Chassis Configuration; Understanding Fast Failover In A Virtual Chassis Configuration - Juniper JUNOS OS 10.3 - SOFTWARE Manual

Complete Software Guide for Junos

Understanding Fast Failover in a Virtual Chassis Configuration

Supported Topologies for Fast Failover
How Fast Failover Works
936
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OS for EX Series Ethernet Switches, Release 10.3
The Virtual Chassis fast failover feature is a hardware-assisted failover mechanism that
automatically reroutes traffic and reduces traffic loss in the event of a link failure or switch
failure. If a link between two members fails, traffic flow between those members must
be rerouted quickly so that there is minimal traffic loss.
Fast failover is effective only for Virtual Chassis members configured in ring topologies
using identical port types.
This topic describes the following:
Supported Topologies for Fast Failover on page 936
How Fast Failover Works on page 936
Effects of Topology Changes on a Fast Failover Configuration on page 941
For fast failover to be effective, the Virtual Chassis members must be configured in a ring
topology. The ring topology can be formed by using either dedicated Virtual Chassis ports
(VCPs) or user-configured uplink module VCPs. Fast failover is supported only in a ring
topology that uses identical port types, for example, either a topology that uses all
dedicated VCPs or one that uses all uplink module VCPs. Fast failover is not supported
in a ring topology that includes both dedicated VCPs and uplink module VCPs. Fast
failover is supported, however, in a Virtual Chassis configuration that consists of multiple
rings.
When fast failover is activated, each VCP is automatically configured with a backup port
of the same type (dedicated VCP, SFP uplink VCP, or XFP uplink VCP). If a VCP fails, its
backup port is used to send traffic. These backup ports act as standby ports and are not
meant for load-balancing purposes.
Fast Failover in a Ring Topology using Dedicated VCPs
When fast failover is activated in a ring topology that uses dedicated VCPs, each VCP is
automatically configured with a backup port of the same type. If a VCP fails, its backup
port is used to send traffic. Figure 11 on page 937 shows normal traffic flow in a ring topology
using dedicated VCPs.
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