Go to www.iana.org then
click on on
IP Address services. This gets to the IANA address assignment page.
To find assignments for the large blocks, scroll down the
page to "Internet Protocol v4 Address Space" (or click this link to
go to the same link):
http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xml.
Because of the IP address shortage, the large blocks that used to be
assigned to companies or other organizations are not assigned to
ARIN or other organizations. This is because the addresses that those with
large blocks were not using need to be in a pool available for assignment
to others.
There are multiple versions of "whois" search facilities. They
include:
The linux "whois" command (e.g. whois malone.edu).
From the icann.com home page, select "Resources" and "WhoisInformation".
"whois.iana.org" (can be clicked from main icann.com page).
The different versions might give slightly different answers.