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NOTE:
When the hello message filter is configured, if hello messages of an existing PIM neighbor fail to
pass the filter, the PIM neighbor will be removed automatically when it times out.
Configuring PIM hello options
In either a PIM-DM domain or a PIM-SM domain, the hello messages sent among routers contain the
following configurable options:
•
DR_Priority
(for PIM-SM only)—Priority for DR election. The device with the highest priority
wins the DR election. You can configure this parameter on all routers in a multi-access network
directly connected to multicast sources or receivers.
•
Holdtime
—The timeout timer of PIM neighbor reachability state. When this timer times out, if
the router has received no hello message from a neighbor, it assumes that this neighbor has
expired or become unreachable.
•
LAN_Prune_Delay
—The delay of prune messages on a multi-access network. This option
consists of LAN-delay (prune message delay), override-interval, and neighbor tracking flag. If
the LAN-delay or override-interval values of different PIM routers on a multi-access subnet are
different, the largest value takes effect. If you want to enable neighbor tracking, be sure to
enable the neighbor tracking feature on all PIM routers on a multi-access subnet.
The LAN-delay setting causes the upstream routers to delay processing received prune messages.
The override-interval sets the length of time that a downstream router can wait before sending a
prune override message. When a router receives a prune message from a downstream router, it
does not perform the prune action immediately. Instead, it maintains the current forwarding state for
a period of LAN-delay plus override-interval. If the downstream router needs to continue receiving
multicast data, it must send a join message within the prune override interval. Otherwise, the
upstream router performs the prune action when the period of LAN-delay plus override-interval times
out.
A hello message sent from a PIM router contains a generation ID option. The generation ID is a
random value for the interface on which the hello message is sent. Normally, the generation ID of a
PIM router does not change unless the status of the router changes (for example, when PIM is just
enabled on the interface or the device is restarted). When the router starts or restarts sending hello
messages, it generates a new generation ID. If a PIM router finds that the generation ID in a hello
message from the upstream router has changed, it assumes that the status of the upstream neighbor
is lost or the upstream neighbor has changed. In this case, it triggers a join message for state update.
If you disable join suppression (enable neighbor tracking), be sure to disable the join suppression
feature on all PIM routers on a multi-access subnet. Otherwise, the upstream router fails to explicitly
track join messages from downstream routers.
Configuring hello options globally
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter public network PIM
view or VPN instance PIM
view.
pim
[
vpn-instance
vpn-instance-name
]
N/A
3.
Configure the priority for DR
election.
hello-option dr-priority
priority
Optional.
1 by default.
4.
Configure PIM neighbor
timeout timer.
hello-option holdtime
interval
Optional.
105 seconds by default.
5.
Configure the prune
message delay time
hello-option lan-delay
interval
Optional.
