Changing The Shortest Path Tree (Spt) Threshold - Dell PowerConnect B-RX Configuration Manual

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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.
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By default, the device switches from the RP to the SPT after receiving the first packet for a given
PIM Sparse group. The device maintains a separate counter for each PIM Sparse source-group pair.
After the device receives a packet for a given source-group pair, the device starts a PIM data timer
for that source-group pair. If the device 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 device receives a packet for the
source-group pair.
You can change the number of packets that the device sends using the RP before switching to
using the SPT.
To change the number of packets the device sends using the RP before switching to the SPT, enter
commands such as the following.
BigIron RX(config)# router pim
BigIron RX(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 device
sends packets using the RP indefinitely and does not switch over to the SPT. If you enter a specific
number of packets, the device 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 device 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.
BigIron RX Series Configuration Guide
53-1001810-01
v12 100.4.8.2
v13 100.16.8.2
v124 124.0.0.1
v125 125.0.0.1
v126 126.0.0.1
v127 127.0.0.1
l1 1.0.8.1
Path through the RP – This is the path the device 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 device 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
device itself as the root of the tree. The first time a device is configured as a PIM router
receives a packet for a PIM receiver, the device sends the packet to the RP for the group. The
device also calculates the SPT from itself to the receiver. The next time the device receives a
PIM Sparse packet for the receiver, the device sends the packet toward the receiver using the
shortest route, which may not pass through the RP.
SM V2 Itself
SM V2 Itself
SM V2 Itself
SM V2 Itself
SM V2 Itself
SM V2 Itself
SM V2 Itself
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Anycast RP
1 None
1 None
1 None
1 None
1 None
1 None
1 None
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