Revised post: Covering Subnet Calculator to understand more about Wildcard Mask

This tool is an update to my previous post:

Simple visual tool to calculate Cisco IOS Wildcard Mask

Notes for Cisco IOS Wildcard Mask

You can simply assume Cisco IOS Wildcard Mask are derived by mapping 1s to 0s and 0s to 1s of equivalent subnet mask in binary notation.


By definition, “0” bits in a wildcard mask denote the bits you must match the base prefix, and “1” bits denote the bits you simply don’t care.

All subnet masks must begin with contiguous “1”s, and rest of the digits must be “0”. On the other hand, no such requirements are for wildcard masks. That is the major difference between subnet mask and wildcard mask.

Updates

I changed my flow of using this Excel file. You simply input “Starting IPv4 Address”, and the number of contiguous hosts you desire to cover with a single IPv4 subnet, and then this Excel file calculate everything else for you.

Getting this Excel file

Original Excel file is here. You need Microsoft Excel software or LibreOffice Calc to open and play with this file.

“ipv4-covering-first-last.xlsx”

If you are familiar with Google Docs, you can also “Use this template” or save this file to Google Drive for viewing and playing.

One more thing…

I also created a demonstration video using this Calculator on YouTube.

I am Li-Ji Hong. And this is my blog “Show IP Protocols”. See you next time!