Digisol DG-GS4826S, Management Manual

Page: 604 / 1344

C
HAPTER
22 | Multicast Routing
Configuring PIM for IPv4
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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.
u
Join/Prune Holdtime – Sets the hold time for the prune state.
(Range: 1-65535 seconds; Default: 210 seconds)
n
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.
n
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.
u
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.
u
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 continue receiving the flow referenced in the
message. (Range: 500-6000 milliseconds; Default: 2500 milliseconds)