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This version of TCPIP.SYS does not support modifications

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After my PC got hit by a surge of lightning a few weeks ago and I have had to take it to a shop to reinstall Windows, the new version seems to conflict with one key Bit Comet setting.Under TCIP/IP Limit it says I have version 5.1.2600.5649 installed but also says "This version of TCPIP.SYS does not support modifications". Strangely enough, my 'New Half Open Limit' is a faint 0. There is then a message at the bottom suggesting that I disable my Windows File Protection.

I am running Windows XP SP2 Dark Version.

I am using AVG free

I am running Bitcomet 1.20

Now my questions are:

Am I currently getting the best speeds possible out of my open connections (like I was before when I could change the HALF OPEN LIMIT?) or is this new TCPIP.SYS throttling my speed? FYI my overall speeds are about 30% down from when I had my previous system- before reinstalling this new version of XP.

I have done the necessary port forwarding and have also patched my half open connections to 70 in my registry using the patch you guys recommended. I guess since I can't actually change the halfopen connections on Bitcomet then opening the ports on the registry isn't going to do anything right?

Honestly, I have read all your tutorials, your wiki and your FAQs and did not find this mentioned anywhere. If anyone else is having this problem- help would be hugely appreciated. Will future versions of BitComet be able to address this issue? Can anything be done?

I apologise humbly if I have left anything out.


Edited by charl1972 (see edit history)
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The half-open connections limit in Win XP doesn't affect your speeds.

It has to do with the maximum number of TCP connections that can be found in a half-open state at any time.

All the other supplementary connection attempts are placed in a waiting queue; as soon as one of the half-open connections reaches the ESTABLISHED state another one from the queue can take its place.

Under normal usage, connections do not stay very long in half-open state (we're talking mili-seconds to seconds at most, here) and you won't see any difference. On the other hand, if your PC gets zombied and tries to launch a SYN-flood attack (launching thousands of half-open connections which will never reach the FULL state) then this limit will prevent it from being a useful "zombie". That is the only reason this was put in place and it doesn't affect normal usage of an Internet connection.

Even with this limit in place, your BitComet will reach its optimum number of established connections in about a minute or so (just about the same as without any limit at all). Once it reached that, the speeds you get are none of this setting's concern.

I'm not sure though, why your version of TCPIP.sys does not support modifications. I use Win XP SP3 and my TCPIP.sys' version is 5.1.2600.5625 therefore, lower than in your SP2 version!

However, I highly doubt that your lower speeds have anything to do with the half-open limit. I've used BitComet for years with tis limit unpatched and always got speeds to the max of my connection.

How about your Global Upload Rate? Have you limited that to 80% of your tested upload speed, in BitComet's options?

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Thanks for all that. I think with all that information my brain has become a 'zombie'. :)

I can see a real noticeable difference when I change the upload amount. I have it at 80kB/s- roughly 80% of my upload speed. This seems to get the best results, though sometimes I am uploading a single torrent quite a bit faster than downloading it! :(

I may well have SP3 and not 2 as I'm not sure what they put on my PC. I also have the feeling he has installed bits of Vista and/or Windows 7 as I see these files and hints of these OS at times. I have googled this problem "This version of TCPIP.SYS does not support modifications" and it seems to be a big problem with many users out there who have more recent versions of the TCPIP.SYS - often once they have updated with windows updates. To date very few have offered suggestions around this other than messing with the TCPIP.SYS- which I don't feel I am confident enough to do. Some have even indicated that perhaps this issue will be resolved in newer version of BC. In other torrent clients I don't have the same issue- but then I have always liked BC and have gotten the best speeds from BC and am not about to change. It's definitely because I reinstalled a later version of windows as I tried earlier versions of BC and same result. The strange thing is the message just below "This version of TCPIP.SYS does not support modifications"- a message there reads: Important notice: in order to make changes to your tcpip.sys systems file Windows File Protection System will need to be temporarily disabled. Your original file will be renamed to "TCPIP.SYS.ORIGINAL"

Is this even possible?

Sorry for the headache, it's just that I have used BC for around 4 years now and this is the first time I'm not getting the speeds I am used to. I have a 3 Meg line and would usually max out at around 500 kB/s- but the main thing was CONSISTENCY- even when I got 250 kB/s for a single file- it would stay there. Now I max out at 300- but files usually hover anywhere between 30-150. The thing is the speed is so much more up and down now- 20 kb/s to 150 to 70 within seconds.

Anyway- if you can think of a way forward that would be great. Otherwise I will keep tampering and googling and hopefully a solution to the TCPIP.SYS issue can be found. Is there any way to install your version or a version that will work?

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The idea that the half-open connections limit needed modifying, arose out of a profound misunderstanding of what it does.

Nobody who has that poor of a grasp on what they're doing should be allowed to muck around with your system.

There's never been any evidence that changing the limit makes any difference in transfer speed.

The limit was put in place in Windows XP. Win98 and WinME were past their support lifetimes before the issue arose, so they were never limited in the first place and never patched to do so. I kept using Win98 (and unpatched Win2K) until just a couple of years ago. Though both were unlimited, bittorrent was not faster under them than under XP. If the modifiers were correct, Win98 should have run rings around XP. It didn't happen.

If your system gets taken over and zombied, it can be used to launch denial-of-service attacks at other sites. One such attack of this kind is called a "syn flood". The half-open limit prevents your computer from launching such an attack on another site. That's all it does. It doesn't prevent YOU from answering, or even from BEING syn-flooded, it just prevents your system from sending a bunch of SYN's real fast. There is no legitimate purpose (only an illegitimate one) for ever doing that -- to drown somebody else in half-connections in order to prevent anyone else from being able to connect to them -- to deny their service.

WinXP will note in the system log that it has bumped into this connection ceiling. Somebody somewhere figured, without ever testing the notion, that eliminating this "error" would speed things up.

It does not.

But, "what, me test?" seems to prevail.

Later versions of tcpip.sys tell you that you can't modify it unless you jump through all kinds of hoops -- in faint hopes that during the process you'll stop and think about what you're doing.

The Vista and (presumably) production versions of Win7 no longer have these issues, nor can they be modified.

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Hmm... I'm sorry I have to be the one to tell you this, but if you don't know how to check your Windows' version and Service Pack (which is as simple as right-clicking on My Computer-->Properties by the way) then I strongly recommend against meddling with your TCPIP.sys or other Registry settings.

The message you're reading is BitComet just trying to tell you that the version of TCPIP.sys your system has is not modifiable. The other message below it's embedded in the GUI and has been there forever; it doesn't change.

It's not BitComet's problem that you have a TCPIP.sys that doesn't support this type of modification. This is a standard message for all Vista and Win 7 versions as well, since those OS's TCPIP.sys don't support modification as well.

It may have to do with the special pirated version of Windows you say you're using, I don't know. As I said, all versions of XP I've used so far didn't have this issue. So, if yours does there is nothing BitComet can do about it. That is a core system file and unless you know exactly what you're doing, you'd better stay away from it.

I could bet that your slow speeds are due to entirely different reasons (perhaps poor availability for the torrents you're downloading now) but if you want to insist on blaming that on the half-open limit, that's your right.

You should try to download and test your speeds with a highly seeded torrent as Open Office, or a Linux distro and see what speed you get there.

Comparing speeds from one torrent to another torrent is like comparing apples with pears; they can be every time different.

Torrent swarms are highly dynamic things and simply comparing yesterday's speeds with today's just won't do. This type of comparison would have to be done over an extensive period of time, with the same torrents (or identically seeded as much as possible) to have any remote relevance.

I'm not saying that you may not have a problem somewhere, along the way but I just don't think it lies where you seek it.

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