IP Subnetting - Eastern Illinois University

IP Subnetting

(Week 4, Wednesday 1/31/2007)

? Abdou Illia, Spring 2007

Structure of IP addresses

Network Part (n)

Local Part (h) Sgmt. part Host part

Class A Class B Class C

nnnnnnnn.hhhhhhhh.hhhhhhhh.hhhhhhhh nnnnnnnn.nnnnnnnn.hhhhhhhh.hhhhhhhh nnnnnnnn.nnnnnnnn.nnnnnnnn.hhhhhhhh

10.0.0.1 ? 126.255.255.255 128.0.0.1 ? 191.255.255.255 192.0.0.1 ? 223.255.255.255

2

Reserved IP addresses

Class A B

IP addresses reserved for private use. Range 10.0.0.0 ? 10.255.255.255 172.16.0.0 ? 172.31.255.255

C

192.168.0.0 ? 192.168.255.255

Address

Special IP addresses. Use

255.255.255.255 Example: 10.255.255.255 127.0.0.1 0.0.0.0 169.254.x.x

Local broadcast to LAN computers

Broadcast to network 10.0.0.0/8

Loopback address (for self addressing)

Prohibited

Automatic Private IP Addressing

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Structure of IP addresses

Network Part

Segment

Host

Part

Part

The division between Network part, Segment part, and Host part is determined by a computer or a router by using a network mask.

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Network mask

A 32 bit number, just like an IP address, where all bits in the Network Part and the Segment Part are set to 1, and all bits in the Host Part are set to 0. Example:

11111111 11111111 11111111 00000000 (or 255.255.255.0 in decimal notation)

Computers use Network mask, along with the IP address, to determine whether or not a destination IP address is on the same logical network.

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Two Virtual LANs

192.168.1.1 255.255.255.0

192.168.1.2 255.255.255.0

192.168.1.3 255.255.255.0

Switch

192.168.2.1 255.255.255.0

192.168.2.2 255.255.255.0

192.168.2.3 255.255.255.0

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2

Two interconnected LANs

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128

The ADDing technique

64 32

Are the following three Class C IP addresses 16

from the same network?

8 4

192.168.1.1, 192.168.1.50 and 192.168.2.1 2

IP:

11000000 10101000 00000001 00000001 192.168.1.1 1

Mask:

11111111 11111111 11111111 00000000 255.255.255.0

Network: 11000000 10101000 00000001 00000000 192.168.1.0/24

IP: Mask: Network:

11000000 11111111 11000000

10101000 11111111 10101000

00000001 11111111 00000001

00110010 00000000 00000000

192.168.1.50 255.255.255.0 192.168.1.0/24

IP: Mask: Network:

11000000 11111111 11000000

10101000 11111111 10101000

00000010 11111111 00000010

00000001 00000000 00000000

192.168.2.1 255.255.255.0 192.168.2.0/24

Network 1: 192.168.1.0/24, i.e network starting at 192.168.1.0 with network mask 255.255.255.0. Network 2: 192.168.2.0/24, i.e network starting at 192.168.2.0 with network mask 255.255.255.0.

8

128

Subnetting a class C network

64 32

16

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Suppose the 192.168.1.0/24 network

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You want to divide that network into two segments

2 1

? You can decide to use the first bit of the fourth octet as

dividing point between your network segments. So, your

network mask would be:

11111111 11111111 11111111 10000000

And you will have about 27 = 128 hosts in each segment.

Segment 1: 192.168.1.0 to 192.168.1.127 Segment 2: 192.168.1.128 to 192.168.1.255

How to determine the two segments

using the ADDing technique?

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128

Subnetting a class C network

64 32

16

Segment 1: 192.168.1.0 to 192.168.1.127

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2

IP:

11000000 10101000 00000001 00000001 192.168.1.1 1

Mask:

11111111 11111111 11111111 10000000 255.255.255.128

Network: 11000000 10101000 00000001 00000000 192.168.1.0/25

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IP:

11000000 10101000 00000001 01111111 192.168.1.127

Mask:

11111111 11111111 11111111 10000000 255.255.255.128

Network: 11000000 10101000 00000001 00000000 192.168.1.0/25

10

128

Subnetting a class C network

64 32

16

Segment 2: 192.168.1.128 to 192.168.1.255

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2

1

IP:

11000000 10101000 00000001 10000000 192.168.1.128

Mask:

11111111 11111111 11111111 10000000 255.255.255.128

Network: 11000000 10101000 00000001 10000000 192.168.1.128/25

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IP:

11000000 10101000 00000001 11111110 192.168.1.254

Mask:

11111111 11111111 11111111 10000000 255.255.255.128

Network: 11000000 10101000 00000001 10000000 192.168.1.128/25

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Question 1

Network A is IP network 192.168.1.x/24 (i.e a Class C network with a default 24-bit mask). Using the IP Subnet Calculator, determine the maximum number of hosts (computers) in each of the Network A's subnets assuming that there are two subnets. You answer: ________.

Using the IP Subnet Calculator, determine the

maximum number of subnets for a Class B

network assuming that the four first bits of the

third octet in each IP address are used as subnet

bits. Your answer: _____. What is the maximum

number of computers for each subnet? Your

answer: ______.

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