My question is about the network stack of Windows7,but I post here since it is closely related to routers and firewalls and pertains to security anyway. Windows7 64bits CIS Dlink modem- router 2542B I changed my Router a few days ago and was unable to assign an adress (x.x.x.2) to my first Windows7-64 pc,while pc2 XPPro has no problem getting an assigned x.x.x.3 and pc3 Xubuntu gets without complaining its x.x.x.4. If I assign its usual x.x.x.2 to my pc1 I immediately lose BB connection. I remove the assigned number from Network and I get back connection immediately....even if I get the same number I wanted....... This is weird since I always used D-Link routers this way, albeit the previous router last configuration was really x.x.x.177, x.x.x.146, x.x.x.129 respectively (and it didnt budge for years even though numbers were not progressive). Now, with Windows7-64 one month old install, its another music.Nothing granted. I thought the completely useless IPV6 group could be the culprit since in Events Viewer I've spotted repeated DHCPNACK messages to the effect the first DHCP request was denied (but i got immediately after the adress) and the Details provide a “6” which makes me think its due to IPV6 disorienting the router. In any case I've now completely disabled via Registry all components IPV6 group ,unticked TCPIP6 group in Network and also disabled IPV6 Random Identifier for good measure. A couple of reboots later the situation seems improved regarding Events DHCP alerts,but I need to ask if disabling this useless -up to now and for a long time still- thing COULD have any after effects security-wise or system-wise. Losing Homegroup capabilities not a factor for me. If nobody can bring negative arguments against this disabling,then ,if everything is all right for a few days I'll also try again reassigning my first pc its x.x.x.2 number!