Concept Guide

Preventing a PIM Router from Forming an Adjacency
To prevent a router from participating in PIM (for example, to congure stub multicast routing), use the following command.
• Prevent a router from participating in PIM.
INTERFACE mode
ip pim neighbor-filter
Setting a Threshold for Switching to the SPT
The functionality to specify a threshold for switchover to the shortest path trees (SPTs) is available on the system. After a receiver
receives trac from the RP, PM-SM switches to SPT to forward multicast trac. Every multicast group has an RP and a unidirectional
shared tree (group-specic shared tree).
The SPT-Threshold is zero, which means that the last-hop designated router (DR) joins the shortest path tree (SPT) to the source upon
receiving the rst multicast packet.
Initially, a single PIM-SM tree called a shared tree to distribute trac. It is called shared because all trac for the group, regardless of the
source, or the location of the source, must pass through the RP. The shared tree is unidirectional; that is, all multicast trac ows only from
the RP to the receivers. Once a receiver receives trac from the RP, PM-SM switches to SPT to forward multicast trac, which connects
the receiver directly to the source.
You can congure PIM to switch over to the SPT when the router receives multicast packets at or beyond a specied rate.
Table 65.
Conguring PIM to Switch Over to the SPT
IPv4 Congure PIM to switch over to the SPT when the multicast
packet rate is at or beyond a specied rate. The keyword innity
directs PIM to never switch to the SPT.
ip pim spt-threshold {|
innity}
CONFIGURATION
IPv6 Congure PIM to switch over to the SPT when the multicast
packet rate is at or beyond a specied rate. The keyword innity
directs PIM to never switch to the SPT.
ip pim spt-threshold {|
innity}
CONFIGURATION
Preventing a Source from Registering with the RP
To prevent the PIM source DR from sending register packets to route processor (RP) for the specied multicast source and group, use the
following command. If the source DR never sends register packets to the RP, no hosts can ever discover the source and create a shortest
path tree (SPT) to it.
• Prevent a source from transmitting to a particular group.
CONFIGURATION mode
ip pim register-filter
In the following example, Source 1 and Source 2 are both transmitting packets for groups 239.0.0.1 and 239.0.0.2. R3 has a PIM register
lter that only permits packets destined for group 239.0.0.2. An entry is created for group 239.0.0.1 in the routing table, but no outgoing
interfaces are listed. R2 has no lter, so it is allowed to forward both groups. As a result, Receiver 1 receives only one transmission, while
Receiver 2 receives duplicate transmissions.
Multicast Features
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