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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)

Overview and History of TCP/IP Host Names and Name Systems 1 2 3 4 TCP/IP Domain Name System (DNS)

Use of the Host Table Name System In Modern Networking

That said, the host table name system has not gone away entirely. There are two circumstances in which this technique is still of value:

• Small “Island” Networks: If you are setting up a small local area network using TCP/IP, and you don't need the names of your devices to be accessible by those outside your network, then guess what? You have the equivalent, of sorts, of the early Internet, and the host table system is as applicable to you as it was to the Internet in the 1970s. You can simply set up host tables on each device and manage them manually. As long as the LAN is small enough that editing these files periodically is not a hassle, this is actually a fast and effective name system, because no exchange of messages is needed for resolution. You can even maintain a master file on one machine and copy it to the others when changes are required using a script, to save time.
  
  
• Providing Local Name Mappings To Supplement DNS: Even though modern systems use DNS for most name resolution, they also usually still support the use of host table files. You can manually enter common name mappings into this file, even for devices that are on the global Internet. Your system can then be set up to consult this list before making use of its assigned DNS server.

The use of the HOSTS file in conjunction with DNS allows you to manually specify mappings for commonly-accessed sites, which may provide a slight performance improvement since there is no need to access a server. Since the HOSTS file doesn't enforce any particular structure to names, it is naturally quite possible to put DNS-style hierarchical names into the file, as I showed in Table 161. The file is loaded into memory and used to override the normal DNS process for names listed in it.

Of course, you then subject yourself to all the potential maintenance headaches of manually-edited files: you must update these files as host names or addresses are changed in the DNS system. For this reason, this second use of the HOSTS file for Internet sites served by DNS is less popular than the use of the file for local machines.

Overview and History of TCP/IP Host Names and Name Systems 1 2 3 4 TCP/IP Domain Name System (DNS)