MASINDE MULIRO UNIVERSITY OF SCIENCE & TECHNOLOGY

ECE 422- DATA COMMUNICATIONS & COMPUTER NETWORKS

 

INTRODUCTION TO INTERNET PROTOCOL (IP) ADDRESSING

 1.0 INTRODUCTION

Every protocol suite defines some type of addressing that identifies computers and networks. IP addresses are no.exception to this rule. There are certain values that an IP address can take; these have been defined by the IEEE committee.

A simple IP address is a lot more than just a number. It tells us the network of which the workstation is part and the node ID.

When the IANA committee sat down for the first time to sort out the range of numbers that were going to be used by all computers, they came up with five different ranges or, as we call them, "classes" of IP addresses.

When an entity applied for IP addresses they were given a certain range within a specific class depending on the size of their network. The classes were:

Class A: The first bit of the first byte is zero, i.e a router only checks the first bit to determine the class,( i.e 1^st byte = 0xxxxxxx)

Class B: First Bit of the first byte is turned on but the second is turned off , (i.e 1^st byte = 10xxxxxx)

Class C: The First two bits of the first byte are always turned on but the third is never on, (i.e i.e 1^st byte = 110xxxxx)

Class D: The First three  bits of the first byte are always turned on but the fourth is never on, (i.e i.e 1^st byte = 1110xxxx)

Class E: The First four bits of the first byte are always turned on (i.e i.e 1^st byte = 1111xxxxx)

 

The first three classes (A, B and C) were used to identify workstations, routers, switches and other devices, whereas the last two classes (D and E) were reserved for special use.

An IP address consists of 32 Bits, which means it's four Bytes long. The first octet (first eight bits or first byte) of an IP address is enough for us to determine the class to which it belongs. And, depending on the class to which the IP address belongs, we can determine which portion of the IP address is the network ID and which is the node ID. Table 1 shows classes A-E and their capacities and features.

Table 1.1 Classful addressing classes and their capacities and features

	LEADING BITS (DECIMAL-RANGE)	NO.  OF NETWORKS	ADDRESSES PER NETWORK	START ADDRESS	END ADDRESS
CLASS A	0  (0 – 127)	128 (27)	16,777,216(224)	0.0.0.0	127.255.255.255
CLASS B	10  (128 – 191)	16,384(214)	65,536(216)	128.0.0.0	191.255.255.255
CLASS C	110 (192 – 223)	2,097,152 (221)	256(28)	192.0.0.0	223.255.255.255
CLASS D	1110  (224 – 239)	Not defined	Not defined	224.0.0.0	239.255.255.255
CLASS E	1111 (240 – 255)	Not defined	Not Defined	240.0.0.0	255.255.255.255

 

For example, if I told you that the first octet of an IP address is "168," then, using the above table, you would notice that it falls within the 128-191 range, which makes it a class B IP address.

 

1.2 UNDERSTANDING THE CLASSFUL IP ADDRESS SYSTEM

Under the classful system, companies were assigned different IP ranges within these classes, depending on the size of their network. For instance, if a company required 1000 IP addresses, it would probably be assigned a range that falls within a class B network which has a capacity of 65,536 addresses per network  rather than a class A (capacity 16,777,216 ) or C (capacity 256). Class A IP addresses were designed for large networks, class B for medium size networks and class C for smaller networks.

 You  need to understand the network ID and node ID concept because it will help us to fully understand why classes exist. Putting it as simply as possible, an IP address gives us two pieces of valuable information, i.e

(a) It tells us which network the device is part of (network ID).

(b) It identifies that unique device within the network (node ID).

Think of the network ID as the town you live in and the node ID as your street in that suburb. You can tell exactly where someone is if you have their town and street name. In the same way, the network ID tells us to which network a particular computer belongs and the node ID identifies that computer from all the rest that reside in the same network.

Figure 1  gives you a small example to help you understand the concept.

Figure 1.1  A local area network with network address 192.168.0.1  and host addresses 192.168.0.2, 192.168.0.3, 192.168.0.4, 192.168.0.5, 192.168.0.6

 

In figure 1, you can see a small network. We have assigned a class C IP range for this network. Remember that class C IP addresses are for small networks.

 The network class helps us determine how the four byte, or 32 bit, IP address is divided between network and node portions. Figure 1.2  shows you (in binary) how the Network ID and Node ID changes depending on the class.

Figure 1.1 Ranges for Network and Host Addresses in Classful Addressing

1.2.1 CLASS A NETWORK

It has a total of 7 bits for the Network ID (the 1^st bit is always set to 0) and 24 bits for the Host ID. Now all we need to do is calculate how much seven bits is. = 128 networks. For the hosts, = 16,777,216 hosts in each network, of which two cannot be used because one is the Network Address and the other is the network broadcast address (see the table towards the end of this page).

Figure 1.2 shows the composition of the various fields in Class A address system.

 Figure 1.2 The composition of a class A address.

 

1.2.2 CLASS B NETWORK

Class B networks have 14 bits for the network ID (Bits 15, 16 are set and can't be changed) and 16 bits for the host ID, that means you can have up to 2¹⁴ = 16,384 networks and 2¹⁶= 65,536 hosts in each network, of which two cannot be used because one is the network address and the other is the network broadcast address. So if I asked you how many "valid" hosts can you have on class B network, you should answer 65,534 and not 65,536.

 

1.2.3 CLASS C NETWORKS

Class C networks have 21 bits for the network ID (Bits 22, 23, 24 are set and can't be changed) and eight bits for the host ID, that means you can have up = 2,097,152 Networks and = 256 hosts in each network, of which two cannot be used because one is the network address and the other is the network broadcast address. So if I asked you how many "valid" hosts you can have on class C network, you should answer 254 and not 256.

  

1.2.4 RESERVED IP ADDRESSES

Some IP addresses that have been reserved for special use. This doesn't mean you can't assign them to a workstation but in the case that you did, it would create serious problems within your network. For this reason it's best to avoid using these IP addresses.

 

 

 

2.0 IP ADDRESSESING IN HOME & ENTERPRISE NETWORKS

 

3.1 BACKGROUNG

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.

Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses.

 

2. PUBLIC AND PRIVATES ADDRESSING

IP addresses can be either public or private. “Public” means an IP address can be reached from the Internet, while “private” means it can’t. For example, in a typical home network, a router has a public IP address on the Internet. The computers, smartphones, game consoles, and other devices behind the router all have unique private IP addresses on the home network. The router acts as an intermediary, forwarding traffic to the local IP addresses that request it. From an outside perspective, all devices on the home network are communicating with the Internet from a single public IP address.

Assuming you’re behind a router performing network address translation, you have two IP addresses that matter. Your computer’s IP address is likely a private IP address, probably starting with 192.168 — is a range of IP addresses specially allocated to private networks. You also likely have a public IP address, which is used when communicating with other computers over the Internet.

 

 

Figure 2.1. A Home Local Area Network with public and private IP addresses

For example, if you’re hosting a server on your computer, people on the Internet will need the public IP address from your router to connect to your server. People behind your router — on the same local network as your computer — will need the local IP address from your computer to connect.

If your computer is connected directly to the Internet with no router sitting in between, your computer’s IP address is a public IP address.

 

Table 2.1 Comparison between Public IP and Private IP address:

	Public IP Address	Private IP Address
Definition	Used for identification of a home/corporate network to the outside world	Used for identification of a network device inside the home network
Uniqueness	It is unique throughout the entire network	Two or more separate networks can have same private IP addresses assigned to different computers
Example	202.60.23.1	192.168.0.3
Usage	Used on the Internet or other WAN	Used on a Local Area Network; for computers not directly connected to the Internet

 

Manufacturers of routers and other networking equipment assign private IP addresses for their resources. They have a commitment to introducing the best in class networking equipment with the most suitable IP addresses. The most special blocks among a list of reserved blocks in our time are as follows.

 

Router manufacturers make use of the block 192.168.x.x worldwide these days. Every user of any brand of a router has to use its private IP address otherwise known as a default IP address for accessing the configuration panel. You can make use of the private Internet Protocol address 192.168.1.1 to access Linksys router’s configuration panel directly.

Once you have decided to configure your router by using the private IP addresses, you have to identify the default IP address of your router at first. You can type in ipconfig in the command prompt and take note of your router’s IP address.

 

2.3  IANA-RESERVED PRIVATE IPV4 NETWORK RANGES

Three non-overlapping ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Today, when needed, such private networks typically connect to the Internet through network address translation (NAT).

	Start	End	No. of addresses
24-bit block (/8 prefix, 1 × A)	10.0.0.0	10.255.255.255	16777216
20-bit block (/12 prefix, 16 × B)	172.16.0.0	172.31.255.255	1048576
16-bit block (/16 prefix, 256 × C)	192.168.0.0	192.168.255.255	65536

Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255.