Netcat - A simple port of 'netcat' (nc) for DOS
2009-04-26 Version
Michael Brutman (mbbrutman@yahoo.com)


Hardware requirements:

  8088 processor or better
  Somewhere between 96KB and 128KB available RAM
  Display: doesn't matter, whatever you have
  Supported Ethernet card


Software requirements:

  DOS 2.0 or newer (DOS 3.3 or newer recommended)
  Packet driver for your Ethernet card


Introduction

  Netcat (nc) is a utility that can send and receive data using
  a TCP/IP socket. It has the ability to open a connection to
  another machine or to listen for incoming connections. Input
  can be entered interactively through the keyboard or redirected
  in from a file. Output can appear on the screen or redirected to
  a file. Nc can be used to send large files or short messages,
  and it can be called from within batch files too.

  Any output that nc creates that is not part of the normal data
  flow is sent to stderr so that your incoming data does not get
  polluted with status messages.


Requirements

  Nc is built using the mTCP library.  The setup instructions for
  mTCP can be found in SETUP.TXT.


Using Nc

  Nc uses the following syntax:

    nc -target <ipaddr> <port>
    nc -listen <port>

  Options are:

    -help               Show basic help text
    -srcport <port>     Use <port> as the source port when connecting
    -st                 SpeedTest (see section below)
    -echo               Turn on local echoing (off by default)

  If you are sending keyboard input to the other machine you signal
  EOF (End of File) by pressing Ctrl-Z. When you do this the TCP/IP
  socket will be shut down in an orderly way and the program will terminate.

  Nc is not a replacement for telnet - it will not negotiate 'telnet'
  parameters. It is good for raw data transfer only. Your best usage of
  nc is probably with another copy of nc on a DOS or Linux system, or as
  a utility to check if particular ports are open and accepting
  communications. When used with another nc on a different platform you
  can use it to send arbitrary data between the two systems, kind of like
  a network version of the copy (or Unix 'cat') command.


Examples

  nc -target 192.168.2.1 2000

    Opens a TCP/IP socket to 192.168.2.1 port 2000 and sends your
    keyboard input to the other machine. Output from the other
    machine will appear on your screen.

  nc -target 192.168.2.5 1234 < input.txt

    Opens a TCP/IP socket to 192.168.2.5 port 1234 and sends the
    file 'input.txt' to the other machine instead of sending your
    keyboard input. The program automatically ends after input.txt
    has been transferred.

  nc -listen 2000 > newfile.txt

    Listens on port 2000 for a connection from a remote machine.
    When the connection is established any incoming data is sent to
    newfile.txt.



The 'SpeedTest' Option

  I use this option for benchmarking. Basically it says that if you
  are receiving data that you should not write it to disk, and that
  if you are sending data you should send 4MB of random data and stop.
  The idea is to eliminate all disk I/O so that I can see how fast the
  TCP/IP code is running under perfect conditions.

  If you are interested in seeing how fast your machine can transfer
  data use nc like this:

    nc -target <target machine port> -st < bogus.bin

      This is the send test. Bogus.bin is not actually read. Nc will
      send 4MB of data.

    nc -target <target machine port> -st > bogus.bin

      This is the receive test. Nc will receive data but not write it
      to disk. It is up to the other side of the connection to set the
      amount of data to be received. Be careful and make sure that the
      filename you use does not already exist, as it will be zeroed out.

  On an XT class machine with an 8 bit Ethernet card I expect to see
  between 35KB and 45KB of data being transferred per second. On a 386-40
  class machine with a 16 bit Ethernet card the number should be in the
  mid 500s.



Limitations

    * Does not support UDP. (Most Unix versions do.)

Changes:

  2008-12-30:

    Small bug fix - was not checking return codes properly on
    the recv call inside of netcat!  Normally not a problem, but
    this can cause an interesting crash if the other side terminates
    the connection uncleanly.

  2008-12-17:

    Major performance improvements!  I've measured from 17 to 32%
    depending on the hardware and whether it was sending or
    receiving.  The performance improvement came from rewriting my
    code that computes elapsed time.

    Local echoing has been turned off.  You can turn it on using
    the new '-echo' command line option.  (You always had to deal
    with it before.)

    Ctrl-Break is now safe to use ..  it will shut down cleanly.

  2008-09-06:

    Netcat now has DNS resolution!  You can use normal server names
    instead of IP addresses.

    Check that the packet driver is loaded before trying to use it.
    TCP/IP stack improvements (Zero window support)


Created July 31st, 2008, Last updated April 26th, 2009
(C)opyright Michael B. Brutman, mbbrutman@yahoo.com