Maximum number of Subnets

Question

If I have been assigned the address 164.12.130.0/23 in a network block. What is the maximum number of subnets that can be defined?

What will be the IP addresses of those subnets.

This is not a Home Work question. I came across this question while reading up an article.

Answer 1

A /23 block contains 512 addresses. 2^(32-23)=512

You can use them to make any number of subnets that you want. For example:

• 2 subnets of 256 addresses (254 hosts, 1 for subnet and one for broadcast)
• 4 subnets of 128 addresses (126 hosts, 1 for subnet and one for broadcast)
• 8 subnets of 64 addresses (62 hosts, 1 for subnet and one for broadcast)

and so on... up to

• 128 subnets of 4 addresses (2 hosts, 1 for subnet and one for broadcast) *This is the max number of useful subnets
• 256 subnets of 2 addresses (May be used for point-to-point-links. RFC 3021)

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In addition you can mix and match, for example:

• 1 subnet of 256 addresses and 2 of 128 addresses
• 2 subnets of 128 addresses, 3 of 64 addresses and 2 of 32 addresses.

It's your necessity the thing that should determine which subnetting is the most useful.