How to identify and monitor network ports after intrusion detection

When analyzing firewall logs or IDS alerts, you have probably come across an unfamiliar source or destination port. The next step in the analysis process is to figure out what service is using that network port so you can determine if it puts your network at risk.

The easiest way to identify and begin monitoring a network port is to look in the services file included with every modern TCP/IP stack. That's C:\WINDOWS\SYSTEM32\DRIVERS\ETC\SERVICES under Windows (Hint: You can use Notepad to view or edit the file -- just double-click on it and choose notepad from the list), or /etc/services under most Unix variants. The Windows 'find' or Unix 'grep' commands can quickly search these files. Very often you won't find the port in the default services file because they usually li

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Once you've found a service that uses the port in question don't assume anything! First, is it really what is seems to be, or did someone switch port numbers? Some ports are commonly used by more than one service, so which is it? Is the service allowed in your environment? Should it be? The following tools will help you find out more about what is really happening.

If all else fails, try searching on Google, but don't make too many assumptions about what you find. The goal is to identify what is actually happening in your environment -- why did you get an alert, why was this log generated, is it malicious or benign. You know your network better than anyone on the Web.

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