Computer Network IP Addressing, Terminology And It's Classes

What is IP Address :

An IP address is a numeric identifier assigned to each machine on an IP network. It designates the specific location of the device on the network.

An IP address is a logical address, not a hardware address network interface card (NIC) used for finding hosts on a local network. IP addressing was designed to allow hosts on one network to communicate with a host on a different network regardless of the type of LANs the hosts are participating in.

IP Terminology :

To learn IP Addressing, you need to understand important terms of Internet Protocol. Some as follows

  • Bit A bit is one binary digit, either a 1 or a 0.
  • Byte A byte is 7 or 8 bits.
  • Octet An octet, made up of 8 bits, is just an ordinary 8-bit binary number.
  • Network Address This is the designation used in routing to send packets to a remote.

for example,,, and

IP Address A logical address used to define a single host; however, IP addresses can be used to reference many or all hosts as well. If you see something written as just IP, it is referring to IPv4. IPv6 will always be written as IPv6.

Broadcast Address The broadcast address is used by applications and hosts to send information to all hosts on a network. Examples include, which designates all networks and all hosts;, which specifies all subnets and hosts on network; and, which broadcasts to all subnets and hosts on network

The Hierarchical IP Addressing Scheme :

An IP address consists of 32 bits of information. These bits are divided into four sections, referred to as octets or bytes, and four octets sum up to 32 bits (8 x 4 32). You can depict an IP address using one of three methods :

  • Dotted-decimal, as in
  • Binary, as in 10101100.00010000.00011110.00111000
  • Hexadecimal, as in AC.10.1E.38

The major advantage of this scheme is that it can handle large number of addresses, 4.3 billion (a 32-bit address,232 or 4,294,967,296).

Network Addressing :

The network address—also called the network number—uniquely identifies each network. Every machine on the same network shares that network address as part of its IP address. In the IP address, for example, 172.16 is the network address.

Host Address :

The host address is assigned to, and uniquely identifies, each machine on a network This part of the address must be unique because it identifies a particular machine an individual as opposed to a network, which is a group. So in the sample IP address, the 30.56 is the host address.

The designers of the Internet decided to create classes of networks based on network size. For the small number of networks possessing a very large number of hosts, they created the rank Class A network. At the other extreme is the Class C network, which is reserved for the numerous networks with a small number of hosts. The class distinction for networks between very large and very small is predictably the Class B network.

IPv4 Structure

Class A Addresses:

In a Class A network address, the first byte is assigned to the network address, and the three remaining bytes are used for the host addresses. The Class A format is as follows :

network. host. host. host

In the A class IP address, the 49 is the network address and 22.102.70 is the host address. Every machine on this particular network would begin with distinctive network address of 49.

Class A network addresses are 1 byte long, with The first bit of that byte reserved and the 7 remaining bits available for manipulation, or addressing. As a result, the theoretical maximum number of Class A networks that can be created is 128. Why? Well, each of the 7 bit positions can be either a 0 or a 1 and 27 gives you 128.

Each Class A address has 3 bytes (24 bit positions) for the host address of a machine. This means there are 224—or 16,777,216 unique combinations and, therefore, precisely that many potential unique host addresses for each Class A network. Because host addresses with the two patterns of all 0s and all 1s are reserved, the actual maximum usable number of hosts for a Class A network is 224 minus 2, which equals 16,777,214.

Range for a Class A network

00000000 = 0

01111111 = 127

Here's an example of how to figure out the valid host IDs in a Class A network address :

  • All host bits off are the network address :
  • All host bits on is the broadcast address :

The valid hosts are the numbers in between the network address and the broadcast address : through Notice that 0s and 255s can be valid host IDs.

All you need to remember when trying to find valid host addresses is that the host bits can't ever be all turned off or all turned on at the same time.

Class B Addresses :

In a Class B network address, the first 2 bytes are assigned to the network address and the remaining 2 bytes are used for host addresses. The format is as follows :

network. network. host. host

For example, in the IP address, the network address is 172.16 and the host address is 30.56.

Range for a Class B network

10000000 = 128

10111111 = 192

B class network address being 2 bytes (8 bits each), we're left with 216 unique combinations. But the Internet designers decided that all Class B network addresses should start with the binary digit 1, then 0. This leaves 14 bit positions available to manipulate, so in reality, we get 16,384 (that is, 214) unique Class B network addresses.

As you can see, a Class B network is defined when the first byte is configured from 128 to 191.

Class B address uses 2 bytes for host addresses. This is 216 minus the two reserved patterns (all 0s and all 1s), for a total of 65,534 possible host addresses for each Class B network.

Here's an example of how to find the valid hosts in a Class B network :

  • All host bits turned off is the network address :
  • All host bits turned on is the broadcast address :

The valid hosts would be the numbers in between the network address and the broadcast, address : through

Class C Addresses :

The first 3 bytes of a Class C network address are dedicated to the network portion of the address, with only 1 measly byte remaining for the host address. Here's the format :

network. network. network. host

Using the example IP address, the network address is 192.168.100 and host address is 102.

There are 221, or 2,097,152, possible Class C networks.

Range for a Class C network

11000000 = 192

11011111 = 223

So, if you see an IP address with a range from 192 up to 223, you'll know it's a Class C IP address. Each unique Class C network has 1 byte to use for host addresses. This gets us to 28, or 256, minus the two reserved patterns of all 0s and all 1s for a total of 254 available host addresses for each Class C.

Here's an example of how to find a valid host ID in a Class C network :

  • All host bits turned off is the network ID :
  • All host bits turned on is the broadcast address :

The valid hosts would be the numbers in between the network address and the broadcast address : through

Class D and E Addresses :

Addresses with the first octet of 224 to 255 are reserved for Class D and E networks. Class D (224—239) is used for multicast addresses and Class E (240—255) for scientific purposes. But they're really beyond the scope of this book, so I'm not going to go into detail about them here. But you do need to know that the multicast range is from through

Private IP Addresses :

These addresses can be used on a private network, but they're not routable through the Internet. This is designed for the purpose of creating a measure of much needed security, but it also conveniently saves valuable IP address space.

If every host on every network had to have real routable IP addresses, we would have run out of available IP addresses to hand out years ago. But by using private IP addresses, ISPs, corporations, and home users need only a relatively tiny group of IP addresses to connect their networks to the Internet. This is economical because they can use private IP addresses on their inside networks and get along just fine.

To accomplish this task, the ISP and the corporation the end users, no matter who they are need to use Network Address Translation (NAT), which basically takes a private IP address and converts it for use on the Internet. NAT provides security in that these IP addresses cannot be seen by external users. External users will only be able to see the public IP address to which the private IP address has been mapped. Moreover, multiple devices in the same private network can use the same, real IP address to transmit out onto the Internet.

Address class Reserved address space

Class A 10.0.O.O through

Class B 172.16.O.O through

Class C through


The IP address range for AP IPA is through The client also configures itself with a default Class B subnet mask of, When you're in your corporate network and you're running a DHCP server, and your host displays that it is using this IP address range, this means that either your DHCP client on the host is not working or the DHCP server is down or can't be reached because of a network issue. For example, if you plug a DHCP client into a port that is disabled, the host will receive an APIPA address.

#bookofnetwork #book_of_network #network_book,learn_netwroking #computer_network #network_tutorials #learn_computer_network #networking #ip #IP_Addressing #What_is_IP_Address #IP_Terminology #Class_A_Addresses #Class_B_Addresses #Class_C_Addresses #Class_D_and_E_Addresses #Private_IP_Addresses #APIPA

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