HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 547

N o t e
If the router is sending the packet to its RP to either join or withdraw from the
group's RP tree, the join or prune list contains a wildcard entry with the RP's
address. An exception to this rule occurs when a router withdraws from an
RP tree in order to join an SP tree. The router only withdraws from the RP
tree as far as traffic from the specific source is concerned, so the prune list
contains the source's address.
If the router is sending the packet in order to join or prune an SP tree, the
group's join or prune list contains the address for the source specific to
that tree.
Receiving (*, G) Join/Prunes. When a router receives a join/prune packet
dealing with the RP tree, it can take these actions:
1. It ignores any group entries in which the wildcard source address does
not match the RP for that group. This is one reason that it is very important
to configure the same RP set on every router in your network.
2. If the join list for a group includes the wildcard source, the router searches
for a (*, G) entry in its multicast routing table that matches that group. (It
creates the entry if it does not exist.) The router then adds the interface
on which it received the message to the entry's outgoing interface list.
In some circumstances, the router can also add the interface to a corre-
sponding (S, G) entry. This allows new hosts to join a multicast group even
after routers have switched to an SP tree for that group.
3. If the group's prune list includes the wildcard source, the router deletes
the interface on which it received the packet from the (*, G) entry's
outgoing interface.
If the interface connects to a multi-access network, the router schedules
the interface for deletion instead of immediately deleting it. This delay
gives other routers in the network the opportunity to override the prune.
(See the discussion of the override delay and propagation delay timers in
"Changing PIM-SM Timers" on page 11-37 for more information.)
Receiving (S, G) Prunes. When a PIM router receives a join/prune message
dealing with the SP tree, it either adds or prunes a connection as follows:
If a group's join list includes the specific source, the router adds the
interface on which it received the packet to the outgoing interface list for
the corresponding (S, G) entry. If necessary, the router creates the entry,
copying the outgoing interface list from the (*, G) entry.
Configuring Multicast Support with PIM-SM
Overview
11-19