We are having a strange problem here where I work (and I don't know how can I debug this).
Our central switch is a stacked 3Com 5500G-EI SFP + 5500G-EI. Leaf switches are 3Com 2948-SPF, connected to the 5500G via optical fiber.
On one of those 2948, there are more 3Com baselines switches.
It's more or less this (http://people.debian.org/~naoliv/misc/network.png
The network is "big" (300 machines more or less) (Yes, I know. "Break this network", "Create sub-nets", etc; if everything goes well, we will have a better network structure someday).
But well, what is happening these days is that the networking is stopping. We work at , and we can't ping the other machines connected to the same switch at  (nor we have communication to the other places). The same happens for people located at other places, like .
It seems to be something that spreads on the entire network, but I don't have idea of what could be this.
There are days that it takes only 10 seconds, then everything gets back to normal. Today it stayed almost 1 hour without network. The strangest thing is that it seems to stop around 5:00h PM
Do you have any ideas of what can cause something like that? Worm, somebody using some malicious program, something wrong on a network cable, a broken switch? What can we use to debug this, please?
Thank you very much! Edit: See comment #5
for more info, please.