What are two features of IPv4 addresses choose two?

Table of Contents Show

Network Part
Subnet Number (Optional)
Class A Network Numbers
Class B Network Numbers
Class C Network Numbers
IPv4 Address Format
Network Part
IPv4 Address Allocation
Types of IPv4 Addresses

System Administration Guide: IP Services

Each network that runs TCP/IP must have a unique network number. Every machine on the network must have a unique IP address. You must understand how IP addresses are constructed before you register your network and obtain its network number. This section describes IPv4 addresses. For information on IPv6 addresses, see IPv6 Addressing.

The IPv4 address is a 32-bit number that uniquely identifies a network interface on a machine. An IPv4 address is typically written in decimal digits, formatted as four 8-bit fields that are separated by periods. Each 8-bit field represents a byte of the IPv4 address. This form of representing the bytes of an IPv4 address is often referred to as the dotted-decimal format.

The bytes of the IPv4 address are further classified into two parts: the network part and the host part. The following figure shows the component parts of a typical IPv4 address, 129.144.50.56.

Figure 5–3 Parts of an IPv4 Address

Network Part

The network part specifies the unique number that is assigned to your network. The network part also identifies the class of network that is assigned. In Figure 5–3, the network part occupies two bytes of the IPv4 address.

Host Part

This is the part of the IPv4 address that you assign to each host. The host part uniquely identifies this machine on your network. Note that for each host on your network, the network part of the address is the same, but the host part must be different.

Subnet Number (Optional)

Local networks with large numbers of hosts are sometimes divided into subnets. If you choose to divide your network into subnets, you need to assign a subnet number for the subnet. You can maximize the efficiency of the IPv4 address space by using some of the bits from the host number part of the IPv4 address as a network identifier. When used as a network identifier, the specified part of the address becomes the subnet number. You create a subnet number by using a netmask, which is a bitmask that selects the network and subnet parts of an IPv4 address. Refer to Creating the Network Mask for IPv4 Addresses for details.

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System Administration Guide: IP Services

The first step in planning for IPv4 addressing on your network is to determine which network class is appropriate for your network. After you have completed this step, you can move to the crucial second step: obtain the network number from the InterNIC addressing authority.

Currently there are three classes of TCP/IP networks. Each class uses the 32-bit IPv4 address space differently, providing more or fewer bits for the network part of the address. These classes are class A, class B, and class C.

Class A Network Numbers

A class A network number uses the first 8 bits of the IPv4 address as its “network part.” The remaining 24 bits compose the host part of the IPv4 address, as the following figure illustrates.

Figure 5–4 Byte Assignment in a Class A Address

The values that are assigned to the first byte of class A network numbers fall within the range 0–127. Consider the IPv4 address 75.4.10.4. The value 75 in the first byte indicates that the host is on a class A network. The remaining bytes, 4.10.4, establish the host address. The InterNIC assigns only the first byte of a class A number. Use of the remaining three bytes is left to the discretion of the owner of the network number. Only 127 class A networks can exist. Each one of these numbers can accommodate a maximum of 16,777,214 hosts.

Class B Network Numbers

A class B network number uses 16 bits for the network number and 16 bits for host numbers. The first byte of a class B network number is in the range 128–191. In the number 129.144.50.56, the first two bytes, 129.144, are assigned by the InterNIC, and compose the network address. The last two bytes, 50.56, compose the host address, and are assigned at the discretion of the owner of the network number. The following figure graphically illustrates a class B address.

Figure 5–5 Byte Assignment in a Class B Address

Class B is typically assigned to organizations with many hosts on their networks.

Class C Network Numbers

Class C network numbers use 24 bits for the network number and 8 bits for host numbers. Class C network numbers are appropriate for networks with few hosts—the maximum being 254. A class C network number occupies the first three bytes of an IPv4 address. Only the fourth byte is assigned at the discretion of the network owners. The following figure graphically represents the bytes in a class C address.

Figure 5–6 Byte Assignment in a Class C Address

The first byte of a class C network number covers the range 192–223. The second and third bytes each cover the range 1– 255. A typical class C address might be 192.5.2.5. The first three bytes, 192.5.2, form the network number. The final byte in this example, 5, is the host number.

IPv4 or Internet Protocol version 4, address is a 32-bit string of numbers separated by periods. It uniquely identifies a network interface in a device. IP is a part of the TCP/IP (Transmission Control Protocol/Internet Protocol) suite, where IP is the principal set of rules for communication on the Internet. An IP address is needed to be allocated on the devices, such as PCs, printers, servers, routers, switches, etc., to be able to communicate with each other in the network and out the Internet.

IPv4 Address Format

IPv4 addresses are expressed as a set of four numbers in decimal format, and each set is separated by a dot. Thus, the term ‘dotted decimal format.’ Each set is called an ‘octet’ because a set is composed of 8 bits. The figure below shows the binary format of each octet in the 192.168.10.100 IP address:

A number in an octet can range from 0 to 255. Therefore, the full IPv4 address space goes from 0.0.0.0 to 255.255.255.255. The IPv4 address has two parts, the network part and the host part. A subnet mask is used to identify these parts.

Network Part

The network part of the IPv4 address is on the left-hand side of the IP address. It specifies the particular network to where the IPv4 address belongs. The network portion of the address also identifies the IP address class of the IPv4 address.

For example, we have the IPv4 address 192.168.10.100 and a /24 subnet mask. /24 simply means that the first 24 bits, starting from the left side, is the network portion of the IPv4 address. The 8 remaining bits of the 32 bits will be the host portion.

Host Part

The host portion of the IPv4 address uniquely identifies the device or the interface on your network. Hosts that have the same network portion can communicate with one another directly, without the need for the traffic to be routed.

IPv4 Address Allocation

The Internet Protocol address can be allocated to hosts or interfaces either manually or dynamically.

Static – static IP address is set manually on the device. It is best practice to set static IP addresses on network devices, such as routers and switches, and on servers as well.
Dynamic – dynamic IP address can be automatically allocated to a device via Dynamic Host Configuration Protocol (DHCP). Dynamic IP addresses are best to be used on end devices, such as PCs.

Types of IPv4 Addresses

We have two types of IP addresses, namely public IP addresses and private IP addresses.

Public IP address – used to route Internet traffic. This is used on the Internet and is given out by Internet Service Providers (ISPs) to their customers.
Private IP address – used in private networks for internal traffics within the LAN. Private addresses are not routable out the Internet.

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