Quick Reference Guide

484 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
PIM Sparse
19
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 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 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.
PowerConnect(config)#router pim
PowerConnect(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.
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.
To change the Join/Prune interval, enter commands such as the following.
PowerConnect(config)#router pim
PowerConnect(config-pim-router)#message-interval 30