TCP/IP Name Resolution (108295)


The information in this article applies to:

  • Microsoft Windows NT Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Advanced Server
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.

MORE INFORMATION

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.
Modification Type:MajorLast Reviewed:11/14/2003
Keywords:kbnetwork KB108295
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