Hi Daniel
for various reasons (legacy mainly) the way matching works in the manual classifier is slightly different to how it works for the entries in the web access control rules.
We added the functions in the web access control rules later, and it's probably simpler to use those to block these requests.
If you need those computers to do other things and succeed at that, you can't just block them by IP.
Do these computers use proxy auto-detection? If so, you can possibly alter the WPAD.DAT file that WinGate sends back to prevent the clients using the proxy for attempts to this site (in the FindProxyForURL function you could return a direct connection, or proxy that doesn't exist so it fails in the client rather than in WinGate).
Yes, the connections to WinGate will consume sockets. the DNS failure shouldn't really be causing any problems, but the connection will consume a license, which can be a problem if these are in short supply.
But the primary issue seems matching. Did you try adding a site in a new web access rule to deny access to this site?
If using the manual classifier, be careful what you choose to match on. If matching on URL, then the matching will expect to see
http://something or
https://something. If matching on site, then it doesn't expect to see the http:// and/or
https://, and so including or omitting these incorrectly can prevent a match.
Regards
Adrien de Croy