KB.15.15

long to wait for the next hello packet from the router. If another packet does not

arrive within that time, the router removes the neighbor adjacency on that VLAN

from the routing table, which removes any flows running on that interface.

Shortening the hello interval reduces the hello hold time. This changes how quickly

other routers will stop sending traffic to the router if they do not receive a new hello

packet when expected. For example, if multiple routers are connected to the same

VLAN and the router requests multicast traffic, all routers on the VLAN receive that

traffic. (Those that have pruned the traffic will drop it when they receive it.) If the

upstream router loses contact with the router receiving the multicast traffic (that is,

fails to receive a hello packet when expected), the shorter hello interval causes it

to stop transmitting multicast traffic onto the VLAN sooner, resulting in less

unnecessary bandwidth use.

(Default: 30 seconds)

Changing the randomized delay setting for PIM-SM neighbor notification

Syntax:

ip pim-sparse hello-delay [0-5]

vlan [vid] ip pim-sparse hello-delay [0-5]

Changes the maximum time in seconds before the router actually transmits the initial

PIM hello message on the current VLAN. In cases where a new VLAN activates with

connections to multiple routers, if all of the connected routers sent hello packets at

the same time, the receiving router could become momentarily overloaded. This

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:

[no] 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)

VLAN context commands for configuring PIM-SM 69