Administrator Guide

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Electing an RP using the BSR Mechanism
Every PIM router within a domain must map a particular multicast group address to the same RP. The group-to-RP mapping may be
statically or dynamically configured. RFC 5059 specifies a dynamic, self-configuring method called the Bootstrap Router (BSR)
mechanism, by which an RP is elected from a pool of RP candidates (C-RPs).
Some routers within the domain are configured to be C-RPs. Other routers are configured to be Bootstrap Router candidates (C-BSRs);
one router is elected the BSR for the domain and the BSR is responsible for forwarding BSM containing RP-set information to other
routers.
The RP election process is as follows:
1. C-BSRs flood their candidacy throughout the domain in a BSM. Each message contains a BSR priority value, and the C-BSR with the
highest priority value becomes the BSR.
2. Each C-RP unicasts periodic Candidate-RP-Advertisements to the BSR. Each message contains an RP priority value and the group
ranges for which it is a C-RP.
3. The BSR collects the most efficient group-to-RP mappings and periodically updates it to all PIM routes in the network.
4. The BSR floods the RP-Set throughout the domain periodically in case new C-RPs are announced, or an RP failure occurs.
Constraints
1. When a multicast group range is removed from the ACL group list, the E-BSR sends the advertisements to the group with hold-time
as 0 only when the C-RP timer expires. Till the timer expires, the C-RP will act as a RP for that multicast group.
2. In E-BSR, if the C-RP advertisements are not in synchronization with the standby, first few BCM C-RP advertisement might not have
the complete list of RP mappings. Due to this, there is a possibility of RP mapping timeout and momentary traffic loss in the network.
3. If you configure a secondary VLT peer as an E-BSR and in case of ICL flap or failover, the VLT lag will be down resulting a BSM
timeout in the PIM domain and a new BSR will be elected. Hence, it is recommended to configure the primary VLT peer as E-BSR.
NOTE:
BSR configuration in the multicast topology should ensure that secondary VLT node is not selected as E-BSR. If
selected as E-BSR during ICL flap or VLT failover, traffic disruption will be reported.
To enable BSR election for IPv4 or IPv6, perform the following steps:
1. Enter the following IPv4 or IPv6 command to make a PIM router a BSR candidate:
CONFIGURATION
ip pim bsr-candidate
ipv6 pim bsr-candidate
2. Enter the following IPv4 or IPv6 command to make a PIM router a RP candidate:
CONFIGURATION
ip pim rp-candidate
ipv6 pim rp-candidate
3. Display IPv4 or IPv6 Bootstrap Router information.
EXEC Privilege
show ip pim bsr-router
PIM Source-Specific Mode (PIM-SSM)
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