IPv4 and Subnetting

CIDR notation

Address class is no longer uniquely identifiable from the address We must find a way of telling routers the size of the

network part of the address Done by including a number along with the network

address

E.g. 73.5.0.0/ 17

• In the above example, the first 17 bits of the address are the network part

• You can search for more example CIDR address blocks at http://www.arin.net

CIDR notation

The CIDR notation will tell you how many IP addresses are available in that subnet.

How does a company allocate a large pool of addresses?

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Ex. UNCW has 152.20.0.0 / 16 which gives them a possible 65,536 IP addresses (2(32-16))

Possible approach to assigning IP addresses:

As soon as a computer comes online, you can assign them the next IP address available.

Desktop in CIS

Laptop in Union

Workstation in Library

How does a company allocate a large pool of addresses?

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Alternative Method:

Each college or building allocated a contiguous set of IP addresses

Desktop in CIS

Laptop in Union

Workstation in Library

CIS152.20.1.0 -152.20.1.255

Fisher Union152.20.2.0 -152.20.2.255

Library152.20.3.0 -152.20.3.255

Subnetting and network structure

Each Ethernet is given a unique subnetwork ID Enables broadcasting within the Ethernet Each computer on the Ethernet must be part of this

network

Subnetting enables the partition of a large address pool into multiple smaller blocks

University campus

Business school subnet131.247.2.0 – 131.247.4.255

Library subnet131.247.1.0 – 131.247.1.255

Engineering subnet131.247.6.0 – 131.247.7.255

Hospital subnet131.247.5.0 – 131.247.5.255

Library Ethernet

Engineering EthernetBusiness School Ethernet

Ho

spita

l Eth

erne

t

Cisco 3600SERIES

0 1

READY

ACTIVE

PCMCIA

1

0

COM AUXSYSTEM RPS

Main campus router

Subnets and IP Addresses

10000011 11110111 00010000 11101011

131 . 247 . 16 . 235

Network ID(USF)

Host ID(worskstation 24 in lab)

Network part of IP address Host part of IP address

What does UNCW’s IP Addresses look like?

3-part interpretation of IP addresses

8

10000011 11110111 00010000 11101011

131 . 247 . 16 . 235

Network ID(USF)

Subnet ID(College of Business)

Host ID(worskstation 24 in

lab)

Network part of IP address

Host part of IP address

Subnet ID component of host part of IP address

Host ID component of host part of IP address

Subnets - How do you decide who gets what address?

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Group of computers on the same LAN with IP numbers using the same prefix

Assigned addresses For example:

• Subnet 152.20.234.x– Computers in CIS labs (x is between 0 & 255)

• Subnet 152.20.244.x & 152.20.196.x – Computers in CIS Offices (x is between 0 & 255)

• Subnet 129.79.125.x– Computers in Cameron

Does anyone see a problem with the subnets above?

Subnet: Example

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CIS

152.20.244.X172.20.101.X

Cameron

172.20.102.X

Psych

172.20.103.X

Library

172.20.104.XR

R

R

R

R

Address: 152.20.5.56

Address: 152.20.5.70

Address: 152.20.244.254 Address: 172.20.104.254

Campus BackboneAddress: 152.20.5.X

Basic Subnetting

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How do we create 2 subnets?

Basic Subnetting

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How do we create 3 subnets?

Basic Subnetting

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How do we create 4 subnets?

Subnetting example

Consider an organization with a /16 network address block (131.247.0.0/ 16) Most medium-large organizations fall in this category Also, most State Universities

Say, after analysis, the organization settles on 5-bit subnet IDs

Example with 5-bit subnet IDs

Subnet ID Campus unit Subnet ID Campus unit Subnet ID Campus unit

00001 (1) College 1 00010 (2) College 2 00011 (3) College 3

00100 (4) College 4 00101 (5) College 5 00110 (6) College 6

00111 (7) College 7 01000 (8) College 8 01001 (9) College 9

01010 (10) College 10 01011 (11) <future college> 01100 (12) <future college>

01101 (13) Dorm 1 01110 (14) Dorm 2 01111 (15) <future dorm>

10000 (16) <future dorm> 10001 (17) Branch campus 1 10010 (18) Branch campus 2

10011 (19) <future branch campus >

10100 (20) Administration 10101 (21) Campus IT

10110 (22) <future expansion>

10111 (23) <future expansion>

11000 (24) <future expansion>

11001 (25) <future expansion>

11010 (26) <future expansion>

11011 (27) <future expansion>

11100 (28) <future expansion>

11101 (29) <future expansion>

11110 (30) <future expansion>

Network ID + subnet ID for colleges in example

Campus unit Subnet ID First 2 parts of IP addresses by college

College 1 00001 10000011.11110111.00001_ _ _ . _ _ _ _ _ _ _ _

College 2 00010 10000011.11110111.00010 _ _ _ . _ _ _ _ _ _ _ _

College 3 00011 10000011.11110111.00011 _ _ _ . _ _ _ _ _ _ _ _

College 4 00100 10000011.11110111.00100 _ _ _ . _ _ _ _ _ _ _ _

College 5 00101 10000011.11110111.00101 _ _ _ . _ _ _ _ _ _ _ _

College 6 00110 10000011.11110111.00110 _ _ _ . _ _ _ _ _ _ _ _

College 7 00111 10000011.11110111.00111 _ _ _ . _ _ _ _ _ _ _ _

College 8 01000 10000011.11110111.01000 _ _ _ . _ _ _ _ _ _ _ _

College 9 01001 10000011.11110111.01001 _ _ _ . _ _ _ _ _ _ _ _

College 10 01010 10000011.11110111.01010 _ _ _ . _ _ _ _ _ _ _ _

Complete subnet addresses for colleges in example

Campus unit Subnet address (binary) Subnet address (decimal)

College 1 10000011.11110111.00001000.00000000 131.247.8.0/ 21

College 2 10000011.11110111.00010000.00000000 131.247.16.0/ 21

College 3 10000011.11110111.00011000.00000000 131.247.24.0/ 21

College 4 10000011.11110111.00100000.00000000 131.247.32.0/ 21

College 5 10000011.11110111.00101000.00000000 131.247.40.0/ 21

College 6 10000011.11110111.00110000.00000000 131.247.48.0/ 21

College 7 10000011.11110111.00111000.00000000 131.247.56.0/ 21

College 8 10000011.11110111.01000000.00000000 131.247.64.0/ 21

College 9 10000011.11110111.01001000.00000000 131.247.72.0/ 21

College 10 10000011.11110111.01010000.00000000 131.247.80.0/ 21

Subnet Masks

Used to make it easier to separate the subnet part of the address from the host part.

Example Subnet: 149.61.10.x Subnet mask: 255.255.255.000 or in binary

11111111.11111111.11111111.00000000

Example Subnets: 149.61.10.1-128, Subnet mask 255.255.255.128 or, in binary:

11111111.11111111.11111111.10000000

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Subnet mask operation

What does a subnet mask do? The 0’s in the subnet mask block (mask) the

corresponding bits in any destination address

The 1’s in the subnet mask allow the corresponding bits to be seen

The Result is the subnet address

How a network is setup for IP addresses

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Determine the Total Number of Hosts

How a network is setup for IP addresses

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Determine the Number and Size of the Networks

How a network is setup for IP addresses

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Allocating Addresses

How a network is setup for IP addresses

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Allocating Addresses

How a network is setup for IP addresses

Within the address range of each IPv4 network, we have three types of addresses:

• Network address - The address by which we refer to the network

• Broadcast address - A special address used to send data to all hosts in the network

• Host addresses - The addresses assigned to the end devices in the network

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Case study – networks in the retail sector

Both Wal-Mart and K-Mart started in 1962

K-Mart grew rapidly at first 250 stores in 1967, compared to 18 Wal-Marts Each K-Mart store had 6 times the revenue of a Wal-Mart

store

2002 K-Mart filed for bankruptcy For the first time, Wal-Mart was the largest company in

America by revenue

Among other factors

Wal-Mart relied on IT First computer network using phone lines in 1977

• To improve inventory refills Satellite network in 1987

• Cut credit card processing time by half EDI, RetailLink

K-Mart relied on managerial expertise Used spreadsheets to track supply and demand