Protocol Transport and Addressing
SSDP is a text-based protocol based on HTTPU. It uses the User Datagram Protocol (UDP) as the underlying transport protocol. Services are announced by the hosting system with multicast addressing to a specifically designated IP multicast address at port number 1900. In IPv4, the multicast address is 239.255.255.250 and SSDP over IPv6 uses the address set ff0X::c for all scope ranges indicated by X.
This results in the following well-known practical multicast addresses for SSDP:
- 239.255.255.250 (IPv4 site-local address)
- (IPv6 link-local)
- (IPv6 site-local)
- (IPv6 organization-local)
- (IPv6 global)
Additionally, applications may use the source-specific multicast addresses derived from the local IPv6 routing prefix, with group ID C (decimal 12).
SSDP uses a NOTIFY HTTP method to announce the establishment or withdrawal of services (presence) information to the multicast group. A client that wishes to discover available services on a network, uses the M-SEARCH method. Responses to such search requests are sent via unicast addressing to the originating address and port number of the multicast request.
Microsoft's IPv6 SSDP implementations in Windows Media Player and Server use the link-local scope address. Microsoft uses port number 2869 for event notification and event subscriptions. However, early implementations of SSDP also used port 5000 for this service.
Read more about this topic: Simple Service Discovery Protocol
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