Linux Means Business: A Case Study of Pakistan On-Line

Linux is being used by an ISP in Pakistan—Mr. Rehman tells us why.

Pakistan On-Line (POL),, is an Internet Service Provider (ISP) operating in major cities of Pakistan. All of its Points of Presence (POPs) are operating on Slackware Linux, with some minor setup variations on each site. The ISP's local backbone uses fiber optic cable from a local telecom company, Pakistan Telecommunication Company Limited. Cisco routers are used at each POP to manage this backbone. POL has multiple links to the Internet and uses routing algorithms to manage traffic.

Other than Internet access services, the company also provides services for network design, installation, web development and hosting, domain name registration, etc. For remote-access services, POL uses Cisco and Xyplex access services at major POPs and Linux with Rocketport cards at smaller sites. Linux is used on HP Netservers and Compaq machines to provide Internet services like SMTP, POP, DNS, WWW, FTP, Proxy, etc. User authentication is done through a RADIUS server running on a Linux machine. User accounting and billing are done through RADIUS for Cisco remote access servers and Syslogd where Xyplex remote access servers are used. The accounting and billing process is also carried out on Linux through custom software developed in C.

Why Linux?

Choosing a network operating system for Internet operations is a very important decision. You need to be certain about the stability of your entire system, as the setup has to serve so many clients around the clock. Nobody can afford a service outage, even for a few minutes. Since we planned to use Intel-based servers, we had to choose between a Windows NT server and Linux. The most important factor was not the cost of the operating system, but the stability of the ISP facility. Our criteria for selecting an operating system depended on the following factors.

Previous experience: we had a very good experience with Linux, as we had already built large Linux-based networks. Some of these are being utililized in a similar environment, and some in educational institutions.

Stability: Linux was well-tested for stability by our staff in operations of different nature for many years. We were quite confident that it would not give us any problems in our operations.

Cost: although the cost of the operating system itself is not a major factor, when you add the other utilities and software required for an ISP, it is something to be considered. Not only is Linux free of cost, but you can also find all the required software for an ISP entirely free on the Internet. This includes mail servers, web servers, FTP and DNS servers that come bundled with Linux, making it a complete Internet solution. Additionally, if any of the available software does not serve a particular purpose, you can easily try one of the many available alternatives. For example, if you feel Sendmail is too complex to administer and have a mixture of UUCP and SMTP services, you can use Smail instead, which is quite easy to administer and a very useful UUCP-to-SMTP gateway.


Ease of administration, customization and support on the Internet is another major issue. If you want support for commercial software, you have to pay someone on a regular basis. Linux is perhaps the only product for which you can get on-line help around the clock from so many experts all over the world without spending a single penny. It is quite fun to go to an IRC channel and join the discussion.

Tools Available with Linux

Although commercial operating system vendors are trying to bundle everything with their products, it is simply impossible for any of these to provide a number of utilities comparable to those available on Linux. People have built many tools and utilities for ISP operations in particular. For example, you can find many tools for analyzing web traffic logs, monitor the utilization of your Internet bandwidth, manage user accounts, check security holes, etc.

Linux Mail Servers

There is simply no match for the mail servers available on Linux. Using Sendmail, qmail or Smail, you can do anything you wish. If you want to go for ease of use in a mixed UUCP and SMTP environment, use Smail 3.2. If you want a complete, thoroughly tested, comprehensive solution, use Sendmail. If you just want to give support for SMTP, IMAP, virtual domains, etc., use qmail and so on. You are free to make your choices depending upon your environment.