Changing The Pim Join And Prune Message Interval - Foundry Networks Switch and Router Installation And Configuration Manual

Changing the Shortest Path Tree (SPT) Threshold
In a typical PIM Sparse domain, there may be two or more paths from a DR (designated router) for a multicast
source to a PIM group receiver.
• Path through the RP – This is the path the Layer 3 Switch uses the first time it receives traffic for a PIM group.
However, the path through the RP may not be the shortest path from the Layer 3 Switch to the receiver.
• Shortest Path – Each PIM Sparse router that is a DR for a multicast source calculates a shortest path tree
(SPT) to all the PIM Sparse group receivers within the domain, with the Layer 3 Switch itself as the root of the
tree. The first time a Foundry Layer 3 Switch configured as a PIM router receives a packet for a PIM receiver,
the Layer 3 Switch sends the packet to the RP for the group. The Layer 3 Switch also calculates the SPT
from itself to the receiver. The next time the Layer 3 Switch receives a PIM Sparse packet for the receiver,
the Layer 3 Switch sends the packet toward the receiver using the shortest route, which may not pass
through the RP.
By default, the device switches from the RP to the SPT after receiving the first packet for a given PIM Sparse
group. The Layer 3 Switch maintains a separate counter for each PIM Sparse source-group pair.
After the Layer 3 Switch receives a packet for a given source-group pair, the Layer 3 Switch starts a PIM data
timer for that source-group pair. If the Layer 3 Switch does not receive another packet for the source-group pair
before the timer expires, it reverts to using the RP for the next packet received for the source-group pair. In
accordance with the PIM Sparse RFC's recommendation, the timer is 210 seconds and is not configurable. The
counter is reset to zero each time the Layer 3 Switch receives a packet for the source-group pair.
You can change the number of packets that the Layer 3 Switch sends using the RP before switching to using the
SPT. To do so, use the following CLI method.
USING THE CLI
To change the number of packets the Layer 3 Switch sends using the RP before switching to the SPT, enter
commands such as the following:
BigIron(config)# router pim
BigIron(config-pim-router)# spt-threshold 1000
Syntax: [no] spt-threshold infinity | <num>
The infinity | <num> parameter specifies the number of packets. If you specify infinity, the Layer 3 Switch sends
packets using the RP indefinitely and does not switch over to the SPT. If you enter a specific number of packets,
the Layer 3 Switch does not switch over to using the SPT until it has sent the number of packets you specify using
the RP.
USING THE WEB MANAGEMENT INTERFACE
You cannot configure PIM Sparse parameters using the Web management interface.

Changing the PIM Join and Prune Message Interval

By default, the Layer 3 Switch sends PIM Sparse Join/Prune messages every 60 seconds. These messages
inform other PIM Sparse routers about clients who want to become receivers (Join) or stop being receivers
(Prune) for PIM Sparse groups.
You can change the Join/Prune message interval using the following CLI method.
NOTE: Use the same Join/Prune message interval on all the PIM Sparse routers in the PIM Sparse domain. If
the routers do not all use the same timer interval, the performance of PIM Sparse can be adversely affected.
USING THE CLI
To change the Join/Prune interval, enter commands such as the following:
BigIron(config)# router pim
BigIron(config-pim-router)# message-interval 30
Syntax: [no] message-interval <num>
December 2000
Configuring IP Multicast Protocols
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