Very slow internet connection over LAN

Question

I've seen similar issues to this on this site and others but I believe that this is a unique (and very strange) situation and nothing I've seen so far has solved the problem. Apologies for the length, but I'm going to try to be as detailed as possible. My networking knowledge isn't particularly good, but I have a grasp on the basics (I'm a software engineer, so it helps to have some sort of idea).

Overview:
I've been using a Windows XP deskop (HP dc7800) for a number of years. I've recently been given a newer desktop (Dell XPS 8300), which I've installed Windows 7 Pro onto. For the past couple of weeks, I've noticed the internet connection speed on my Windows XP desktop gradually decreasing. I was told that it's probably a hardware issue and seeing how I was getting a new desktop, I didn't let it bother me. I've just got Windows 7 installed and I'm having exactly the same problems on there as well.

I don't have any problems connecting to other systems on the LAN. I can access network drives just fine, and with no speed issues. My Windows XP desktop is at the stage where it can barely connect to the internet - it takes around 2 minutes just to load Google.com via Firefox. My new Windows 7 desktop is a little faster, but it's still very sluggish. The main problem is when I try to download anything, via either of the desktops (for example, I've tried to download Firefox and Chrome on my Windows 7 desktop). The download speed is hovering between 1 and 5 KB/s. Consequently, even trying to run Windows Updates is impossible.

Both PCs are connected to the work LAN via ports in my office. There are another two people in the office and their PCs (they have a desktop and a laptop each) are fine. literally the only two PCs with a problem are sitting on my desk.

Things that I've ruled out

1. External network connection
   Obviously this isn't an issue as the other people in the office aren't having a problem. If there was a general problem with the connection, we'd all have the same problem.

2. Cabling
   The cables from the ports in my office to the server room are fine. If I plug my own personal laptop (XP) into either of the ports, my internet connection speed is as fast as I'd expect it to be. Likewise, if I plug my new desktop straight into the switch in the server room, it's still ridiculously slow.

3. My domain account
   My XP desktop logs on to the domain in the office. My Windows 7 desktop doesn't - it uses a local account, and it hasn't been connected to the domain yet. I've also tried other domain accounts on my Windows XP desktop and they all get the same problem. Likewise, I've signed on using my domain account on one of my colleagues' (working) desktops and I have no problems with connection speeds on their desktops. Given the combinations of accounts and desktops, that rules out an account issue (i.e. no throttling set up against my account).

4. Internet settings
   All PCs in the office use the same internet/network settings. We're all set to obtain IP and DNS addresses automatically, and running ipconfig /all on both my desktops, my personal laptop and one of my colleagues' desktops shows that they're all practically the same (aside from IP address, MAC address etc. that will obviously differ). The rest of the settings (gateway, subnet mask etc.) are the same.

5. IPv6
   This is turned off on my Windows 7 desktop and not even an option on the Windows XP desktop.

6. Virus/malware
   My Windows 7 desktop is a clean install. I've literally installed Windows 7, created a user account and logged on. That's all. I've also recently run a full scan on my Windows XP desktop and that came up clean.

7. DNS cache
   I've flushed my DNS cache, disabled and re-enabled the connections etc. and run a whole series of other random network related command line commands that I've found on various forums.

8. Hardware
   This isn't a hardware issue. I've used an Ubuntu LiveCD on my Windows 7 desktop to boot into Ubuntu (without installing) and connected to the internet just fine. Download speeds are as expected (i.e. working), which rules out it being a problem with the network card on that desktop.

9. Drivers
   I've made sure that both desktops have the latest network card drivers.

What does that leave? All I can think of is that there's an issue somewhere in the server room configuration itself - for example, I'm wondering if someone has changed some routing information on one of the servers without logging it anywhere, or something along those lines. As I said, my networking knowledge isn't great, but I've pretty much run out ideas and I can't find anything else online that helps, having tried most suggestions. I'm based in a small satellite office, and I've been going backwards and forwards with our support team (in our main office) to try to resolve this, but they're not on site so it's a case of try to fix things myself if possible.

Any suggestions would be gratefully received. Any time I come up with an idea, a bit of testing usually proves that it isn't the case and I'm still no closer to having a working internet connection!

Solution

There appears to be a problem with the network switch. There are various issues which I'm not really knowledgeable enough about networking to even try to explain, but the bottom line is that it's a hardware issue.

Comments

[ganesh]

A very interesting question, though it would seem a job for your workplace IT staff and not for the end user.

[Jeedee]

Indeed, and they're looking into it. As they're all remote though, I'm seeing if I can do anything from this end. Having ruled out the possibilities above, that's answered a lot of potential "what if?" questions. I was hoping that someone here might have a suggestion that I could either try myself or suggest to the support team.

[ganesh]

Re routing: That is usually done on IP base. Try this: Boot (slow) windows 7. Note the IP. Boot Ubuntu (fast) on the same desktop. Did you get the same IP? If not manually change it and add the result to the post (e.g. also slow, or not). While you are at it check duplex settings. (Many weird issues arise when duplex is either mis-configured or when the 'auto' setting gets it wrong. You can set that on your computers and the remote IT staff can log into the switch to see what it the settings are. Your remote IT staff can also try forcing the switch to 10mbit to see if that changes anything.

[xstnc]

@Hennes Good point about duplex. I would have a look at that. Mismatch in duplex does ALOT of funny stuff :) Routing issues, firewall issues and such is also something to check!

[Jeedee]

I've already tried changing the Duplex settings. It's currently set to Auto, but I've tried the other options as well (10Mb Full, 10Mb Half, 100Mb Full and 100Mb Half) with no change. I'll check the IP address now - I'm sure it was the same, but it doesn't hurt to double check.

[Jeedee]

I've just checked the Ubuntu connection settings and they're exactly the same (i.e. same IP, DNS, gateway etc.) as they are for Win7.

[ganesh]

A good idea, however it requires that the replacement PC has been installed and online for the past couple of weeks.

[Jeedee]

The computer names are very different. The XP desktop's name follows an old convention based around OS and user's initials. The Win7 desktop's name follows a new convention based around office location and user's initials. The first 9 characters (location) are the same as one other (working) PC in the office. I've changed the name of the Win7 desktop to something totally unique, just in case, and it hasn't made a difference. Thanks for the suggestion, though.