IP addresses are a piece of networking knowledge that anyone working in the communications industry simply has to understand. When we run into network faults — a router that will not connect, switches that cannot communicate, and so on — a basic understanding of IP addresses is usually enough to solve these everyday problems. Let’s take a look together with the Fangyuan editor.

• Introduction

In everyday life, every electronic device we use to get online has an IP address, just as every person has a name. IP addresses are divided into IPV4 and IPV6; when we speak of an IP address, we mean an IPV4 address. IPV4 (Internet Protocol Version 4) is version 4 of the Internet protocol. Before V4 there were IPV1, IPV2 and IPV3, and there are likewise IPV5 and IPV6; IPV5 died out during the experimental stage, and IPV6 is what will replace IPV4. (For example, IPV4 addresses: 192.168.1.1, 114.114.114.114; IPV6 addresses: 2001::1.)

Note: the IP discussed below refers to IPV4 addresses. 1. IP is the name of an electronic device. The three giants of the Internet use IP to connect device to device and person to person.

• What is an IP address?

The IP addresses we commonly see are decimal. The decimal system we learned in primary school, in which ten ones make a ten, is exactly that. But what is an IP address really? An IP address is made up of binary digits, converted to decimal to make it easier for people to remember. A digression: why do people use decimal while machines use binary? As children we counted on our fingers, and when our fingers were not enough we marked the count with something else. Since a person has only ten fingers, this produced the decimal system. Machines, by contrast, use circuits that are ‘on’ or ‘off’, which map exactly onto 0 or 1, and this formed the binary system. 1. How decimal is calculated: (1010)10 = 1×103 + 0×102 + 1×101 + 0×100. 2. How binary is calculated: (1010)2 = 1×23 + 0×22 + 1×21 + 0×20. 3. Converting binary to decimal: an IP address consists of 32 binary bits, and converting it to decimal makes it easier to remember. 4. The composition of an IP address: an IP address has two parts, the network part and the host part. For example, if the network parts are the same, the devices are on the same subnet (the host parts may differ). What does the same subnet (the same broadcast domain) mean? It is like people in the same room: they can communicate basically by shouting, which is what we call broadcasting. Different subnets are like people in different rooms — under normal circumstances they cannot communicate with each other.

• Converting number bases with the calculator

Open the calculator (type calc in search): Calculator → View → Scientific. Select Decimal, enter 255 and click Binary, and the decimal value is now converted to binary. Converting binary to decimal works the same way.

• Types of IP address

IP addresses are divided into classes A, B, C, D and E. Classes A, B and C: the types of IP address we commonly use in daily life. Class D: multicast addresses; a few of the commonly used ones are covered in routing protocols, and user multicast addresses are studied in CCIE. Class E: reserved for Internet experiments and development only.

Note: Class A begins with 0 in the first bit, Class B begins with 10 in the first two bits (the remaining bits are arbitrary); Class C begins with 110 in the first three bits (the remaining bits are arbitrary); Class D begins with 1110 in the first four bits (the remaining bits are arbitrary); Class E begins with 11110 in the first five bits (the remaining bits are arbitrary), among which addresses starting with 127 and 0 are special addresses. 1. The composition of Class A, B and C IP addresses: network part (NETWORK) and host part (HOST). 2. The range and role of IP addresses: the mind map is as follows: 3. Special addresses within IP addresses. 4. Public and private addresses.