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On the shared-media LAN, the propagation delay and override interval are used as follows:
If a router receives a prune message on its upstream interface, it means that there are
downstream routers on the shared-media LAN. If this router still needs to receive multicast
data, it must send a join message to override the prune message within the override
interval.
When a router receives a prune message from its downstream interface, it does not
immediately prune this interface. Instead, it starts a timer (the propagation delay plus the
override interval). If interface receives a join message before the timer expires, the router
does not prune the interface. Otherwise, the router prunes the interface.
If you enable neighbor tracking on an upstream router, this router can track the states of the
downstream nodes for which the joined state holdtime timer has not expired. If you want to
enable neighbor tracking, you must enable it on all PIM routers on a shared-media LAN.
Otherwise, the upstream router cannot track join messages from every downstream routers.
•
Generation ID
—A router generates a generation ID for hello messages when an interface is
enabled with PIM. The generation ID is a random value, but only changes when the status of
the router changes. 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 router has changed.
In this case, it sends a join message to the upstream router for status update. You can configure
an interface to drop hello messages without the generation ID options to promptly know the
status of an upstream router.
You can configure hello message options for all interfaces in PIM view or for the current interface in
interface view. The configuration made in interface view takes priority over the configuration made in
PIM view.
Configuring hello message options globally
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter PIM view.
pim
[
vpn-instance
vpn-instance-name
]
N/A
3.
Set the DR priority.
hello-option dr-priority priority
The default setting is 1.
4.
Set the neighbor lifetime.
hello-option holdtime time
The default setting is 105
seconds.
5.
Set the PIM message
propagation delay for a
shared-media LAN.
hello-option lan-delay delay
The default setting is 500
milliseconds.
6.
Set the override interval.
hello-option
override-interval interval
The default setting is 2500
milliseconds.
7.
Enable neighbor tracking.
hello-option neighbor-tracking
By default, neighbor tracking is
disabled.
Configuring hello message options on an interface
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter interface view.
interface interface-type
interface-number
N/A
3.
Set the DR priority.
pim hello-option
dr-priority priority
The default setting is 1.
4.
Set the neighbor lifetime.
pim hello-option holdtime time
The default setting is 105
seconds.
