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Configuring IPv6 PIM hello options
In both an IPv6 PIM-DM domain and an IPv6 PIM-SM domain, the hello messages sent among
routers contain the following configurable options:
•
DR_Priority
(for IPv6 PIM-SM only)—Priority for DR election. The higher the priority is, the
easier it is for the router to win DR election. You can configure this parameter on all routers in a
multi-access network directly connected to IPv6 multicast sources or receivers.
•
Holdtime
—The timeout timer of IPv6 PIM neighbor reachability state. When this timer times out,
if the router has received no hello message from an IPv6 PIM 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 IPv6 PIM routers on a multi-access
subnet are different, the largest value takes effect. If you want to enable neighbor tracking, be
sure to enable the neighbor tracking feature on all IPv6 PIM routers on a multi-access subnet.
The LAN-delay setting causes the upstream routers to delay forwarding received prune messages.
The override-interval sets the length of time that a downstream router can 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
IPv6 multicast data, it must send a join message within the prune override interval. Otherwise, the
upstream route will perform the prune action when the period of LAN-delay plus override-interval
times out.
A hello message sent from an IPv6 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
an IPv6 PIM router does not change unless the status of the router changes (for example, when IPv6
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 an IPv6 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, be sure to disable the join
suppression feature on all IPv6 PIM routers on a multi-access subnet. Otherwise, the upstream
router will fail to explicitly track join messages from downstream routers.
Configuring hello options globally
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter public network IPv6
PIM view or VPN instance
IPv6 PIM view.
pim ipv6
[
vpn-instance
vpn-instance-name
]
N/A
3.
Configure the priority for DR
election.
hello-option dr-priority
priority
Optional.
1 by default.
4.
Configure IPv6 PIM neighbor
timeout timer.
hello-option holdtime
interval
Optional.
105 seconds by default.
5.
Configure the prune
message delay time
(LAN-delay).
hello-option lan-delay
interval
Optional.
500 milliseconds by default.
6.
Configure the prune override
interval.
hello-option override-interval
interval
Optional.
2500 milliseconds by default.
