Graceful Routing Engine Switchover - Dell PowerConnect J-EX4200-24T Software Manual

Dell PowerConnect J-Series Ethernet Switch Complete Software Guide for Junos OS

Graceful Routing Engine Switchover

Virtual Chassis Software Upgrade and Failover Features
Link Aggregation
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Engine components of the member switches, and has full control over the Virtual Chassis
configuration.
The backup Routing Engine, which is in the backup of the Virtual Chassis configuration,
runs Junos OS in the backup role. It stays in sync with the master Routing Engine in terms
of protocol states, forwarding tables, and so forth. If the master becomes unavailable,
the backup Routing Engine takes over the functions that the master Routing Engine
performs.
You can configure graceful Routing Engine switchover (GRES) in a Virtual Chassis
configuration, allowing the configuration to switch from the master Routing Engine in
the master to the backup Routing Engine in the backup with minimal interruption to
network communications. When you configure GRES, the backup Routing Engine
automatically synchronizes with the master Routing Engine to preserve kernel state
information and forwarding state. Any updates to the master Routing Engine are replicated
to the backup Routing Engine as soon as they occur. If the kernel on the master Routing
Engine stops operating, the master Routing Engine experiences a hardware failure, or
the administrator initiates a manual switchover, mastership switches to the backup
Routing Engine.
When the backup Routing Engine assumes mastership in a redundant failover
configuration (that is, when graceful Routing Engine switchover is not enabled), the
Packet Forwarding Engines initialize their state to boot up state before they connect to
the new master Routing Engine. In contrast, in a graceful switchover configuration, the
Packet Forwarding Engines do not reinitialize their state, but resynchronize their state
with the new master Routing Engine. The interruption to the traffic is minimal.
J-EX4200 switches provide these features for increased resiliency in Virtual Chassis
configurations:
Virtual Chassis atomic software upgrade—When you upgrade software in a Virtual
Chassis configuration, the upgrade will either succeed or fail on all member switches,
preventing the situation in which only some of the Virtual Chassis member switches
are upgraded.
Virtual Chassis fast failover—A hardware-assisted failover mechanism that
automatically reroutes traffic and reduces traffic loss in the event of a link failure.
Virtual Chassis split and merge—If there is a disruption to the Virtual Chassis
configuration due to member switches failing or being removed from the configuration,
the Virtual Chassis configuration splits into two separate Virtual Chassis.
You can combine multiple physical Ethernet ports to form a logical point-to-point link,
known as a link aggregation group (LAG) or bundle. A LAG provides more bandwidth than
a single Ethernet link can provide. Additionally, link aggregation provides network