value randomizes the transmission delay to a time between 0 and the hello delay setting. Using 0 means no
delay.
After the router sends the initial hello packet to a newly detected VLAN interface, it sends subsequent hello
packets according to the current Hello Interval setting.
Not used with the no form of the ip pim command.
(Default: 5 seconds)
Enabling or disabling lan prune delay
Syntax:
ip pim-sparse lan-prune-delay
no ip pim-sparse lan-prune-delay
vlan [vid] ip pim-sparse lan-prune-delay
no vlan [vid] ip pim-sparse lan-prune-delay
Enables the LAN prune delay option on the current VLAN. With lan-prune-delay enabled, the router informs
downstream neighbors how long it will wait before pruning a flow after receiving a prune request.
Other downstream routers on the same VLAN must send a join to override the prune before the lan-prune-
delay time if they want the flow to continue. This prompts any downstream neighbors with multicast receivers
continuing to belong to the flow to reply with a join. If no joins are received after the lan-prune-delay period,
the router prunes the flow.
The propagation-delay and override-interval settings (below) determine the lan-prune-delay
setting.
Uses the no form of the command to disable the LAN prune delayoption.
(Default: Enabled)
Changing the Lan-prune-delay interval
Syntax:
ip pim-sparse propagation-delay [250-2000]
vlan [vid] ip pim-sparse propagation-delay [250-2000]
ip pim-sparse override-interval [500-6000]
vlan [vid] ip pim-sparse override-interval [500-6000]
A router sharing a VLAN with other multicast routers uses these two values to compute the lan-prune-delay
setting (above) for how long to wait for a PIM-SM join after receiving a prune packet from downstream for a
particular multicast group.
Multiple routers sharing VLAN
A network may have multiple routers sharing VLAN "X." When an upstream router is forwarding traffic from
multicast group "X" to VLAN "Y," if one of the routers on VLAN "Y" does not want this traffic, it issues a prune
response to the upstream neighbor. The upstream neighbor then goes into a prune pending state for group "X"
on VLAN "Y." (During this period, the upstream neighbor continues to forward the traffic.) During the pending
period, another router on VLAN "Y" can send a group "X" join to the upstream neighbor. If this happens, the
upstream neighbor drops the prune pending state and continues forwarding the traffic. But if no routers on the
VLAN send a join, the upstream router prunes group "X" from VLAN "Y" when the lan-prune-delay timer
expires.
Chapter 4 PIM-SM (Sparse Mode) 91
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