3Com S7902E, Configuration Manual

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1-8
Figure 1-6 VRRP in load sharing mode
Host A
Host B
Host C
Router A
Backup
Router B
Backup
Router C
Master
VRRP group 2 VRRP group 3 VRRP group 1
Master
Backup
Backup Backup
Master
Backup
Network
A router can be in multiple VRRP groups and hold a different priority in different group.
In Figure 1-6 , three VRRP groups are present:
z
VRRP group 1: Router A is the master; Router B and Router C are the backups.
z
VRRP group 2: Router B is the master; Router A and Router C are the backups.
z
VRRP group 3: Router C is the master; Router A and Router B are the backups.
For load sharing among Router A, Router B, and Router C, hosts on the LAN need to be configured to
use VRRP group 1, 2, and 3 as the default gateways respectively. When configuring VRRP priorities,
make sure that each router holds such a priority in each VRRP group that it will take the expected role in
the group.
VRRP Load Balancing Mode
Overview
When VRRP works in the standard protocol mode, only the master can forward packets and the
backups are in the state of listening. Although you can create multiple VRRP groups to implement load
sharing among multiple routers, hosts on the LAN need to be configured with different gateways, thus
making the configuration complicated.
When VRRP works in the load balancing mode, namely, besides virtual gateway redundancy, VRRP
realizes load balancing. The working principle is as follows: associate a virtual IP address with multiple
virtual MAC addresses to make each router in a VRRP group correspond to a virtual MAC address. In
this way, each router in this VRRP group can forward packets. In the load balancing mode, you need to
create only one VRRP group to realize load balancing among multiple routers, thus avoiding that the
backups are always in the idle state and the network resources are not fully utilized.