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= ROOT|Technical|Proxy_Docs|rfc1928.txt =

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   a new socket.  The BND.PORT field contains the port number that the
   SOCKS server assigned to listen for an incoming connection.  The
   BND.ADDR field contains the associated IP address.  The client will
   typically use these pieces of information to notify (via the primary
   or control connection) the application server of the rendezvous
   address.  The second reply occurs only after the anticipated incoming
   connection succeeds or fails.

RFC 1928                SOCKS Protocol Version 5              March 1996

   In the second reply, the BND.PORT and BND.ADDR fields contain the
   address and port number of the connecting host.


   The UDP ASSOCIATE request is used to establish an association within
   the UDP relay process to handle UDP datagrams.  The DST.ADDR and
   DST.PORT fields contain the address and port that the client expects
   to use to send UDP datagrams on for the association.  The server MAY
   use this information to limit access to the association.  If the
   client is not in possesion of the information at the time of the UDP
   ASSOCIATE, the client MUST use a port number and address of all

   A UDP association terminates when the TCP connection that the UDP
   ASSOCIATE request arrived on terminates.

   In the reply to a UDP ASSOCIATE request, the BND.PORT and BND.ADDR
   fields indicate the port number/address where the client MUST send
   UDP request messages to be relayed.

Reply Processing

   When a reply (REP value other than X'00') indicates a failure, the
   SOCKS server MUST terminate the TCP connection shortly after sending
   the reply.  This must be no more than 10 seconds after detecting the
   condition that caused a failure.

   If the reply code (REP value of X'00') indicates a success, and the
   request was either a BIND or a CONNECT, the client may now start
   passing data.  If the selected authentication method supports
   encapsulation for the purposes of integrity, authentication and/or
   confidentiality, the data are encapsulated using the method-dependent
   encapsulation.  Similarly, when data arrives at the SOCKS server for
   the client, the server MUST encapsulate the data as appropriate for
   the authentication method in use.

7.  Procedure for UDP-based clients

   A UDP-based client MUST send its datagrams to the UDP relay server at
   the UDP port indicated by BND.PORT in the reply to the UDP ASSOCIATE
   request.  If the selected authentication method provides
   encapsulation for the purposes of authenticity, integrity, and/or
   confidentiality, the datagram MUST be encapsulated using the
   appropriate encapsulation.  Each UDP datagram carries a UDP request
   header with it:

RFC 1928                SOCKS Protocol Version 5              March 1996

      |RSV | FRAG | ATYP | DST.ADDR | DST.PORT |   DATA   |
      | 2  |  1   |  1   | Variable |    2     | Variable |

     The fields in the UDP request header are:

          o  RSV  Reserved X'0000'
          o  FRAG    Current fragment number
          o  ATYP    address type of following addresses:
             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
          o  DATA     user data

   When a UDP relay server decides to relay a UDP datagram, it does so
   silently, without any notification to the requesting client.
   Similarly, it will drop datagrams it cannot or will not relay.  When
   a UDP relay server receives a reply datagram from a remote host, it
   MUST encapsulate that datagram using the above UDP request header,
   and any authentication-method-dependent encapsulation.

   The UDP relay server MUST acquire from the SOCKS server the expected
   IP address of the client that will send datagrams to the BND.PORT
   given in the reply to UDP ASSOCIATE.  It MUST drop any datagrams
   arriving from any source IP address other than the one recorded for
   the particular association.

   The FRAG field indicates whether or not this datagram is one of a
   number of fragments.  If implemented, the high-order bit indicates
   end-of-fragment sequence, while a value of X'00' indicates that this
   datagram is standalone.  Values between 1 and 127 indicate the
   fragment position within a fragment sequence.  Each receiver will
   have a REASSEMBLY QUEUE and a REASSEMBLY TIMER associated with these

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