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IPv6 Multicast BSR

IPv6 Multicast BSR

Sources: here and here.

The Boot Strap Router (BSR) protocol consists of three types of routers:

Standard - does not participate in BSR or RP elections but forwards multicast traffic
BSR - The router which makes the decision about what is the current active RP
RP - The router which is part of the multicast forwarding tree

The protocol performs the same function as Cisco�s proprietary Auto-RP. Unlike Auto-RP, BSR does not use any dense-mode groups to flood candidate RP and RP mapping information. Instead, the information is flooded using PIM messages, on hop-by-hop basis.

To prevent the BSR advertisements crossing an AS boundary use the use the ipv6 pim bsr-border  (or ip pim bsr-border) command to administratively disable bootstrap router (BSR) messages from being sent or received through an interface. 


You can configure a set of routers to be the BSR as follows:

IPv4
ip pim bsr-candidate < Interface-Name > [hash-mask-length] [priority]

Default priority = 0; If there are multiple routers with zero priority then highest ip address wins.

 

IPv6
ipv6 pim [vrf vrf-name] bsr candidate bsr ipv6-address [hash-mask-length] [priority priority-value]

Default priority = 0; If there are multiple routers with zero priority then highest ip address wins.

To configure a set of routers to be the RPs use:

IPv4
ip pim rp-candidate <PIM-Enabled-Interface> [group-list] [interval] [priority <0-255>].

Default priority = 0; This is really to be considered as a metric (ie lowest number wins). Zero in this case is the best priority.

Default Group-List = If you do not specify this then it means ALL addresses.


As the BSR splits the multicast address space across a number of RPs there is no need to default to highest ip address. This is called �group range to RP set mapping�.


IPv6
ipv6 pim [vrf vrf-name] bsr candidate rp ipv6-address [group-list access-list-name] [priority priority-value] [interval seconds] [scope scope-value] [bidir]


Default priority = 0; This is really to be considered as a metric (ie lowest number wins). Zero in this case is the best priority.


As the BSR splits (or load balances) the multicast address space across a number of RPs there is no need to default to highest ip address. This is called �group range to RP set mapping�. The algorithm (same for v4 and v6) to split this mapping between the RPs is described here. However the simplest way to discover which group address maps to which RP is to use the following commands:

IPv4
show ip pim rp-hash X.X.X.X

IPv6
show ipv6 pim group-map X:X:X::X





This is the network diagram I used to test the this information.


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