IPv4 Subnetting invalid entry causing network address of zero

When assigning an IP address and subnet mask combination to a host in IPv4, the resulting network address must be a non-zero value, otherwise, the configuration is considered invalid.

For example, let’s use take a look at the 10.1.1.1/4 address. The /4 subnet is equivalent to a 240.0.0.0 subnet. Let's look at it in binary:

  • 10.1.1.1 = 00001010.00000001.00000001.00000001
  • 240.0.0.0 = 11110000.00000000.00000000.00000000

To get the network address, we AND the IP address with the subnet mask:

00001010.00000001.00000001.00000001
11110000.00000000.00000000.00000000

00000000.00000000.00000000.00000000

The result is 0.0.0.0, which is not an acceptable network address.

If you try to apply this IP address/subnet mask combination to a Windows PC, you get the following error message:

IPv4_subnetting_network_zero_error.PNG

https://forum.networklessons.com/t/what-is-subnetting/1395/31?u=lagapides