Scan IP ports without Windows Firewall restrictions

A properly configured Windows Firewall is great for security, but can also impede your own security scans. Learn how to bypass a secure Windows Firewall and scan for a user's IP address with this advice from Jonathan Hassell.

Question: To perform a network security test, I'm using an IP scanner to check on IP addresses. However, some of my users use the Microsoft Firewall, which, in turn, hides their IP addresses. Is there a way that will allow me to scan their IP addresses?
- Posed by a SearchWindowsSecurity.com reader.

Jonathan Hassell offered this response:

I assume you're talking about a port scanning regimen in which you are using some sort of automated tool that pegs each machine on a given network or subnet or a subset of network addresses thereof to determine what services are running based on which ports respond to the network security test. It's true that the Microsoft Firewall, properly configured, will put the machine into a stealth mode, which hides most of the surface area of a machine from attack. This is a good thing. It's what you want.

Windows Firewall security
Tuning Windows Vista security: The firewall

Managing Microsoft's Windows Firewall

If you want a more definitive result, I suggest using an old machine and a downloaded copy of Linux (it's freely available, as you may know) and then use the Nmap program to perform an in-depth IP scan. As long as you identify the range of IP addresses you're looking for, Nmap can provide a reasonably definitive answer to your question of which machines are advertising services to the general Internet public.

About the author: Jonathan Hassell is an author, consultant and speaker residing in Charlotte, N.C. Jonathan's books include RADIUS and Learning Windows Server 2003 for O'Reilly Media and Hardening Windows for Apress. His work is seen regularly in popular periodicals such as Windows IT Pro magazine, SecurityFocus, PC Pro and Microsoft's TechNet Magazine. He speaks around the world on topics including networking, security and Windows administration. He can be reached at jhassell@gmail.com.

This was first published in July 2007

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