mDNS multicast Domain Name System

mDNS resolves host names to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, packet formats and operating semantics as the unicast Domain Name System (DNS).
Wikipedia

Zeroconf

It is a set of technologies that automatically creates a usable computer network based on TCP/IP when computers or network peripherals are interconnected. It does not require manual operator intervention or special configuration servers for Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS).

Bonjour

Bonjour is a networking technology developed by Apple that makes it easy to set up and use devices and services on a network. Bonjour locates devices such as printers, other computers, and the services that those devices offer on a local network using multicast Domain Name System (mDNS) service records.

Overview

When an mDNS client needs to resolve a host name, it sends an IP multicast query message that asks the host having that name to identify itself. That target machine then multicasts a message that includes its IP address. All machines in that subnet can then use that information to update their mDNS caches.

Any host can relinquish its claim to a domain name by sending a response packet with a time to live (TTL) equal to zero.

By default, mDNS only and exclusively resolves host names ending with the .local top-level domain (TLD). This can cause problems if that domain includes hosts which do not implement mDNS but which can be found via a conventional unicast DNS server. Resolving such conflicts requires network-configuration changes that violate the zero-configuration goal.

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