Validate IP Addresses and Slash Notation

I’m currently working on a project that requires the user to provide a target IPv4 address within a LAN for a network analysis. The address may indicate a single host (i.e. or it may use “slash notation” to designate a group of IP addresses according to the Classless Inter-Domain Routing (CIDR) Chart (i.e.

Google found several regular expressions that were supposed to filter out valid IP addresses but none of them included the slash notation, and many of them didn’t even work correctly.

I finally decided to write my own from scratch and put it all in a function to determine if an IP address (or network) is valid. I believe it works as expected:

Let me know if this helps you!You may freely use this code if you wish, but I’m not officially releasing it under any open source license because I need my other code that integrates this to remain closed source.

Update: Found a little bug and corrected it.

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