This came from Poor Roger's Home Page at http://home.earthlink.net/~rogergoodman.
Poor Rogerís New & Improved Method for
SubNet Masking

LOW Order BITS (Hosts):

7

6

5

4

3

2

1

0

value

128

64

32

16

8

4

2

1

                 

value

128

192

224

240

248

252

254

255

High Order BITS (Nets):

1

2

3

4

5

6

7

8


Quickly scribble down the above table in this fashion: How to use:

DEFAULT SUBNET MASKS

 

Looking only at the 1st octet

   

Class

High Bits

Value Range

Octets used for Net ID

Default Subnet Mask

A

0

1-126

1st octet only

255.0.0.0

B

10

128-191

1st 2 octets

255.255.0.0

C

110

192-223

1st 3 octets

255.255.255.0

   

224

   

To quickly produce the above table, do the following:

This came from Poor Roger's Home Page at http://home.earthlink.net/~rogergoodman.