606 BigIron RX Series Configuration Guide53-1001986-01Changing the Shortest Path Tree (SPT) threshold23BigIron RX(config-pim-router)#show ip pim sparseGlobal PIM Sparse Mode SettingsHello interval : 30 Neighbor timeout : 105Bootstrap Msg interval: 60 Candidate-RP Advertisement interval: 60Join/Prune interval : 60 SPT Threshold : 1Inactivity interval : 180 SSM Enabled : NoHardware Drop Enabled : YesRoute Selection : mc-non-default uc-non-default mc-default uc-default---------+----------------+----+---+----------------------+------+-------------+Interface|Local |Mode|Ver| Designated Router |TTL |Multicast ||Address | | |Address Port |Thresh|Boundary |---------+----------------+----+---+----------------------+------+-------------+v12 100.4.8.2 SM V2 Itself 1 Nonev13 100.16.8.2 SM V2 Itself 1 Nonev124 124.0.0.1 SM V2 Itself 1 Nonev125 125.0.0.1 SM V2 Itself 1 Nonev126 126.0.0.1 SM V2 Itself 1 Nonev127 127.0.0.1 SM V2 Itself 1 Nonel1 1.0.8.1 SM V2 Itself 1 NoneChanging the Shortest Path Tree (SPT) thresholdIn a typical PIM Sparse domain, there may be two or more paths from a DR (designated router) fora multicast source to a PIM group receiver.• Path through the RP – This is the path the BigIron RX uses the first time it receives traffic for aPIM group. However, the path through the RP may not be the shortest path from the BigIron RXto the receiver.• Shortest Path – Each PIM Sparse router that is a DR for a multicast source calculates ashortest path tree (SPT) to all the PIM Sparse group receivers within the domain, with theBigIron RX itself as the root of the tree. The first time a BigIron RX is configured as a PIM routerand receives a packet for a PIM receiver, the BigIron RX sends the packet to the RP for thegroup. The BigIron RX also calculates the SPT from itself to the receiver. The next time theBigIron RX receives a PIM Sparse packet for the receiver, the BigIron RX sends the packettoward 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 givenPIM Sparse group. The BigIron RX maintains a separate counter for each PIM Sparse source-grouppair.After the BigIron RX receives a packet for a given source-group pair, the BigIron RX starts a PIMdata timer for that source-group pair. If the BigIron RX does not receive another packet for thesource-group pair before the timer expires, it reverts to using the RP for the next packet received forthe source-group pair. In accordance with the PIM Sparse RFC’s recommendation, the timer is 210seconds and is not configurable. The counter is reset to zero each time the BigIron RX receives apacket for the source-group pair.You can change the number of packets that the BigIron RX sends using the RP before switching tousing the SPT.To change the number of packets the BigIron RX sends using the RP before switching to the SPT,enter commands such as the following.BigIron RX(config)# router pimBigIron RX(config-pim-router)# spt-threshold 1000Syntax: [no] spt-threshold infinity |
