Microsoft KB Archive/108295

= TCP/IP Name Resolution =

Article ID: 108295

Article Last Modified on 11/14/2003

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APPLIES TO


 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Workstation 3.1
 * Microsoft Windows NT Advanced Server 3.1

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This article was previously published under Q108295



SUMMARY
TCP\IP under Windows NT allows a computer to communicate over a network with another computer by using either an IP address, a host name, or a NetBIOS name. However, when one computer attempts to communicate with another computer using one of these three naming conventions, that name must ultimately be resolved to a hardware address. The following are the steps used by TCP\IP to resolve a host name and a NetBIOS name to a hardware address.



Host Name Resolution Using a Hosts File

 * 1) Computer A enters a command using the host name of Computer B.
 * 2) The HOSTS file on Computer A (contained in the %SystemRoot%\system32\drivers\etc directory ) is parsed. When the host name of Computer B is found, it is resolved to an IP address.
 * 3) The Address Resolution Protocol (ARP) is then used to resolve the IP address of Computer B to its hardware address. If Computer B is on the local network, its hardware address will be obtained by using the ARP cache or by sending a local broadcast asking for a reply from Computer B with its hardware address. If Computer B is on a remote network, ARP will determine the hardware address of the default gateway for routing to Computer B.

NOTE: Host name resolution using a Domain Name Server (DNS) is similar to the steps outlined above. Instead of parsing the HOSTS file in Step 2, the DNS looks up the host name of Computer B in its database and resolves it to an IP address.

NetBIOS Name Resolution

 * 1) Computer A enters a Windows NT command using the NetBIOS name of Computer B.
 * 2) The NetBIOS name cache on Computer A is checked for the IP address that corresponds to the NetBIOS name of Computer B.
 * 3) If the IP address of Computer B is found in the NetBIOS name cache, ARP will resolve the IP address to Computer B's hardware address (see Step 3 of the Host Name Resolution Using A Hosts File section above). If, however, the NetBIOS name is not resolved from the NetBIOS name cache, Computer A broadcasts a name request with the NetBIOS address of Computer B.
 * 4) If Computer B is on the local network, Computer A will receive a response to its name request broadcast containing the IP address of Computer B. ARP will then resolve Computer B's IP address to its hardware address.
 * 5) If Computer B is on a remote network, Computer A will not receive a reply to its name request broadcast. The LMHOSTS file on Computer A (contained in the %SystemRoot%\system32\drivers\etc directory) is then parsed. If a mapping for the NetBIOS name of Computer B exists, it is resolved to its IP address. Since this is the IP address of a remote computer, ARP will determine the hardware address of the default gateway for routing to Computer B.

Additional query words: prodnt

Keywords: kbnetwork KB108295

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