Juniper EX9200 Features Manual page 24

High Availability Feature Guide for EX9200 Switches
4
NOTE: Due to its synchronization requirements and logic, NSR/GRES
performance is limited by the slowest Routing Engine in the system.
Mastership switches to the backup Routing Engine if:
The master Routing Engine kernel stops operating.
The master Routing Engine experiences a hardware failure.
The administrator initiates a manual switchover.
NOTE: To quickly restore or to preserve routing protocol state information
during a switchover, GRES must be combined with either graceful restart or
nonstop active routing, respectively. For more information about graceful
restart, see "Graceful Restart Concepts" on page
about nonstop active routing, see
page 35.
If the backup Routing Engine does not receive a keepalive from the master Routing Engine
after 2 seconds (4 seconds on M20 routers), it determines that the master Routing Engine
has failed and: takes mastership.
The Packet Forwarding Engine:
Seamlessly disconnects from the old master Routing Engine
Reconnects to the new master Routing Engine
Does not reboot
Does not interrupt traffic
The new master Routing Engine and the Packet Forwarding Engine then become
synchronized. If the new master Routing Engine detects that the Packet Forwarding
Engine state is not up to date, it resends state update messages.
NOTE: Starting with Junos OS Release 12.2, if adjacencies between the
restarting router and the neighboring peer 'helper' routers time out, graceful
restart protocol extensions are unable to notify the peer 'helper' routers about
the impending restart.Graceful restart can then stop and cause interruptions
in traffic.
To ensure that these adjacencies are kept, change the hold-time for IS-IS
protocols from the default of 27 seconds to a value higher than 40 seconds.
65. For more information
"Nonstop Active Routing Concepts" on
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