BSR configuration and election
There should be multiple BSR candidates configured in a PIM-SM domain so that if the elected BSR becomes
unavailable, another router will take its place. In the BSR election process, the BSR candidate configured with the
highest priority number is selected. Where the highest priority setting is shared by multiple candidates, the
candidate having the highest IP address is selected. In the event that the selected BSR subsequently fails,
another election takes place among the remaining BSR candidates. To facilitate a predictable BSR election,
configure a higher priority on the router you want elected as the BSR for the domain.
NOTE:
A router serving as the BSR for a domain should be central to the network topology. This helps to
ensure optimal performance and also reduce the possibility of a network problem isolating the BSR.
BSR role in fault recovery
If the hold-time maintained in the BSR for a given C-RP's latest advertisement expires before being refreshed by
a new advertisement from the C-RP, the non-reporting C-RP is removed from the domain. In this case, the
removed C-RP's multicast groups are re-assigned to other C-RPs. (If no other C-RPs or static RPs in the domain
are configured to support a multicast group from the non-reporting C-RP, that group becomes unavailable in the
domain.)
RP
Instead of flooding multicast traffic as is done with PIM-DM, PIM-SM uses a set of multiple routers to operate as
RPs. Each RP controls multicast traffic forwarding for one or more multicast groups as follows:
• Receives traffic from multicast sources (S) via a DR.
• Receives multicast joins from routers requesting multicast traffic.
• Forwards the requested multicast traffic to the requesting routers.
Note that the routers requesting multicast traffic are either edge routers or intermediate routers. Edge routers are
directly connected to specific multicast receivers using ICMP to request traffic. Intermediate routers are on the
path between edge routers and the RP. This is known as a RP Tree (RPT) where only the multicast address
appears in the routing table. For example:
( *, G ), where:
* = a variable (wildcard) representing the IP address of any multicast source
G = a particular multicast group address.
NOTE:
The software supports up to 100 RPs in a given PIM-SM domain.
Defining supported multicast groups
An RP in the default candidate configuration supports the entire range of possible multicast groups. This range is
expressed as a multicast address and mask, where the mask defines whether the address is for a single address
or a range of contiguous addresses:
Multicast address
Mask
Address range
224.0.0.0
240.0.0.0
224.0.0.0 - 239.255.255.255
An alternate way to express the above (default) address and mask is:
120
Aruba 3810 / 5400R Multicast and Routing Guide for ArubaOS-
Switch 16.08
