Juniper PTX5000 Hardware Manual page 481

statements at the [edit groups] hierarchy level and use the apply-groups statement. For instructions,
see the Junos OS Administration
When a primary host subsystem is taken offline or during a primary role switch, the backup host
subsystem becomes the primary, and the backup Routing Engine assumes Routing Engine functions. The
primary 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 primary and the Packet Forwarding Engine components reset and connect to the new
primary Routing Engine. All kernel and forwarding processes are restarted. When the switchover to
the new primary 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 routers detect that the PTX5000 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 protocol process (rpd) on both Routing Engines. In addition, nonstop active routing
preserves TCP connections maintained in the kernel.
• Graceful restart is configured—Graceful restart provides extensions to routing protocols so that
neighboring helper routers restore routing information to a restarting router. These extensions signal
neighboring routers about the graceful restart and prevent the neighbors from reacting to the router
restart and from propagating the change in state to the network during the graceful restart period.
Neighbors provide the routing information that enables the restarting router to stop and restart
routing protocols without causing network reconvergence. Neighbors are required to support
graceful restart. The routing protocol process (rpd) restarts. A graceful restart interval is required. For
certain protocols, a significant change in the network can cause graceful restart to stop.
Library.
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