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December 13, 2007
Master Port Scanning with Nmap
Master Port Scanning with Nmap:
What's on your network and how vulnerable is it to a hacker attack? Having a clear picture of this is a vital part of effective network administration, and one way to build up such a picture is by network mapping using a port scanner.
Port scanning is the art of sending packets onto the network and analyzing what comes back – and what doesn't. By sending packets to specific ports and IP addresses it's possible to build up a picture of the IP addresses of devices that are connected, what OSes they are running, what ports they have open, and the services running on those ports. (Of course there are other ways of doing this, but since port mapping is one of the first types of reconnaissance a hacker is likely to perform, doing your own port mapping will give you a clear idea of what hackers may find out.)
There are many open source port mappers, the best known one of which is called Nmap (short for network mapper.) Nmap is available for Linux, Windows, Solaris and other platforms, from http://insecure.org/nmap/ . It's a very flexible scanner with stealth scan options designed to evade intrusion detection systems (IDS), and by using these you can get practice in spotting the signs of intrusion attempts in your logs.
In this article we'll be looking at some of the more straightforward uses of Nmap. The examples used are based on Nmap 4.20 running on Linux, but the same commands should work on any other platform. If you read our article about building a portable security tool with the ASUS Eee PC and Ubuntu, Nmap is an excellent candidate for immediate installation.
This is the next in a series Paul's been working on explaining how some of the more common network security tools you can find in the open source world work. Good practical examples to get the budding pen tester started.
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