Technical Documentation

Enabling Join Suppression

PIM join suppression enables a router on a multiaccess network to defer sending join messages to an upstream router when it sees identical join messages on the same network. Eventually, only one router will send these join messages and the other routers will suppress identical messages. Limiting the number of join messages improves scalability and efficiency by reducing the number of messages sent to the same router.

Use the reset-tracking-bit statement to enable PIM join suppression on each multiaccess downstream interface. This statement resets a tracking bit field (T-bit) on the LAN prune delay hello option from the default of 1 (join suppression disabled) to 0 (join suppression enabled).

When multiple identical join messages are received, a random join suppression timer is activated, with a range of 66 through 84 milliseconds. The timer is reset each time join suppression is triggered.

Use the override-interval statement to set the maximum time in milliseconds to delay sending override join messages. When a router sees a prune message for a join it is currently suppressing, it waits before it sends an override join message. Waiting helps avoid multiple downstream routers sending override join messages at the same time. This is a random timer with a value of 0 through the maximum override value.

Use the propagation-delay statement to set a value in milliseconds for a prune pending timer, which specifies how long to wait before executing a prune on an upstream router. During this period, the router waits for any prune override join messages that may be currently suppressed. The period for the prune pending timer is the sum of the override-interval value and the value specified for propagation-delay.

Use the show protocols pim command to see if the reset-tracking-bit statement is configured, indicating that join suppression is enabled, and to view the values set for the override-interval and propagation-delay statements.

These statements can be included for PIM protocols at the global level or the interface level, and for logical systems and routing instances.

A sample configuration at the [edit protocols pim] hierarchy level follows:


user@host# show configuration protocols pim
reset-tracking-bit;
propagation-delay 600;
override-interval 2500;
rp {
	static {
		address 77.7.7.7;
        }
    }
interface fe-0/2/2.0 {
	reset-tracking-bit;
	propagation-delay 600;
	override-interval 2500;
}

Published: 2010-04-16