598 BigIron RX Series Configuration Guide53-1001810-01PIM Sparse23Rendezvous Point (RP).To enhance overall network performance, device use the RP to forward only the first packetfrom a group source to the group’s receivers. After the first packet, the device calculates theshortest path between the receiver and source (the Shortest Path Tree, or SPT) and uses theSPT for subsequent packets from the source to the receiver. The device calculates a separateSPT for each source-receiver pair.NOTEBrocade recommends that you configure the same ports as candidate BSRs and RPs.RP paths and SPT pathsFigure 91 shows two paths for packets from the source for group 239.255.162.1 and a receiver forthe group. The source is attached to PIM Sparse router A and the recipient is attached to PIMSparse router C. PIM Sparse router B in is the RP for this multicast group. As a result, the defaultpath for packets from the source to the receiver is through the RP. However, the path through theRP sometimes is not the shortest path. In this case, the shortest path between the source and thereceiver is over the direct link between router A and router C, which bypasses the RP (router B).To optimize PIM traffic, the protocol contains a mechanism for calculating the Shortest Path Tree(SPT) between a given source and receiver. PIM Sparse routers can use the SPT as an alternative tousing the RP for forwarding traffic from a source to a receiver. By default, the device forward thefirst packet they receive from a given source to a given receiver using the RP path, but forwardsubsequent packets from that source to that receiver through the SPT. In Figure 91, the device Aforwards the first packet from group 239.255.162.1’s source to the destination by sending thepacket to router B, which is the RP. Router B then sends the packet to router C. For the second andall future packets that router A receives from the source for the receiver, router A forwards themdirectly to router C using the SPT path.NOTEBrocade recommends that you configure the same ports as candidate BSRs and RPsConfiguring PIM SparseTo configure a device for PIM Sparse, perform the following tasks:• Configure the following global parameter:• Enable the PIM Sparse mode of multicast routing.• Configure the following interface parameters:• Configure an IP address on the interface• Enable PIM Sparse.• Identify the interface as a PIM Sparse border, if applicable.NOTEYou cannot configure a Brocade routing interface as a PMBR interface for PIM Sparse in thecurrent software release.• Configure the following PIM Sparse global parameters:• Identify the device as a candidate PIM Sparse Bootstrap Router (BSR), if applicable.
