3Com Switch 8800 Advanced Software V5 Configuration Guide

766 CHAPTER 54: VRRP CONFIGURATION
Principles of VRRP
1 With VRRP enabled, the routers determine their respective roles in the standby
group by priority. The router with the highest priority becomes the master, while
the others are the backups. The master sends VRRP advertisement packets
periodically to notify the backups that it is working properly, and each of the
backups starts a timer to wait for advertisement packets from the master.
2 In preemption mode, when a backup receives a VRRP advertisement, it compares
the priority in the packet with that of its own. If its priority is lower, it remains a
backup; otherwise, it becomes the master.
3 In non-preemption mode, the router in the standby group remains as a master or
backup as long as the master does not fail. The backup will no become the master
even if the former is configured with a higher priority.
4 If the timer of a backup expires but the backup still does not receive any VRRP
advertisement packet, it considers that the master fails and starts the election
process to elect a new master for forwarding packets.
Operation Modes of
VRRP (Taking IPv4-Based
VRRP for Example)
Master/backup
In master/backup mode, only one router, the master, provides services. When the
master fails, a new master is elected from the original backups. This mode requires
only one standby group, in which each router holds different priorities and the one
with the highest priority becomes the master, as shown in
Figure 233.
Figure 233 VRRP in master/backup mode
At the beginning, Router A is the master and therefore can forward packets to
external networks, while Router B and Router C are backups and are thus in the
state of listening. If Router A fails, Router B and Router C will elect for the new
master. The new master takes over the forwarding task to provide services to hosts
on the LAN.
Load balancing
You can create more than one standby group on an interface of a router, allowing
the router to be the master of one standby group but a backup of another at the
same time.
Host A
Host B
Host C
Router A
Master
Router B
Backup
Router C
Backup
Virtual IP address:
10.1.1.1/24
10. 1.1 .2/ 24
10. 1.1 .3/ 24
10. 1.1 .4/ 24
Network