What is a protocol?

A protocol is a well-defined specification that allows computers to communicate across a network. In a way, protocols define the "grammar" that computers can use to "talk" to each other.

What is IP?

IP stands for "Internet Protocol". It can be thought of as the common language of computers on the Internet. There are a number of detailed descriptions of IP given elsewhere, so we won't cover it in detail in this document. However, it is important to know a few things about IP in order to understand how to secure your computer. Here we'll cover IP addresses, static vs. dynamic addressing, NAT, and TCP and UDP Ports.

What is an IP address?

IP addresses are analogous to telephone numbers - when you want to call someone on the telephone, you must first know their telephone number. Similarly, when a computer on the Internet needs to send data to another computer, it must first know its IP address. IP addresses are typically shown as four numbers separated by decimal points, or "dots". For example, 10.24.254.3 and 192.168.62.231 are IP addresses.

If you need to make a telephone call but you only know the person's name, you can look them up in the telephone directory (or call directory services) to get their telephone number. On the Internet, that directory is called the Domain Name System or DNS for short. If you know the name of a server, say www.broadband-service-uk.com, and you type this into your web browser, your computer will then go ask its DNS server what the numeric IP address is that is associated with that name.

Every computer on the Internet has an IP address associated with it that uniquely identifies it.

However, that address may change over time, especially if the computer is: dialling into an Internet Service Provider (ISP), connected behind a network firewall, connected to a broadband service using dynamic IP addressing.

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