Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

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  Name System Issues, Concepts and Techniques

Name Registration Methods, Administration and Authorities 1 2 Efficiency, Reliability and Other Name Resolution Issues and Features

As we discussed earlier in this section, using a name system creates two “parallel” identification systems for computers: the numbers used by machines and the names used by people. The job of the name system is to integrate these two schemes. Name registration allows humans to specify which machines use which names. This is only half the process, however; we also need a way for machines to take a name given to them by a human and translate it into the “real” address it can actually use for communication. This is called name resolution.

Name resolution, also sometimes called name translation, mapping or binding, is the most well-known aspect of name systems, because it is where most of the “heavy lifting” of a name system occurs. The name space is generally set up once, and name registration occurs infrequently: only when names must be created or changed. In contrast, every user of a name system instructs the machines he or she uses to perform name resolution, hundreds or even thousands of times a day.

There are several different techniques that can be use for name resolution. How this function is implemented depends a great deal on the other two name system functions, name space and name registration. As you might imagine, a simple name system with a simple name registration method will most often use a simple resolution method as well. Complex hierarchical systems with distributed databases require more sophistication in how names are resolved.

There are three common name resolution methods.

The table used for table-based name registration is consulted by a device when resolution needs to be performed. The table tells the device how to transform the name of the machine it needs to contact into an address.

This technique obviously corresponds to table name registration; it is the simplest and least capable of the three methods. Table name resolution is suitable for standalone use only in very small name systems, but can be a supplement to other methods as well.

When a device needs to resolve a name, it broadcasts a query that says something to this effect: “I need to send to the device named 'X', who is that?” The device whose name is 'X' responds back saying “I'm 'X' and my numeric address is 'N'”.

This is the complement of broadcast name registration, of course. It too can only be used in simple systems where every device can hear a broadcast. The use of broadcasts also makes it wasteful of network bandwidth.

Servers are programmed with software that allows them to respond to name resolution requests sent by clients. These servers take the name in the request, look up the associated numeric identifier in a database, and send it back in a response.

This technique is, of course, generally used in conjunction with database name registration. It is the most complex of name resolution methods, but is also the most efficient, and the only one that can really work properly on a large, distributed hierarchical name system.

Name Registration Methods, Administration and Authorities 1 2 Efficiency, Reliability and Other Name Resolution Issues and Features