Configuring Pim Hello Options - 3Com S7906E Configuration Manual

With the hello message filter 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

No matter in a PIM-DM domain or a PIM-SM domain, the hello messages sent among routers contain
many configurable options, including:
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 the routers in a multi-access network directly
connected to multicast sources or receivers.
Holdtime: the timeout time 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 (namely, 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 will take effect. If you want to enable neighbor tracking, the neighbor
tracking feature should be enabled on all PIM routers on a multi-access subnet.
The LAN-delay setting will cause the upstream routers to delay processing received prune messages.
The override-interval sets the length of time a downstream router is allowed to 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 prune override message within the prune override interval; otherwise, the upstream route
will perform the prune action when the period of LAN-delay plus override-interval time 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 (namely, enable neighbor tracking), the join suppression feature should
be disabled on all PIM routers on a multi-access subnet; otherwise, the upstream router will fail to
explicitly track which downstream routers are joined to it.
Configuring hello options globally
Follow these steps to configure hello options globally:
To do...
Enter system view
Use the command...
system-view
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Remarks
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