Connecting to the Internet through a Windows computer and a PPP connection
This guide shows how to connect a DOS computer to the Internet with a Windows computer serving as a gateway. This is useful if you have a DOS computer with no Ethernet card or no DOS driver for it, or the DOS computer is physically impossible or difficult to connect to an Ethernet socket, and you have a Windows computer nearby with e. g. a wireless Internet connection.
You will need a RS-232 ("null modem") cable and a Windows computer that is connected to the Internet. The guide assumes Windows XP, but will probably apply to newer versions as well.
Follow this guide until (and including) step 3. It is meant for a TiVo, but that is not important.
In Incoming TCP/IP properties, choose "Specify TCP/IP addresses" and specify a range. You should choose the smallest range possible as Windows will apparently assign the DOS computer a different address each time, which will make configuration of DOS Internet applications harder because you will have to edit configuration files each time. For example, I use the range x.x.x.120 to x.x.x.121 and Windows always assigns the latter. This step might not be necessary, but my attempts to connect failed until I did this.
Run EPPPD.EXE on the DOS computer. Assuming you are using the COM1 port at 115200 baud, run EPPPD com1 115200 local. The Windows computer should respond.
You can now start using your DOS Internet applications. The Arachne Web browser is a good one to start with, as is the mTCP set of applications. For Arachne, run SETUP.BAT and when you get to the TCP/IP setup, choose "Packet Wizard", then "Detect packet driver". It should be detected and you can then configure TCP/IP (DNS server, gateway, etc.).
Now, with the "Incoming Connections" connection configured, the serial port you are using for the connection on the Windows computer will not be available for other applications. To free it, go to the connection's properties in Network Connections and uncheck the serial cable's checkbox. To allow the DOS computer to connect, check it again.