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Internet speed slow, but fast on the Domain Controller?

Posted on 2013-01-30
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Last Modified: 2013-02-18
Our Internet speed has been horribly slow for our facility for the clients since I started working here. I'm starting on troubleshooting it and get it going for them. As a non-related side project we had to re-do the wiring for the facility. So everything is running on Cat6, with new cisco routers and cisco gig switches etc. I was hoping the problem would disappear after that project but it hasn't.

Network speed is great for all of the machines,  we haven't had much issue with that.

However the Internet speed is very slow. We have a 20 mg connection coming in for our small facility. I went on our domain controller (SBS 2011) that's plugged into a core switch, and I'm getting close to 16mg, which is great. However if I plug a client PC into the same switch they only receive about 1mg.

I figured it might have to do something with DNS. So I pinged Google.com and received about 46 ms latency. I then pinged Google's IP address and received bout 43 ms latency.

So I figured this would eliminiate possability of a issue for dns? Our forwarders are pointing at Google's DNS 8.8.8.8.

To make it even more complicated, "some" user machines are reiceiving about 4mg connection speeds after doing a speedtest. Though not too many of them are. But oddly they're all plugged into the same switch.

What else could be causing this? I'm stumped!
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Question by:Pancake_Effect
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by:foxpc123
ID: 38837142
Could you try a quick test by putting a non-domain machine, say a test laptop, set the network connection so that it uses the default gateway IP address to be the IP address of the router which connects directly to the interner and also the DNS IP address to be the same, and then see what the speedtest is like.

I just want to know if using the router for DNS results in a quicker test or whether the results are the same you can see then whether the SBS is having an impact.

We had some really strange results with HP machines with NIC's to do with task offloading that took ages to find out.

So using a machine that you know and can verify independently of the domain helps to provide a baseline and then we can move from there.
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by:Pancake_Effect
ID: 38837351
I did that and it was still receiving terrible speed, only 1mg. Again oddly I just went to another computer that's on our domain, and they're receiving around 10mg. There seems to be no ryhme or reason other than they're different manufactures. It's the same OS, but we do have a mixed brand here between dell, acer, and lenovo.

These computer have gig ethernetcards, so they can't be that bad. Maybe it's a setting on the card?? Any idea what may be causing it? I mean it sounds like it would have to be something with the ethernet cards or a local machine setting if the other random computers are running fine on the same switch.
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by:Pancake_Effect
ID: 38837358
I see one difference on the nic card is that one of the computers that is running fine has jumbo packets disabled, where the other one has a default setting of 1500 with no disable option however. Not sure if it's that or possibly any other setting.
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by:foxpc123
ID: 38837438
My thought on this would have to be the introduction of a test machine in which you have confidence.

So test a machine which works in a network that you have confidence in and you obtain a speed which is consistent with that particular network. Once you have that then introduce that machine into this network and then by isolation - try to establish where the issue is.

So you have your test machine - connect this to the internet router and then remove all other network connections from that router, so only your test machine and the router are the only network connections. Then confirm the speed test.

If this is good then move to the next point in the network. If the speed is terrible, then we need to investigate the network settings associated with that router and it's ethernet port. That way we can start to eliminate the potential causes of the issue.

If we start to mix machines, network connections and differing speeds, it just gets confusing and really hard to identify where the cause of the issues lie. Divide and conquer is the way forward - let me know how you get on.
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Assisted Solution

by:giltjr
giltjr earned 100 total points
ID: 38837749
Are all desktop computers running the same OS with the same patch level?

Are they all patched?

Do you run with the Windows Firewall enabled?

How are you testing the Internet speed?

Can you install something like Wireshark on a PC that is getting real bad performance and on one that is getting good performance and run whatever speed test you are doing and get a packet capture.  Then compare the two?
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by:avcontrol
avcontrol earned 100 total points
ID: 38838854
First - you should isolate whether it is network or PC's issue, as it was advised foxpc123 .
If this is network, then you probably should post network diagram and have your routers/switches configuration reviewed, IP addressing, DHCP server scopes and so on.
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by:Pancake_Effect
ID: 38839883
Thanks guys, giltjr I took your advice and looked at the firewall. We don't use windows firewall, but we do use Symantecs. We have Symantec endpoint protection 12.1. After disabling it, it shot up from .46mb download speed, to a full 8mg connection which is great for the users.

Now I have to figure out why Symantec is cutting the Internet speed......
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foxpc123 earned 300 total points
ID: 38840085
There's a big article here on Symantec within EE;

http://www.experts-exchange.com/Virus_and_Spyware/Anti-Virus/Q_25044678.html

It may be worth a read - a long one by the look of it!
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