3Com Switch 8800 Advanced Software V5 Configuration Guide

762 CHAPTER 54: VRRP CONFIGURATION
There are two VRRP versions: VRRPv2 and VRRPv3. VRRPv2 is based on IPv4, while
VRRPv3 is based on IPv6. The two versions implement the same functions but
provide different commands.
Basic Concepts of VRRP This section introduces some concepts used throughout this document:
■ “VRRP standby group” on page 762
■ “VRRP priority” on page 763
■ “Preemption mode” on page 763
■ “Interface tracking” on page 763
■ “Authentication mode” on page 763
VRRP standby group
VRRP combines a group of routers on a LAN (including a master and multiple
backups) into a virtual router called standby group.
The VRRP standby group has the following features:
■ A host on the LAN only needs to know the IP address of the virtual router and
uses the IP address as the next hop of the default route.
■ Every host on the LAN communicates with external networks through the
virtual router.
■ Routers in the standby group use a certain election mechanism to elect the
gateway. Once the router acting as the gateway fails, the other routers in the
standby group elect a new gateway to undertake the responsibility of the failed
router.
Figure 230 Network diagram for a virtual router
As shown in Figure 230, Router A, Router B, and Router C form a virtual router,
which has its own IP address. Hosts on the Ethernet use the virtual router as the
default gateway.
In fact, only one of the three routers acts as the gateway, and the other two are
backups.
Host A
Host B
Host C
Router A
Router B
Router C
Virtual router
Network