SSDP

SSDP stands for Simple Service Discovery Protocol. It is a network protocol used for advertising and discovering network services and devices, most notably as part of the Universal Plug and Play (UPnP) framework. SSDP operates over UDP and relies on multicast messaging to enable automatic discovery without user configuration. In IPv4 networks, discovery commonly occurs via the multicast address 239.255.255.250 on port 1900; IPv6 deployments use corresponding link-local multicast addresses, with responses directed back to the requester.

In a typical interaction, a control point (such as a media player or home automation hub) sends a request known as an M-SEARCH to the SSDP multicast group to locate devices offering desired services. Devices that match the search respond with a unicast UDP reply containing information such as a location URL, which points to an XML description of the device and its services. Devices can also publish their presence and availability by broadcasting NOTIFY messages, indicating states such as ssdp:alive or ssdp:byebye. A device description often includes metadata like device type, manufacturer, model, and service endpoints, enabling control points to query and control the device.

SSDP is widely used by UPnP devices, including networked printers, cameras, media servers, and smart home gadgets. It is designed for simplicity and zero-configuration discovery but has security and privacy drawbacks: it has no built‑in authentication, can be abused for reconnaissance or denial-of-service amplification, and can expose devices to unintended networks if multicast traffic is not properly contained. Networks often filter or block SSDP traffic to mitigate these risks.

See also UPnP, multicast, mDNS.