Table 79: Effect Of Taking The Host Subsystem Offline - Juniper T4000 Hardware Manual

T4000 Core Router Hardware Guide
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Table 79: Effect of Taking the Host Subsystem Offline

Type of Host
Subsystem Effect of taking the Host Subsystem Offline
Nonredundant host The router shuts down.
subsystem
Backup host The functioning of the router is not interrupted. The backup host subsystem
subsystem is hot-removable and hot-insertable.
Master host The backup host subsystem becomes the master. The backup Routing
subsystem Engine assumes Routing Engine functions. The master host subsystem is
hot-pluggable. Removal or failure of the master Routing Engine affects
forwarding and routing based on the high availability configuration:
Dual Routing Engines without any high availability features
enabled—Traffic is interrupted while the Packet Forwarding Engine is
reinitialized. 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.
Graceful Routing Engine switchover (GRES) is enabled—Graceful
Routing Engine switchover preserves interface and kernel information.
Traffic is not interrupted. However, graceful Routing Engine switchover
does not preserve the control plane. Neighboring routers detect that
the 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.
NOTE:
Junos OS Release 12.1R2 and later for T4000 routers.
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.
Nonstop active routing is supported on Junos OS Release 12.1R2 and
later for T4000 routers,
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.
Graceful Routing Engine switchover (GRES) is supported on
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