Product guide

PIM-SM (Sparse Mode)
PIM-SM Operation and Router Types
the BSR candidate configured with the highest priority number is selected.
Where the highest priority setting is shared by multiple candidates, the candi-
date 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. (Refer to
“Changing the Priority Setting for a BSR-Candidate Router” on page 4-36.)
Note A router serving as the BSR for a domain should be central to the network
topology. This will help 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, then 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, then that group
becomes unavailable in the domain.)
Rendezvous Point (RP)
Instead of flooding multicast traffic as is done with PIM-DM, PIM-SM uses a
set of multiple routers to operate as rendezvous points (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
directly connected to specific multicast receivers using IGMP to request the
traffic, or are intermediate routers on the path between the edge routers and
the RP. This operation forms an RP Tree (RPT) where only the destination
multicast address appears in the RP routing table. This is represented as
follows:
( *, G ), where:
* = a variable (wildcard) representing the IP address of any multicast
source
G = a particular multicast group address.
The software supports up to 100 RPs in a given PIM-SM domain.
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