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VRRP has two versions: VRRPv2 and VRRPv3. VRRPv2 supports IPv4 VRRP. VRRPv3 supports
IPv4 VRRP and IPv6 VRRP.
VRRP standard mode
In VRRP standard mode, only the master in the VRRP group can provide gateway service. When the
master fails, the backup routers elect a new master to take over for nonstop gateway service.
Figure 30 VRRP networking
As shown in Figure 30, Router A, Router B, and Router C form a virtual router, which has its own IP
address. Hosts on the subnet use the virtual router as the default gateway.
The router with the highest priority among the three routers is elected as the master, and the other
two are backups.
Router priority in a VRRP group
VRRP determines the role (master or backup) of each router in a VRRP group by priority. A router
with higher priority is more likely to become the master.
A VRRP priority can be in the range of 0 to 255, and a greater number represents a higher priority.
Priorities 1 to 254 are configurable. Priority 0 is reserved for special uses, and priority 255 is for the
IP address owner. The router acting as the IP address owner in a VRRP group always has a running
priority of 255 and acts as the master as long as it operates correctly.
Preemption
A router in a VRRP group operates in either non-preemptive mode or preemptive mode.
• Non-preemptive mode—When a router in the VRRP group becomes the master, it acts as the
master as long as it operates correctly, even if a backup router is later assigned a higher priority.
Non-preemptive mode helps avoid frequent switchover between the master and backup
routers.
• Preemptive mode—A backup starts a new master election and takes over as master when it
detects that it has a higher priority than the current master. Preemptive mode makes sure the
router with the highest priority in a VRRP group always acts as the master.
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