WHAT IS
SLiRP

SLiRP is a free TCP/IP emulator over the (C)SLIP/PPP link-level protocols which allows a normal user with a shell account on a UNIX system to act like a real (C)SLIP/PPP account. This means you can use programs like Netscape, Mosaic, ftp etc. from your home machine with only a shell account.

Computer Services does not support this program and recommends you use your own ISP service to connect to the Internet.

SLiRP is not bug free. We have identified a problem with binary file transfers where the very last byte doesn't get saved to a file. Therefore, consider this VERY unreliable for FTP and software downloads using your web browser.

Specific Examples

Below are links to examples of how to do this with specific programs and platforms. If you get SLiRP running on a platform/program not mentioned here, please help out others and document how it is done and email it to gti@hopi.dtcc.edu.

Technical Information

You MUST exec slirp, don't just run it. You may lose data if you fail to heed this caution. Read below for details.

Setting up a SLIP line, especially with an emulator like SLiRP is not an easy task. Computer Services does not support this product at this time due to the complexity of this product and the differences in all of the SLIP client software packages on the market today. With each package, setup will be different. You may want to read the SLiRP Home Page, the Slirp manual and configuration notes for some pointers. In addition, as we and others encounter different setups, we will document them here. To put it another way, SLiRP is experimental, not supported by Computer Services, and may be withdrawn from the system without notice if problems develop.

When using SLiRP on hopi, please remember the following points:

  • It is not supported by Computer Services (have I said it enough yet!)
  • exec slirp instead of just running slirp. This saves the system about 800K because exec will cause your shell to be removed (which you don't need). More importantly, if SLiRP crashes, your shell will not be around anymore. If the shell remains running and SLiRP crashes, your shell will try and interpret the SLIP data comming down the line and attempt to execute it as shell commands. In rare cases, this could cause data loss in your account or other weird behavior. Be safe, "exec slirp" at all times.
  • You absolutely have to put the terminal server in binary mode for this to work. More on this later.
  • Please do not abuse this service, especially during our peak dialin hours of 17:00-01:00 Sunday through Thursday.
  • Systems operation staff may terminate your SLiRP link if it has been in use for hours and all modems are in use.
  • SLiRP is not a full-featured SLIP/PPP link. Some things don't work.
  • If you want to login to hopi while SLiRP is up, you will need to do so with a "telnet" type terminal program, NOT the program you normally use. You should also telnet to 10.0.2.2 instead of hopi.dtcc.edu. You'll get far better response that way.
  • Remember, your account is non-transferable. You are the only person authorized to access the Internet via Delaware Tech's network, even if you are at home.

Yeah, yeah, yeah, no problem. So what is it then?

SLiRP is a pseudo SLIP/PPP emulator. It is not the real thing. In order for your home computer to work on the Internet, it must have its own IP address. SLiRP works around this by assigning your home computer a fake IP address of 10.0.2.15. Stuff you send to the "net" is translated into the host IP address at Delaware Tech and sent out. Data meant to your PC is routed up to it via SLiRP. To all hosts on the Internet, you will appear to be originating from the host you run SLiRP on, not your PC.

However, this makes it difficult for a connection on the Internet to find your PC. For example, if you run an FTP server on your PC. This is actually a good feature. Improper setup of an FTP server on your home computer opens it up for intruders from the Internet to get into it. (It is possible to do it if you really want to, "man slirp" on hopi for the instructions).

What do I need to use this?

You need SLIP or PPP software for your home computer. Commercial Internet packages come with this software. Personal Netscape Navigator sells for about $39 in most computer stores and has a SLIP dialer included in it as well as an Internet email program and other goodies. This runs under Windows or a Mac.

Set your home computer's IP settings to the following values:

  • IP address: 10.0.2.15
  • Netmask: 255.255.255.0
  • Gateway: 138.123.84.1
  • DNS address: 10.0.2.3 and/or 138.123.84.240

I have SLIP or PPP at home, now what?

This is where it gets ugly. The steps you will take are:

  1. At the dtcc net% prompt enter: stty local ^\
    This allows you to get back to the terminal server with the CTRL-\ key combo. NOTE: If your terminal and/or script supports sending a BREAK key down the line, the above step is not needed.
  2. Log in to your shell account as normal. Some SLIP dialers allow you to login interactively to your shell before kicking SLIP in. This is the best. If not, you'll have to login with your normal telecom program. Make sure your program does not "drop dtr" when it exits. If your telecom program hangs up your modem on exit, get another one.
  3. Put terminal server into binary, non-interruptable, mode.
    1. Press CTRL-\ (aka ^\) (or BREAK key)
    2. At the dtcc net% prompt enter: dli set session passall
    3. At the dtcc net% prompt enter: fg
  4. At the $ prompt, enter: exec slirp (or exec slirp -P if you want to run PPP)
  5. If you logged in via a telecom program, exit it now without logging out and then run your SLIP software to a "direct connect" line. If your SLIP dialer allowed you to login interactively, set it to "Connect" and away you go.

How do you make this thing quit?

Not easily! To quit SLiRP, you need to send 5 zeroes (0) down the line, one second apart. You can't do this if you are telnet'd, since the zeroes will be wrapped in an IP packet. You need to quit all of your network programs, like telnet, web browser, etc, and then rerun your original telecom program. Then press the zero key five times with a second between each press. Pulling the phone line out of the wall will probably also work, but I'm too paranoid to trust it myself!

If you use PPP, you can cause slirp to hang up gracefully by creating a .slirprc file in your home directory and put the line "ppp_exit" in the file. Then just disconnect your session.

UPDATE: Development of slirp may start again.

Go to Delaware Tech Home Page

Last page update: 19 October 1999
Source Document: None
Official URL for this page: http://www.stanton.dtcc.edu/stanton/cs/slirp/
Page Maintained by: George Imburgia
Originally developed by Ken Weavering