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2007-10-26

Path Maximum Transmission Unit (PMTU) Black Hole Routers

Windows XP SP3 promises detection of Black Hole Routers, which is supposed to improve over all networking experience especially for laptops. While investigating the subject, I came across a good, comprehensive article about PMTU (Path Maximum Transmission Unit) at Microsoft site.

By default PMTU Black Hole Discovery for TCP/IP is disabled on Windows XP machines. It can be enabled though:

Setting: EnablePMTUBHDetect
Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Value Type: REG_DWORD Value: 1

"Changes in PMTU black hole router detection in Windows Server 2003 and in Windows Vista" is a good follow up article.

Enabling of PMTU Black Hole detection and changes are all result of Microsoft's "Next Generation TCP/IP Stack".

The Cable Guy from Microsoft has an article on enhancements that "Next Generation TCP/IP Stack" (terrible name IMHO) offers.
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