Chapter 20
| Multicast Routing
Configuring PIM for IPv4
– 761 –
Parameters
These parameters are displayed:
Common Attributes
◆ VLAN – Layer 3 VLAN interface. (Range: 1-4094)
◆ Mode – PIM routing mode. (Options: Dense, Sparse, None)
◆ IP Address – Primary IP address assigned to the selected VLAN.
◆ Hello Holdtime – Sets the interval to wait for hello messages from a
neighboring PIM router before declaring it dead. Note that the hello holdtime
should be greater than or equal to the value of Hello Interval, otherwise it will
be automatically set to 3.5 x the Hello Interval. (Range: 1-65535 seconds;
Default: 105 seconds, or 3.5 times the hello interval if set)
◆ Hello Interval – Sets the frequency at which PIM hello messages are
transmitted out on all interfaces. (Range: 1-65535 seconds; Default: 30 seconds)
Hello messages are sent to neighboring PIM routers from which this device has
received probes, and are used to verify whether or not these neighbors are still
active members of the multicast tree. PIM-SM routers use these messages not
only to inform neighboring routers of their presence, but also to determine
which router for each LAN segment will serve as the Designated Router (DR).
When a router is booted or first configured to use PIM, it sends an initial hello
message, and then sets its Hello timer to the configured value. If a router does
not hear from a neighbor for the period specified by the Hello Holdtime, that
neighbor is dropped. This hold time is included in each hello message received
from a neighbor. Also note that hello messages also contain the DR priority of
the router sending the message.
If the hello holdtime is already configured, and the hello interval is set to a
value longer than the hello holdtime, this command will fail.
◆ Join/Prune Holdtime – Sets the hold time for the prune state. (Range: 1-65535
seconds; Default: 210 seconds)
â–
PIM-DM: The multicast interface that first receives a multicast stream from a
particular source forwards this traffic to all other PIM-DM interfaces on the
router. If there are no requesting groups on that interface, the leaf node
sends a prune message upstream and enters a prune state for this multicast
stream. The prune state is maintained until the join/prune holdtime timer
expires or a graft message is received for the forwarding entry.
â–
PIM-SM: The multicast interface that first receives a multicast stream from a
particular source forwards this traffic only to those interfaces on the router
that have requests to join this group. When there are no longer any
requesting groups on that interface, the leaf node sends a prune message
upstream and enters a prune state for this multicast stream. The protocol
maintains both the current join state and the pending RPT prune state for
this (source, group) pair until the join/prune interval timer expires.
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