Cisco Systems 78-11741-02 manual How the Idling Policy Works, Keeping VCs from Idling, Idled

Configuring IP Multicast Routing

Configuring IP Multicast over ATM Point-to-Multipoint Virtual Circuits

Idling Policy

An idling policy uses the ip pim vc-countnumber interface configuration command to limit the number of VCs created by PIM. When the router stays at or below this number value, no idling policy is in effect. When the next VC to be opened will exceed the number value, an idling policy is exercised. An idled VC does not mean that the multicast traffic is not forwarded; the traffic is switched to VC 0. The VC 0 is the broadcast VC that is open to all neighbors listed in the map list. The name “VC 0” is unique to PIM and the mrouting table.

How the Idling Policy Works

The idling policy works as follows:

•The only VCs eligible for idling are those with a current 1-second activity rate less than or equal to the value configured by the ip pim minimum-vc-rateinterface configuration command on the ATM interface. Activity level is measured in packets per second (pps).

•The VC with the least amount of activity below the configured ip pim minimum-vc-ratepps rate is idled.

•If the ip pim minimum-vc-ratecommand is not configured, all VCs are eligible for idling.

•If other VCs are at the same activity level, the VC with the highest fanout (number of leaf routers on the multipoint VC) is idled.

•The activity level is rounded to three orders of magnitude (less than 10 pps, 10 to 100 pps, and 100 to 1000 pps). Therefore, a VC that has 40 pps activity and another that has 60 pps activity are considered to have the same rate, and the fanout count determines which one is idled. If the first VC has a fanout of 5 and the second has a fanout of 3, the first one is idled.

•Idling a VC means releasing the multipoint VC that is dedicated for the multicast group. The traffic of the group continues to be sent; it is moved to the static map VC. Packets will flow over a shared multipoint VC that delivers packets to all PIM neighbors.

•If all VCs have a 1-minute rate greater than the pps value, the new group (that exceeded the ip pim vc-countnumber) will use the shared multipoint VC.

Keeping VCs from Idling

You can configure the minimum rate required to keep VCs from being idled. By default, all VCs are eligible for idling. To configure a minimum rate, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip pim minimum-vc-rate pps	Sets the minimum activity rate required to keep VCs from being
	idled.

Cisco IOS IP Configuration Guide

IPC-437