A host sends an ARP Request message with the destination address being its own IP address. This operation is called gratuitous ARP. Gratuitous ARP provides the following functions:
Checks duplicate IP addresses: Normally, the host does not receive an ARP Reply message after sending an ARP Request message with the destination address being its own IP address. If a reply is received, it indicates that another host is assigned the same IP address.
Declares a new MAC address: If the host has replaced its network card and hence its MAC address has changed, the host sends a gratuitous ARP message to declare the MAC address change to all hosts before the aging of ARP entries.
Notifies master/slave switchover of devices in a VRRP backup group.
