I'm sure that if you use something like TCPOptimizer ( http://www.speedguide.net/downloads.php ), it will create the relevant MTU entries in the Registry even for XP Home as it probably did for my XP MCE/XP Pro. It's spec. does not exclude XP Home.

Edited by XRaySpeX (Thu 19-Nov-09 15:21:20)

Come on now, zebedee, there was no way that I or any other punter could possibly have known that these Registry settings weren't available, when we purchased WinXP Home! The same applies to lots of other features of Windows. Many of us who bought the Home version did so because we didn't think the extra cost of the Pro version was worth it. Several of my ex-colleagues who work in the IT field bought Home machines for they and their families' use at home precisely with that in mind. It's just unfortunate that, over the years, we've encountered one or two annoying limitations of the Home version.

TCP Optimiser? Now, that rings a bell. I think I've also used that, in the dark and distant past, with Win2K. My memory of it is very vague now but I've a feeling that you're right, that it does create entries in the Register. However, my doubt would be whether it actually works with WinXP Home. I think it's maybe useful for literally creating a value that you choose but is no use if what you want to find out is the current unmodified default value in the Registry - because if it ain't there, you can't get it!

Anyway, I'm happy with how things are now, so there's no need to contemplate such things. Thanks for reminding me, though.

I read somewhere, maybe in this thread, that if it ain't there, then it defaults to 1500.

TCP Optimiser is useful for calculating an optimal value, not just a value of your choice; it takes the hard work outta all those repeated Pings that you may have wot of!

In reply to a post by meditator:

Yes, as my slightly earlier reply indicated, I've now changed my router MTU to 1500. Thus far, no problems.

Sorry I didn't/can't see that post? I can see you mentioned "I'm beginning to conclude..." but can't find any reference where you actually changed things.

People here are trying to help - but it's not always easy

Many Windows inbuilt default values have no actual matching registry entry unless the default is changed, at which time the appropriate registry value is created, either manually or by an application such as TCPOpitimzer.

TCPOptimzer has a Registry tab which shows the actual registry values for anything that does have a default registry entry. It also has an MTU tab that allows you to to a run a fragmentation test on any site you enter. It also has a latency test tab and BDP calculator to help your optimise your connection for your commonest sites. Though the makers of TCPOptimizer also have a test page on their site www.speedguide.net that does much the same thing for you and will give you suggested values for your PC and its connection.

that EnablePMTUDiscovery, or viewing an MTU value in the Registry, is not available in Windows XP Home

that's what DrTCP does, it allows you to see/change/insert the relevant values. Works here on XP home.

there isn't a registry entry for MTU unless one has been created, the lack of one means it's using 1500 coded in somewhere. DrTCP shows it up.

Yes, my thanks once again go to those who've reminded me in this thread of both Dr TCP and TCP Optimiser. I have used them in the past, in the days when I was using Win2K, I think. In the end, I gave up using them, as they didn't help for what I was trying to do at the time.

As for now, what I've been trying to do is (a) find out from others what they think is a fairly optimised value for Windows MTU, so that I can appropriately set the MTU of my router, and (b) if possible, to look in Windows Registry and read the current Windows MTU. Several of you have been kind enough to recommend the value 1500 to me and consequently I'm now using that value. I've not, however, been able to see a default MTU value in the Registry, as it's now apparent that, in WinXP Home edition, no such data is shown there. This doesn't matter, though, as I'm content to use the value that everyone's recommended.

Just out of interest, are there any of you using WinXP who are not using the default MTU of 1500? If so, which value are you using, and does it definitely cater for all the websites you use?

Edited by deleted (Fri 20-Nov-09 15:52:39)

Just out of interest, are there any of you using WinXP who are not using the default MTU of 1500?

turned out I was using 1470 as the machine had been running over a Sharedband link aggregation system. As it was set on the PC I had no issue accessing sites as the router was at 1500.

Problems only arise when a PC fires bigger packets than the hole in the router allows to pass.