RFC 1928                SOCKS Protocol Version 5              March 1996

   authentication method to be used, authenticates with the chosen
   method, then sends a relay request.  The SOCKS server evaluates the
   request, and either establishes the appropriate connection or denies
   it.

   Unless otherwise noted, the decimal numbers appearing in packet-
   format diagrams represent the length of the corresponding field, in
   octets.  Where a given octet must take on a specific value, the
   syntax X'hh' is used to denote the value of the single octet in that
   field. When the word 'Variable' is used, it indicates that the
   corresponding field has a variable length defined either by an
   associated (one or two octet) length field, or by a data type field.

   The client connects to the server, and sends a version
   identifier/method selection message:

                   +----+----------+----------+
                   |VER | NMETHODS | METHODS  |
                   +----+----------+----------+
                   | 1  |    1     | 1 to 255 |
                   +----+----------+----------+

   The VER field is set to X'05' for this version of the protocol.  The
   NMETHODS field contains the number of method identifier octets that
   appear in the METHODS field.

   The server selects from one of the methods given in METHODS, and
   sends a METHOD selection message:

                         +----+--------+
                         |VER | METHOD |
                         +----+--------+
                         | 1  |   1    |
                         +----+--------+

   If the selected METHOD is X'FF', none of the methods listed by the
   client are acceptable, and the client MUST close the connection.

   The values currently defined for METHOD are:

          o  X'00' NO AUTHENTICATION REQUIRED
          o  X'01' GSSAPI
          o  X'02' USERNAME/PASSWORD
          o  X'03' to X'7F' IANA ASSIGNED
          o  X'80' to X'FE' RESERVED FOR PRIVATE METHODS
          o  X'FF' NO ACCEPTABLE METHODS

   The client and server then enter a method-specific sub-negotiation.



RFC 1928                SOCKS Protocol Version 5              March 1996

   Descriptions of the method-dependent sub-negotiations appear in
   separate memos.

   Developers of new METHOD support for this protocol should contact
   IANA for a METHOD number.  The ASSIGNED NUMBERS document should be
   referred to for a current list of METHOD numbers and their
   corresponding protocols.

   Compliant implementations MUST support GSSAPI and SHOULD support
   USERNAME/PASSWORD authentication methods.

4.  Requests

   Once the method-dependent subnegotiation has completed, the client
   sends the request details.  If the negotiated method includes
   encapsulation for purposes of integrity checking and/or
   confidentiality, these requests MUST be encapsulated in the method-
   dependent encapsulation.

   The SOCKS request is formed as follows:

        +----+-----+-------+------+----------+----------+
        |VER | CMD |  RSV  | ATYP | DST.ADDR | DST.PORT |
        +----+-----+-------+------+----------+----------+
        | 1  |  1  | X'00' |  1   | Variable |    2     |
        +----+-----+-------+------+----------+----------+

     Where:

          o  VER    protocol version: X'05'
          o  CMD
             o  CONNECT X'01'
             o  BIND X'02'
             o  UDP ASSOCIATE X'03'
          o  RSV    RESERVED
          o  ATYP   address type of following address
             o  IP V4 address: X'01'
             o  DOMAINNAME: X'03'
             o  IP V6 address: X'04'
          o  DST.ADDR       desired destination address
          o  DST.PORT desired destination port in network octet
             order