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VNC Viewer Listener
Port 5500 is primarily associated with Virtual Network Computing (VNC) in 'listening' mode, allowing a server-side VNC viewer to wait for remote client connections. This facilitates reverse connections for remote desktop sharing and remote support. Standard VNC normally involves the client connecting to the remote server, but in some deployments, the server initiates a connection back to a listening viewer to bypass firewalls and NAT restrictions..
Port 5500 is used predominantly in VNC software suites, specifically for the 'listening viewer' functionality. In this setup, rather than a client initiating a connection to a server running on a remote system, the remote system (sometimes called the 'server' in typical VNC parlance) initiates a reverse connection back to the user's 'viewer' that is listening on port 5500. This inversion of the typical client/server model is especially useful for connecting to hosts behind restrictive NAT, as it avoids manual port forwarding.
The VNC protocol transmits framebuffer updates, keyboard, and mouse events using a relatively simple protocol based on the RFB (Remote Framebuffer) specification. The connection on port 5500 generally uses plain, unencrypted TCP sessions, depending on the VNC implementation in use, and may require user authentication.
Support tools such as UltraVNC, RealVNC, and TightVNC can use this method for assisting with remote troubleshooting. The VNC software listening on port 5500 waits for incoming reverse connections, which can be a convenience for tech support scenarios but poses certain security and configuration considerations.