PIM Designated Router
Devices configured for IP multicast send PIM hello messages to determine which device will be the designated
router (DR) for each LAN segment (subnet). The hello messages contain the device
’
s IP address, and the
device with the highest IP address becomes the DR.
The DR sends Internet Group Management Protocol (IGMP) host query messages to all hosts on the directly
connected LAN. When operating in sparse mode, the DR sends source registration messages to the rendezvous
point (RP).
By default, multicast devices send PIM router query messages every 30 seconds. By enabling a device to send
PIM hello messages more often, the device can discover unresponsive neighbors more quickly. As a result,
the device can implement failover or recovery procedures more efficiently. It is appropriate to make this
change only on redundant devices on the edge of the network.
PIM Sparse-Mode Register Messages
Dataless register messages are sent at a rate of one message per second. Continuous high rates of register
messages might occur if a DR is registering bursty sources (sources with high data rates) and if the RP is not
running PIM Version 2.
By default, PIM sparse-mode register messages are sent without limiting their rate. Limiting the rate of register
messages will limit the load on the DR and RP, at the expense of dropping those register messages that exceed
the set limit. Receivers may experience data packet loss within the first second in which packets are sent from
bursty sources.
Preventing Use of Shortest-Path Tree to Reduce Memory Requirement
Understanding PIM shared tree and source tree will help you understand how preventing the use of the
shortest-path tree can reduce memory requirements.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
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IP Multicast Optimization: Optimizing PIM Sparse Mode in a Large IP Multicast Deployment
PIM Designated Router