Windows Vista causes router to be unreachable during downloading

Unanswered Question
Jan 29th, 2008

I have a strange problem and I don't know if it is specific to the Windows Vista operating system or my network configuration. Here is my scenario, I have 2 Windows Vista Ultimate clients that causes all other users on the network to not be able to connect to the internet when either of the Windows Vista clients are downloading files from the internet. During my testing I would open a command prompt from one of the clients and perform a transient ping to the inside interface of the 2651XM router that is used to terminate a DSL connection to the internet. During the download process the ping packets begin to become increasingly worse with response times until the Windows Vista client reaches over 500KB/s and then the router becomes completely unresponsive or I begin to see severe packet loss.

I have all clients connecting to a 3560G switch and their gateways are set for a PIX515E that has its E1 interface configured on a vlan'd interface (VLAN200) on the 3560G and its E0 configured on another switchport but configured for a different vlan (VLAN300). The PIX515E is configured to use the 2651XM router as its gateway to the internet and the 2651XM's Fa0/0 is configured on the same vlan as the PIX515E's E0 (VLAN300) and the 2651XM's interface Fa0/1 is configured for the same vlan as all connecting clients and the PIX515E's E1 (VLAN10). Hope this makes sense.

What kind of tools/commands can be run on each device (Vista client, 3560G, PIX515E, 2651XM) to find out what is causing this issue?

I have this problem too.
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robert.horrigan Wed, 01/30/2008 - 09:23

Do a show proc cpu on the switch and router when you download and see what happens to the resoures. Do a show interface (to the internet) and see what the tx/rx is when they are downloading. If the tx/rx is maxed out - there you go. Make sure you clear counters before this testing and then show all interfaces involved and look for errors, crc, etc.

Joseph W. Doherty Wed, 01/30/2008 - 17:02

What might be causing your issue is Vista's new "Next Generation" TCP/IP stack. Specifically in this instance, its default (I believe) advertisement of very large TCP receive windows. With a cooperate sender, this allows Vista clients to often pull data much faster. Try at a command line on your Vista clients "netsh interface tcp set global autotuninglevel=disabled". ("netsh interface tcp set global autotuninglevel=normal" will restore.)

If deactivation of this Vista feature cures the problem, you could try other Vista autotunninglevel options that mimic XP or you can pursue what might be a FIFO queuing issue for large traffic flows through your environment.

david.keil Thu, 01/31/2008 - 15:15

Sorry all, been a while since keeping up with my original post. It turns out that there are tuners such as TweakVI, TuneUp2008 and TweakNow 2006 that the clients are using and not choosing the right type of connection. They were choosing LAN capabilities increasing the TCP windows size to a point that it was flooding the router. I set everything back to factory default and was able to resolve the issue. Please be aware of Vista or any clients trying to adjust things on their own without the consent of the network team. Thanks.

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