A Source's Dr - HP 7102dl - ProCurve Secure Router Configuration Manual

Configuring Multicast Support with PIM-SM
Overview
N o t e
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3. The router receives multicasts on the SP tree.
As soon as the original router receives a packet on the incoming interface
for the (S, G) entry, it sets the entry's SPT-bit, signaling that the SP tree is
active. The router now drops any packets except those from the SP
neighbor.
4. The router prunes itself from the RP tree.
When it sets the SPT-bit for the entry, the router also sends a source-
specific prune to its upstream RP neighbor. This prune removes the router
from the RP tree, but only for traffic from that specific source. (The
source-specific prune, which has its RP-bit set, is described in "PIM-SM
Packets" on page 13-18.)
This process only occurs if the best connection to the source is through a
different interface than the best connection to the RP.

A Source's DR

A source's DR follows these steps in the transition from the RP to the SP tree:
1. The DR receives traffic from a multicast source and unicasts them to
the RP.
As soon as the DR receives the first multicast packet from a directly
connected source, it creates an (S, G) entry. The DR encapsulates the
multicast packets in register packets and unicasts them to the RP for
distribution over the RP tree.
2. The DR prunes itself from the RP tree.
At the same time, the DR sends a source-specific prune towards the RP
to remove itself from the RP tree for traffic from this source.
3. The source, and through it the source's DR, becomes the root of the
SP tree.
As edge routers build an SP tree, the DR receives (S, G) joins. When the
DR receives an (S, G) join on an interface, it adds that interface to the
outgoing interface list for its (S, G) entry. The DR can forward multicasts
along an SP tree at the same time that it sends register packets to the RP.
4. The DR stops sending register packets to the RP after it receives a
register-stop.
After the RP joins an SP tree, it sends a register-stop to the DR. The DR
starts the register-suppression timer in its (S, G) entry and stops sending
register packets to the RP.