This PowerShell script will collect all Netlogon.log files from the Domain Controllers, export the last x lines and combine it into one file of unique IP Addresses in CSV format. This easily and simply allows you to then identify any missing subnets that need to be added and associated to an Active Directory Site.
Yes, there are a couple of good examples of this type of script already available on the Internet. The trouble with them is that they would not produce reliable results, especially across environments where Domain Controllers were not all at the same Windows Server versions. Not a great practice, but it does happen in the larger environments where migrations are completed in phases. I’ve previously blogged about the change to the fields in the Netlogon.log file. I also found that other scripts were quite inefficient when reading and collecting the Netlogon.log files over WAN connections. The Report the AD Missing Subnets from the NETLOGON.log script by Francois-Xavier CAT was the best available. So I used it as a base to help derive the results I was after.