Redundant Routing Engines; Graceful Routing Engine Switchover - Juniper JUNOS OS 10.3 - SOFTWARE Manual

Complete Software Guide for Junos

Redundant Routing Engines

Graceful Routing Engine Switchover

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OS for EX Series Ethernet Switches, Release 10.3
Two to ten EX4200 switches can be interconnected to create a Virtual Chassis
configuration that operates as a single network entity. Every Virtual Chassis configuration
has a master and a backup. The master acts as the master Routing Engine and the backup
acts as the backup Routing Engine. The Routing Engine provides the following
functionality:
Runs various routing protocols
Provides the forwarding table to the Packet Forwarding Engines (PFEs) in all the
member switches of the Virtual Chassis configuration
Runs other management and control processes for the entire Virtual Chassis
configuration
The master Routing Engine, which is in the master of the Virtual Chassis configuration,
runs Juniper Networks Junos operating system (Junos OS) in the master role. It receives
and transmits routing information, builds and maintains routing tables, communicates
with interfaces and Packet Forwarding 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.
GRES on EX4200 switches supports software features in Junos OS Release 9.2 or later
for EX Series switches.
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