You need a good understanding of TCP/IP to be able to follow the details of the discussions of packet filtering in this book. If you are not already familiar with TCP/IP , we strongly recommend that you read at least this appendix. This appendix is adapted from Chapters 1 and 2 of TCP/IP Network Administration by Craig Hunt (O'Reilly & Associates, 1992). See that book for complete information about administering TCP/IP -based services.
The name TCP/IP refers to an entire suite of data communications protocols. The suite gets its name from two of the protocols that belong to it: the Transmission Control Protocol and the Internet Protocol. Although there are many other protocols in the suite, TCP and IP are certainly two of the most important.
The popularity of the TCP/IP protocols on the Internet did not grow rapidly just because the protocols were there, or because military agencies mandated their use. They met an important need (worldwide data communication) at the right time, and they had several important features that allowed them to meet this need. These are:
The open nature of TCP/IP protocols requires publicly available standards documents. All protocols in the TCP/IP protocol suite are defined in one of three Internet standards publications. A number of the protocols have been adopted as Military Standards ( MIL STD ). Others were published as Internet Engineering Notes ( IEN ) - though the IEN form of publication has now been abandoned. But most information about TCP/IP protocols is published as Requests for Comments ( RFC ). RFC s contain the latest versions of the specifications of all standard TCP/IP protocols. As the name "Request for Comments" implies, the style and content of these documents is much less rigid than most standards documents. RFC s contain a wide range of interesting and useful information, and are not limited to the formal specification of data communications protocols.
As a network system administrator, you will no doubt read many of the RFC s yourself. Some contain practical advice and guidance that is simple to understand. Other RFC s contain protocol implementation specifications defined in terminology that is unique to data communications.