Asnlookup: Look up IP addresses registered and owned by a specific organization

This tool will search an updated database for a specific organization’s ASN then use the latter to look up all IP addresses (IPv4 and IPv6) registered and owned by the organization.

What is an ASN Number

An autonomous system number (ASN) is a unique number assigned to an autonomous system (AS) by the Internet Assigned Numbers Authority (IANA). An AS consists of blocks of IP addresses which have a distinctly defined policy for accessing external networks and are administered by a single organization.


This script should be used during reconnaissance phase to identify properties owned by the company, and run a port scan on it to identify open ports and publicly exposed services.


Tested on Python >= 2.7 and Python 3.5

$ git clone && cd Asnlookup
$ pip install -r requirements.txt (or pip3 install -r requirements.txt if you're using Python3)
$ python -o <Organization>

Port Scanning

The tool exports the list of IP addresses as a text file which you can use with other tools such as Masscan. On the other hand, the tool supports Nmap and Masscan port scanning but it requires you to already have both installed on your machine. How to?

  • For Nmap:
- On CentOS

yum install nmap

- On Debian

apt-get install nmap

- On Ubuntu

sudo apt-get install nmap

- Mac OS

brew install nmap

Please refer to

To scan the IP addresses, append to the command -m arugment for Masscan or -n for Nmap:

$ python -m -o <Organization>

You can also pass your own Nmap/Masscan arguments (Default for nmap: -p 1-65535 -T4 -A -v; default for Masscan: -p0-65535 --rate 200).

$ python -m="<Masscan arguments>" -o <Organization>

Example using Nmap with custom arguments:

$ python -n="--top-ports 65535" -o twitter

It will export the result to a text file in the output directory (E.g: ./output/salesforce.txt) then run nmap.

Also read: DemonSaw – Free Cross Platform Information Sharing


For smaller organizations the ASN will usually be that of their ISP whereas the hostname might not. One example of this is, a GitHub IP address. The ASN is AS27357 (Rackspace Hosting), but the hostname is


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