Table 93: Effect Of Taking The Host Subsystem Offline - Juniper MX2020 Hardware Manual

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causes the router to shut down. The effect of taking the master host subsystem offline
varies depending on your configuration of high availability features.
Table 93 on page 403 explains the effect of taking the host subsystem offline.

Table 93: 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 CB-RE
subsystem assumes routing engine functions. The master host subsystem is
hot-pluggable. Removal or failure of the master CB-RE affects forwarding
and routing based on the high availability configuration:
Dual CB-RE 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 CB-RE is complete, routing convergence takes place and
traffic is resumed.
Graceful CB-RE switchover is enabled—Graceful CB-RE switchover
preserves interface and kernel information. Traffic is not interrupted.
However, graceful CB-RE 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 CB-RE switchover must be combined with nonstop
active routing.
Nonstop active routing is enabled (graceful CB-RE switchover must be
configured for nonstop active routing to be enabled)—Nonstop active
routing supports CB-RE switchover without alerting peer nodes that a
change has occurred. Nonstop active routing uses the same
infrastructure as graceful CB-RE 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 CB-REs. 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.
Chapter 23: Maintaining Components
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