H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – Multicast
H3C S7500E Series Ethernet Switches Chapter 5 PIM Configuration
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 Note:
z Generally, a smaller distance from the filter to the multicast source results in a more
remarkable filtering effect.
z This filter works not only on independent multicast data but also on multicast data
encapsulated in register messages.
5.5.4 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:
z 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.
z 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. You can configure this
parameter on all routers in the PIM domain. If you configure different values for
this timer on different neighboring routers, the largest value will take effect.
z LAN_Prune_Delay: the delay of prune messages on a multi-access network. This
option consists of LAN-delay (namely, prune delay), override-interval, and
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