This appendix includes two sections. The first section contains an abbreviated introduction to networking, with the emphasis on security issues. The second section provides a quick review of the basic math that is used in various parts of this book.

A-1 Network Security Basics

There are three kinds of death in this world. There’s heart death, there’s brain death, and there’s being off the network.

—Guy Almes

A-1.1 Introduction

In this section, we give a condensed introduction to networking, presented through the prism of security. Networking is a large and complex topic. Here, we’ll cover the minimal amount of information that is required elsewhere in this textbook, and we’ll also add a few passing comments on network-specific security issues that are of independent interest.

A network consists of hosts and routers. The term host is a catchall for a wide variety of network-connected devices, including laptops, desktop computers, servers, cell phones, PDAs, etc. The purpose of the network is to transfer data between the hosts. Ideally, we’d like the network to be transparent to users. We’re primarily concerned with the mother of all networks, the Internet.1

A network has an edge and a core. The hosts mentioned above live at the edge, while the core consists of an interconnected mesh of routers. The purpose of the core is to route data through the network from host to host. A generic network diagram appears in Figure A-1.

Figure A-1: Network

The Internet is a packet ...

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