TCP/IP Name Resolution

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SUMMARY
TCP\IP under Windows NT allows a computer to communicate over a networkwith another computer by using either an IP address, a host name, or aNetBIOS name. However, when one computer attempts to communicate withanother computer using one of these three naming conventions, that namemust ultimately be resolved to a hardware address. The following are thesteps used by TCP\IP to resolve a host name and a NetBIOS name to ahardware address.
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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 tothe steps outlined above. Instead of parsing the HOSTS file in Step 2, theDNS looks up the host name of Computer B in its database and resolves it toan 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.
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Article ID: 108295 - Last Review: 12/04/2015 09:51:20 - Revision: 2.0

Microsoft Windows NT Advanced Server 3.1, Microsoft Windows NT Workstation 3.1, Microsoft Windows NT Advanced Server 3.1

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