TABLE OF CONTENTS INFOSEC Best Practice #107
Strictly control IP assignment.
One of the key pieces of information for a hacker is knowledge of the IP address ranges within an organization. Additionally, knowledge of the exact IP address of servers and other mission-critical machines can help a hacker focus an attack on these systems. IP addresses can be obtained by buying a block of addresses from Internic or from an organization's Internet Service Provider. Addresses can be bought as class C licenses (256 addresses) or class B licenses (32,000 addresses). Class B licenses are usually reserved for service providers and large companies. There are very few class B licenses around and they are very expensive. Almost all companies will purchase Class C licenses as blocks of 256. If there is no connection to a public network using IP and there are no plans to hook into such a public network in the future (highly unlikely), then the company can use their own IP addresses when setting up systems. Also, if firewalls and proxy servers are used to separate the internal network from the public network, then all the systems internal to the company do not need legal IP addresses since the proxy server will use its own address to communicate with the public network. Most companies buy blocks of legal licenses because they do not know how they might want to communicate in the future and therefore do not want to have to reconfigure their computers with new IP addresses.
