3Com 4800G Series, Configuration Manual

Page: 655 / 1246

Configuring PIM Common Information 655
neighbor tracking flag bit. You can configure this parameter on all routers in
the PIM domain. If different LAN-delay or override-interval values result from
the negotiation among all the PIM routers, the largest value will take effect.
The LAN-delay setting will cause the upstream routers to delay processing received
prune messages. If the LAN-delay setting is too small, it may cause the upstream
router to stop forwarding multicast packets before a downstream router sends a
prune override message. Therefore, be cautious when configuring this parameter.
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 time
defined by LAN-delay. 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
LAN-delay timer 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 (namely, enable neighbor tracking), the upstream
router will explicitly track which downstream routers are joined to it. The join
suppression feature should be enabled or disabled on all PIM routers on the same
subnet.
Configuring hello options globally
Follow these steps to configure hello options globally:
To do… Use the command… Remarks
Enter system view system-view -
Enter PIM view pim -
Configure the priority for DR
election hello-option dr-priority
priority
Optional
1 by default
Configure PIM neighbor
timeout time hello-option holdtime
interval
Optional
105 seconds by default
Configure the prune delay
time (LAN-delay) hello-option lan-delay
interval
Optional
500 milliseconds by default
Configure the prune override
interval hello-option
override-interval
interval
Optional
2,500 milliseconds by default
Disable join suppression hello-option
neighbor-tracking Optional
Enabled by default