Networks - What IP address range can be used for a specific subnet mask?

Issue

When using CIDR (Classless Inter Domain Routing) or Supernet subnet masks is not always obvious what range of IP addresses can be used.

Product Line

TAC I/NET, TAC Vista, Andover Continuum, Satchwell MicroNet, Satchwell Sigma, TAC I/A Series, SmartStruxure Solution

Environment

IP networking where non 255 subnet masks are used.

Ethernet

Network

Subnet Masks

IP Address

Network Address

Subnet Calculator

Cause

There is a need for an easy way to determine the range of valid IP addresses for the Subnet Mask being used.

Resolution

When subnet masks with values other than 255 are used; it is not always obvious what is the range of valid IP addresses, this is often called Supernetting. The website link below can calculate the range of valid addresses for any specified subnet value.

Here is an example of the issue:

An existing network has a network address of 192.168.242.64 with a subnet mask of 255.255.255.224

A new network was created with a network address of 192.168.242.95 with a subnet mask of 255.255.255.224.

When 192.168.242.95 is requested the problem occurs.

  • Using a subnet mask of 255.255.255.224 allows a network address, 30 host address and a broadcast address.

Using the existing network as an example;

  • 192.168.242.64 is the network address.
  • 192.168.242.65 to 192.168.242.94  (30 addresses).
  • 192.168.242.95 is the broadcast address.

The network address of the new network was set as 192.168.242.95, which is actually the broadcast address of the existing network.

The correct network address of the new network is 192.168.242.96, the details are shown below.

  • 192.168.242.96 is the network address.
  • 192.168.242.97 to 192.168.242.126  (30 addresses).
  • 192.168.242.127 is the broadcast address.

Visit the following website for a CIDR / Supernet calculator, enter one of the IP addresses in the network and the subnet mask and the calculator will tell you the range of addresses within the same subnet:

http://www.subnet-calculator.com/cidr.php

In addition to the online calculator, a number of different subnet-calculator programs are available for Android, Apple and Windows Smartphones and for Windows computers.