Black Box LGB6026A, Management Manual

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HAPTER
22 | Multicast Routing
Configuring PIM for IPv4
The override interval and the propogation delay are used to calculate
the LAN prune delay. If a downstream router has group members which
want to continue receiving the flow referenced in a LAN prune delay
message, then the override interval represents the time required for
the downstream router to process the message and then respond by
sending a Join message back to the upstream router to ensure that the
flow is not terminated.
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Propagation Delay – The time required for a LAN prune delay
message to reach downstream routers. (Range: 100-5000
milliseconds; Default: 500 milliseconds)
The override interval and propogation delay are used to calculate the
LAN prune delay. If a downstream router has group members which
want to continue receiving the flow referenced in a LAN prune delay
message, then the propagation delay represents the time required for
the LAN prune delay message to be propgated down from the upstream
router to all downstream routers attached to the same VLAN interface.
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Trigger Hello Delay – The maximum time before transmitting a
triggered PIM Hello message after the router is rebooted or PIM is
enabled on an interface. (Range: 0-5 seconds; Default: 5 seconds)
When a router first starts or PIM is enabled on an interface, the hello
delay is set to random value between 0 and the trigger hello delay. This
prevents synchronization of Hello messages on multi-access links if
multiple routers are powered on simultaneously.
Also, if a Hello message is received from a new neighbor, the receiving
router will send its own Hello message after a random delay between 0
and the trigger hello delay.
Dense-Mode Attributes
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Graft Retry Interval – The time to wait for a Graft acknowledgement
before resending a Graft message. (Range: 1-10 seconds; Default: 3
seconds)
A graft message is sent by a router to cancel a prune state. When a
router receives a graft message, it must respond with an graft
acknowledgement message. If this acknowledgement message is lost,
the router that sent the graft message will resend it a number of times
(as defined by Max. Graft Retries).
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Max. Graft Retries – The maximum number of times to resend a Graft
message if it has not been acknowledged. (Range: 1-10; Default: 3)
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State Refresh Origination Interval – The interval between sending
PIM-DM state refresh control messages. (Range: 1-100 seconds;
Default: 60 seconds)
The pruned state times out approximately every three minutes and the
entire PIM-DM network is reflooded with multicast packets and prune
messages. The state refresh feature keeps the pruned state from
timing out by periodically forwarding a control message down the
distribution tree, refreshing the prune state on the outgoing interfaces
of each router in the tree. This also enables PIM routers to recognize