entityknowledgestatus: reference-onlydemovalidation-test
mDNS
mDNS
Summary
Multicast DNS (RFC 6762) — a protocol that lets devices on a local network resolve each
other’s hostnames (e.g. printer.local) without a central DNS server, by having each device
answer for its own name over multicast. Almost always deployed alongside DNS-SD (RFC 6763) for
zero-config service discovery; together they’re the mechanism behind Bonjour, Avahi, and most
smart-home device auto-discovery.
Relations
| Subject | Predicate | Object |
|---|---|---|
| ESPHome | uses | mDNS |
| mDNS | enables | zero-config service discovery |
| mDNS | requires | link-local multicast (224.0.0.251, UDP 5353) |
Key Facts
- Paired with DNS-SD (RFC 6763) for service discovery, not just name resolution
- Multicast is link-local by default — does not cross routers/VLANs without a reflector
- Common failure mode: a device becomes undiscoverable purely because it moved network segments, with no other symptom
When to Use
Reach for this page when troubleshooting “device isn’t showing up” reports for anything that relies on auto-discovery (ESPHome, printers, Chromecast-style devices) — check VLAN/guest-network segmentation before assuming a device-side fault.
Sources
Created as part of a 2026-08-29 end-to-end workflow validation exercise — safe to remove.