VRRP application
Master/backup
In master/backup mode, only the master forwards packets, as shown in Figure 15. When the master fails, a new master is elected from among the backups. This mode requires only one VRRP group, and each router in the group has a different priority. The one with the highest priority becomes the master.
Figure 15: VRRP in master/backup mode
Assume that Router A is acting as the master to forward packets to external networks, and Router B and Router C are backups in listening state. When Router A fails, Router B and Router C elect a new master to forward packets for hosts on the subnet.
Load sharing
A router can join multiple VRRP groups. With different priorities in different VRRP groups, the router can act as the master in one VRRP group and a backup in another.
In load sharing mode, multiple VRRP groups provide gateway services. This mode requires a minimum of two VRRP groups, and each group has one master and multiple backups. The master roles in the VRRP groups are assumed by different routers, as shown in Figure 16.
Figure 16: Load sharing of VRRP
A router can be in multiple VRRP groups and have a different priority in each group.
As shown in Figure 16, the following VRRP groups exist:
VRRP group 1—Router A is the master. Router B and Router C are the backups.
VRRP group 2—Router B is the master. Router A and Router C are the backups.
VRRP group 3—Router C is the master. Router A and Router B are the backups.
To implement load sharing among Router A, Router B, and Router C, perform the following tasks:
Configure the virtual IP addresses of VRRP group 1, 2, and 3 as default gateway IP addresses for hosts on the subnet.
Assign the highest priority to Router A, B, and C in VRRP group 1, 2, and 3, respectively.