# Maximum number of Subnets [duplicate]

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.

• Technically, you could have a single `/23` network, or you can use `/32` networks for things like loopbacks, and that will give you 512 networks with one host each. It really depends on how many hosts you require on each network. Feb 24, 2016 at 6:58

## 1 Answer

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)

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.

• Little addition to `256 subnets of 2 addresses (none for hosts, 1 for subnet and one for broadcast)` - as referred in RFC 3021, you may use such /31 networks on point-to-point-links, where only 2 addresses will be in use. Such networks have no dedicated broadcast or network address, just the two IPs for both ends of the connection. This is e.g. supported by Cisco IOS from version 12.2(2)T upwards, maybe read up on this here.
– xpac
Feb 24, 2016 at 13:27