Tunneling proxy may have various meanings; but most time, this refers to socks proxy. As the name suggests, socks proxy use sock 4 or 5 protocol, which performs at an intermediate layer between the presentation layer and the transport layer.
Socks (tunneling) proxy can be used for any form of TCP or UDP socket connection. This means it can be used for most application software (in addition to http connections), e.g., instant messenger.
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