Chapter 51
| Multicast Routing Commands
PIM Multicast Routing
– 1201 –
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-if)#ip pim sparse-mode
Console(config-if)#exit
Console(config)#ip multicast-routing
Console(config)#router pim
Console(config)#ip pim spt-threshold infinity group-prefix 224.1.0.0
0.0.255.255
Console#
ip pim dr-priority This command sets the priority value for a Designated Router (DR) candidate. Use
the no form to restore the default setting.
Syntax
ip pim dr-priority priority-value
no ip pim dr-priority
priority-value - Priority advertised by a router when bidding to become the
DR. (Range: 0-4294967294)
Default Setting
1
Command Mode
Interface Configuration (VLAN)
Command Usage
â—† More than one PIM-SM router may be connected to an Ethernet or other
shared-media LAN. If multicast hosts are directly connected to the LAN, then
only one of these routers is elected as the DR, and acts on behalf of these hosts,
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