642 CHAPTER 47: PIM CONFIGURATION
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CAUTION:
■ All the interfaces of the same router must work in the same PIM mode.
■ PIM-DM cannot be used for multicast groups in the SSM group grange.
Enabling State Refresh An interface without the state refresh capability cannot forward state refresh
messages.
Follow these steps to enable the state refresh capability:
Configuring State
Refresh Parameters
To avoid the resource-consuming reflooding of unwanted traffic caused by
timeout of pruned interfaces, the router directly connected with the multicast
source periodically sends an (S, G) state refresh message, which is forwarded hop
by hop along the initial multicast flooding path of the PIM-DM domain, to refresh
the prune timer state of all the routers on the path.
A router may receive multiple state refresh messages within a short time, of which
some may be duplicated messages. To keep a router from receiving such
duplicated messages, you can configure the time the router must wait before
receiving the next state refresh message. If a new state refresh message is received
within the waiting time, the router will discard it; if this timer times out, the router
will accept a new state refresh message, refresh its own PIM state, and reset the
waiting timer.
The TTL value of a state refresh message decrements by 1 whenever it passes a
router before it is forwarded to the downstream node until the TTL value comes
down to 0. In a small network, a state refresh message may cycle in the network.
To effectively control the propagation scope of state refresh messages, you need
to configure an appropriate TTL value based on the network size.
Follow these steps to configure state refresh parameters:
To do… Use the command… Remarks
Enter system view system-view -
Enter interface view interface interface-type
interface-number
-
Enable state refresh pim state-refresh-capable Optional
Enabled by default
To do… Use the command… Remarks
Enter system view system-view -
Enter PIM view pim -
Configure the interval
between state refresh
messages
state-refresh-interval
interval
Optional
60 seconds by default
Configure the time to wait
before receiving a new state
refresh message
state-refresh-rate-limit
interval
Optional
30 seconds by default
Configure the TTL value of
state refresh messages
state-refresh-ttl ttl-value Optional
255 by default
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