Chapter 20
| Multicast Routing
Configuring PIM for IPv4
– 766 –
Configuring Global
PIM-SM Settings
Use the Routing Protocol > PIM > SM (Configure Global) page to configure the rate
at which register messages are sent, the source of register messages, and switch
over to the Shortest Path Tree (SPT).
Parameters
These parameters are displayed:
◆ Register Rate Limit – Configures the rate at which register messages are sent
by the Designated Router (DR) for each (source, group) entry. (Range: 1-65535
packets per second: Default: disabled)
This parameter can be used to relieve the load on the designated router (DR)
and rendezvous point (RP). However, because register messages exceeding the
limit are dropped, some receivers may experience data packet loss within the
first few seconds in which register messages are sent from bursty sources.
◆ Register Source – Configures the IP source address of a register message to an
address other than the outgoing interface address of the DR that leads back
toward the RP. (Range: VLAN 1-4094; Default: The IP address of the DR’s
outgoing interface that leads back to the RP)
When the source address of a register message is filtered by intermediate
network devices, or is not a uniquely routed address to which the RP can send
packets, the replies sent from the RP to the source address will fail to reach the
DR, resulting in PIM-SM protocol failures. This type of problem can be
overcome by manually configuring the source address of register messages to
an interface that leads back to the RP.
◆ SPT Threshold – Prevents the last-hop PIM-SM router from switching to
Shortest Path Source Tree (SPT) mode. (Options: Infinity, Reset; Default: Reset,
to use the SPT)
The default path for packets from a multicast source to a receiver is through the
RP. However, the path through the RP is not always the shortest path. Therefore,
the router uses the RP to forward only the first packet from a new multicast
group to its receivers. Afterwards, it calculates the shortest path tree (SPT)
directly between the receiver and source, and then uses the SPT to send all
subsequent packets from the source to the receiver instead of using the shared
tree. Note that when the SPT threshold is not set by this command, the PIM leaf
router will join the shortest path tree immediately after receiving the first
packet from a new source.
Enable the SPT threshold by selecting “Reset” to force the router to use the
shared tree for all multicast groups, or just for the specified multicast groups.
(This is the default setting.)
◆ Group Address – An IP multicast group address. If a group address is not
specified, the shared tree is used for all multicast groups.
◆ Group Mask – Subnet mask that is used for the group address.
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