HOWTO: NULL Modem TCP/IP network connection between Linux and Windows

Linux PPP server
----------------

The first step is to install the pppd demon and optionally the mgetty to use it on dialup modem, but this howto only covers the null modem (serial) part.
Once installed you must to create the following files:

/etc/sysctl.conf

  net.ipv4.ip_forward=1

/etc/ppp/options

  # demon
  persist
  noauth
  auth

  # compress
  bsdcomp 12,15
  deflate 12,15

  # common options
  proxyarp
  lock
  passive
  lcp-echo-interval 8
  lcp-echo-failure 6
  nologfd
  crtscts
  local

  # Windows compat
  connect 'chat TIMEOUT 20000 CLIENT CLIENTSERVER'

  # port settings
  /dev/ttyS0
  115200

/etc/ppp/options.ttyS0

  # server ip : client ip 
  10.0.2.15:10.0.2.100
  netmask 255.255.255.0
  ms-dns 77.88.8.8

/etc/ppp/pap-secrets

  # user    server    password    ip
  user    *    userPass    *

You can launch the pppd demon on init or inittab.

Linux PPP client
----------------

Now in the client you must also install the pppd demon and create the following files:

/etc/ppp/options

  # common options
  defaultroute
  lock
  passive
  lcp-echo-interval 8
  lcp-echo-failure 6
  nologfd
  crtscts
  local

  # Windows compat
  connect 'chat -v -f /etc/ppp/win.chat'

  # port settings
  /dev/ttyS0
  115200

/etc/ppp/options.ttyS0

  user user

/etc/ppp/win.chat

  TIMEOUT 10
  '' CLIENT\c

**Windows PPP client

------------------**

If you use Windows, also can connect to the network. The first step is download a null modem driver (e.g. MDMCBXNT.INF) and install it.

Now only is necessary create a new phone connection with the "NT Direct Connection" modem on 115200 bauds.