At least twice a week I find myself visiting ip2cidr.com, the IP to CIDR converter. Since the owner/author of the site hasn't release the source code, and I love a challenge, I developed my own version. The guys at the job find the tool useful, and after a few minor bug fixes, I've made the IP Range to CIDR tool available for use here at Nullamatix.com.
Linux and most other Unix derivatives provide the ability to create null routes. Let's say for instance a Linux server is being attacked by hundreds of IPs from 126.96.36.199/16. No problem..