Link-Local Multicast Name Resolution (LLMNR) is a Network Protocol that is used for Name resolution based on DNS packet format operating in Layer 2 (local link) specified in RFC 4795. It is a fall-back mechanism when DNS fails. The system which needs to resolve a hostname will send out a multicast query using LLMNR and the system having the requested hostname respond will respond with it’s IP address. It operates on UDP port 5355.
RFC Reference
RFC 4795 – Link-Local Multicast Name Resolution (LLMNR)