Chapter 4 Objectives Upon completion you will be able to: Classful Internet Addressing Understand IPv4 addresses and classes Identify the class of an IP address Find the network address given an IP address Understand masks and how to use them Understand subnets and supernets

Introduction of IP The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet is called the Internet address or IP address. An IP address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet. IP addresses are unique. They are unique in the sense that each address defines one, and only one, connection to the Internet. Two devices on the Internet can never have the same address. The topics discussed in this section include: Address Space Notation

An IP address is a 32-bit address. Note:

The IP addresses are unique. Note:

The address space of IPv4 is 2 32 or 4,294,967,296. Note:

Dotted-decimal notation

The binary, decimal, and hexadecimal number systems are reviewed in Appendix B. Note:

Change the following IP addresses from binary notation to dotted-decimal notation. a b c d Example 1 Solution We replace each group of 8 bits with its equivalent decimal number (see Appendix B) and add dots for separation: a b c d

Change the following IP addresses from dotted-decimal notation to binary notation. a b c d Example 2 Solution We replace each decimal number with its binary equivalent: a b c d

Classful Addressing IP addresses, when started a few decades ago, used the concept of classes. This architecture is called classful addressing. In the mid-1990s, a new architecture, called classless addressing, was introduced and will eventually supersede the original architecture. However, part of the Internet is still using classful addressing, but the migration is very fast. The topics discussed in this section include: Recognizing Classes Netid and Hostid Classes and Blocks Network Addresses Mask

Occupation of the address space

Finding the class in binary notation

Finding the class in decimal notation

Netid and hostid

Millions of class A addresses are wasted. Note:

Blocks in class A

Blocks in class B

Many class B addresses are wasted. Note:

Blocks in class C

The number of addresses in class C is smaller than the needs of most organizations. Note:

Class D addresses are used for multicasting; there is only one block in this class. Note:

Class E addresses are reserved for future purposes; most of the block is wasted. Note:

Subnetting A single network address to span multiple physical network is called subnet addressing or subnetting. Subnetting an IP network can be done for various reasons including: –Use of different physical media –Preservation of address space –Security –Control network traffic

IP addresses are designed with two levels of hierarchy. Note:

A network with two levels of hierarchy (not subnetted)

A network with three levels of hierarchy (subnetted)

Addresses in a network with and without subnetting

Hierarchy concept in a telephone number

Default mask and subnet mask

What is the subnetwork address if the destination address is and the subnet mask is ? Example 15 Solution We apply the AND operation on the address and the subnet mask. Address ➡ Subnet Mask ➡ Subnetwork Address ➡

Figure 4.25 Comparison of a default mask and a subnet mask

Supernetting In Supernetting an organization can combine several class C blocks to create a large range of address. By doing this, an organization can apply for a set of class C blocks instead of just one. –For example, an organization that needs 1000 address can be granted four class c blocks.

Assigning Address We have two choices We can choose the blocks Randomly, Based on set of Rules.

the blocks randomly, the routers outside of the organization If we choose treat each block separately. They think each block belong to a different site. In this way each router will have N entries in its routing table where N is the number of blocks. This strategy may increase the size of the routing table tremendously. Assigning Address (Randomly)

The other choice is to make a superblock out of the blocks so that each router has only one entry in a routing table. To do so, we need to follow a set of rules when we assign the blocks. The number of blocks must be power of 2(1,2,4,8..). The blocks must be contiguous in the address space. If the number of blocks is N, the third bye must be divisible by N. Assigning Address (based on rules)

Figure 4.26 A supernetwork

In subnetting, we need the first address of the subnet and the subnet mask to define the range of addresses. In supernetting, we need the first address of the supernet and the supernet mask to define the range of addresses. Note:

Figure 4.27 Comparison of subnet, default, and supernet masks

The idea of subnetting and supernetting of classful addresses is almost obsolete. Note:

Figure 4.10 Masking concept

Figure 4.11 AND operation

Table 4.2 Default masks

Note that we must not apply the default mask of one class to an address belonging to another class. Note:

Special Purpose of IP Addresses The topics discussed in this section include:  Network broadcast  Directed broadcast  Limited broadcast  Loopback address

Table 4.3 Special addresses

Figure 4.13 Network address

Directed Broadcast Address According to the standard any address with the host id consisting of all 1s is reserved for directed broadcast When the packet is sent to such an address a single copy of the packet is transferred across the internet from the source. Routers along the path use the netid portion of the address when choosing a path,they do not look at the host portion.

Figure 4.14 Example of direct broadcast address

Disadvantage of Directed Broadcast Address The chief disadvantage of directed broadcast is that it requires knowledge of the network address.

Limited or local network broadcast address All 1s for the netid and hostid(32-bits) defines a broadcast address in the current network. A host that want to send a message to every other host can use this address as a destination address in an IP packet. A router will block a packet having this type of address to confine(limited) the broadcasting to the local network.

Figure 4.15 Example of limited broadcast address

Loopback Address The IP address with the first byte equal to 127 is used for the loopback address. Which is an address used to test the software on a machine. When this address is used,a packet never leaves a machine ; it simply returns to the protocol software. It can be used to test IP software. –For example, an application such as “ping” can send a packet with a loopback address as the destination address to see if the IP software is capable of receiving and processing a packet.

Figure 4.18 Example of loopback address

Weaknesses in Internet Addressing Most obvious disadvantage is that address refer to network connection not to the host computer. If a host computer moves from one network to another, its IP address must change. Changing network address can be incredibly time consuming and difficult to debug.

The topics subnetting and supernetting are not included in this chapter in your textbook. you must refer your textbook also. Note: