Configuring and Debugging SLIP and PPP Connections


There is amazingly little information available about how to setup and run a SLIP or PPP connection, especially for SGI systems. This WWW tree is my attempt to rectify that lack.

This WWW tree provides general information on how to setup and run a dialup IP connection on an SGI workstation. There is also information on how to select and configure a modem, and how to get or build a modem cable. There are also tips on how to track down a problem.


Supporting SGI's customers is not part of my job description, but we are encouraged to do what we can if it doesn't impact our normal work. I used to support SGI employees SLIP and PPP needs, I am also providing the information to the net at large. If you need additional help, I will provide it as my time permits. Please send me email (address at the bottom of the page) about any errors that you find in this document. Make sure that you are sending me a valid email address (not all are), there's not much I can do if you don't...

I realize that there is a lot of information in these pages, and it appears intimidating at first glance. Dialup IP is a complex problem, and it usually takes many years to learn the kind of information I've made available here. I try to improve the pages when the questions I get imply that they are confusing. However, questions from the net are starting to take too much of my time, and if I don't see some evidence in your question that you've read this info, I may not help.

PLEASE! I don't have any experience (that I'm going to admit to, anyway) on anything except SGI systems (and it isn't Microsloth!), so please restrict your questions to IRIX related issues! Because of my time constraints, I've had to make a new policy of ignoring unrelated questions and invalid email addresses. Thank you.

NOTE: I have changed jobs within SGI. I no longer have anything to do with supporting PPP, or modems, or ... These pages are likely to have little future updating, and I will have even less time to answer your questions. Please be patient and understanding...

Configuring SLIP and PPP

There are several steps to configure SLIP or PPP on an SGI (aka IRIS) workstation. Each major section is it's own page:

I don't (yet) have any first-hand experience with any version of IRIX past 6.2, since they are hardware specific, and I don't have any of the new hardware... This is really only a problem with the O2. Fortunately, few things really changed (mostly serial port speed, and the addition of a mostly-correct PPP GUI), so the pages are still applicable, if somewhat incomplete.

When Things go Wrong: Debugging SLIP and PPP problems

IP over serial lines is a complex problem, and there are a lot of independent pieces involved: the computer, the phone lines, the modem & cable, the (PPP or SLIP) software at each end, not to mention TCP/IP itself! It's amazing that things work as well as they do. But when it doesn't work, you have to try to figure out what happened. The following pages are a rather serious stab at walking you through the troubleshooting process:

If you have trouble accessing these web pages, here is a link to an older (though not yet completely obsolete) straight ASCII SLIP and PPP configuration document.

I hope and intend that this documentation can help you with your PPP connection problems. My other commitments (like work) permitting, I will attempt to help you on issues not covered, or that you are unclear on. Please make sure that you provide me a valid return email address! (I won't try to fix it).

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These pages started life as edited versions of the ones I wrote to support SLIP and PPP inside SGI. Since I don't do that any more...

Scott Henry <>

Last modified: Sun Feb 1 13:22:18 1998