[ggg2]

this will not help much as some google products use IPs (4 and 6) directly too.

[dredmorbius]

CIDR blocks are your friend, at the firewall.

[jakeogh]

Know of a lib to manage them?

[dredmorbius]

Not offhand. The Routeviews project is a useful way to turn them up, though.

http://www.routeviews.org/routeviews/

Particularly reverse DNS queries.