SSDP UPnP Discovery uses which port?

SSDP UPnP Discovery uses which port?

• A. 80
• B. 1902
• C. 21
• D. 1900

Answer: (D)

The key idea is that SSDP discovery, which UPnP uses to locate devices on a local network, operates on a dedicated UDP port. SSDP discovery messages are sent to the multicast address 239.255.255.250 on port 1900, and devices listen on that port to discover services. That standard port is what makes it possible for a control point to broadcast a discovery request and have devices respond without knowing each device’s IP in advance. The other ports listed correspond to different protocols (for example, 80 is HTTP, 21 is FTP) and are not used for the standard UPnP SSDP discovery process. So the port used for SSDP discovery is 1900.

The key idea is that SSDP discovery, which UPnP uses to locate devices on a local network, operates on a dedicated UDP port. SSDP discovery messages are sent to the multicast address 239.255.255.250 on port 1900, and devices listen on that port to discover services. That standard port is what makes it possible for a control point to broadcast a discovery request and have devices respond without knowing each device’s IP in advance. The other ports listed correspond to different protocols (for example, 80 is HTTP, 21 is FTP) and are not used for the standard UPnP SSDP discovery process. So the port used for SSDP discovery is 1900.