IP Addresses

Mark Woodhouse and Arthur Manning

IP Addressing

• Used packets created in Layer 3 of the Open Systems Interconnection (OSI) Model

• Hierarchical addressing scheme

• Example: Structure of this course

Course StructureCCAI

Semester 1 Semester 2

Layer 3 Layer 4

IP Addresses Subnetting

. IP Addresses. Semester 1 . Layer 3CCAI

IP Address Structure

• Four binary octets (bytes) in dotted-decimal format

Example:

208 . 142 . 79 . 225

8 bits 8 bits 8 bits 8 bits

IP Address Parts

130 . 142 . 79 . 225

Network Part Host Part

Balance between Network and Host parts of the IP addressvaries, based on the “Class” of the IP Address

IP Address Classes

• Class “A” addresses

– 1st Octet has a decimal value between 1 and 126 (first binary digit is 0)

– Allows for a maximum of ~16 million hosts

108 . 142 . 79 . 225Network Host

IP Address Classes

• Class “B” addresses

– 1st Octet has a decimal value between 128 and 191 (first 2 binary digits are 10)

– Allows for a maximum of ~65 thousand hosts

128 . 142 . 79 . 225Network Host

IP Address Classes

• Class “C” addresses

– 1st Octet has a decimal value between 192 and 223 (first 3 binary digits are 110)

– Allows for a maximum of 254 hosts

208 . 142 . 79 . 225Network Host

IP Address Classes

• Class “D” and “E” addresses

– 1st Octet has a decimal value above 223 (first 3 binary digits are 111)

– Used for special purposes, not generally available

Two Special IP Addresses

• Network Address:

all host bits set to zero

208 . 142 . 79 . 0Network Host

Two Special IP Addresses

• Broadcast Address:

all host bits set to one

208 . 142 . 79 . 255Network Host

Broadcast packets are forwarded to all hostson the network!

IP Address Classes - Exercise

Tell me which class the following addresses belong to:

201 . 181 . 7 . 42

128 . 17 . 47 . 146

3 . 1 . 1 . 2

184 . 11 . 72 . 55

193 . 4 . 9 . 9

Class C

Class B

Class A

Class B

Class C

Subnets

Mark Woodhouse and Arthur Manning

What is Subnetting?

• Borrowing 2 or more bits from the HOST portion of the IP address to extend the NETWORK portion.

• Divides your allotted IP addresses into separate, discrete networks

• Final host part of the IP address must contain at least 2 bits

Benefits of Subnetting

• Limits the extent of Broadcast Domains– Instead of going to all IP addresses on the

network, broadcasts are forwarded only to those machines on the same subnet

• Better organization of IP addresses within the enterprise

• Different media might be used for different LAN segments

Subnet Mask

Indicates what portion of the IP address represents the network

10001100.10110011.11110000.1100100011111111.11111111.00000000.00000000

10001100.10110011.00000000.00000000

140 . 179 . 240 . 200

Class B addressClass B Net Mask

Network Part

140 . 179

Default Subnet Masks

• Class A Subnet Mask– 255 . 0 . 0 . 0

• Class B Subnet Mask– 255 . 255 . 0 . 0

• Class C Subnet Mask– 255 . 255 . 255 . 0

Borrowing Host Bits to Subdivide theNetwork Space

• At least 2 bits must be borrowedfrom the host part of the IP address

• At least 2 bits must be left for the Host part of the IP address

Example Class B Subnet Mask

11111111.11111111.11100000.00000000

255 . 255 . 224 . 0

Network Part Host Part

11111111.11111111.00000000.00000000

255 . 255 . 0 . 0

Network Part Host Part

Three bits borrowed fromHost Part to extend theNetwork Part of the address

Example Class B Subnet

000001010011100101110111

Network Address – Can’t be Used001 – Useable Subnet Address010 – Useable Subnet Address011 – Useable Subnet Address100 – Useable Subnet Address101 – Useable Subnet Address110 – Useable Subnet AddressBroadcast Address – Can’t be Used

000001010011100101110111

Network Address – Can’t be Used001 – Useable Subnet Address010 – Useable Subnet Address011 – Useable Subnet Address100 – Useable Subnet Address101 – Useable Subnet Address110 – Useable Subnet AddressBroadcast Address – Can’t be Used

PossibleNetworks

Host Addresses on the 011 Subnet

01100000.0000000001100000.0000000101100000.00000010 . . .01111111.1111110101111111.1111111001111111.11111111

Network AddressUseable AddressUseable Address .. .Useable AddressUseable AddressBroadcast Address

(32 x 256)-2 = 8190 Total Useable Hosts on the 011 Subnet

Subnet Host