Administrator Guide
225.0.1.40 165.87.50.5
226.1.1.1 165.87.50.5
To display the assigned RP for a group range (group-to-RP mapping), use the show ip pim rp mapping command in EXEC
privilege mode.
Dell#show ip pim rp mapping
PIM Group-to-RP Mappings
Group(s): 224.0.0.0/4, Static
RP: 165.87.50.5, v2
Configuring a Designated Router
Multiple PIM-SM routers might be connected to a single local area network (LAN) segment. One of these routers is elected to
act on behalf of directly connected hosts. This router is the designated router (DR).
The DR is elected using hello messages. Each PIM router learns about its neighbors by periodically sending a hello message out
of each PIM-enabled interface. Hello messages contain the IP address of the interface out of which it is sent and a DR priority
value. The router with the greatest priority value is the DR. If the priority value is the same for two routers, then the router with
the greatest IP address is the DR. By default, the DR priority value is 192, so the IP address determines the DR.
● Assign a DR priority value.
INTERFACE mode
ip pim dr-priority priority-value
● Change the interval at which a router sends hello messages.
INTERFACE mode
ip pim query-interval seconds
● Display the current value of these parameter.
EXEC Privilege mode
show ip pim interface
Electing an RP using the BSR Mechanism
Every PIM router within a domain must map a particular multicast group address to the same RP. The group-to-RP mapping may
be statically or dynamically configured. RFC 5059 specifies a dynamic, self-configuring method called the Bootstrap Router
(BSR) mechanism, by which an RP is elected from a pool of RP candidates (C-RPs).
Some routers within the domain are configured to be C-RPs. Other routers are configured to be Bootstrap Router candidates
(C-BSRs); one router is elected the BSR for the domain and the BSR is responsible for forwarding BSM containing RP-set
information to other routers.
The RP election process is as follows:
1. C-BSRs flood their candidacy throughout the domain in a BSM. Each message contains a BSR priority value, and the C-BSR
with the highest priority value becomes the BSR.
2. Each C-RP unicasts periodic Candidate-RP-Advertisements to the BSR. Each message contains an RP priority value and the
group ranges for which it is a C-RP.
3. The BSR collects the most efficient group-to-RP mappings and periodically updates it to all PIM routes in the network.
4. The BSR floods the RP-Set throughout the domain periodically in case new C-RPs are announced, or an RP failure occurs.
Constraints
1. When a multicast group range is removed from the ACL group list, the E-BSR sends the advertisements to the group with
hold-time as 0 only when the C-RP timer expires. Till the timer expires, the C-RP will act as a RP for that multicast group.
2. In E-BSR, if the C-RP advertisements are not in synchronization with the standby, first few BCM C-RP advertisement might
not have the complete list of RP mappings. Due to this, there is a possibility of RP mapping timeout and momentary traffic
loss in the network.
3. If you configure a secondary VLT peer as an E-BSR and in case of ICL flap or failover, the VLT lag will be down resulting a
BSM timeout in the PIM domain and a new BSR will be elected. Hence, it is recommended to configure the primary VLT peer
as E-BSR.
684
PIM Sparse-Mode (PIM-SM)