UPnP device discovery — a router, TV, printer, or media box announcing itself on the LAN.
SSDP is the discovery half of UPnP: devices multicast NOTIFY announcements to 239.255.255.250:1900 and answer M-SEARCH queries with a URL to their XML device description. It shows up on scans because consumer routers, smart TVs, game consoles, printers, and NAS boxes all run a UPnP stack by default. On a router it usually fronts the IGD service that lets any LAN host open inbound port forwards without authentication.
Do not expose
SSDP is a well-known UDP reflection/amplification vector (CISA measured a 30.8x bandwidth amplification factor) and internet-facing UPnP IGD lets strangers punch holes through your NAT.
$ printf 'M-SEARCH * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\nMAN: "ssdp:discover"\r\nMX: 1\r\nST: ssdp:all\r\n\r\n' | nc -u -w 2 239.255.255.250 1900Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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