Chapter 20
| Multicast Routing
Configuring PIM for IPv4
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Dense-Mode Attributes
◆ Graft Retry Interval – The time to wait for a Graft acknowledgement before
resending a Graft message. (Range: 1-10 seconds; Default: 3 seconds)
A graft message is sent by a router to cancel a prune state. When a router
receives a graft message, it must respond with an graft acknowledgement
message. If this acknowledgement message is lost, the router that sent the
graft message will resend it a number of times (as defined by Max. Graft
Retries).
◆ Max. Graft Retries – The maximum number of times to resend a Graft message
if it has not been acknowledged. (Range: 1-10; Default: 3)
◆ State Refresh Origination Interval – The interval between sending PIM-DM
state refresh control messages. (Range: 1-100 seconds; Default: 60 seconds)
The pruned state times out approximately every three minutes and the entire
PIM-DM network is re-flooded with multicast packets and prune messages. The
state refresh feature keeps the pruned state from timing out by periodically
forwarding a control message down the distribution tree, refreshing the prune
state on the outgoing interfaces of each router in the tree. This also enables PIM
routers to recognize topology changes (sources joining or leaving a multicast
group) before the default three-minute state timeout expires.
This command is only effectively for interfaces of first hop, PIM-DM routers that
are directly connected to the sources of multicast groups.
Sparse-Mode Attributes
◆ DR Priority – Sets the priority advertised by a router when bidding to become
the Designated Router (DR). (Range: 0-4294967294; Default: 1)
More than one PIM-SM router may be connected to an Ethernet or other
shared-media LAN. If multicast hosts are directly connected to the LAN, then
only one of these routers is elected as the DR, and acts on behalf of these hosts,
sending periodic Join/Prune messages toward a group-specific RP for each
group. A single DR is elected per interface (LAN or otherwise) using a simple
election process.
The router with the highest priority configured on an interface is elected as the
DR. If more than one router attached to this interface uses the same priority,
then the router with the highest IP address is elected to serve as the DR.
If a router does not advertise a priority in its hello messages, it is assumed to
have the highest priority and is elected as the DR. If more than one router is not
advertising its priority, then the router with the highest IP address is elected to
serve as the DR.
◆ Join/Prune Interval – Sets the interval at which join/prune messages are sent.
(Range: 1-65535 seconds; Default: 60 seconds)
By default, the switch sends join/prune messages every 60 seconds to inform
other PIM-SM routers about clients who want to join or leave a multicast group.
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