Computing the lan-prune-delay setting


ip pim-dense [propagation-delay[250-2000]] 
 vlan[vid]ip pim-dense [propagation-delay[250-2000]] 
 ip pim-dense [override-interval[500-6000]] 
 vlan [vid]ip pim-dense [override-interval[500-6000]]

A routing switch sharing a VLAN with other multicast routers uses these two values to compute the lan-prune-delay setting for how long to wait for a PIM-DM Join after receiving a prune packet from downstream for a particular multicast group.

Defaults: propagation-delay=500 milliseconds; override-interval = 2500 milliseconds

Upstream router prune

A network may have multiple routing switches sharing VLAN "X". When an upstream routing switch initially floods traffic from multicast group "X" to VLAN "Y", if one of the routing switches on VLAN "Y" does not want this traffic, it issues a prune response to the upstream neighbor. The upstream neighbor then goes into a prune pending state for group "X" on VLAN "Y". (During this period, the upstream neighbor continues to forward the traffic.)

During the prune pending period, another routing switch on VLAN "Y" can send a group "X" Join to the upstream neighbor. If this happens, the upstream neighbor drops the prune pending state and continues forwarding the traffic. If no routers on the VLAN send a Join, the upstream router prunes group "X" from VLAN "Y" when the lan-prune-delay timer expires.