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Configuring IP Multicast Routing
Configuring IP Multicast over ATM Point-to-Multipoint Virtual Circuits
IPC-437
Cisco IOS IP Configuration Guide
Idling Policy
An idling policy uses the ip pim vc-count number 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-rate interface 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-rate pps rate
is idled.
• If the ip pim minimum-vc-rate command 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-count number) 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.