ECS4660-28F_Management Guide-R03

C HAPTER 21 | Multicast Routing
Configuring PIM for IPv4
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state and the pending RPT prune state for this (source, group) pair
until the join/prune interval timer expires.
◆ LAN Prune Delay – Causes this device to inform downstream routers
of how long it will wait before pruning a flow after receiving a prune
request. (Default: Disabled)
When other downstream routers on the same VLAN are notified that
this upstream router has received a prune request, they must send a
Join to override the prune before the prune delay expires if they want
to continue receiving the flow. The message generated by this
command effectively prompts any downstream neighbors with hosts
receiving the flow to reply with a Join message. If no join messages are
received after the prune delay expires, this router will prune the flow.
The sum of the Override Interval and Propagation Delay are used to
calculate the LAN prune delay.
◆ Override Interval – The time required for a downstream router to
respond to a LAN Prune Delay message by sending back a Join
message if it wants to continue receiving the flow referenced in the
message. (Range: 500-6000 milliseconds; Default: 2500 milliseconds)
The override interval and the propagation delay are used to calculate
the LAN prune delay. If a downstream router has group members which
want to continue receiving the flow referenced in a LAN prune delay
message, then the override interval represents the time required for
the downstream router to process the message and then respond by
sending a Join message back to the upstream router to ensure that the
flow is not terminated.
◆ Propagation Delay – The time required for a LAN prune delay
message to reach downstream routers. (Range: 100-5000
milliseconds; Default: 500 milliseconds)
The override interval and pro po gat ion delay are used to calculate the
LAN prune delay. If a downstream router has group members which
want to continue receiving the flow referenced in a LAN prune delay
message, then the propagation delay represents the time required for
the LAN prune delay message to be propagated down from the
upstream router to all downstream routers attached to the same VLAN
interface.
◆ Trigger Hello Delay – The maximum time before transmitting a
triggered PIM Hello message after the router is rebooted or PIM is
enabled on an interface. (Range: 0-5 seconds; Default: 5 seconds)
When a router first starts or PIM is enabled on an interface, the hello
delay is set to random value between 0 and the trigger hello delay. This
prevents synchronization of Hello messages on multi-access links if
multiple routers are powered on simultaneously.
Also, if a Hello message is received from a new neighbor, the receiving
router will send its own Hello message after a random delay between 0
and the trigger hello delay.