上の無視です・・すいません
MTU1448、RWIN64768 （XP/2000用）
以下///行は除きコピー、.regで保存、ダブルクリック、再起動

////
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces]
"MTU"=dword:000005A8
"TcpWindowSize"=dword:0000FD00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"DefaultTTL"=dword:00000080
"SackOpts"=dword:00000001
"Tcp1323Opts"=dword:00000000
"TcpMaxDupAcks"=dword:00000003
"TcpWindowSize"=dword:0000FD00
"EnablePMTUDiscovery"=dword:00000001
"EnablePMTUBHDetect"=dword:00000000
////ここまで

戻す時
////
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces]
"MTU"=-
"TcpWindowSize"=-
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"DefaultTTL"=-
"SackOpts"=-
"Tcp1323Opts"=-
"TcpMaxDupAcks"=-
"TcpWindowSize"=-
"EnablePMTUDiscovery"=-
"EnablePMTUBHDetect"=-
////ここまで