A user will have an IP for their host in cases where the server does not resolve or mask it.
The host is a string and no meaning is attached to it. Comparisons are string based. It's not practical to perform a lookup on every host you see, not that it should be done even if it were.
Sorry, i think its could be very usual againts flood or something like that .. Anyway if not i think at an other solution; to resolve the IP by MAC adress.. cause all MAC adress is unique so..
You don't have access to the mac address, the mac address has nothing to do with an IP, and mac addresses can be changed. To ignore a line you need to have the information you're basing that decision on at the time you receive the message. You can't wait to resolve the IP address of every user to decide if you display a message or not. And you shouldn't be resolving hundreds of IPs anyway.