Open Source network analysis & diagnosis tools?

Hello LinuxManagers,

I'm after an open source tool (or set of tools) to analyse LAN
performance, in the same theme as Iperf or traffic-vis.  This could
include some kind of discovery or mapping features, but not rely on SNMP. 
The idea is to be able to walk into an organisation with little or no
preparation or administrative privileges, and use a tool set quickly
determine bottlenecks, benchmark performance, get some meaningful stats
off key pieces of infrastructure in the MDF, DMZ, perhaps check firewall
configs from a user perspective and so forth.  In other words, something
beyond the basic security auditing, but not as thorough as to require
passwords etc.

I've scanned through the archives of this list but there hasn't been much
activity on this topic lately and I just wondered if anyone has any
experience or knowledge of some new cutting-edge projects, cos there's a
lot of this type of stuff springing up out there now.  It's probably time
for an update & summary so the list archives can include all the recent
developments out there.

So, any takers?  Any pointers to some good projects (whether beta, in
development or commercial-grade) much appreciated.  The only criteria is
it must be open source & preferably Linux based of course :)

Luke
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