An Internet address is made of four bytes (32 bits) that define the host connection to a network.

It is uniquely and universally defines the connection of a host or a router to the internet.

Two Types: Classful Addressing Classless Addressing

Five Types: Class A ( Unicast) Class B (Unicast) Class C (Unicast) Class D ( Multicast) Class E ( Future Use)

Unicast: Communication from one source to one destination.

Multicast: Communication from one source to a group of destination

Broadcast: Communication from one source to many destinations , which are in same network.

Binary Notation: 4 bytes (32bits) binary number 10000000 00001011 00000011 00011111 Decimal Notation: Internet address are usually written in

decimal form with decimal point separated the bytes.

Finding the Class in Binary Notation

Finding the Class in Dotted – Decimal Notation

In classful addressing each class is divided into fixed of

blocks.

All hostid bytes are 0s. The network address defines the network to the rest of the

Internet. The network address is the first address in the block. Given the network address , we can find the class of the

address.

A Network with Two Levels of Hierarchy

Addressing without Subnets

Network and Host Addresses

A Network with Three Levels of Hierarchy

Addresses with and without Subnetting

A network administrator knows the network address and subnet address , but a router doesnot. The router outside the organisation use a default mask; the router inside the organisation use a subnet mask.

A 32 – bit number called the mask. Two types: Default mask ( Identify the network address) Class A 255. 0 . 0 . 0 /8 Class B 255.255.0.0 /16 Class C 255. 255. 255. 0 /24 Subnet mask ( Identify the subnet address)

A bitwise AND operation between IP address and default mask yields a network address.

Note that zeros bit are used to mask out the host number resulting the network address.

Example: IP Address: 190. 240. 7. 91 Default Mask: 255. 255. 0. 0 Network address: 190. 240. 0. 0

The number of 1’s in a subnet mask is more than the number of 1’s in the corresponding default mask.

In other words , in a subnet mask , we change some of the Rightmost 0s in the default mask to make a subnet mask.

The number of subnets is determined by the number of extra 1s. If the number of extra 1s is n, the number of subnets is 2 to the n.

A bitwise AND operation between IP address and subnet mask yields a subnet address.

Example: IP Address: 190. 240. 33. 91 Subnet Mask : 255. 255. 224.0 /19 Subnet address: 190.240. 32. 0

The idea of classful addressing has created many Problems. Until mid – 1990’s , a range of address meant a block of addresses in class A,B,C.

The minimum number of address granted to an organization was 256 ( Class C); the maximum was 16,777,216 (Class A).

In addition what about a small business that needed only 16 addresses?

During 1990s, ISP came into prominence. An ISP can be granted several class B or Class C blocks and then subdivide the range of addresses in group of 2 , 4 , 8, or 16 address), giving a range to a household or a small business. This is called the classless address.

A better way to define a block of addresses is to select any address in the block and mask. A mask is a 32 bit number in which the n leftmost bits are 1s and the 32 – n rightmost bits are 0s. However , in classless addressing the mask for a block can take any value from 0 to 32.

Address: 205.16.37.39/28 11001101 00010000 00100101 00100111

Mask : 11111111 11111111 11111111 11110000 First address( Network address): 11001101 000100000 00100101 00100000

Address: 205.16.37.39/28 11001101 00010000 00100101 00100111 Mask complement : 00000000 00000000 00000000 00000111 Last address : 11001101 00010000 00100101 00101111

Number of addresses in a block: 232-28 =24 = 16

In 1987, RFC 1009 specified that a subnetted network could use more than one subnet mask.

When an IP network is assigned more than one subnet mask, it is considered a network with variable length subnet masks.

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Benefits› Efficient use of the organization’ s

assigned IP address space.

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Assume that a network administrator has decided to configure the 130.5.0.0/16 network with a /22 extended-network prefix.

This disign allows for 64 subnets with 1,022 hosts each.

Fine if the organization plans to deploy a number of large subnets.

What about the occasional small subnet containing only 20 or 30 hosts?

About 1,000 IP host addresses wasted for every small occasional subnet!

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Assume in previous example that administrator is also allowed to configure the 130.5.0.0/16 network with a /26 extended-network-prefix.

/26 permits 1024 subnets with 62 hosts each.

The /26 prefix would be ideal for small subnets with less than 60 hosts, while /22 prefix is well suited for larger subnets up to 1000 hosts.

Addresses for private networks

A NAT implementation

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Addresses in a NAT