Sometime in the distant past, I was aware of Universal Plug and Play (UPnP), but I didn’t know much about it. It’s a technology that allows devices in the home to talk to each other without prior configuration — it allows auto-discovery and configuration of printers and media servers, among other things.
The auto-discovery happens via SSDP (Simple Service Discovery Protocol). A device joins a network and announces “I’m here!”, and then other device can choose to respond. Even if the device gets a different IP address, it can still be uniquely identified by its unique identifier (UUID).
Here’s more information about UPnP and related protocols that run on the home network:
UPnP protocol (no authentication):
- Discovery (SSDP)
- Description – HTTPU and HTTPMU
- Event notification
UPnP has well defined device profiles for:
- Audio & Video — DLNA, and
Internet Gateway Device Protocol
Retrieve external IP addr
- Enumerate port mappings
- Add/Remove port mappings & port forwarding: firewall-hole-punching
Devices Profile for Web Services (DPWS)
Other protocols that help on the home network:
- LLMNR: Link-local Multicast Name Resolution — implemented by Microsoft in Windows.
- mDNS (multicast DNS) runs on port 5353. Uses .local hostnames.
- DNS-SD: DNS service discovery. Can use DNS or mDNS.
Apple’s Bonjour uses mDNS and DNS-SD. Linux’s Avahi uses IPv4LL, mDNS, and DNS-SD. Linux’s systemd has “systemd-resolve”, a command-linetool to resolve hostnames on a network via DNS, mDNS, and LMMNR.