I work for a company on my university's campus, helping with general IT problems and some web development. But lately there has been a problem that has me and my boss completely stumped. We, plus one contractor, make up the entire IT department, so I'm reaching out to you for help.

All around the office, we have wall jacks. These collect in a closet down the hall and all plug into a switch. This switch, along with our individual server jacks, plugs into another switch, and that switch plugs into our firewall hardware. Then the firewall is connected out to our campus network. Our campus internet is, well, very fast. I don't know exactly the terms, tiers, etc., but we have thousands of students and downloads can run as fast as 10 MB/s at night; uploads are sometimes even faster. I think we're practically ISP level. In short, I have a lot of faith that it is not the campus side of things that is causing a problem, combined with other evidence I'll mention in a moment.

So our symptoms: web browsing is fast. Web pages, images, etc. load instantly. No problems there. But then when I go to download something, the download starts fast but very quickly (a matter of seconds) drops to nearly 0. Often it will actually drop to 0 and time out. This happens with even very small files, 1 MB or less.

It smells to me like a QoS sort of thing. I'm not entirely sure, and I wanted to get your opinions first. My boss is hesitant to touch our firewall, much less let me touch it, and it was set up and is managed by a consultant remotely.

These problems don't seem tied to a time of the day. I've tried downloads after 5:00 and still the same thing happens.

From my desk, I can turn on my wireless adapter and pick up the campus wireless access point. If I unplug ethernet and connect to it, downloads are fast. This adds to my suspicion that it's limited to our company network.

Also, a number of weeks ago the consultant upgraded our firewall firmware. Suddenly everything was very fast. I tested with downloads from Sun and speedtest.net and things were blazing fast, as they should be with our campus internet! It was wonderful, and I figured the slow speeds were an old firmware bug. In a matter of days, things steadily declined until they were back to the old symptoms.

Oh, and we have antivirus installed on every computer, and we keep it up to date. Though I suppose the possibility is still there that someone could have spyware which is bogging down our internet, in which case what is the easiest/best way to find this out? (maybe this should go in a separate question)

Thank you for your patience in reading all of this. Do you have any ideas as to what I can try? Is this something that you've experienced before? What sort of tools or methods can I use to try and diagnose the problem?

P.S. everything here is Windows. Windows Server 2003 and 2008 on our servers, and Windows XP on employees' machines.

Update: We are submitting a ticket to the university to just take a look and see if they see anything unusual and/or can suggestion methods for us to try and pinpoint our problem. Hopefully they'll be helpful! I'll update this to let you know what goes on.

Update again: We found a hub (yes, a HUB) right between our campus connection and our firewall. It had only those two ethernet cables plugged into it, nothing else. After removing the hub, our speeds have jumped up to several mbps. However in talking with the campus, we got them to run a gigabit line to our firewall in place of the 100mbps line. As of friday, we are at about 65 mbps up and down (according to speedtest.net at 8am)!! Go NC State!!