MTU advice

I'm currently using 1500 on both machines and the router. The figure of 1458 has been mentioned wrt to IDNet, I'd appreciate any experience people have on the best choice.

Thanks.

I use 1500 with Path MTU Discovery set to "On", and let it sort itself out- works fine for me

Unless you're lucky enough to have rock stable download speeds, I don't think it's worth trying to tune MTU/RWIN much- the variations you get are swamped by the speed changes due to traffic variation (aka contention- BT, not IDNet as far as I can tell).

I've had speed tests range from about 6700Kbps down to an occasional one less than 900Kbps, so I don't try to tune

Thanks, Bill. Living in Milton Keynes, at the end of a long length of aluminium, I have an IP profile of 2500kbps, so I can only drool at your speeds. However, I do get fairly consistent speed tests at 2400kbps down - one advantage of not being able to go much faster I guess.

I must admit I'm quite happy with my speeds, even though they vary all over the place (BT claim my exchange isn't contended.... yeah, right )

According to Samknows, I'm only just over a kilometre from the exchange- 8128 down, 448 up and a profile of 7150

You know how to make a boy feel jealous, Bill...

I've had consistent high speeds of approx. 4 to 6.5 Mbps for months - then my exchange went Red a month ago (using this checker: Zen Support - Exchange Checker) -- and surprisingly I still got good speeds for 2-3 weeks, now it's plummeted:
Downstream 878.8 Kbps ( = 0.9 Mbps )
Upstream 366.4 Kbps ( = 0.4 Mbps )

Things can certainly change fast ...

S

I know, look at Nildram.

Update:
I went out after I posted above speed test, returned 45 mins later to find connection dropped (very rare here), re-booted router [with 30 minutes unplugged], speed now:
Downstream 5,251.7 Kbps ( = 5.1 Mbps )
Upstream 373.1 Kbps ( = 0.4 Mbps)

stale sessions? with an ongoing Red exchange status, I don't jump to any conclusions.

S

Toes crossed for you.

I was just wondering if it's really worth me tweaking the MTU and RWIN? I searched back to a few other threads based on this and different people tried different values... the problem is I've tried to set my MTU to 1500, but it keeps getting detected as 1458 by dslreports.com.

I tried using 2 tools (TCPOptimizer and DrTCP) however I had to manually change the registry because these 2 don't seem to be writing to the registry under the latest build of Windows Vista (the registry protection blocks it) so I did that and it still hasn't really done anything.

I'm always trying to get that last ounce of speed if I can change a few things, but I don't know if it matters as much as it used to (as on 2Mb).

Any ideas/suggestions please?
Thanks

I can't help on Vista- I still use Win98SE, and when I move off that it will be to a Linux variant, not another MS product....

THBS, if you can get good speeds with your current values, I don't see much point in chasing the last few bytes/sec. Mainly because you'll never know when you've got them- if your exchange is even remotely like mine you could easily make a deleterious change but get a higher speed on the next test because the contention has changed....

When you can get a consistent high speed not too far from your BRAS rate it might be worth playing with the settings, otherwise it's a waste of effort.

IMHO of course

Njord. The fact that your MTU is being shown as smaller than you've set it on your client, could mean that your router/modem is/are set to a lower MTU. Some D-Link modems/routers default to a lower MTU than the standard 1500.

I've always preferred http://www.speedguide.net/analyzer.php for connection checking. I also never see any difference in making it smaller
MTU 1500 if you use an adsl router with PPPoA encapsulation
MTU 1492 if you use a separate adsl modem and router, with the modem in bridge mode, and the router set to PPPoE.

I do however, increase the Receive Window size, as this can increase transfer speeds from distant hosts. The above checker will give you a hand, but this is what I've got mine set to...
255552 (MSS x 44 * scale factor of 4) <-- current value

As I have an MTU of 1492 (bridge mode, PPPoE), my MSS is 1452...if you had an MTU of 1500 like most people, your MSS would be 1460.

Check out the above site, lots of help there too

Thanks for that info mate. At the moment I'm using a Netgear DG834G router with PPPoA and the latest firmware, so I'm not sure if that has a similar MTU as the default a bit like the D-Link. There is no way of changing it in the setup of the router as far as I am aware.

Thanks for your advice anyway guys. The SpeedGuide.net TCP/IP Analyzer explains things well

Bill... to be honest I don't blame you for going to Linux instead of another MS Product. Good old embrace, extend and extinguish..... Vista is very pretty though and then the novelty wares off.

. There is no way of changing it in the setup of the router as far as I am aware. ///////

Settings/advanced/WAN setup/mtusize.

Thanks a lot for that... had the router for 2 years and didn't even notice that was there. Much appreciated!

I use a Netgear 834GT. I find that an MTU of 1430 gives me a download speed on the Namesco tester of c1914, whereas an MTU of 1500 pulls it down to c1840.

Michael

Yep, I have used 1430 / 55600 for a long time now on fixed 2M and found that to be generally best. I gave up tweaking a while ago ... it was quite frustrating

Just did a bit of research and got this from Wikipedia, so I don't have to worry about the RWIN in Windows Vista.

"Another significant change that will improve network throughput is the automatic resizing of TCP Receive window. The receive window (RWIN) is the buffer that is used to temporarily hold incoming TCP data. Receive window auto tuning functionality continually monitors the bandwidth and the latency of TCP connections individually and optimize the receive window for each connection. The window size will be increased in high-bandwidth (~5 Mbit/s+) or high-latency (>10ms) situations. With a large receive window, more data can be transferred at a time, so less time is spent waiting for acknowledgements for TCP packets, thereby boosting the data throughput rates considerably. It also tracks whether any intermediate routers drop the larger data packets, in which case it automatically scales back the packet size."