Correct Answer: A
A SOCKS based server operates at the Session layer of the OSI model.
SOCKS is an Internet protocol that allows client-server applications to transparently use the services of a network firewall. SOCKS is an abbreviation for "SOCKetS". As of Version 5 of SOCK, both UDP and TCP is supported.
One of the best known circuit-level proxies is SOCKS proxy server. The basic purpose of the protocol is to enable hosts on one side of a SOCKS server to gain access to hosts on the other side of a SOCKS Server, without requiring direct "IP-reachability" The protocol was originally developed by David Koblas, a system administrator of MIPS Computer Systems. After MIPS was taken over by Silicon Graphics in 1992, Koblas presented a paper on SOCKS at that year's Usenix Security Symposium and SOCKS became publicly available. The protocol was extended to version 4 by Ying-Da Lee of NEC.
SOCKS includes two components, the SOCKS server and the SOCKS client.
The SOCKS protocol performs four functions:
Making connection requests
Setting up proxy circuits
Relaying application data
Performing user authentication (optional)