©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200311

Chapter 4

IP Addresses:Classful Addressing

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200322

CONTENTSCONTENTS• INTRODUCTION• CLASSFUL ADDRESSING• OTHER ISSUES• A SAMPLE INTERNET

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200333

4.1 Introduction• An IP address is a 32-bit address that identifies a connection to

the Internet.• The IP addresses are universally unique.• The address space of IPv4 is 232 or 4,294,967,296.• IP address is written as a Binary (hexadecimal) or a Dotted-

Decimal (w/out leading zeros) notation. See examples in the textbook.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200344

CLASSFUL ADDRESSING4.24.2

• The IP address space (all possible IP values) is divided into five classes: A, B, C, D, and E.

161

161

81

41

21

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200355

Finding the class of an IP address11stst Byte Byte decimal decimal valuesvalues

0 0 -- 127127

128128--191191

192192--223223

224224--239239

240240--255255

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200366

Example 5Example 5

How can we prove that we have 2,147,483,648 addresses in class A?

SolutionSolution

In class A, only 1 bit defines the class. The remaining 31 bits are available for the address. With 31 bits, we can have 231 or 2,147,483,648 addresses.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200377

Example 6 (Continued)Example 6 (Continued)

Find the class of the address:

11000001 10000011 00011011 11111111

SolutionSolution

The first 2 bits are 1; the third bit is 0. This is a class C address.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200388

Example 7Example 7

Find the class of the address:

227.12.14.87

SolutionSolution

The first byte is 227 (between 224 and 239); the class is D.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 200399

Example 7 (Continued)Example 7 (Continued)

Find the class of the address:

193.14.56.22

SolutionSolution

The first byte is 193 (between 192 and 223);the class is C.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031010

Netid and hostid

• Only classes A, B, and C addresses are subdivided.• Exercise: How many different “Netid”s and “Host”s in each of

the classes A, B, C?Hostid’s

• 2^24 = 16,777,216• 2^16 = 65,536• 2^8 = 256

Netid’s• 2^(8-1) = 128• 2^(16-2) = 16,384• 2^(24-3) = 2,097,152

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031111

Blocks in class A

Millions of class A addresses Millions of class A addresses are wasted. are wasted.

One Block (One Block (NetidNetid 10) is for Private 10) is for Private Addresses. Addresses.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031212

Blocks in class B

Many class B addresses Many class B addresses are wasted.are wasted. 16 Blocks are reserved for Private 16 Blocks are reserved for Private

Addresses. Addresses.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031313

Blocks in class C

The number of addresses in The number of addresses in a class C block is smaller than a class C block is smaller than

the needs of most organizations. the needs of most organizations. 256 Blocks are reserved for 256 Blocks are reserved for

Private Addresses. Private Addresses.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031414

Class D addresses (ONE block) Class D addresses (ONE block) are used for multicasting; are used for multicasting;

Each address define one group. Each group member Each address define one group. Each group member has a multicast and a has a multicast and a unicastunicast IP addressIP address

Class E addresses (ONE block) are reserved for special Class E addresses (ONE block) are reserved for special purposes (limited broadcast) ; most of the block is purposes (limited broadcast) ; most of the block is

wasted. wasted.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031515

Network AddressesNetwork Addresses

1. The network address is the first address in the block.

2. The network address defines the network to the rest of the Internet.

3. Given the network address, we can find the class of the address, the block, and the range of the addresses in the block

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031616

Example 9Example 9

Given the network address 17.0.0.0, find the class, the block, and the range of the addresses.

SolutionSolution

The class is A because the first byte is between 0 and 127. The block has a netid of 17. The addresses range from 17.0.0.0 to 17.255.255.255.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031717

Example 10Example 10

Given the network address 132.21.0.0, find the class, the block, and the range of the addresses.

SolutionSolution

The class is B because the first byte is between 128 and 191. The block has a netid of 132.21. The addresses range from 132.21.0.0 to 132.21.255.255.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031818

Example 11Example 11

Given the network address 220.34.76.0, find the class, the block, and the range of the addresses.

SolutionSolution

The class is C because the first byte is between 192 and 223. The block has a netid of 220.34.76. The addresses range from 220.34.76.0 to 220.34.76.255.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20031919

IP address → Network Address

1. Find the class, then the Netid, then set Hostid = 0Example: IP=134.45.78.2 is a class B (128-191) with Netid=134.45, so its network address is 134.45.0.0

2. Use a Mask which is a 32-bit binary number that gives the first address in the block (the network address) when bitwise ANDed with an address in the block.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032020

Default Masks

255.255.255.0C

255.255.0.0B

255.0.0.0A

Mask in dotted-decimalClass

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032121

The network address is the The network address is the beginning address of each block.beginning address of each block.

It can be found by applying It can be found by applying the default mask tothe default mask to

any of the addresses in the block any of the addresses in the block (including itself).(including itself).

It retains the It retains the netidnetid of the block of the block and sets the and sets the hostidhostid to zero. to zero.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032222

Example 12Example 12

Given the address 23.56.7.91 and the default class A mask, find the beginning address (network address).

SolutionSolution

The default mask is 255.0.0.0, which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is 23.0.0.0.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032323

Example 13Example 13

Given the address 132.6.17.85 and the default class B mask, find the beginning address (network address).

SolutionSolution

The default mask is 255.255.0.0, which means that the first 2 bytes are preserved and the other 2 bytes are set to 0s. The network address is 132.6.0.0.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032424

We must not We must not apply the default mask apply the default mask

of one class to of one class to an address belonging an address belonging

to another class. to another class.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032525

• IP addresses are almost depleted even though the number of devices on the Internet is much less than 2^32.

• Remedies to this problem are discussed in Chapter 5

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032626

OTHER ISSUES

4.134.13

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032727

Multihomed devices

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032828

Special Addresses

1. Network Address2. Direct Broadcast Address3. Limited Broadcast Address4. This Host on This Network5. Specific Host on This Network6. Loopback Address

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20032929

Network addresses

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033030

Example of direct broadcast address

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033131

Example of limited broadcast address

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033232

Example of this host on this address

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033333

Example of specific host on this network

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033434

Example of loopback address

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033535

Private AddressesPrivate Addresses

A number of blocks in each class are assigned for private use. They are not recognized globally.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033636

UnicastUnicast, Multicast, and , Multicast, and Broadcast AddressesBroadcast AddressesUnicast communication is one-to-one.

Multicast communication is one-to-many. (Class D address defining the Groupid)

Broadcast communication is one-to-all.

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033737

A SAMPLE INTERNET

WITH CLASSFUL ADDRESSES

4.44.4

©The McGraw-Hill Companies, Inc., 2000 © Adapted for use at JMU by Mohamed Aboutabl, 20033838

Sample internet