mDNS
also: Multicast DNS, Avahi, Bonjour (Apple's implementation), zeroconf
mDNS (Multicast DNS) is a protocol that allows computers on a local network to discover and communicate with each other by hostname without needing a central DNS server.
mDNS enables zero-configuration networking by letting devices broadcast and resolve hostnames (.local addresses) directly on the LAN using multicast packets. When you type ping mycomputer.local, mDNS handles the lookup without relying on a traditional DNS infrastructure.
The protocol works by having each host listen on multicast address 224.0.0.251:5353 and respond to queries for its own hostname. This is particularly useful for home networks, small offices, and IoT devices where setting up a DNS server isn't practical.
Common implementations include Avahi (Linux), Bonjour (Apple), and systemd-resolved. For example, a printer on your WiFi network can advertise itself as printer.local so any device can discover and communicate with it automatically without manual configuration.