If a Windows Vista-based Dynamic Host Configuration Protocol (DHCP) client computer is restarted and if the DHCP Server service is not available, the client will not maintain a valid lease. Therefore, you cannot access some network resources.

In a Worldwide Interoperability for Microwave Access (WiMAX) network, you have a Windows Vista-based Dynamic Host Configuration Protocol (DHCP) client computer. After this client computer receives a DHCPNACK packet, the computer incorrectly rejects the DHCPOFFER packet from the DHCP server. This DHCPOFFER packet contains a new IP address. The client computer does not accept the new IP address until two DHCPOFFER packets are exchanged between the server and the client. This behavior slightly delays the client computer when it obtains a new valid IP address.

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.

For example, consider the following scenario:

• On a Windows Vista-based DHCP client computer, you establish a Secure Sockets Layer (SSL) VPN connection to a remote VPN server.
• You disconnect the SSL VPN connection.
• You put the computer to sleep or into hibernation.
• You resume the computer from sleep or from hibernation.

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.

Consider the following scenario:

• You are running a Windows Vista-based computer or a Windows Server 2008-based computer.
• The computer has multiple IP addresses.
• You run the gethostbyname function.

In this scenario, the gethostbyname function returns the IP addresses in numeric order. Therefore, the IP address that has the lowest number is returned first. You expect the primary IP address to be returned first.

Consider the following scenario:

• You are running a Windows Vista-based computer.
• You use an application to programmatically set a static IP address for a network adapter.
• This application uses the EnableStatic method of the Win32_NetworkAdapterConfiguration class.
  In this scenario, the operation may regularly fail.

Note: For example, you can use some virtual private networking (VPN) tools to programmatically set a static IP address for a network adapter.

Consider the following scenario:

• You are running a Windows Vista-based computer in a network environment. There are multiple computers in this network.
• You assign or change the IP address for the Windows Vista-based computer. You do this either manually or by using an application.

In this scenario, you receive the following error message about a network error that concerns duplicate address detection (DAD):

Windows has detected an IP address conflict. Another computer on this network has the same IP address as this computer. Contact your network administrator for help resolving this issue. More details are available in the System event log.

Additionally, the following event is logged in the System log:

Event ID: 4199
Event Source: Tcpip
Event Type: Error
Description:
The system detected an address conflict for IP address  with the system having network hardware address . Network operations on this system may be disrupted as a result. 

On a Windows Vista-based client computer, you cannot obtain an IP address or options from the Dynamic Host Configuration Protocol (DHCP) server. Instead, the computer uses an Automatic Private IP Addressing (APIPA) IP address.

Note: This problem does not occur in Windows XP or in Microsoft Windows 2000.

In Windows Vista, the TCP/IPv4 default gateway address is deleted when you use the Netsh command-line tool to configure the network interface IP address for the Dynamic Host Configuration Protocol (DHCP).

For example, you type the following command at a command prompt:

netsh interface ipv4 set address name=”Local Area Connection” source=dhcp

If you check the default gateway address by using the ipconfig command, you see that the IPv4 default gateway address is deleted.

Note: This problem occurs if the network interface has already configured by using DHCP.

You successfully establish a dial-up connection in Windows Vista to another computer or to the Internet. However, the IP address of the default gateway for the connection is 0.0.0.0. For example, when you run the ipconfig command at the command prompt, the default gateway appears as 0.0.0.0.

You do not experience this behavior in Microsoft Windows XP or in other earlier versions of the Windows operating system.

When the GUID of a network adapter changes on a client computer that is running Windows Vista, the computer registers an old IP address that was associated with the old GUID.

The client computer also registers new IP addresses that are associated with the new GUID. However, because the client computer registers old IP addresses, another client computer may try to use the old IP address. If the old address is not valid, a connection failure may occur.