H3C Technologies H3C S12500-X Series Switches - Manual (Page 93)

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Configuring PIM hello message options
In either a PIM-DM domain or a PIM-SM domain, hello messages exchanged 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 option for all the routers in a shared-media LAN that directly
connects to the multicast source or the receivers.
• Holdtime—PIM neighbor lifetime. If a router does not receive a hello message from a neighbor
when the neighbor lifetime timer expires, it regards the neighbor failed or unreachable.
• LAN_Prune_Delay—Delay of forwarding prune messages on a shared-media LAN. This option
consists of LAN delay (namely, prune message delay), override interval, and neighbor tracking
support (namely, the capability to disable join message suppression).
The prune message delay defines the delay time for a router to forward a received prune message
to the upstream routers. The override interval defines a period for a downstream router to override
a prune message. If the prune message delay or override interval on different PIM routers on a
shared-media LAN are different, the largest value takes effect.
A router does not immediately prune an interface after it receives a prune message from the
interface. Instead, it starts a timer (the prune message 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 (or disable the join message suppression function)
on an upstream router to track the states of the downstream nodes that have sent the join message
and 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
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 prune message delay. hello-option lan-delay delay
The default setting is 500
milliseconds.