© N. Ganesan, All rights reserved.

Chapter

IP Addressing Format

Questions

• How many bits are there in a TCP/IP address?• Name the components of a typical TCP/IP

address?• What is the difference between the old IPv4 and

the new IPv6 addresses?• Explain the difference between network ID and

host ID.• Name the classes of IP addresses. What are the

purpose and function of each class of addressing • Compute the number of networks and hosts that

can be supported in each class of address.

Questions Cont.

• List the restrictions placed on the assignment of addresses.

• Choose a IP class as an example and list the valid range of network and host addresses for that class.

Chapter Modules

• IP Address Format and Components

• Classes of Addresses• Scope of Addresses and

Restrictions

© N. Ganesan, All rights reserved.

Module 1

IP Address Format

Overview

• The IP address format discussed in this presentation applies to IPv4

• An IP address is composed of 32 bits that is viewed as being divided into 4 octets– One octet is made up of 8 bits

IP Address Format

10101111 11001100 10000001 00110011

32 bits divided into 4 octets for convenience

175 204 129 51

Converted into decimals for easy representation and remembrance

An Example in Binary-to-Decimal Conversion

Binary 1 0 0 1

Factor 8 4 2 1

Decimal=Binary * Factor

8 0 0 1 8+1= 9

Binary 1001 = Decimal 9

IP Addressing Components

Network ID Host ID

32 bits

The New IP Address

• The new IP address known as IPv6 has 128 bits– www.whatis.com

IP Component Reference

Internet

Host ID

Host ID

Network ID

End of Module 1

© N. Ganesan, All rights reserved.

Module 2

Classes of IP Addresses

Classes of IP Addresses

• IP addresses have been divided into classes– They are namely Classes A, B C, D and

E• Classes A, B and C are used for

commercial purpose• Class D is used for multicasting • Class E is used for experimental

purpose

Commercial Classes

• Classes A, B and C • Class A is for very large organizations

– Few, if any, are available

• Class B is used in medium size organizations– A few may be still be available

• Class C is used in small organizations– Often further divided and issued to smaller

organizations and individuals

Subnetting

• There is no strict rule as to who may use a certain class of address

• An enterprise such as an ISP can own a large Class B address space and subnet it into smaller spaces for its customers

Class D

• Reserved for IP multicasting• The first four higher-order bits are

set to 1 1 1 0 respectively• Microsoft supports Class D

addresses for multicasting• Multicasting is the process of

delivering media over the Internet at reduced bandwidths

A Note on Multicasting

• Multicasting delivers a single stream of medial to a router and the receiving end

• The router then multiplies and delivers the stream to local clients

• As such, only one stream travels along the Internet thus saving bandwidth

• In the case of Unicasting, multiple streams travel along the Internet to reach each client separately

Unicasting

3 Streams

Multicasting

1 Stream onInternet

3 Streams Locally

Alternative Methods of Delivering Media

• Unicasting– Easy to implement– Higher bandwidth is required for

transmission• Multicasting

– More involved in setting up – Uses bandwidth more efficiently

• Broadcasting

Class E

• Experimental addresses reserved for possible future use

• The first four higher-order bits are set to 1 1 1 1 respectively

End of Module 2

© N. Ganesan, All rights reserved.

Module 3

IP Formats for Commercial Classes

Class A Assignment Format

8 bits 8 bits 8 bits 8 bits

Network ID (8 bits)

Host ID (24 bits)

Number of Class A Networks and Nodes

• The first higher-order bit is always set to 0

• Total number of networks supported is 126 = 27 - 2 – All zeros and all ones are not allowed

• Total number of hosts supported per network is 16,777,214 = 224 - 2– All zeros and all ones are not allowed

Restrictions on Zeros and Ones

• The initial RFC 950 forbade the use of zeros and ones– All zeros prevented some early

routing protocols from operating correctly

– All ones may result in a conflict with a special broadcast address known as the all-subnets directional broadcast address

Easing of Restrictions

• RFC 1812 now eases the restriction and allows the use of zeros and ones in a CIDR-compliant environment

• CIDR– Classless Inter-Domain Routing (CIDR)– Explained under subnets

Class B Assignment Format

8 bits 8 bits 8 bits 8 bits

Network ID (16 bits)

Host ID (16 bits)

Number of Class B Networks and Nodes

• The first two higher-order bits are always set to 1 and 0 respectively

• Total number of networks supported is 16384 = 214 - 2 – All zeros and all ones are not allowed

• Number of hosts supported per network is 65,534 = 216 - 2 – All zeros and all ones are not allowed

Class C Assignment Format

8 bits 8 bits 8 bits 8 bits

Network ID (24 bits)

Host ID (8 bits)

Number of Class C Networks and Nodes

• The first three higher order bits are always set to 1, 1 and 0 respectively

• Total number of networks supported is 2,097,152 = 221 - 2 – All zeros and all ones are not allowed

• Number of hosts supported per network is 254 = 28 - 2– All zeros and all ones are not allowed

Overcoming the Limited Number of IP Addresses

• By dynamically assigning IP addresses to the clients– DHCP– DHCP is also used for better management of

network

• Network Address Translation (NAT) – Assign fictitious IP addresses to the clients– Often, implemented with hardware firewalls– NAT provides security as well

End of Module 3

© N. Ganesan, All rights reserved.

Module 3

Scope and Restriction of IP Addresses

Restrictions on Network ID Assignments

• In class A, network ID 127 is reserved for loop back functions

• All bits of a network ID cannot be set to ones – Reserved for use as an IP broadcast address

• All bits of a network ID cannot be set to zeros– Reserved for a specific host on the local host – Packets destined to this specific address will

not be routed

Loop Back Function

• Loop back function simply tests itself– Eg: 127.0.0.1 performs a test on the

machine itself

• localhost is another way of testing the loopback function

Valid Network IDs for Classes

Class BeginningNetwork ID

Ending NetworkID

A 1.0.0.0 126.0.0.0

B 128.0.0.0 191.255.0.0

C 192.0.0.0 223.255.255.0

Restrictions on Host ID Assignments

• All the bits of a host ID cannot be set to ones– Reserved as the broadcast IP address

to send a packet to all the hosts

• All the bits of a host ID cannot be set to zeros either– Reserved to represent the IP network

address

Valid Host IDs for Classes

Class Beginning Host ID

Ending Host ID

A w.0.0.1 w.255.255.254

B w.x.0.1 w.x.255.254

C w.x.y.1 w.x.y.254

Summary of Networks and Hosts Supported in Each

Class

NetworkID Portion

AvailableNetworks

Hosts per Networks

A 126 16,777,214

B 16,384 65,534C 2,097,15

2254

End of Module

© N. Ganesan, All rights reserved.

Module 4

Private IP Addresses

End of Module 4

END OF MODULEEND OF MODULE

END OF CHAPTEREND OF CHAPTER