Network monitoring software

[Vladislav S. Davidzon]

[Please excuse the cross-posting]

Good afternoon,

I am looking for some good network monitoring software.  We are
currently trying to deal with an intermittent packet loss problem,
which we don't seem to be able to track down to any specific machines, 
at least not with the resources we currently have.  I need something that
would allow me to pinpoint the source of the problem, whether network
cards or bad hubs.  

We are running on a TCP/IP network consisting of Windows NT,
Windows 95, FreeBSD, Linux, SunOS and BSDI workstations & servers.

If you are aware of any such software, please e-mail me directly, and I
will summarize for the lists.  

Thanks


Vladislav