TCP/IP Definitions

Part of the TCP/IP For Dummies Cheat Sheet

Knowing your way around TCP/IP is key if you want to manage a network successfully. The definitions in the following list explain the basics, such as what an IP address is, and they also clarify the various nets you deal with — extranets, intranet, and subnetting — as well other key terms.

  • CIDR (Classless InterDomain Routing): A way to conserve on IP addresses. An IP addressing design that replaces the traditional Class A, B, C structure, CIDR allows one IP address to represent many IP addresses. A CIDR address looks like a regular IP address with a “suffix” on the end, such as 192.200.0.0/12. The suffix is an IP prefix.

  • extranet: A private/public hybrid network that uses TCP/IP to share part of an intranet with an outside organization. An extranet is the part of an intranet that outsiders can access over the Internet. Be sure to have good security practices if you have an extranet.

  • intranet: An organization’s private network. If your intranet is built on TCP/IP protocols, applications, and services, it’s also an Internet.

  • IP address: The 32-bit (IPv4) or 128-bit (IPv6) numeric address for a computer. You must have an IP address to be connected to the Internet. An IP address consists of two parts: the network piece and the host piece. An IPv4 example: 127.0.0.1; an IPv6 example: 0:0:0:0:0:0:0:1 (::1 for short).

  • loopback address: IP shorthand for you — actually, your computer. The loopback is a special IP address (127.0.0.1) that isn’t physically connected to any network hardware. You use it to test TCP/IP services and applications without worrying about hardware problems.

  • Network Address Translation (NAT): Helps the Internet not run out of IP addresses by translating an IP address (perhaps not unique) on one network to another IP address on a different network — usually, the Internet. IPv6 does away with the need for NAT address help, but NAT, unintentionally, also provides firewall security.

  • subnetting: Dividing one large Internet into smaller networks (subnets) in which they all share the same network portion of an IP address.

  • TCP/IP (Transmission Control Protocol/Internet Protocol): The guts and the rules of the Internet and World Wide Web. A set of protocols, services, and applications for linking computers of all kinds.

  • Virtual private network (VPN): A private network that runs over the public Internet. You can build a VPN at low cost by using the Internet (rather than your own system of private — and expensive — lines) with special security checks and a tunneling protocol. Companies are beginning to use a private virtual network for both extranets and wide-area intranets.

  • Voice over Internet Protocol (VoIP): Are you spending too much on phone calls? Get rid of your phone service. You can make phone calls from anywhere to anywhere that has a computer, free VoIP software, and a fast Internet connection. Even better, it’s free. You can call from Buenos Aires to Nairobi for free with VoIP. It doesn’t have to be computer to computer, either. You can also use VoIP to call a regular telephone number.

Are you acronym challenged? If you don’t know what a particular acronym means, visit WhatIs? where you can find thousands of definitions for Internet and security acronyms.

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TCP/IP For Dummies Cheat Sheet

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