After you resume a Windows Vista-based DHCP client computer from sleep or from hibernation, the computer may lose its IP address. This problem may occur if there is more than one network interface on the computer, such as a real network interface and a virtual private network (VPN) interface.
Microsoft described the scenario reported by end users, revealing that it involves bridging a Vista-based DHCP machine with a remote VPN server via a Secure Sockets Layer (SSL) VPN connection. According to the software company, cutting off the connection, and then placing in and subsequently resuming the PC from sleep or hibernation modes, will result in Vista losing the DHPC IP.
“In this scenario, the computer loses the IP address that was assigned to it by the DHCP server. Instead, an Automatic Private IP Addressing (APIPA) address, such as 169.254.0.1, is assigned to the client computer. Therefore, you cannot access some network resources,” Microsoft added.