RP paths and SPT paths
•PMBR - A PIM device that has some interfaces within the PIM domain and other interface outside the PIM domain. PBMRs connect the PIM domain to the Internet.
•BSR - The Bootstrap Router (BSR) distributes RP information to the other PIM Sparse devices within the domain. Each PIM Sparse domain has one active BSR. For redundancy, you can configure ports on multiple devices as candidate BSRs. The PIM Sparse protocol uses an election process to select one of the candidate BSRs as the BSR for the domain. The BSR with the highest BSR priority (a
•RP - The RP is the meeting point for PIM Sparse sources and receivers. A PIM Sparse domain can have multiple RPs, but each PIM Sparse multicast group address can have only one active RP. PIM Sparse devices learn the addresses of RPs and the groups for which they are responsible from messages that the BSR sends to each of the PIM Sparse devices. In the example in Figure 5 on page 95, PIM Sparse device B is the RP. Port 2/2 is configured as a candidate Rendezvous Point (RP). To enhance overall network performance, the Brocade device uses the RP to forward only the first packet from a group source to the group’s receivers. After the first packet, the Brocade device calculates 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 Brocade device calculates a separate SPT for each
NOTE
It is recommended that you configure the same ports as candidate BSRs and RPs.
RP paths and SPT paths
Figure 5 on page 95 shows two paths for packets from the source for group 239.255.162.1 and a receiver for the group. The source is attached to PIM Sparse device A and the recipient is attached to PIM Sparse device C. PIM Sparse device B in is the RP for this multicast group. As a result, the default path for packets from the source to the receiver is through the RP. However, the path through the RP sometimes is not the shortest path. In this case, the shortest path between the source and the receiver is over the direct link between device A and device C, which bypasses the RP (device 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 devices can use the SPT as an alternative to using the RP for forwarding traffic from a source to a receiver. By default, the Brocade device forwards the first packet they receive from a given source to a given receiver using the RP path, but forward subsequent packets from that source to that receiver through the SPT. In Figure 5 on page 95, device A forwards the first packet from group 239.255.162.1’s source to the destination by sending the packet to device B, which is the RP. Device B then sends the packet to device C. For the second and all future packets that device A receives from the source for the receiver, device A forwards them directly to device C using the SPT path.
Configuring PIM Sparse
To configure a Brocade 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.
•Configure the following PIM Sparse global parameters:
96 | FastIron Ethernet Switch IP Multicast Configuration Guide |
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