TCP File Transfer behind NAT

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  • Saurabh
    #1

    TCP File Transfer behind NAT

    Dear All,

    Can anyone tell me, how to write such a program that can transfer
    files (either binary or text) behind NAT devices( such as for
    computers behind firewalls and routers and other NAT devices) using
    TCP socket programming.

    I have a mechanism through which the public IP of the router and Port
    number will be forwarded to me. But after that I am not sure that
    simple TCP/IP socket programming will suffice or I need to do
    something more for that.

    If you have any article link or article or any example that shows how
    the File Transfer can be done for such a case then please help me
    regarding this.

    Any sought of help or idea will be appreciated from you all.

    from-
    Saurabh Srivastava
    Tags: None
    • Walter Roberson
      #2
      Re: TCP File Transfer behind NAT

      In article <e31e2eb9-7b46-4d1a-939a-132e35f6bbcf@u1 0g2000prn.googl egroups.com>,
      Saurabh <sendsaurabh@gm ail.comwrote:
      >Can anyone tell me, how to write such a program that can transfer
      >files (either binary or text) behind NAT devices( such as for
      >computers behind firewalls and routers and other NAT devices) using
      >TCP socket programming.
      The C standards do not know anything about networking, let alone
      NAT. Networking matters are platform dependant. You should ask
      in a development newsgroup that supports your operating system.
      --
      "History is a pile of debris" -- Laurie Anderson

        Comment

        • Antoninus Twink
          #3
          Re: TCP File Transfer behind NAT

          On 3 Apr 2008 at 10:11, Saurabh wrote:
          Dear All,
          >
          Can anyone tell me, how to write such a program that can transfer
          files (either binary or text) behind NAT devices( such as for
          computers behind firewalls and routers and other NAT devices) using
          TCP socket programming.
          >
          I have a mechanism through which the public IP of the router and Port
          number will be forwarded to me. But after that I am not sure that
          simple TCP/IP socket programming will suffice or I need to do
          something more for that.
          No, you don't need to do anything unusual: from the outside, NAT is
          completely transparent, so you can just deal with whatever port number
          on the external-facing router and it will take care of forwarding it
          within its internal network as required.

          The only problems that might arise are if you're using some complicated
          secure tunneling arrangement that confuses the NAT front end.

            Comment

            • Richard Tobin
              #4
              Re: TCP File Transfer behind NAT

              In article <slrnfvaitk.9v2 .nospam@nospam. invalid>,
              Antoninus Twink <nospam@nospam. invalidwrote:
              >No, you don't need to do anything unusual: from the outside, NAT is
              >completely transparent, so you can just deal with whatever port number
              >on the external-facing router and it will take care of forwarding it
              >within its internal network as required.
              >
              >The only problems that might arise are if you're using some complicated
              >secure tunneling arrangement that confuses the NAT front end.
              Or if you're using a protocol such as FTP, which sends addresses
              (port numbers) as part of the data itself. Then the NAT device
              doesn't know to set up a mapping, and even if it did the port
              number carried in the message would be wrong.

              NAT implementations usually know about a handful of protocols of
              this kind, and inspect and munge the data accordingly. Alternatively
              the program may use some other protocol such as upnp to inform
              the router.

              -- Richard
              --
              :wq

                Comment

                • Antoninus Twink
                  #5
                  Re: TCP File Transfer behind NAT

                  On 3 Apr 2008 at 21:44, Richard Tobin wrote:
                  In article <slrnfvaitk.9v2 .nospam@nospam. invalid>,
                  Antoninus Twink <nospam@nospam. invalidwrote:
                  >
                  >>No, you don't need to do anything unusual: from the outside, NAT is
                  >>completely transparent, so you can just deal with whatever port number
                  >>on the external-facing router and it will take care of forwarding it
                  >>within its internal network as required.
                  >>
                  >>The only problems that might arise are if you're using some complicated
                  >>secure tunneling arrangement that confuses the NAT front end.
                  >
                  Or if you're using a protocol such as FTP, which sends addresses
                  (port numbers) as part of the data itself. Then the NAT device
                  doesn't know to set up a mapping, and even if it did the port
                  number carried in the message would be wrong.
                  >
                  NAT implementations usually know about a handful of protocols of
                  this kind, and inspect and munge the data accordingly. Alternatively
                  the program may use some other protocol such as upnp to inform
                  the router.
                  You're right, of course, but I think modern NAT devices handle many
                  common protocols transparently to outside users - this will almost
                  certainly be the case for FTP or whatever protocol the OP intends to use
                  to transfer his files.

                    Comment

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