While this system of keeping an active list of a company's netblocks works great -- beware. It can suck up memory and result in "cannot allocate memory" errors. Example: building a list for Apple (AS6185) will give you a large list of small netblocks in 17.x.x.x. However, "whois 22.214.171.124" shows that 126.96.36.199/8 is a direct allocation to Apple, so specifying a network alias with a /8 takes a lot less memory. Google is even worse with 7400+ IPv4 netblocks from the whois ASN output.