Users Guide

Every PIM router within a domain must map a particular multicast group address to the same RP. With BSR, group-to-RP mapping is
dynamic. You can configure a subset of routers within a domain as C-RPs. Each PIM router selects an RP for a multicast group from the
list of group-to-RP mappings learnt from the BSR messages.
The RP election process is:
1. The C-BSRs announce their candidacy throughout the domain in BSMs. Each BSM contains a BSR priority. The C-BSR with the
highest priority becomes the BSR.
2. Each C-RP unicasts periodic candidate RP advertisements to the BSR. Each message contains an RP priority value and the multicast
group ranges for which the router is a C-RP.
3. The BSR determines the most efficient and stable group-to-RP mapping, which is called the RP-set formation.
4. The BSR sends the group-to-RP mapping sets to all the multicast routers. To select an RP from a set of RPs, multicast routers use
the algorithm that is specified in RFC 4601.
5. The BSR sends the group range-to-RP mappings to all the routers in the domain.
Configuration notes
• A PIM router supports only one candidate BSR per VRF instance.
• A PIM router supports only one candidate RP per VRF instance.
• You can configure a PIM BSR candidate and an RP candidate with Layer 3 (L3) VLAN, Loopback, physical, or port channel interface.
The system derives the IP address from this interface to determine the BSR or RP address.
• PIM BSR and RP candidate configurations are not supported on VXLAN bridge interfaces.
• Before you configure a candidate BSR:
• Enable multicast routing globally and establish PIM neighborship between routers. Ensure that the unicast routing table is
populated.
• Configure an IP address on the candidate BSR interface.
• Before you configure a candidate RP:
• Enable multicast routing globally and establish PIM neighborship between routers. Ensure that the unicast routing table is
populated.
• Ensure that the candidate RP can reach all the nodes in your network.
• (Optional) Configure an ACL with source as any and destination as a valid multicast group address. If you do not configure an
ACL, the router advertises itself as the RP for the entire multicast range, which is 224.0.0.0/4.
NOTE:
• When you associate an ACL without any rules to an RP candidate, the system behaves differently depending
on the order of the configuration:
• If you create the ACL without any rules first and then associate it with the RP candidate, the router denies
all multicast groups.
• If you associate an ACL to an RP candidate that is not yet created in the system, and then configure the
ACL without any rules, the router advertises itself as the RP for the entire multicast range, 224.0.0.0/4.
• Do not use deny rules in the ACL that is used for RP candidate because it does not have any significance.
To configure dynamic RP using the BSR mechanism:
1. Configure a candidate BSR using the ip pim bsr-candidate command.
OS10# configure terminal
OS10(config)# interface ethernet 1/1/9
OS10(conf-if-eth1/1/9)# ip address 10.1.1.8/24
OS10(conf-if-eth1/1/9)# no shutdown
OS10(conf-if-eth1/1/9)# exit
OS10(config)# ip pim bsr-candidate ethernet 1/1/9 hash-mask-len 31 priority 255
To view the PIM candidate and elected BSR:
OS10# show ip pim bsr-router
This system is the Bootstrap Router (v2)
BSR address: 10.1.1.8
BSR Priority: 255, Hash mask length: 31
Next bootstrap message in 00:00:57
This system is a candidate BSR
Candidate BSR address: 11.1.1.8, priority: 255, hash mask length: 31
724
Multicast