Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual page 159

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Table 21: Behavior of Routing Protocols During a Unified In-Service
Software Upgrade (continued)
Protocol Behavior
LDP Unified ISSU warns you if the hello timers or the keepalive timers are not
long enough to survive the forwarding plane upgrade.
LDP sends out hello messages and keepalive messages immediately before
and immediately after both the SRP module switchover and the forwarding
plane restart, independent of the interval since it last sent them.
OSPF OSPF timers are not negotiable between peers. Unified ISSU generates a
warning if the hello timers or the keepalive timers are not long enough to
survive the forwarding plane upgrade.
OSPF begins a graceful restart before the SRP module switchover. When
you configure graceful restart before the unified in-service software upgrade,
you must ensure that the graceful restart times are long enough to allow
recovery.
OSPF sends out hello messages and keepalive messages immediately
before and immediately after forwarding plane restart, independent of the
interval since it last sent them.
PIM If necessary, temporarily lengthens the hold times in hello messages. PIM
guarantees that at least one hello message with a lengthened hold time is
sent to each neighbor.
If necessary, increases the join-prune hold time. PIM guarantees that at
least one join-prune message with a lengthened hold time is sent to each
neighbor.
RIP RIP timers do not affect unified ISSU.
RSVP-TE If necessary, temporarily lengthens the graceful restart timers to survive
the SRP module switchover.
If necessary, lengthens the hello timers to survive the forwarding plane
upgrade.
You might want some or all traffic to be routed around the upgrading router rather than
accept a forwarding loss during the forwarding interruption. To do so, you must configure
your routing protocols appropriately. For example, you might raise the link cost in IS-IS
and OSPF, causing their neighbors to seek alternate routes that have lower link costs. In
PIM, you can set the priority for the router interface to zero to ensure that the upgrading
router is not selected as a designated router.
Application Support for Unified ISSU on page 115
Chapter 5: Configuring a Unified In-Service Software Upgrade
137