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 Book is Here... and Now On Sale!

Read offline with no ads or diagram watermarks!
The TCP/IP Guide

Custom Search







Table Of Contents  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)
                9  TCP/IP Domain Name System (DNS)
                     9  DNS Name Servers and Name Resolution
                          9  DNS Resolution Concepts and Resolver Operations

Previous Topic/Section
DNS Name Resolution Efficiency Improvements: Caching and Local Resolution
Previous Page
Pages in Current Topic/Section
12
3
Next Page
DNS Reverse Name Resolution Using the IN-ADDR.ARPA Domain
Next Topic/Section

DNS Name Resolution Process
(Page 3 of 3)

Changes to Resolution to Handle Special Cases

This example is highly simplified, and also only shows one possible way that servers might be set up. For one thing, it is possible that even though “compsci.googleplex.edu” is in a separate zone from “googleplex.edu”, they might use the same server. In that case, one iteration in the process would be skipped. The example also above doesn't show what happens if an error occurs in the process.

If the domain name entered was an alias, indicated by a CNAME record, this would change the processing as well. CNAME records are used to allow a “constant” name for a device to be presented to the outside world while allowing the actual device that corresponds to the name to vary inside the organization. When a CNAME is used, it changes the name resolution process by adding an extra step: first we resolve the alias to the canonical name and then resolve the canonical name.

For example, Web servers are almost always named starting with “www.”, so at XYZ Industries we want people to be able to find our Web site at “www.xyzindustries.com”. However, the Web server may in fact be shared with other services on “bigserver.xyzindustries.com”. We can set up a CNAME record to point “www.xyzindustries.com” to “bigserver.xyzindustries.com”. Resolution of “www” will result in a CNAME pointing to “bigserver”, which is then itself resolved. If in the future our business grows and we decide to upgrade our Web service to run on “biggerserver.xyzindustries.com”, we just change the CNAME record and users are unaffected.


Previous Topic/Section
DNS Name Resolution Efficiency Improvements: Caching and Local Resolution
Previous Page
Pages in Current Topic/Section
12
3
Next Page
DNS Reverse Name Resolution Using the IN-ADDR.ARPA Domain
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.