Graceful Routing Engine Switchover; Link Aggregation; Nonstop Active Routing - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Graceful Routing Engine Switchover

Link Aggregation

Nonstop Active Routing

Copyright © 2010, Juniper Networks, Inc.
because multiple devices can be managed as a single device, and a simplified Layer 2
network topology that minimizes or eliminates the need for loop prevention protocols
such as Spanning Tree Protocol (STP). A Virtual Chassis improves high availability by
introducing a variety of failover mechanisms; if a member switch, a line card, or an interface
fails on a switch that is a member of a Virtual Chassis, for instance, traffic to that switch,
line card, or interface can be rerouted within the Virtual Chassis.
Juniper Networks EX4200 Ethernet Switches or EX8200 switches can form a Virtual
Chassis.
You can configure graceful Routing Engine switchover (GRES) on a switch with redundant
Routing Engines or on a Virtual Chassis, allowing control to switch from the master
Routing Engine to the backup Routing Engine with minimal interruption to network
communications. When you configure graceful Routing Engine switchover, 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 the boot 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 to
that of the new master Routing Engine. The interruption to traffic is minimal.
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
redundancy by load-balancing traffic across all available links. If one of the links should
fail, the system automatically load-balances traffic across all remaining links. In a Virtual
Chassis, LAGs can be used to load-balance network traffic between member switches.
The number of Ethernet interfaces you can include in a LAG and the number of LAGs you
can configure on a switch depend on the switch model.
Nonstop active routing (NSR) provides high availability in a switch with redundant Routing
Engines by enabling transparent switchover of the Routing Engines without requiring
restart of supported routing protocols. Both Routing Engines are fully active in processing
protocol sessions, and so each can take over for the other. The switchover is transparent
to neighbor routing devices, which do not detect that a change has occurred.
To use nonstop active routing, you must also configure graceful Routing Engine switchover.
Chapter 50: High Availability—Overview
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