How to find location of an IP Address Without using APIs?

More of a theoretical question. Yes开发者_如何学Python, I know those types of questions are frowned upon here. But suppose APIs like MaxMind GeoIP's didn't exist, and you wanted to build a service that translated IP addresses to the city it's in. What would you do? How would you go about solving that problem?

1. Use the whois database to find out who the IP is allocated to.
2. Use DNS to do a reverse lookup on the IP address.
3. Use traceroute to guess the location based on the routers leading up to the host

As an example, lets look at stackoverflow.com (64.34.119.12)

$ whois 64.34.119.12 | egrep "(OrgName)|(City)|(State)|(Country)"
OrgName:        Peer 1 Network Inc.
City:           New York
StateProv:      NY
Country:        US

whois shows us that they're probably in NY, NY.

$ host 64.34.119.12
12.119.34.64.in-addr.arpa domain name pointer stackoverflow.com.

Reverse DNS (PTR record) doesn't help here. However, a lot of ISPs do have region specific reverse DNS entries that can help with this process (especially for dynamically assigned hosts). As an example:

$ host 24.25.195.1
1.195.25.24.in-addr.arpa domain name pointer sndgca-dns-cac-01.san.rr.com.

This host is obviously identified and located by it's PTR record: a Time Warner (Road Runner) caching DNS server in San Diego, CA.

Now, back to the stackoverflow.com locating process:

$ traceroute stackoverflow.com
traceroute to stackoverflow.com (64.34.119.12), 64 hops max, 40 byte packets
ms
 (... removed the first few hops ...)
 8  ae-6-6.ebr1.Chicago1.Level3.net (4.69.140.189)  30.9 ms  28.855 ms  25.183 ms
 9  ae-2-2.ebr2.NewYork2.Level3.net (4.69.132.66)  54.373 ms  54.197 ms  48.171 ms
10  ae-6-6.ebr2.NewYork1.Level3.net (4.69.141.21)  48.250 ms  50.712 ms  51.293 ms
11  ae-62-62.csw1.NewYork1.Level3.net (4.69.148.34)  59.493 ms ae-82-82.csw3.NewYork1.Level3.net (4.69.148.42)  51.694 ms ae-62-62.csw1.NewYork1.Level3.net (4.69.148.34)  58.315 ms
12  ae-3-89.edge1.NewYork1.Level3.net (4.68.16.142)  51.529 ms ae-2-79.edge1.NewYork1.Level3.net (4.68.16.78)  50.77 ms ae-3-89.edge1.NewYork1.Level3.net (4.68.16.142)  50.567 ms
13  10ge-te-1-1.nyc-75bre-dis-2.peer1.net (216.187.115.77)  50.776 ms  51.193 ms  56.166 ms
14  gig2-0.nyc-gsr-b.peer1.net (216.187.123.5)  54.994 ms  58.813 ms  51.794 ms
15  gwny01.stackoverflow.com (64.34.41.58)  54.121 ms  52.65 ms  54.166 ms
16  * * *
(... remaining time outs removed ...)

The traceroute output confirms our suspicion that stackoverflow.com is hosted in NY, NY.

That's one way to tackle geolocation without an API.

Im really guessing here but this may work.

IP ranges are assigned by IANA to regional providers. There are five of them. In turn each regional provider assign IP ranges to end users and internet service provides. If you can get/buy the information from the regional providers and their ISP clients you are in business.