See, There r several no of network monitoring sw in the market. No one can be guaranteed u this is the best ! Various people have various opinions. Though u didn’t mention here what OS u r using. I am providing an in-built tool for Server 2003
1. Open Add/Remove Programs in the Control Panel
2. Click the Add/Remove Windows Components button
3. Select Management and Monitoring Tools, and then click Details
4. In this window, select the Network Monitor Tools check box, and then click OK
5. Click Next, if prompted for additional files insert ur Windows 2003 Server CD or type the appropriate network path to these files
6. Click finish with installation is complete
Top : ManageEngine OpManager <a href=”http://”>www.manageengine.com</a>
2. iptraf (u have to download from: http://iptraf.seul.org/download.html) it’s free
5. Nagios (u have to download from: www.nagios.org/download)
Hope this may help u !
@ PrabhuVairak provided the link, the SW is not free, when I tried to download it indicates for 30 days trial version. Would u like to mention here what OS u r using ! Because, SW are different for various OS. And hope, u know it very well….
And also <b>Carlosdl</b> provided a very good link here! u have to look it also !