Pim Sparse Mode - Juniper EX9200 Features Manual

High Availability Feature Guide for EX9200 Switches

PIM Sparse Mode

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processes OSPF LSAs as usual. When the helper routers no longer receive grace LSAs
from the restarting router or the topology of the network changes, the helper routers also
resume normal operation.
NOTE: For more information about the standard helper mode implementation,
see RFC 3623, Graceful OSPF Restart.
Starting with Release 11.3, Junos OS supports the restart signaling-based helper mode
for OSPF graceful restart configurations. The helper modes, both standard and restart
signaling-based, are enabled by default. In restart signaling-based helper mode
implementations, the restarting router relays the restart status to its neighbors only after
the restart is complete. When the restart is complete, the restarting router sends hello
messages to its helper routers with the
header. When a helper router receives a hello packet with the
the helper router returns a hello message to the restarting router. The reply hello message
from the helper router contains the
enable the restarting router to keep track of the helper routers that are syncing up with
it. When all helpers complete the synchronization, the restarting router exits the restart
mode.
NOTE:
For more information about restart signaling-based graceful restart helper
mode implementation, see RFC 4811, OSPF Out-of-Band Link State Database
(LSDB) Resynchronization, RFC 4812, OSPF Restart Signaling, and RFC 4813,
OSPF Link-Local Signaling.
Restart signaling-based graceful restart helper mode is not supported for
OSPFv3 configurations.
PIM sparse mode uses a mechanism called a generation identifier to indicate the need
for graceful restart. Generation identifiers are included by default in PIM hello messages.
An initial generation identifier is created by each PIM neighbor to establish device
capabilities. When one of the PIM neighbors restarts, it sends a new generation identifier
to its neighbors. All neighbors that support graceful restart and are connected by
point-to-point links assist by sending multicast updates to the restarting neighbor.
The restart phase completes when either the PIM state becomes stable or when the
restart interval timer expires. If the neighbors do not support graceful restart or connect
to each other using multipoint interfaces, the restarting router uses the restart interval
timer to define the restart period.
( ) bit set in the hello packet
restart signal RS
ResyncState flag and the ResyncTimeout
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bit set in the header,
RS
timer that