Understanding Fast Failover In An Ex4200 Virtual Chassis - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Complete Software Guide for Junos

Understanding Fast Failover in an EX4200 Virtual Chassis

Supported Topologies for Fast Failover
How Fast Failover Works
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OS for EX Series Ethernet Switches, Release 10.4
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 in an EX4200 Virtual Chassis. 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 906
How Fast Failover Works on page 906
Effects of Topology Changes on a Fast Failover Configuration on page 911
For fast failover to be effective, the EX4200 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 907 shows normal traffic flow in a ring topology
using dedicated VCPs.
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