1250 BigIron RX Series Configuration Guide53-1002253-01IPv6 PIM sparse49• BSR – The Bootstrap Router (BSR) distributes RP information to the other PIM Sparse routerswithin the domain. Each PIM Sparse domain has one active BSR. For redundancy, you canconfigure ports on multiple routers as candidate BSRs. The PIM Sparse protocol uses anelection process to select one of the candidate BSRs as the BSR for the domain. The BSR withthe highest BSR priority (a user-configurable parameter) is elected. If the priorities result in atie, then the candidate BSR interface with the highest IP address is elected. In the example inFigure 144, PIM Sparse router B is the BSR. Port 2/2 is configured as a candidate BSR.• RP – The RP is the rendezvous point for PIM Sparse sources and receivers. A PIM Sparsedomain can have multiple RPs, but each PIM Sparse multicast group address can have onlyone active RP. PIM Sparse routers learn the addresses of RPs and the groups for which theyare responsible from messages that the BSR sends to each of the PIM Sparse routers. In theexample in Figure 144, PIM Sparse router B is the RP. Port 2/2 is configured as a candidateRendezvous Point (RP).To enhance overall network performance, the BigIron RX uses the RP to forward only the firstpacket from a group source to the group’s receivers. After the first packet, the devicecalculates the shortest path between the receiver and source (the Shortest Path Tree, or SPT)and uses the SPT for subsequent packets from the source to the receiver. The devicecalculates a separate SPT for each source-receiver pair.NOTEBrocade recommends that you configure the same ports as candidate BSRs and RPs.RP paths and SPT pathsFigure 144 shows two paths for packets from the source for group fec0:1111::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 alternativeto using the RP for forwarding traffic from a source to a receiver. By default, the BigIron RX forwardthe first 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 144, the BigIronRX A forwards the first packet from group fec0:1111::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.Configuring PIM sparseTo configure a BigIron RX for IPv6 PIM Sparse, perform the following tasks:• Configure the following global parameter• Enable the IPv6 PIM Sparse mode of multicast routing• Enable the IPv6 unicast-routing• Configure the following interface parameters:
