HP 6125XLG - Page 123

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The LAN delay defines the PIM message propagation delay. The override interval defines a period
for a router to override a prune message. If the propagation delay or override interval on different
PIM routers on a shared-media LAN are different, the largest ones apply.
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
the interface receives a join message before the timer expires, the router does not prune the
interface. Otherwise, the router prunes the interface.
You can enable the neighbor tracking function on an upstream router to track the states of the
downstream nodes for which the joined state holdtime timer has not expired. If you want to enable
the neighbor tracking function, 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 in PIM view or interface view. The configurations made in PIM
view are effective on all interfaces and the configurations made in interface view are effective on only the
current interface. If you configure hello message options in both PIM view and interface view, the
configuration in interface view always takes precedence.
Configuring hello message options globally
Ste
p
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.
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 the neighbor tracking
function.
hello-option neighbor-tracking
By default, the neighbor tracking
function is disabled.
Configuring hello message options on an interface
Ste
p
Command Remarks
1. Enter system view.
system-view
N/A