Juniper M40E Hardware Manual page 52

M40e Multiservice Edge Router Hardware Guide
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The host module components are hot-pluggable, as described in "M40e Field-Replaceable
Units (FRUs)" on page 157. Removal or failure of one or both components in the standby
host module does not affect router function. Removal or failure of one or both components
in the master host module 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.
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.
If you do not configure graceful Routing Engine switchover, graceful restart, or nonstop
active routing, you can configure automatic Routing Engine mastership failover. For
information about configuring automatic mastership failover, see the Junos OS System
Basics Configuration Guide.
NOTE: Router performance might change if the backup Routing Engine's
configuration differs from the former master's configuration. For the most
predictable performance, configure the two Routing Engines identically,
except for parameters unique to each Routing Engine.
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