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Chapter 4Chapter 4IP Addressing : IP Addressing : Classful AddresClassful Addres

singsing

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4.1 Introduction4.1 Introduction

For a host to communicate with any other host

Need a universal identification system

Need to name each host

Internet address or IP address is a 32-bit address that

uniquely defines a host or a router on the internet

The IP addresses are unique in the sense that two

devices can never have the same address. However, a

device can have more one address.

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NotationNotation

Binary notation

01110101 10010101 00011101 11101010

32 bit address, or a 4 octet address or a 4-byte address

Decimal point notation

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Notation (cont’d)Notation (cont’d)

Hexadecimal NotationHexadecimal Notation

- 8 hexadecimal digits- 8 hexadecimal digits

- Used in network programming- Used in network programming

0111 0101 1001 0101 0001 1101 1110 1010

75 95 1D EA

0x75951DEA

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4.2 Classful Addressing4.2 Classful Addressing Occupation of address space

In classful addressing, the address space is divided into five classes: A, B, C, D, and E.

Finding the class in binary notation

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Classful Addressing (cont’d)Classful Addressing (cont’d)

Finding the address class

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Classful Addressing (cont’d)Classful Addressing (cont’d)

Finding the class in decimal notation

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Netid and HostidNetid and Hostid

Each IP address is made of two parts; netid and hostid.

Netid defines a network; hostid identifies a host on that network.

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Netid and Hostid (cont’d)Netid and Hostid (cont’d)

IP addresses are divided into five different classes: A, B, C, D, and E

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Classes and Blocks Blocks in class A

Class A is divided into 128 blocks with each block having a different netid.

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

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Classes and Blocks (cont’d) Class B is divided into 16,384 blocks with each block having a diffe

rent netid

Many class B addresses Many class B addresses are wasted.are wasted.

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Classes and Blocks (cont’d)

Class C is divided into 2,097,152 blocks with each block having a diff

erent netid.

The number of addresses in The number of addresses in a class C block a class C block is smaller than is smaller than the needs of most the needs of most organizationsorganizations

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Classes and Blocks (cont’d)

Class D addresses are used for multicasting;

there is only one block in this class.

Class E addresses are reserved for special purposes;

most of the block is wasted.

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Network AddressNetwork Address

The network address is the first address.

The network address defines the network to the rest of t

he Internet.

Given the network address, we can find the class of th

e address, the block, and the range of the addresses in

the block

In classful addressing, the network address

(the first address in the block) is the one that is assigne

d to the organization.

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Mask Mask

A mask is a 32-bit binary number that gives the first address in the

block (the network address) when bitwise ANDed with an address i

n the block.

Masking concept

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Mask (cont’d)Mask (cont’d)

AND Operation

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

n be found by applying the default mask to any of the addresses i

n the block (including itself). It retains the netid of the block and s

ets the hostid to zero. (refer table 4.2)(refer table 4.2)

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4.3 Others Issues4.3 Others Issues

Multihomed devices (computers, or routers)

A computer that is connected to different networks

Having more than one address

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Special AddressesSpecial Addresses

Some parts of the address space in class A, B, C for special addresses

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Special AddressesSpecial Addresses

Network address : an address with the hostid all set to 0s

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Special Addresses (cont’d)Special Addresses (cont’d) Direct Broadcast Address : Used by a router to send a packet to all

hosts in a specific network

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Special Addresses (cont’d)Special Addresses (cont’d) Limited Broadcast Address : all 1s for the netid and hostid (32bits)

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Special Addresses (cont’d)Special Addresses (cont’d) This Host on This Network : used by a host at bootstrap time when

it does not know its IP address

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Special Addresses (cont’d)Special Addresses (cont’d) Specific Host on This Network : used by a host to send a message

to another on the same network

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Special Addresses (cont’d)Special Addresses (cont’d) Loopback Address :

IP address of the first byte : 127Used to test the software on a machine Used by a client process to send a message to a server process on the same machine“Ping”

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Private AddressesPrivate Addresses

A number of blocks in each class are assigned for

private use. They are not recognized globally.

Class Netid Total

Class A 10.0.0 1

Class B 172.16 to 172.31 16

Class C 192.68.0 to 192.68.255 256

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Unicast, Multicast, and Broadcast AddressesUnicast, Multicast, and Broadcast Addresses

Unicast communication is one-to-one.

Multicast communication is one-to-many.

Broadcast communication is one-to-all.

Multicast delivery will be discussed in depth in Chapter

14.

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Unicast, Multicast, and Broadcast Addresses (cont’d)Unicast, Multicast, and Broadcast Addresses (cont’d)

Assigned Multicast addresses : starting with a 224.0.0 prefix

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Unicast, Multicast, and Broadcast Addresses (cont’d)Unicast, Multicast, and Broadcast Addresses (cont’d)

Unicast Addresses : one-to-one

Multicast addresses : one-to-many; class D address

Used as a destination address

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Unicast, Multicast, and Broadcast Addresses (cont’d)Unicast, Multicast, and Broadcast Addresses (cont’d)

Multicast address for conferencing : starting with a 224.0.1 prefix

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Unicast, Multicast, and Broadcast Addresses (cont’d)Unicast, Multicast, and Broadcast Addresses (cont’d)

Broadcast addresses : one-to-all

Allowed only at the local level

Limited broadcast address (all 1s) Direct broadcast address (netid: specific, hostid: all 0s)

No broadcasting is allowed at the global level

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A Sample Internet with Classful AddressA Sample Internet with Classful Address

Token Ring LAN (Class C), Ethernet LAN (Class B), Ethernet LAN (Class A) ,

Point-to-point WAN, A Switched WAN

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4.4 Subnetting and Supernetting4.4 Subnetting and Supernetting

Subnetting

A network is divided into several smaller networks with each subnetwork (or subnet) having its subnetwork address

Supernetting

Combining several class C addresses to create a larger range of addresses

IP Addresses are designed with two levels of hierarchy

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SubnettingSubnetting

Classes A, B, C in IP addressing are designed with two levels of hierarchy (not subnetted)

Netid and Hostid

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Subnetting (cont’d)Subnetting (cont’d) Further division of a network into smaller networks called subnetworks

R1 differentiating subnets

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Subnetting (cont’d)Subnetting (cont’d)

Three levels of hierarchy : netid, subnetid, and hostid

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Subnetting (cont’d)Subnetting (cont’d)

Three steps of the routing for an IP datagram

Delivery to the site, delivery to the subnetwork, and delivery to the host

Hierarchy concept in a telephone number

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Subnet MaskSubnet Mask A process that extracts the address of the physical network (network/sub

network portion) from an IP address

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Finding the Subnet Mask AddressFinding the Subnet Mask Address

Given an IP address, we can find the subnet address the same way we found the network address in the previous chapter. We apply the mask to the address. We can do this in two ways: straight or short-cut.

Straight Method

In the straight method, we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address.

Example 15Example 15

What is the subnetwork address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0?

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Finding the Subnet Mask Address (cont’d)Finding the Subnet Mask Address (cont’d)

Solution

11001000 00101101 00100010 00111000

11111111 11111111 11110000 00000000

11001000 00101101 001000000000 0000000000000000

The subnetwork address is 200.45.32.0.

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Comparison of a default mask and a subnet mask

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Supernetting Supernetting

A block of class x addresses

For example,

An organization that needs 1,000 addresses can be granted four class C addresses

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Supernetting (cont’d)Supernetting (cont’d)

4 class C addresses combine to make one supernetwork

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Supernet MaskSupernet Mask

In subnetting, we need the first address of the subnet aIn subnetting, we need the first address of the subnet a

nd the subnet mask to define the range of addresses.nd the subnet mask to define the range of addresses.

In supernetting, we need the first address of the super

net and the supernet mask to define the range of addre

sses.

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Supernet Mask (cont’d)Supernet Mask (cont’d)

Comparison of subnet, default, and supernet masks