IP to authoritative CIDR webservices

[morrowc.lists at gmail.com (Christopher Morrow)]

On Tue, Dec 15, 2009 at 12:18 AM, William Pitcock
<nenolod at systeminplace.net> wrote:
> Hi,
>
> On Mon, 2009-12-14 at 21:12 -0800, Paul Ferguson wrote:
>> On Mon, Dec 14, 2009 at 8:57 PM, William Pitcock
>> <nenolod at systeminplace.net> wrote:
>>
>> > Hi,
>> >
>> > Does anyone know of a webservice that converts a given IP into the
>> > public CIDR range that belongs to? ?I am developing a tool where IP to
>> > CIDR conversion based on RIR whois data would be useful for implementing
>> > filtersets.
>> >
>>
>> WHOIS?
>>
>> Alternatively, use the Team Cymru tool to find the AS, then the CIDR Report
>> portal to determine all perfixes originated by the AS in question:
>>
>> http://asn.cymru.com/
>
> Looks like their WHOIS server in verbose mode will do the trick for what
> I want, as it provides predictable output. ?Thank you.

there's also the lightish weight routeviews DNS zone data:
$ host -W 6 -R 10 -t txt 50.35.2.128.asn.routeviews.org
50.35.2.128.asn.routeviews.org descriptive text "9" "128.2.0.0" "16"

128.2.35.50 lives in 128.2.0.0/16 from ASN9

-chris
(thanks to joe/joel/dmm and capitan kemp)