VRRP
also: Virtual Router Redundancy Protocol
VRRP (Virtual Router Redundancy Protocol) is a networking protocol that allows multiple physical routers to share a single virtual IP address, ensuring automatic failover if the active router fails.
VRRP enables high availability for network gateways by coordinating a group of routers to act as one virtual router. One router becomes the master and handles traffic destined for the virtual IP, while others remain in backup state. If the master fails to send heartbeat messages, a backup automatically takes over.
This is commonly used in enterprise networks where the default gateway must remain accessible. For example, if your local network's gateway is 192.168.1.1 (the virtual IP), two physical routers can run VRRP: one actively routing traffic, the other silently monitoring. When the active router goes down, the backup seamlessly becomes the master within seconds, and clients never lose connectivity.
VRRP operates at OSI Layer 3 and uses multicast heartbeats (224.0.0.18) to maintain state synchronization. On Linux, VRRP is typically implemented using tools like keepalived, which combines VRRP with health checks to manage virtual IPs across clustered systems.