NetList is a small networking and security auditing script coded in Ruby by Eric Rafaloff. The tool takes a search term as an input parameter, and it will query the ARIN database for an organization and all of its related networks. This open-source utility can assist a pen tester in finding out which networks are owned by the target, and noting them for a later scan and audit.
Read more here - http://blog.ericrafaloff.com/2012/08/02/netlist-script/
Download NetList from here - https://github.com/EricR/netlist