Chapter 1. Introduction

This chapter provides an overview of some of the basic features and terminology of the Internet, and introduces various issues discussed in greater detail throughout this document.

The Internet Today

The Internet is a vast, connected network of heterogeneous computer resources, spanning the globe and growing daily. Increasingly, individuals and organizations are finding access to the Internet to be of importance for a wide variety of services pertinent to their businesses and other interests, including electronic mail, access to vast information archives, and keeping abreast of current developments in a host of areas.

Undoubtedly the most recent spur to the growth of interest in Internet access is the development of the World Wide Web, which provides for both a “friendly” graphical interface to Internet resources and a standardized means of presenting and accessing them. Products designed for this market, such as WebFORCE, allow their users to establish an Internet presence that can be seen and accessed around the world.

Network Security and Firewalls

This document addresses an important aspect of this internetworked accessibility: the need to establish and maintain the security of local computers and computer networks. Specifically, computer sites have a need and a right to determine the privacy and safety of their data from competitive interests as well as outright software vandalism. The Internet presents ways to share data that you want to share, but you must take measures to protect data that you want protected.

Network Security Issues

If you are connecting to the Internet, you should configure your connection so that you do not unwittingly risk the exposure or corruption of important data. You should know exactly which (if any) data you are making publicly accessible, and you should guard against the possibility of unwanted intruders gaining access to your site. The Internet has many known (and some famous) instances of unwanted intrusions, vandalism, and so on, and acknowledging and acting on such possibilities is the best way to ensure that your Internet presence is a pleasurable and profitable one.

While it is beyond the scope of this document to detail particular instances of malicious or criminal activity on computer networks, a great deal of such information is available on the Internet itself, and makes for useful reading for those responsible for computer security (refer to Chapter 3 for pointers to additional information).

In general, you need to establish a line of defense between your trusted computer resources (your internal network) and the computer resources publicly accessible through the Internet (the external network). This line of defense should shield you from direct, external accesses, and it may be as simple as a single router[1] or computer host or as complex as multiple routers and an entire computer network. Behind this line, you choose the degree to which you want to allow internal, trusted users access to the Internet, and the degree to which external users can access internal resources.

What Is a Firewall?

The line between the external world of untrusted hosts and the internal world of trusted hosts is established by creating a firewall. A firewall is a combination of computer hardware and software that allows you to restrict interactions with the Internet to the degree you desire. The simple formula is the more access you allow, the greater the security concerns; the greater the restrictions you place on access, the easier it is to monitor and maintain security. The trade off is really one of ease of use vs. peace of mind. For system and network administrators, this often translates as balancing the wishes of users with the needs and capacities of the administrator(s). The balance achieved must be determined individually for each site. Silicon Graphics can only present the issues here and point to other resources for additional information and services to help you establish your policies.

An example of a simple firewall is shown in Figure 1-1. In this illustration, a single computer host such as an Indy is configured with two network interfaces to become what is known as a dual-homed host—a host with a presence on each of two different networks. When it is configured as described in this document, it represents a single, controlled obstruction between your internal network and the Internet where you can focus your security efforts. In this document, the term firewall host refers to an IRIX host configured for network security.

Figure 1-1. A Simple Firewall Environment


The firewall does not in any way restrict interactions on your internal network. Local hosts may share resources in the same way they did before connecting to the firewall. What is different is that now, to the extent determined by your site policy, these hosts may interact with external sites as well. Chapter 2 presents some scenarios of how you might configure a network with a dual-homed host.

Firewall Design Philosophy

The key to administering network security is the firewall. While there are important issues concerning internal security, those issues are the same regardless of whether or not you are connected to the Internet (for references on UNIX system security, refer to Chapter 3, “Additional Resources”).

Regarding the firewall itself, you should:

  • limit users—if possible, limit users to the sole administrator of the system. If additional users are necessary, refer to Chapter 2, “Controlling Internet Access With a Firewall,” for a discussion of issues regarding password protection and educating users.

  • limit services—the more services you allow, the more possible security holes you present. In addition and in general, the more complex the software providing these services the more chance for compromise, and the newer the software, the less chance it has been well tested in the “real world.”

  • monitor the system—this document helps you configure the IRIX software of your firewall to maintain log files that can provide information on accesses to your firewall host, including time of access and unsuccessful access attempts. Also, make use of the many standard UNIX tools such as w(1), ps(1), and so on that give you snapshots of current system activities.

World Wide Web Issues

There is the same security issue inherent in accessing software on the World Wide Web that has always been an issue when acquiring software from any unknown or untrusted source. When a user clicks on a browser button for a network resource, what is invoked is unknown. A click, for example, could download an executable PostScript file with a potential for damage. Users should be aware of this issue If this is a serious concern at your site, you may consider isolating and limiting those hosts with World Wide Web access.

If you are setting up the Netsite server for your World Wide Web site, refer to Appendix B of the Netsite Communications Server Administrator's Guide, particularly the sections on “HTTP User Access Control” and “Make Your Server Safe”.

Refer to “Internet Resources” for a pointer (URL) to additional information on security issues related to the World Wide Web.



[1] This document is concerned with establishing the secure firewalls possible with a computer host or network, not with the limited firewall protection of a router-only configuration.