Da li koristis PPPoE? Promeni MTU ratu interfejsa. Probaj koje vrednosti odgovaraju 1492, 1488, 1480.
Evo i primer sa sajta:
http://www.speedguide.net/read_articles.php?id=157
Setting MTU overrides the default MTU for the network interface it is added to. Note that if EnablePMTUDiscovery is set to 1, TCP will use the smaller value of this local MTU and the "Discovered" MTU of the underlying network connection. If you'd rather use only the MTU value specified here, you'd have to disable PMTUDiscovery, which would prevent your system from detecting the network MTU.
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces
MTU="1500" (DWORD, valid range is from 68 to MTU of network).
Note: For Windows XP PPPoE, there is an additional location for MTU that might need to be adjusted (to 1480, or up to 1492 as per the PPPoE specs), depending on the PPPoE software you use. Check the following location in the Registry:
HKLM\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0
ProtocolMTU="1480"