C
HAPTER
46
| Multicast Routing Commands
PIM Multicast Routing
– 1107 –
ip pim spt-threshold This command prevents the last-hop PIM router from switching to Shortest
Path Source Tree (SPT) mode. Use the no form to allow the router to
switch over to SPT mode.
SYNTAX
ip pim spt-threshold infinity [group-prefix group-address mask]
no ip pim spt-threshold infinity
group-address - An IP multicast group address. If a group address
is not specified, the command applies to all multicast groups.
mask - Subnet mask that is used for the group address.
DEFAULT SETTING
The last-hop PIM router joins the shortest path tree immediately after the
first packet arrives from a new source
COMMAND MODE
Global Configuration
COMMAND USAGE
â—† 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.
â—† This command forces the router to use the shared tree for all multicast
groups, or just for the specified multicast groups.
â—† Only one entry is allowed for this command.
EXAMPLE
This example prevents the switch from using the SPT for multicast groups
224.1.0.0~224.1.255.255.
Console(config)#ip pim spt-threshold infinity group-prefix 224.1.0.0
0.0.255.255
Console#
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