IP address

• Universally accepted addressing method is required so that all hosts can communicate with each other

• TCP/IP based network is assigned with unique addresses known as IP addresses

IP address

• Network layer addresses (IP addresses) are 32 bits long.

• Presented as four octets in dotted decimal format.

• IP address has two components: Network ID and Host ID.

IP address format

IP address classes

• Different class addresses reserve different amounts of bits for Network and Host portions of the address

• Provide flexibility required to support different size networks

HH H

H

HH

IP address classes: Class A

IP address classes: Class A

• First bit of a Class A address is always 0.

• First 8 bits identify network part of the address.

• Possible network address from 1.0.0.0 to 127.0.0.0.

• Remaining three octets used for the host portion of the address.

• Each class A network have up to 16,777,214 possible IP addresses.

IP address classes: Class B

IP address classes: Class B• First 2 bits of Class B address is always 10.• First two octets identify network part of the

address.• Possible network address from 128.1.0.0 to

191.254.0.0.• Remaining two octets used for host portion of

the address.• Class B network have up to 65.534 possible IP

addresses.

IP address classes: Class C

IP address classes: Class C• First 3 bits of a Class C address is always 110.• First three octets identify network part of the

address.• Possible network address from 192.0.1.0 to

223.255.254.0.• Remaining last octet used for host portion of

the address.• Class C network have up to 254 possible IP

addresses.

Binary and decimal conversion

Fast conversion

Bits on the IP address

• Network Bits :– Identifies network ID– Identifies class of the IP address– All of bits are 0: not allowed

• Host Bits :– Identifies host ID– All of bits are 0: reserved for network address– All of bits are 1: reserved for broadcast address

IP address classes: Summary

• 1.0.0.0 - 126.0.0.0 : Class A.

• 127.0.0.0 : Loopback network.

• 128.1.0.0 - 191.254.0.0 : Class B.

• 192.0.1.0 - 223.255.254.0 : Class C.

• 224.0.0.0 - 239.255.255.255: Class D, multicast.

• >= 240.0.0.0 : Class E, reserved.

Network address

• provide a convenient way to refer to all of the addresses on a particular network or subnetwork.

• Two hosts with differing network address require a device, typically a router, in order to communicate.

• An IP address that ends with binary 0s in all host bits is reserved for the network address.

Broadcast address

• Broadcast goes to every host with a particular network ID number.

• IP address that ends with binary 1s in all host bits is reserved for the directed broadcast address.

• An IP address with binary 1s in all network bits and host bits is reserved for the local broadcast address.

Example: 172.16.20.200

• 172.16.20.200 is Class B address

• Network portion: 172.16

• Host portion: 20.200

• Network address: 172.16.0.0

• Broadcast address: 172.16.255.255

Private addresses

• According to RFC-1918.• Organizations make use of the private

Internet address space for hosts that require IP connectivity within their enterprise network, but do not require external connections to the global Internet.

• Class A: 10.0.0.0.• Class B: 172.16.0.0 - 172.31.0.0.• Class C: 192.168.0.0 - 192.168.255.0.

Reserved addresses

• The bits that define the host portion of an IP address should not be all “1”. Any IP address with the host portion consisting of all “1” is interpreted as “all host”.

– Example : 128.1.255.255 means all hosts on network number 128.1

Reserved addresses

• The bits that define the host portion of an IP address should not be all “0”. Any IP address with the host portion consisting of all “0” is interpreted as network address.

– Example : 128.1.0.0 means network number.

Reserved addresses

• The bits used to define the network portion of an IP address should not be all “0”. A network portion address of all “0” is interpreted as “this network”.

– Example : 0.0.0.63 means Host 63 on this network.

Reserved addresses

• The Class A network number 127.x.x.x is assigned as “Loop-back” function. This means that a datagram sent by a higher-level protocol to a Network 127 address should loop back inside the host.

Review

• Classes of IP address and range of IP on each class.

• Determine network portion and host portion in a IP address.

• Understand about broadcast addresses.

• Understand about valid host address.

• Binary and Decimal conversion.

Introduction to Subnetworks

What Is a Subnet?• Series of Networks within a Network

• Created by subdividing Host address field and creating a Subnetwork Field

• All Hosts on a Subnetwork share a common subnetwork address

Why Subnet a Network?• Provides Greater Organization of Large

Networks (Class A 16 Million Hosts!)

• Allows Additional Networks (subnets) without applying for additional IPs

• Gives local administrators more control

• Provides a Third Level of Hierarchy

• Reduces the Size of Broadcast Domains

How Do You Create Subnets?• Bits are Borrowed from the Host Field

– This Creates a Subnet Field in the IP address

Class C SubnetsNetworkNetwork Network Host

S HH H H H HS

Two Bits Borrowed from the Host Field to form a third layer of hierarchy - A Subnet Field

Two Bits must always remain so a maximum of 6 Bits may be borrowed from a Class C networkHow many bits can be borrowed from a Class B network? From a Class A network?

Class C SubnetsNetworkNetwork Network Host

S HH H H H HS

The number of Subnets Created is calculated using the following formula:

# Subnets Created = 2# Borrowed Bits

Class C SubnetsS HH H H H HS

Borrow 2 Bits = 22 = 4 Subnets

S SS H H H HS

Borrow 4 Bits = 24 = 16 Subnets

S HS H H H HS

Borrow 3 Bits = 23 = 8 Subnets

Class C SubnetsS SS S H H HS

Borrow 5 Bits = 25 = 32 Subnets

Borrow 7 Bits = CannotTwo Host Bits Must Remain

S SS S S H HS

Borrow 6 Bits = 26 = 64 Subnets

• If you Borrow 2 Host Bits you do NOT get 4 Subnets. Why?

• Remember the Network Address and Broadcast Address - Both of these addresses are Reserved, they cannot be used!

How Many Subnets?Borrow 2 Bits = 22 = 4 Subnets

How Many Hosts/Subnet?NetworkNetwork Network Host

S HH H H H HS

The number of Hosts per subnet is calculated using the following formula:

# Hosts/Subnet = 2# Host Bits Remaining

# Hosts = 26 = 64 hosts/subnet

• If there are 6 Host Bits remaining you do NOT get 64 Hosts/Subnet. Why?

• Each subnetwork has its own Subnetwork Address and Broadcast Address - Both of these addresses are Reserved and cannot be used!

• Thus only 62 Hosts are available.

How Many Hosts/Subnet?6 Host Bits Remain = 26 = 64 Hosts

• Remember to subtract 2 for the Network Address and Broadcast Address.

• Remember to subtract 2 for the Subnetwork Address and Subnetwork Broadcast Address.

Formulas to Remember!

# Subnets Created = 2# Borrowed Bits

# Hosts/Subnet = 2# Host Bits Remaining

Determining Network/Host ID• Given 2 IP addresses 192.20.1.5.and

192.20.6.8. The subnet mask is 255.255.255.0. Determine the network address and the host address, also decide whether the message need to be send through the router.

Determining Network/Host ID192.20.1.5 = 11000000.00010100.00000001.00000101

255.255.255.0 = 11111111.11111111.11111111.00000000

Network ID = 11000000.00010100.00000001.00000000 => 192.20.1.0

Host ID = 00000000.00000000.00000000.00000101 => 0.0.0.5

192.20.6.8 = 11000000.00010100.00000110.00001000

255.255.255.0 = 11111111.11111111.11111111.00000000

Network ID = 11000000.00010100.00000110.00000000 => 192.20.6.0

Host ID = 00000000.00000000.00000000.00001000 => 0.0.0.8

Determining Network/Host ID• Given 2 IP addresses 192.20.1.5 and

192.20.6.8. The subnet mask is 255.255.0.0. Determine the network address and the host address, also decide whether the message need to be send through the router.

Determining Network/Host ID192.20.1.5 = 11000000.00010100.00000001.00000101

255.255.0.0 = 11111111.11111111.00000000.00000000

Network ID = 11000000.00010100.00000000.0000

=> 192.20.0.0

Host ID = 00000000.00000000.00000001.00000101=> 0.0.1.5

192.20.6.8 = 11000000.00010100.00000110.00001000

255.255.0.0 = 11111111.11111111.00000000.00000000

Network ID = 11000000.00010100.00000000.00000000 => 192.20.0.0

Host ID = 00000000.00000000.00000110.00001000 => 0.0.6.8

Determining Network/Host ID• Suppose a Class B IP address is 191.20.0.0

and the subnet mask is 255.255.224.0. Find the number of subnet available and state the subnet addresses. How many hosts can each subnet have ?

Determining Network/Host ID191.20.x.x = 10111111.00010100.xxxxxxxx.xxxxxxxx

255.255.224.0 = 11111111.11111111.11100000.00000000

Network ID = 10111111.00010100.xxx00000.00000000

=> 191.20.x.0

As extra 3 bits is added into the subnet mask, we have increased the bits available for the network ID. Now, we can have 6 [(2^3) – 2 ] different Network ID.

Determining Network/Host ID10111111.00010100.00100000.00000000 => 191.20.32.0

10111111.00010100.01000000.00000000 => 191.20.64.0

10111111.00010100.01100000.00000000 => 191.20.96.0

10111111.00010100.10000000.00000000 => 191.20.128.0

10111111.00010100.10100000.00000000 => 191.20.160.0

10111111.00010100.11000000.00000000 => 191.20.192.0

Each subnet can have [2^13 –2] = 8190 hosts.