Network monitoring tools

[Ryan Golhar]

Can anyone recommend a good, free network monitoring tool?

I have a lab of about 20 Linux boxes connected to a switch.  It seems
like every once in a while, the performance of all the machines drops
dramatically, and I believe its related to the network, as all the home
directories are NFS mounted, but not sure where.

I'd like to get some sort of an idea of network usage and what is taking
up the bandwidth.  

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Ryan Golhar
Computational Biologist
The Informatics Institute at
The University of Medicine & Dentistry of NJ

Phone: 973-972-5034
Fax: 973-972-7412
Email: golharam at umdnj.edu