Juniper IGP - CONFIGURATION GUIDE V11.1.X, Руководство по настройке

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minimizes these effects by providing a mechanism by which a restarting router can
do the following:
■
Notify neighboring IS-IS routers that it is restarting and request help
resynchronizing its LSP database. Neighbors with active adjacencies to the
restarting router can thereby reestablish these adjacencies without having to
reset them.
■
Determine when complete LSP database synchronization with its neighbors has
occurred.
■
Optimize the process of LSP database synchronization while minimizing
temporary routing disruption.
IS-IS graceful restart on E Series routers supports both restart and helper capabilities.
These capabilities mean that an E Series router can not only notify neighboring IS-IS
routers that it is restarting and request help resynchronizing its LSP database, but
can also cooperate with other restarting routers to help them with the restart process.
How Graceful Restart Works
Graceful restart is disabled on the router by default. When you enable graceful restart
by issuing the
nsf ietf command, the router sends restart requests to neighboring
routers to notify them that it is restarting. The restarting router includes the restart
TLV (type 211) in its hello PDUs to signal the other routers that it supports graceful
restart and to request help resynchronizing its LSP database. Including the restart
TLV in hello packets also ensures that neighboring routers will maintain their active
adjacencies to the restarting router and keep the restarting router in the network
topology.
Graceful restart uses a set of configurable timers to support the restart mechanism.
Table 15 on page 338 briefly describes these timers and lists the associated commands
that you can use to configure the timer values on the router.
Table 15: IS-IS Graceful Restart Timers
Associated Command Description Timer
“nsf interface wait” on
page 381
Sets the maximum time (in seconds) that the router
waits for all interfaces with IS-IS adjacencies to come
up before completing the restart process Interface
wait
“nsf t1” on page 381 Sets the time interval (in seconds) between restart
requests sent by the router, and the number of times
that the router resends unacknowledged restart
requests T1
“nsf t2” on page 382 Sets the maximum time (in seconds) that the router
waits for the LSP database to synchronize T2
“nsf t3” on page 382 Sets the maximum time (in seconds) that the restarting
router waits before setting the overload bit to indicate
that graceful restart has failed T3
338 ■
Overview
JUNOSe 11.0.x IP, IPv6, and IGP Configuration Guide