prune packet that can include:
a join for an (S, G) entry with at least one outgoing interface
a prune for an (S, G) entry with no outgoing interfaces
Packet Includes Sent to
prune for the group upstream RP neighbor
with a specific source
address (RP-bit set)
prune for the group upstream RP neighbor
with a specific source
address (RP-bit set)
join for the group with new upstream RP
a wildcard address neighbor
join for the group with new upstream SP
a specific source neighbor
address