Forgive what may sound like a newbie question, but I've looked and can not find this answer and would really like to find an elegant solution. When I find an IP behaving badly in my logs, I look-up the provider. Sometimes you get the range of IPs belonging to this outfit 100.123.00.0 - 100.255.124.054 (made up) and sometimes you get the block info 100.123.00/14 (or /24 or /16, etc.) 1. Is there a url out that there will always output the block info? I'm interested in banning the blocks. 2. Am I too dimwitted to know by looking at the IP range given in my example that there is a well known formula that should tell me that the resulting block is always a /12 or /14, etc? 3. Some whois look-ups offer flags to modify the results (like http://www.apnic.net/apnic-bin/whois.pl) but no matter how I set them I can't seem to get the blocks to show. Thanks in advance!
Found a better tool here: http://www.dnsstuff.com/ Using the tool for "CIDR/Netmask Enter CIDR range or IP" Hope this helps others.