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Random decrease in Internet speed on a domain network

By fnanfne ·
Hi there.

As in the title of this discussion, we're experiencing a decrease in Internet speed on our network. This seems to be happening at random times.

Our network consists of a server running Windows server 2003 with up to 20 other wired nodes running Windows XP including three network printers. We also have a WLAN with a WPA2 encryption.

We have a BT 2wire router and two Ciso swithches.

I suspected the casue of this problem might be any of the following:

1) a General problem with our server
2) The downloading of torrents over the wireless
3) a Physical problem with the cabling on our network.
4) a Problem on our ISP's side.
4) a Problem with our router

Our server acts as a DHCP, DNS and WINS server. a Few weeks ago, the DHCP stopped working on our server. When I open the DHCP console/window, the status says "Not Connected" on the right hand pane. When I click on the server located in the left pane, the status suddenly changes to *Active* and only then does our server lease IP addresses. I have disabled DHCP on our server as a result and enabled DHCP on our router for now. What could be the cause of this?

Our server does a daily back up to a tape drive and this takes 8hours. I initially thought this backup process might cause the problem but we still experience a slow Internet speed even if no backup is running.

The downloading of torrents really fills the pipe but when I disable the wireless, a slow Internet speed is realised once again. Is there a practical/cheap way of blocking torrent downloading without having to buy a Cisco switch(with packet inspection) for ?2000?

The third possibility is not likely as a physical cabling problem would just mean no connection to start with.

As for the ISP. Well, we have a 16MB broadband connection with PIPEX and have a contention ratio of 20-1. I have run a lot of broadband speed tests and found that our speed does fluctuate between 3 and 12MB/sec. Is this a direct indication of a problem on our IPS's side or could these readings point to another problem? PIPEX remains confident that there's nothing wrong on their side.

Our router is a very good one. ALL other routers we had (Thompson, Netgear and a Linksys one) had to be rebooted at least twice per week as they just froze. The BT never had to be rebooted even once, touch wood! So I can't see that our router is faulty.

As I mentioned before, this happens randomly and the speeds are sometimes slower than dail-up! Some websites open lightning fast while others take forever and sometimes the Inernet browser just gives up saying it can't find/open the address. This points to a DNS problem, or does it? How can I change our primary DNS server to another one? Our primary DNS server is our server running Windows server 2003 and the secondary one is pointed to our router. Can I simply change it in the Network properties > TCP/IP > properties page?

Any help/ideas would be greatly appreciated!

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One issue you state is not an issue

by robo_dev In reply to Random decrease in Intern ...

Your DHCP console and the DHCP server are two different things.

'Not connected' simply means that the DHCP console is not connected to the DHCP server, it is not an indication that the DHCP server has a problem.

When you "click" the server the status should change to ** Active **, which means the console is now connected to the DHCP server. You should confirm that the DHCP server is working correctly by looking at the Leases under your Scope(s). You can also turn on audit logging on the general tab of the server properties. You can also right click the server and view statistics.

My guess is one of three things are going on:

1) switch cabling, hardware, or configuration issue.

2) User malware/virus issue. Some viruses use PCs to do things like denial-of-service attacks, sending millions of UDP packets from one of your PCs.

3) The Torrent issue you mentioned.

My advice would be to:

Look at port statistics in the switches...this could identify things like duplex mis-negotiation (100 half duplex vs. 100 full).

Install a simple 10/100 hub in between the router and LAN, and setup a PC running the free WireShark protocol analyzer. This will tell you what's going on.

I would also install a simple ping-plotter application to ping your ISP and keep track of the response time on that end. Some ISPs have HUGE problems with DNS, so the simple fix in some cases is to use a DNS server on the Internet other than your ISP-provided DNS server.

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by fnanfne In reply to One issue you state is no ...

robo_dev I thank you for your reply and for taking the time to read through my problem!

I just want to rephrase my DHCP problem:

When I open the DHCP console, "DHCP" is highlighted in the left pane and it says "not connected" in the right hand pane.

Now, just beneath "DHCP" in the left pane, is the name of my "DHCP server". When I click on that, I see that it's **Active** in the right hand pane.

Now, if I highlight "DHCP" again, I see that the status in the right hand pane changed from "Not connected" to "Running"

I actually ran some tests earlier on and the server did not lease any IP addresses but started doing so when I opened the console, clicked on my DHCP server and back to "DHCP". Only after the status changed to "Running", did the server respond to IP requests.

Below are three links of screenshots I took to support my findings:

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