Linux Firewalls, Third Edition

The IP

The Internet Protocol is the basis on which the Internet operates. Together with protocols at other layers, the IP layer provides communications for countless applications. IP is a connectionless protocol providing layer 3 routing functions.

IP Addressing and Subnetting

As you already know, but I feel compelled to write, IP addresses for version 4 of IP consist of four 32-bit numbers separated by periods, known as the “dotted quad” or “dotted decimal” notation. Although seemingly everyone understands or at least has seen an IP address, it certainly seems as though fewer and fewer understand subnetting and the subnet masks that are an important part of the IP addressing scheme. This section briefly looks at IP addressing and subnetting. ...