VRRP (Virtual Router Redundancy Protocol) is a fault-tolerant protocol. VRRP protocol can help to constitute a router backup group in a LAN, the VRRP router is equivalent to a virtual router. A host in LAN only need to know this virtual router's IP address and doesn’t need to know the IP address of the specific router. When set the host’s default gateway as the virtual router’s virtual IP address, host can use the virtual gateway to communicate with the external network.