Before we describe a gateway machine, it may make sense to ask ourselves (or our customers) what such a system is expected to do.
First, they want email. They want their users to be able to receve email addressed to 'user@xyz.com' and to be able to exchange email internally. At first, they will say that mailing lists are not important (this sucks you in to the project), but later it becomes vitally important. At first, they will say that it is not important to be able to send email to multiple local recipents, but that also will become important.
But the ISP probably wants to dump all of the mail into one mailbox, for you to get mail using a variation of the POP protocol. If you are lucky, your ISP will allow the mail to collect in thier spool area, for you to retreve using SMTP when you are connected. Some ISP's will allow UUCP access to your mail. SMPT and UUCP access is good, because you get all of the email address information, especially the 'envelope' addresses. Unfortunatly, the most common protocol, POP, does not keep the envlope addresses, so you may not be able to determine who the mail was really intended for.
The second request, these days, is access to the web. Employees have convinced the bosses that they can't get their job done without easy access to the web - and they don't want to do anything special to get connected.
There will finally be a need for file transfers. Someone will want to run ftp, at least to get the latest copy of the Netscape browser.
Oh - did I mention that there is a mixture of systems, and OS's on the local network. There will be commercial unices, there will be conventional PC systemss, and there will be a need for them to all access the Internet, and to share files and printers.
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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.