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Half-Open Outbound TCP Connections Limit Removed in Windows 7 and Vist


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#1
Broni

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No patch needed anymore...

http://www.mydigital...patch-required/



Looking for half-open concurrent TCP connections limit patcher? Microsoft introduces a limit (of 10) to restrict number of allowed simultaneous outgoing half-open TCP connections in Windows XP SP2 in a bid to prevent virus or malicious program to make unlimited infectious connections to other system when a PC is compromised. The limit continues to exist in Windows Vista RTM and SP1. Result is event ID 4226 with error message “TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts”, and fanatic search for patched TCPIP.sys or half-open TCP connections limit memory value crack by many Windows users, especially P2P and torrent downloaders.

Microsoft appears to have a change of heart on the half-open outbound TCP connection attempts limit with the release of Windows Vista SP2 and Windows 7, probably due to the fact that the limit never effective in stopping the spreading of worms and viruses, or Microsoft has grown more confident about security feature of newer operating system.

According to Notable Changes in Windows Server 2008 SP2 and Windows Vista SP2 document published in conjunction with the release of SP2 RTM:

SP2 removes the limit of 10 half open outbound TCP connections. By default, SP2 has no limit on the number of half open outbound TCP connections.


The complete removal of the limit for half-open outbound TCP connections, which is defaulted to 10, was finalized with the release of Windows Server 2008 and Vista SP2 Build 17506. In fact, the half-open outgoing TCP connection limit has been bypassed by default since Windows Vista SP2 RC Build 16670. Previously, the changelog of SP2 showed that Microsoft looks like going to “add a registry key that enables modification of the maximum number of open TCP connections to increase application compatibility”.

Instead, Microsoft adds a registry key that allows user or administrator to enable (turn on) or disable (turn off) the half-open TCP connections limit in Windows Vista with Service Pack 2 and in Windows Server 2008 with Service Pack 2.
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#2
Ferrari

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I'm really surprised none of the malware guys wanted to comment on this. I barely know what the heck it is talking about but it sounds good I guess.

Thanks for sharing Broni. :)
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#3
Broni

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Microsoft introduces a limit (of 10) to restrict number of allowed simultaneous outgoing half-open TCP connections in Windows XP SP2

...which in general was slowing down your internet connection, especially while downloading, uploading.
Special patch was needed to bypass the above limitation.
Vista SP2 removed that restriction.
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#4
Ferrari

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That's what I pretty much got out of it, but wasn't 100% sure my understanding was correct. Does this all apply to Windows 7 RC? Does XP Pro SP3 have that restriction then? I haven't done any patch.

I ask because, 7 does seem a bit speedier when I'm using Firefast compared to it in XP Pro. Maybe this is why?

EDIT: FYI, 7 and XP Pro are on the same computer, Dual Boot.

Edited by Ferrari, 27 June 2009 - 11:06 PM.

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#5
Broni

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I'm pretty sure, if Vista SP2 removes that limitation, it's not present in Win 7.
I don't think, it was fixed in XP SP3.
It's easy to find out.
Open Event Viewer, and under "Warnings" look for Event ID 4226.
If it's present, the limitation is there.
Patch: http://www.mydigital...7-vista-and-xp/
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#6
Roman Pope

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Ouch, I've done this patching before, but only once. I completely forgot about the limitation.
I have another question: what would be close to optimal number of open half-ports?
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#7
Broni

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I believe, for XP, it was recommended to set it to 500-600
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#8
Broni

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I've done this patching before, but only once

Some Windows updates will restore original tcpip.sys file, so I used to check Event Viewer after each "updates Tuesday" for Event ID 4226. Over couple of years, I had to reapply the patch only once.
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