ZyXEL GS-4012F/4024 User Manual download pdf (Page 190)

GS-4012F/4024 User’s Guide

Chapter 31 VRRP 190

CHAPTER 31

VRRP

This chapter shows you how to configure and monitor the Virtual Router Redundancy

Protocol (VRRP) on the switch.

31.1 Overview

Each host on a network is configured to send packets to a statically configured default gateway

(this switch). The default gateway can become a single point of failure. Virtual Router

Redundancy Protocol (VRRP), defined in RFC 2338, allows you to create redundant backup

gateways to ensure that the default gateway of a host is always available.

In VRRP, a virtual router (VR) represents a number of physical layer-3 devices. An IP address

is associated with the virtual router. A layer-3 device having the same IP address is the

preferred master router while the other Layer-3 devices are the backup routers. The master

router forwards traffic for the virtual router. When the master router becomes unavailable, a

backup router assumes the role of the master router until the master router comes back up and

takes over.

The following figure shows a VRRP network example with the switches (A and B)

implementing one virtual router VR1 to ensure the link between the host X and the uplink

gateway G. Host X is configured to use VR1 (192.168.1.20) as the default gateway. If switch

A has a higher priority, it is the master router. Switch B, having a lower priority, is the backup

router.

Figure 101 VRRP: Example 1

If switch A (the master router) is unavailable, switch B takes over. Traffic is then processed by

switch B.

172.21.1.100

172.21.1.1

172.21.1.10

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ZyXEL GS-4012F/4024 User Manual Page 190