Circuit Layer Proxy

Definition of Circuit Layer Proxy in the Network Encyclopedia.

What is Circuit Layer Proxy?

Circuit Layer Proxy is any service or server that provides proxy services using a specially installed component on the client computer to form a circuit between the proxy server and the client computer. Circuit layer proxies support a wider variety of protocols than application layer proxies.

Microsoft Proxy Server version 2 was a product that combined firewall and proxy server functions and had two Microsoft Windows NT services for providing circuit-level proxy functions:

  • The Winsock Proxy Service enables Windows Sockets clients such as Microsoft NetShow Player, RealAudio, and Internet Relay Chat (IRC) to function as if they are directly connected to the Internet. The Winsock Proxy Service provides Windows NT Challenge/Response Authentication with clients, regardless of whether the clients support it, and supports Windows Sockets version 1.1–compatible applications on computers running Windows. The Winsock Proxy Service can control access by port number, protocol, and user or group. Ports can be enabled or disabled for specific users or groups, and the list of users that can initiate outbound connections on a given port can differ from the list of users that can listen for inbound connections on that port.
  • The SOCKS Proxy Service includes support for the SOCKS 4.3a protocol. The SOCKS Proxy Service provides support for Macintosh-based and UNIX-based client computers, while the Winsock Proxy Service supports only Windows-based computers. SOCKS uses Transmission Control Protocol (TCP) and can be used to control access to the Telnet, File Transfer Protocol (FTP), Gopher, and Hypertext Transfer Protocol (HTTP) protocols. The SOCKS Proxy Service does not support RealAudio, streaming video, or NetShow clients.

See also: Application Layer Proxy


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