We've added a simple 'valid' IP tester to GuardianAdmin and Ban Utilities.
Apparently there are some Admins out there who add improperly configured IP addresses to Guardian's IP list and then can't figure out why their forum is throwing 403 and 500 errors.

The IP tester does not check if the IP address in question is one that is in use. It simply checks that the syntax of the IP is valid. For instance
178.17.174.196 is valid
178.17.174196, 178..17.174.196, and 260.17.174.196 are not

1762::B03:1:AF18 is valid but
1762::B03::1:AF18 is not

(The second set of IPs are IPv6 and I have yet to actually see one of those in the error log here but we need to be prepared for them. The tester may pass some illegal IPv6 configurations since I have yet to find a pre-built regex for testing IPv6 that actually works.)

Also, since this forum is on an Apache 2.4 server, the Apache 2.4 Mod is in the process of being rewritten as well since support for blocking domain names in .htaccess was inadvertently dropped. (Again, although I have yet to see a YaBB .htaccess file with domain names in it, it is supported by .htaccess and by Guardian. I have not yet found anything online that says wildcards (*) are still allowed in domain names. They were in Apache 2.2.  )