Service Manual

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 platform. 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 53. 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 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
519