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DSL connection problems - speed gets progressively worse.

Posted on 2004-09-23
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Last Modified: 2010-03-18
Okay, here's the groundwork.
We've got a 14 computer LAN set up.  All of the clients (12) are running Windows XP Home, 2 servers (1 Win2003, 1 XP Pro).  All of the computers in the LAN are connected to an ADSL 1.5 Mbps internet connection through a Belkin router and a Next Gen ADSL modem (I believe it is an Etherfast II).  ISP called on Monday and wanted to adjust our static IP (no problem).  We configured the router and reconnected to the modem/router.  Now for the past three days, my internet connection fluctuates in speed from 40k - 1500k.  When I contacted the ISP, they claim there is nothing wrong on their side of the connection.  Here is what we've done thus far.  Tried three separate routers (2 of which were brand new), wireless connections act the same way (fluctuate).  Previously, we had no issues with the service.  Only thing that I believe could be a problem is that when I was keying in our IP, the router came back with an error about our IP not being in the right subnet (although it is what the ISP gave me).  Anyone have any ideas?  I'm at my wits end.  I know it has to be something on their end as we had no problems until after we change the IP.  Thanks and here's hoping I can regain my insanity.
 
I-LAN
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Question by:ILANCOMPUTER
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by:KaiserSose
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Your problem could really be anywhere but try this....

I assume that you have a set up like    Internet ---------  Modem ---------- Router -----------  Switch::::::::::::::hosts  

Unplug the switch from the router and plug in a machine and surf to http://performance.toast.net/   and do their speed test a few times.  See what kind of speed you can get.  If it sucks, then the problem is your ISP.  If it is good, then chances are that it is your network.

dave
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Tim Holman earned 500 total points
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You could well be infected with a virus or worm that is chewing up all the bandwidth...  do the Belkin router logs reflect large amounts of LAN activity ?
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by:crissand
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It can be a MTU problem. See here:

Change MTU to 1500.
Open an MSDOS command prompt, and just use ping -l 1472 -f www.dslreports.com
Reduce 1472 by 10 until you no longer get the "packet needs to be fragmented" error message, then increase by 1 until you find the max command line number for ping.
Add 28 more to this (since you specified ping packet data size, not including a packet header of 28 bytes) AND THIS IS YOUR MaxMTU.

The error of correct mtu is somehow related to vpn over wireless, but I found this test as good for maximizing bandwith utulization.
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by:ILANCOMPUTER
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Tim,
Thanks.  You know it's usually the most obvious things that cause the problems and that was our case.  After you mentioned the logs I went and shut down all systems save one and then watched the activity.  The LAN activiity skyrocketed after only 15 seconds .  I then went online and ran housecall which found a couple of trojan viruses that my Norton hadnt keyed on.  Now the system is back up and running at full speed.  Thanks for the quick response, I just assumed (shame on me) that with Norton running it would catch any virus activiity.  You get the full points and my business will not be hurt for another day.

I-LAN Digital Entertainment
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by:Tim Holman
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Glad to be of assistance !  There are always a few worms/viruses that will always get onto your systems before you get the change to update your signatures, and will generally stay there as they disable the anti-virus system's ability to disinfect them, EVEN when patched...  
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