Web Management Guide-R06

Chapter 20 | Multicast Routing
Configuring PIMv6 for IPv6
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◆ 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)
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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.
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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.
◆ LAN Prune Delay – Causes this device to inform downstream routers of how
long it will wait before pruning a flow after receiving a prune request.
(Default: Disabled)
When other downstream routers on the same VLAN are notified that this
upstream router has received a prune request, they must send a Join to
override the prune before the prune delay expires if they want to continue
receiving the flow. The message generated by this command effectively
prompts any downstream neighbors with hosts receiving the flow to reply with
a Join message. If no join messages are received after the prune delay expires,
this router will prune the flow.
The sum of the Override Interval and Propagation Delay are used to calculate
the LAN prune delay.
◆ Override Interval – The time required for a downstream router to respond to a
LAN Prune Delay message by sending back a Join message if it wants to