Port 5353
Multicast DNS
Multicast DNS (mDNS) is a zero-configuration networking protocol that facilitates hostname resolution without a central DNS server, primarily within small local networks. It allows devices to discover each other and communicate seamlessly, especially helpful in consumer and IoT environments where manual network configuration is impractical..
Technical Details
Multicast DNS (mDNS) is a protocol designed for resolving hostnames to IP addresses within small networks that lack a dedicated DNS server. This is accomplished by leveraging multicast UDP packets sent to all devices on the local subnet using the reserved address 224.0.0.251 on UDP port 5353. When a device queries for a hostname, it multicasts the request, and the target system responds directly if it owns the address.
mDNS is a core component of Zero-Configuration Networking (ZeroConf), popularly implemented in Apple's Bonjour service. It cooperates with DNS Service Discovery (DNS-SD) to offer a combined solution for locating network services like printers, file sharing, or media streaming devices without manual configurations or infrastructure.
Technically, mDNS reuses much of the classic DNS packet structure and semantics but restricts query scope by sending messages to a multicast address. Consequently, it reduces the need for centralized management in small or dynamic environments. However, as it relies heavily on multicast, its operation is bounded to the local subnet and not suitable for wide-area resolution.