mod_asn is an Apache module doing lookups of the autonomous system (AS)[1], and
the network prefix[2] which contains a given (clients) IP address.

It is written with scalability in mind. To do high-speed lookups, it uses the
PostgreSQL ip4r datatype[3] that is indexable with a Patricia Trie[4] algorithm to
store network prefixes. This is the only algorithm that can search through the
~250.000 existing prefixes in a breeze.

It comes with script to create such a database (and keep it up to date) with
snapshots from global routing data - from a router's "view of the
world", so to speak.

Apache-internally, the module sets the looked up data as env table variables,
for perusal by other Apache modules. In addition, it can send it as response
headers to the client.

It is published under the Apache License, Version 2.0.

Source code can be obtained here: http://svn.poeml.de/svn/mod_asn/

Author: Peter Poeml

Links:
[1] http://en.wikipedia.org/wiki/Autonomous_system_(Internet)
[2] http://en.wikipedia.org/wiki/Subnetwork
[3] http://pgfoundry.org/projects/ip4r/
[4] http://en.wikipedia.org/wiki/Radix_tree