Rp Paths And Spt Paths; Configuring Pim Sparse - Dell PowerConnect B-RX Configuration Manual

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PIM Sparse

RP paths and SPT paths

Figure 91
the group. The source is attached to PIM Sparse router A and the recipient is attached to PIM
Sparse router C. PIM Sparse router 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 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 to
using the RP for forwarding traffic from a source to a receiver. By default, the device forward 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
forwards the first packet from group 239.255.162.1's source to the destination by sending the
packet to router B, which is the RP. Router B then sends the packet to router C. For the second and
all future packets that router A receives from the source for the receiver, router A forwards them
directly to router C using the SPT path.
NOTE
Brocade recommends that you configure the same ports as candidate BSRs and RPs

Configuring PIM Sparse

To configure a device for PIM Sparse, perform the following tasks:
•
•
•
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Rendezvous Point (RP).
To enhance overall network performance, device use the RP to forward only the first packet
from a group source to the group's receivers. After the first packet, the 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 device calculates a separate
SPT for each source-receiver pair.
NOTE
Brocade recommends that you configure the same ports as candidate BSRs and RPs.
shows two paths for packets from the source for group 239.255.162.1 and a receiver for
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.
NOTE
You cannot configure a Brocade routing interface as a PMBR interface for PIM Sparse in the
current software release.
Configure the following PIM Sparse global parameters:
•
Identify the device as a candidate PIM Sparse Bootstrap Router (BSR), if applicable.
Figure 91, the device A
BigIron RX Series Configuration Guide
53-1001810-01