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

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IPv6 PIM sparse
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RP paths and SPT paths

Figure 139
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 BigIron RX 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
RX A forwards the first packet from group fec0:1111::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.

Configuring PIM sparse

To configure a BigIron RX for IPv6 PIM Sparse, perform the following tasks:
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BSR – The Bootstrap Router (BSR) distributes RP information to the other PIM Sparse routers
within the domain. Each PIM Sparse domain has one active BSR. For redundancy, you can
configure ports on multiple routers 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 user-configurable parameter) is elected. If the priorities result in a
tie, then the candidate BSR interface with the highest IP address is elected. In the example in
Figure 139, 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 Sparse
domain can have multiple RPs, but each PIM Sparse multicast group address can have only
one active RP. PIM Sparse routers 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 routers. In the
example in Figure 139, PIM Sparse router B is the RP. Port 2/2 is configured as a candidate
Rendezvous Point (RP).
To enhance overall network performance, the BigIron RX uses 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 fec0:1111::1 and a receiver for
Configure the following global parameter
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Enable the IPv6 PIM Sparse mode of multicast routing
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Enable the IPv6 unicast-routing
Configure the following interface parameters:
Figure 139, the BigIron
BigIron RX Series Configuration Guide
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