Diagnosing and resolving IP addressing problems


The current IP address settings of a computer can be obtained as discussed in "viewing network configuration information" on page 672. If a computer is having problems accessing network resources or communicating with other computers, an IP addressing problem might exist. Take a close look at the IP address currently assigned, as well as other IP address settings, and use the following tips to help in your troubleshooting:

  • If the IPv4 address currently assigned to the computer is in the range to, the computer is using Automatic Private IP Addressing (APIPA). An automatic private IP address is assigned to a computer when it is configured to use DHCP and its DHCP client cannot reach a DHCP server. When using APIPA, Windows Server 2008 will automatically periodically check for a DHCP server to become available. If a computer doesn't eventually obtain a dynamic IP address, the network connection usually has a problem. Check the network cable, and if necessary trace the cable back to the switch or hub into which it connects.
  • If the IPv4 address and the subnet mask of the computer are currently set as, the network is either disconnected or someone attempted to use a static IP address that duplicated another IP address already in use on the network. In this case, you should access Network Connections and determine the state of the connection. If the connection is disabled or disconnected, this should be shown. Right-click the connection and select Enable or Diagnose as appropriate. If the connection is already enabled, you will need to modify the IP address settings for the connection.
  • If the IP address is dynamically assigned, make sure that another computer on the network isn't using the same IP address. You can do this by disconnecting the network cable for the computer that you are working with and pinging the IP address in question. If you receive a response from the ping test, you know that another computer is using the IP address. This computer probably has an improper static IP address or a reservation that isn't set up properly.
  • If the IP address appears to be set correctly, check the subnet mask, gateway, DNS, and WINS settings by comparing the network settings of the computer you are troubleshooting with those of a computer that is known to have a good network configuration. One of the biggest problem areas is the subnet mask. When subnetting is used, the subnet mask used in one area of the network might look very similar to that of another area of the network. For example, the subnet mask in one IPv4 area might be, and it might be in another IPv4 area.

When you are using static IP addressing, you can check the current IPv4 or IPv6 settings by entering ipconfig /all at a command prompt. The display of the ipconfig /all command includes IPv4/IPv6 addresses, default routers, and DNS servers for all interfaces. You can also check IPv4 and IPv6 addressing separately. To check the IPv4 addressing configuration, enter netsh interface IPv4 show address. To check IPv6 addressing, enter netsh interface IPv6 show address. To use netsh to show the configuration of a remote computer use the -r RemoteComputerName command line option. For example, to display the configuration of the remote computer named corpserver26, you would enter netsh -r corpserver26 interface IPv4 show address.

To make changes to the configuration of IP interfaces, use the netsh interface IPv4 set interface and netsh interface IPv6 set interface commands. To add the IP addresses of DNS servers, use the netsh interface IPv4 add DNS and netsh interface IPv6 add DNS commands.

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