To solve the email problem, we must first get the mail into the POP mailbox on the ISP's server, then get the mail to the local system, and finally, deliver it to the correct user.
We don't have to let the ISP simply deposit email into our POP mailbox. We have tools like procmail available to us, which allows us to filter for spam, redirect messages for specific users to other addresses, or othrwise process the mail as it arrives.
We can fetch the mail from the ISP using a tool such as popclient or fetchmail. Fetchmail is probably the preferred tool for this application, as it has the capability of looking at the headers and delivering mail to the local machine's SMTP listener addressed to the appropriate user(s). Of course, there is still the problem of mailing lists (and SPAM) that was sent with the address in a Bcc: field which has been stripped away.
This has two phases. First, we need to hide the local network behind the one IP address provided by the ISP (which may be different each time we connect), and secondly, we need to connect to the Internet 'on demand'.
The first problem is solved with IP Masquerade, a kernel feature that allows the gateway machine to send IP packets on for the local machine, and to insure that the response gets to the correct local machine.
The second problem can be solved with the diald package, which can establish the connection when needed, and can insure that the connection is re-established when the ISP or the phone company break the circuit.
File transfer in the IP Masquerade environment depends on a specific kernel module which can be compiled when you build your kernel. The problem is that there are two data channels between the computers, the control channel, which is established by the client, and the data channel that can be established by either machine.
A very good solution to the OS interoperability problem is provided by the samba package. Using samba, we can allow UNIX computers to print on PC printers, PC's to print on UNIX printers, and UNIX to share files with the PC's.
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Copyright ©, 1997, Ben Spade. Permission is given to copy or link to this document, as long as this notice remains intact.