Juniper PTX5000 Hardware Manual page 420

PTX5000 Packet Transport Router Hardware Guide
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NOTE: For information about configuring high availability features such as
graceful Routing Engine switchover (GRES) and nonstop active routing (NSR),
see the Junos OS High Availability Library for Routing Devices.
Both Routing Engines should be running the same Junos OS release.
If the backup Routing Engine's configuration differs from the former master's
configuration, packet transport router performance might change . For the
most predictable performance, configure the two Routing Engines identically,
except for parameters unique to each Routing Engine.
To configure Routing Engine-specific parameters and still use the same
configuration on both Routing Engines, include the appropriate configuration
statements under the
level and use the
Administration Library.
When a master host subsystem is taken offline or during a mastership switch, the backup
host subsystem becomes the master, and the backup Routing Engine assumes Routing
Engine functions. The master host subsystem is hot-pluggable. During the switchover to
the backup Routing Engine:
Dual Routing Engines without any high availability features enabled—Traffic is
interrupted while the Packet Forwarding Engine is reinitialized. Packet forwarding halts
while the standby Routing Engine becomes the master and the Packet Forwarding
Engine components reset and connect to the new master Routing Engine. All kernel
and forwarding processes are restarted. When the switchover to the new master
Routing Engine is complete, routing convergence takes place and traffic is resumed.
GRES is supported on Junos OS Release 12.1X48 and later.
GRES is enabled—Graceful Routing Engine switchover preserves interface and kernel
information. Traffic is not interrupted. The backup Routing Engine immediately assumes
Routing Engine functions and there is no interruption to packet forwarding. However,
graceful Routing Engine switchover does not preserve the control plane. Neighboring
packet transport routers or routers detect that the packet transport router has restarted
and react to the event in a manner prescribed by individual routing protocol
specifications. To preserve routing without interruption during a switchover, graceful
Routing Engine switchover must be combined with nonstop active routing.
Nonstop active routing is supported on Junos OS Release 12.1X48R3 and later.
Nonstop active routing is enabled (graceful Routing Engine switchover must be
configured for nonstop active routing to be enabled)—Nonstop active routing supports
Routing Engine switchover without alerting peer nodes that a change has occurred.
Nonstop active routing uses the same infrastructure as graceful Routing Engine
switchover to preserve interface and kernel information. However, nonstop active
routing also preserves routing information and protocol sessions by running the routing
re0 and re1 statements at the
statement. For instructions, see the Junos OS
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