This one has me totally stumped

[Exfso (Peter)]

I have 4 computers at home, all windows 7 pro on a local network and connected to NBN on a 100/40 plan. So far so good.
My download speeds are excellent as I am only 150metres from the node, so I regularly get 96Mbps or 12.5megs /sec downloads. Recently and only on one computer my download speeds have started to fluctuate enormously on a typical download range from 45Megs/sec to 4Megs /sec. Not bad considering my theoretical max is 12.5Megs /sec. How is this happening??? The other computers are not an issue and speeds stay pretty well constant at 12-12.5 Megs/sec for an identical download. My deduction is it is a setting on the one computer causing the issue, not the Modem/router, but I am totally lost where to start fault finding this one
Any ideas on this one you tech gurus??

[acropolite (Phil)]

Could be the ethernet port flapping, i.e. unable to decide whether it is to run at Gigabit or 100mb speed. I’d try fixing the ethernet port on the offending PC to 100mb as a starting point.

[Exfso (Peter)]

Thanks Phil, the Ethernet was plugged into the on board connector, put a PCi Ethernet card in, and it is still doing the same. As I said this was all fine a week ago and I have not done a thing in my opinion that would cause this, bloody windows hey!!

[Exfso (Peter)]

Whatever the issue was, it appears to have fixed itself I suspect it may be an NBN stuff up but why only one computer was acting up is beyond me...

[Exfso (Peter)]

Now I am really confused as is my ISP. Their speed test shows 95.6mbps download which is excellent. Yeah right. I cannot get any more than 4MB/s downloads on any computer in my house, regardless of time of day. I was regularly getting 12.5MB/s prior to this crud.
We have Netflix and it is virtually unusable as it keeps dropping out now.
Aussie are sending me a loan modem to see what difference that makes, but I am not holding my breath that is for sure. I have done ping and trace tests which are apparently fine, I mentioned the "throttling" word yesterday and they got rather upset saying they most definitely don't do that.
I have updated the firmware on my Modem/router to the latest with no change. So any ideas on this mess would be most appreciated.

[JA]

Originally Posted by Exfso

Now I am really confused as is my ISP. Their speed test shows 95.6mbps download which is excellent.

How does their speedtest compare with others, such as speedtest.net ?

Originally Posted by Exfso

I have updated the firmware on my Modem/router to the latest with no change. So any ideas on this mess would be most appreciated.

Look for any damage however slight to the cabling or connectors. Swap any available cables (esp to the router) to test for any changes.

[Exfso (Peter)]

Speedtest with Ookla is good, changed and checked cables. Even swapped another modem today, same issue..

[Wavytone]

Two things come to mind, both related to network address translation (NAT) not being configured properly in the router connecting you to the NBN.

1. Multiple computers/phones/t/tablets sharing the the same address without NAT will behave similarly. Turn everything off except one device and try that.

2. Buried deep in the tcp/ip setting is the maximum transmission unit (MTU) size that defines the transport layer block size. Normally with NAT this should be 1492 or less but if it’s larger the comms sort-of works but is slow and links often stall, as you describe, yet tests will pass.

Up to you to check that in Windows - and you may need to resort to the command line.

[Exfso (Peter)]

Nick, my MTU is showing 1492. As I said I tried another brand modem today and the results were still the same.