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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?
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.
Workstation in Library
Desktop in CIS
Laptop in Union
5-4
How does a company allocate a large pool of addresses?
Alternative Method:
Each college or building allocated a contiguous set of IP
addresses
Fisher Union
152.20.2.0 152.20.2.255
Library
152.20.3.0 152.20.3.255
CIS
152.20.1.0 152.20.1.255
Laptop in Union
Desktop in CIS
Workstation in Library
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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
Hospital Ethernet
University campus
Library Ethernet
Hospital subnet
131.247.5.0 – 131.247.5.255
Library subnet
131.247.1.0 – 131.247.1.255
Cisco 3600
SERIES
0 1
1
ACTIVE
0
READY
SYSTEM
COM
RPS
PCMCIA
AUX
Main campus router
Business School Ethernet
Business school subnet
131.247.2.0 – 131.247.4.255
Engineering Ethernet
Engineering subnet
131.247.6.0 – 131.247.7.255
Subnets and IP Addresses
Network part of IP address
Host part of IP address
10000011 11110111 00010000 11101011
131 .
247 .
Network ID
(USF)
16 .
235
Host ID
(worskstation 24 in lab)
What does UNCW’s IP Addresses
look like?
3-part interpretation of IP addresses
Network part of IP address
10000011 11110111 00010000 11101011
131 .
247 .
Network ID
(USF)
16 .
235
Subnet ID
Host ID
(College of (worskstation 24 in
Business)
lab)
Host part of IP address
Subnet ID component of host part of IP address
Host ID component of host part of IP address
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Subnets - How do you decide who gets what address?
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?
5-9
Subnet: Example
Address: 152.20.244.254
Address: 172.20.104.254
Address: 152.20.5.56
CIS
R
152.20.244.X
172.20.101.X
Library
R
172.20.104.X
R
Address: 152.20.5.70
Cameron
172.20.102.X
R
Psych
R
172.20.103.X
Campus Backbone
Address: 152.20.5.X
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Basic Subnetting
How do we create
2 subnets?
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Basic Subnetting
How do we create
3 subnets?
5 - 12
Basic Subnetting
How do we create
4 subnets?
5 - 13
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 >
<future
expansion>
<future
expansion>
<future
expansion>
10100 (20)
Administration
10101 (21)
Campus IT
10111 (23)
<future
expansion>
<future
expansion>
<future
expansion>
11000 (24)
<future
expansion>
<future
expansion>
<future
expansion>
10110 (22)
11001 (25)
11100 (28)
11010 (26)
11101 (29)
11011 (27)
11110 (30)
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
Determine the Total Number of Hosts
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How a network is setup for IP addresses
Determine the Number and Size of the Networks
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How a network is setup for IP addresses
Allocating Addresses
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How a network is setup for IP addresses
Allocating Addresses
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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
5 - 24
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