Register-Stop Packets; Bootstrap Packets; Hellos; Asserts - HP 7102dl - ProCurve Secure Router Configuration Manual

Configuring Multicast Support with PIM-SM
Overview
13-26

Register-Stop Packets

After an RP begins receiving multicasts on the SP tree, it no longer needs the
register packets. The RP sends register-stops to the DR for the source, instruct-
ing the DR to stop sending the encapsulated traffic. Register-stops are trig-
gered when the RP has an (S, G) with the STP-bit set and receives a register
packet.
A router also sends register-stops when it receives encapsulated traffic for a
group for which it does not have an entry or for which the entry includes no
outgoing interfaces.

Bootstrap Packets

Some PIM routers receive an RP-set (the list of all candidate RPs and the
multicast groups that each can support) from bootstrap packets. Because you
must statically configure an RP-set on a ProCurve Secure Router, it does not
send or receive bootstrap packets.

Hellos

Routers periodically send PIM hellos out all interfaces. Neighbors set a
timeout for the router based on a value in the packet. If the neighbor does not
receive a hello from the router within this interval, it times out the connection.
If the timed-out router was the DR for the subnet, another router on the subnet
becomes DR.

Asserts

In a multi-access subnet, routers may receive redundant multicasts from each
other. When a router receives a multicast packet on one of the outgoing
interfaces for the group, the router knows that this packet has been sent, not
by its upstream neighbor, but by another router on the subnet. The router
drops the packet and multicasts an assert to all PIM routers in the subnet.
The assert identifies the multicast stream in question with the multicast source
and the group addresses. The assert also includes the metric for the router's
connection to the source. All PIM routers in the subnet listen for the asserts.
They choose the router with the best (lowest) metric to become the subnet's
sole forwarder for this multicast stream. All other routers delete the interface
on that subnet from the outgoing interface list for the multicast route.
Figure 13-10 illustrates this process.