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Creating Multicast Boundaries and Domains
A PIM domain is a contiguous set of routers that all implement PIM and are configured to operate within a common boundary
defined by PIM multicast border routers (PMBRs).
PMBRs connect each PIM domain to the rest of the Internet.
Create multicast boundaries and domains by filtering inbound and outbound bootstrap router (BSR) messages per interface. The
following command is applied to the subsequent inbound and outbound updates. Timeout removes existing BSR advertisements.
● Create multicast boundaries and domains by filtering inbound and outbound BSR messages per interface.
ip pim bsr-border
● Remove candidate RP advertisements.
clear ip pim rp-mapping
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.
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.
PIM Sparse-Mode (PIM-SM)
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