Fairbanks FB3000 Kernel Program Operators Manual - Manual (Page 61)

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Appendix VII: SOCKS Information
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".
─ Clients behind a firewall, needing to access exterior servers, may connect
to a SOCKS proxy server instead. Such a proxy server controls the
eligibility of the client to access the external server and passes the request
on to the server.
─ SOCKS can also be used in the opposite way, allowing the clients outside
the firewall (exterior clients) to connect to servers inside the firewall
(internal servers).
A typical SOCKS 4 connection request looks like the following (each number is one
byte).
Client to SOCKS Server:
Field 1: SOCKS version number, 1 byte, must be 0x04 for this version
Field 2: Command code, 1 byte:
─ 0x01 = Establish a TCP/IP stream connection.
─ 0x02 = Establish a TCP/IP port binding.
Field 3: Network byte order port number, 2 bytes.
Field 4: Network byte order IP address, 4 bytes.
Field 5: The user ID string, variable length, terminated with a null (0x00).
Server to SOCKS client:
Field 1: Null byte.
Field 2: Status, 1 byte:
─ 0x5a = Request granted.
─ 0x5b = Request rejected or failed.
─ 0x5c = Request failed because client is not running identd (or not
reachable from the server).
─ 0x5d = Request failed because client's identd could not confirm the user ID
string in the request.
Field 3: 2 arbitrary bytes, that should be ignored.
Field 4: 4 arbitrary bytes, that should be ignored.