# of Subnets question

[Accessdabbler]

I have the book "Upgrading and Repairing Networks" by Terry William Ogletree.

Inside the front cover, there is a listing of all possible subnets for Class A, B and C groups.

Here is an example of the listing:

Subnet Mask: 255.128.0.0
# of Subnets: 1-2

Subnet Mask: 255.192.0.0
# of Subnets: 3-4

Subnet Mask: 255.224.0.0
# of Subnets: 5-8

My question is, why is the "# of Subnets" shown as a range instead of an absolute number. For example, shouldn't the number of subnets read 2, 4, and 8?

I'm thinking it is written this way is to help you decide what subnet mask to use depending on how many subnets you need. For example, if you need 5 subnets, use 255.224.0.0. However, the way it is written in the book, it makes it sound as if you can't have 4 subnets using the 225.224.0.0 subnet mask.

 

[manarth]

You're right - it should be written as an absolute number.

A standard Class A SN is 255.0.0.0

If you subnet this with SN 255.128.0.0, you can divide your class A network into a maximum of 2 subnetworks.

Class A subnetted to 255.224.0.0 allows you to divide your Class A network into a MAXIMUM of 6 subnets, each allowing a maximum of 2097150 hosts.

http://www.ralphb.net/IPSubnet/class_a.html

supplies a representation of subnetting a Class A network.

http://www.ralphb.net/IPSubnet/class_b.html

for Class B

http://www.ralphb.net/IPSubnet/class_c.html

for Class C.
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