C
HAPTER
46
| Multicast Routing Commands
PIM Multicast Routing
– 1106 –
COMMAND MODE
Global Configuration
COMMAND USAGE
â—† When the ip pim rp-candidate command is entered, the router
periodically sends PIMv2 messages to the BSR advertising itself as a
candidate RP for the specified group addresses. The IP address of the
designated VLAN is sent as the candidate’s RP address. The BSR places
information about all of the candidate RPs in subsequent bootstrap
messages. The BSR uses the RP-election hash algorithm to select an
active RP for each group range. The election process is performed by
the BSR only for its own use. Each PIM-SM router that receives the list
of RP candidates from the BSR also elects an active RP for each group
range using the same election process.
â—† The election process for each group is based on the following criteria:
â–
Find all RPs with the most specific group range.
â–
Select those with the highest priority (lowest priority value).
â–
Compute a hash value based on the group address, RP address,
priority, and hash mask included in the bootstrap messages.
â–
If there is a tie, use the candidate RP with the highest IP address.
â—† This distributed election process provides faster convergence and
minimal disruption when an RP fails. It also serves to provide load
balancing by distributing groups across multiple RPs. Moreover, when
an RP fails, the responsible RPs are re-elected on each router, and the
groups automatically distributed to the remaining RPs.
â—† To improve failover recovery, it is advisable to select at least two core
routers in diverse locations, each to serve as both a candidate BSR and
candidate RP. It is also preferable to set up one of these routers as both
the primary BSR and RP.
EXAMPLE
The following example configures the router to start advertising itself to
the BSR as a candidate RP for the indicated multicast groups.
Console(config)#ip pim rp-candidate interface vlan 1 group-prefix 224.0.0.0
255.0.0.0
Console(config)#end
Console#show ip pim rp mapping
PIM Group-to-RP Mappings
Groups : 224.0.0.0/8
RP address : 192.168.0.2/32
Info source : 192.168.0.2/32, via bootstrap, priority: 0
Uptime : 00:00:51
Expire : 00:01:39
Console#
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