You could be even cleverer, and use the response to my node on boolean logic with IP addresses -- I found busunsl's response the most helpful.

Once you have INTs, and you mask them against the relevent netmask, you can merely do an AND to determine if they're in the same subnet. This also allows non-octet aligned subnets (for example, 10.53.80.0/24)

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RatArsed