Windows 7 / Networking

---

How to Troubleshoot Name Resolution Problems

Computers use numeric IP addresses (such as 192.168.10.233 or 2001:db8::1) to identify each other on networks. However, IP addresses are difficult for people to remember, so we use more friendly host names (such as www.contoso.com). Name resolution is the process of converting a host name to an IP address, and DNS is by far the most common name resolution technique.

Many apparent connectivity problems are actually name resolution problems. If any of the following problems occur, the client will be unable to contact a server using its host name:

• DNS servers have failed.
• The network connecting the client to the DNS server has failed.
• A host name is missing from the DNS database.
• A host name is associated with an incorrect IP address. Often, this happens because a host has recently changed IP addresses and the DNS database has not been updated.
• The client does not have DNS servers configured or is configured with the incorrect DNS server IP addresses.

To diagnose a name resolution problem, follow these steps:

1. Open the Network And Sharing Center by clicking Start, clicking Network, and then clicking Network And Sharing Center. If a red X is displayed over a network link, click the link to start Windows Network Diagnostics and follow the prompts that appear. Windows Network Diagnostics can solve many common configuration problems. If Windows Network Diagnostics does not identify or resolve the problem, continue following these steps.
2. Verify that you can connect to other computers using IP addresses. If you cannot connect to servers by using their IP address, the source of your problem is network connectivity rather than name resolution. See the section titled "How to Troubleshoot Network Connectivity Problems" earlier in this tutorial. If you can connect to servers by using their IP address but not by using their host names, continue following these steps.
   Note When your network is working properly, look up the IP addresses of several different computers, including computers on your subnet, other subnets on your intranet, and computers on the Internet. Test the IP addresses to verify that they respond to Ping requests. Keep this list available so that you can use the IP addresses to test for network connectivity without relying on name resolution.
3. Open a command prompt and use Nslookup to look up the host name you are attempting to contact, as the following example shows.
   Nslookup www.sourcedaddy.com
   
   Examine the output.
   • If Nslookup displays addresses or aliases for the host name, name resolution was successful. Most likely, the server you are trying to reach is offline, you have a connectivity problem preventing you from reaching the server, the application you are using is misconfigured, or the DNS server database is incorrect. See the sections titled "How to Troubleshoot Network Connectivity Problems" and "How to Troubleshoot Application Connectivity Problems" earlier in this tutorial. If you believe the DNS server database is incorrect, contact your DNS server administrator.
   • If Nslookup displays only "DNS request timed out," the DNS server is not responding. First, repeat the test several times to determine whether it is an intermittent problem. Then, use the ipconfig command to verify that the client computer has the correct DNS servers configured. If necessary, update the client computer's DNS server configuration. If the DNS server's IP addresses are correct, the DNS servers or the network to which they are connected are offline. Contact the server or network administrator for additional assistance.
   • If Nslookup displays the message "Default servers are not available," the computer does not have a DNS server configured. Update the client network configuration with DNS server IP addresses or configure the computer to acquire an address automatically.
4. If you can connect to the server from a different client computer, run ipconfig /all from a command prompt to determine which DNS servers the client computer is configured to use. If the IP addresses are different, consider changing the problematic client computer to use those IP addresses.