mDNS / Bonjour Service Type Reference
Common mDNS / DNS-SD service type names with brief descriptions.
Overview
The mDNS / Bonjour service type reference lists the common DNS-SD service names you will see advertised on a local network: _http._tcp, _printer._tcp, _airplay._tcp, _ssh._tcp, _workstation._tcp, and dozens more. Each entry pairs the service type with a short description of what kind of device or protocol announces it.
Network administrators auditing the chatter on a LAN, developers writing a Bonjour browser, and security analysts identifying unknown advertisements all want a quick service-type lookup. Long-tail keywords covered: what does _airplay._tcp mean in mDNS, list common Bonjour service types, and DNS-SD service type registry.
How it works
Multicast DNS (mDNS, RFC 6762) lets hosts on a single link resolve names and discover services without a unicast DNS server. DNS-Based Service Discovery (DNS-SD, RFC 6763) layers a naming convention on top: a service type is _service._proto, where _proto is _tcp or _udp. Instances advertise themselves with PTR records pointing from the service type to a specific instance name, and an SRV record gives the host and port. TXT records carry additional metadata.
The Apple-coined name "Bonjour" is the same protocol under a brand. Android calls it Network Service Discovery (NSD). Linux uses Avahi. All three are wire-compatible.
Examples
_http._tcp— generic web service, advertised by many embedded devices._printer._tcp— IPP/Bonjour printer discovery._airplay._tcp— Apple AirPlay (audio/video casting)._ssh._tcp— SSH service announcement, common on Linux workstations.
FAQ
What is the .local domain?
.local is the special-use TLD reserved for mDNS (RFC 6762). Anything under .local is resolved by multicast on the local link, not by unicast DNS.
Why does my printer show up twice?
Many printers advertise multiple service types — _printer._tcp, _ipp._tcp, _pdl-datastream._tcp — each representing a different printing protocol on the same device.
Can mDNS leak information off my network?
The multicasts are link-scoped, so they should not leave the local segment. But misconfigured guest networks or open Wi-Fi can leak announcements between users. Treat advertised service info as public on whatever LAN you join.
How do I see what is advertised on my network?
Use avahi-browse -a on Linux, dns-sd -B _services._dns-sd._udp on macOS, or any Bonjour browser app. Browsers like Discovery on iOS work too.