TCP/IP Name Resolution

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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.

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.