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!

The whole site in one document for easy reference!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 4 (IP, IPv4)
                     9  IP Addressing
                          9  IP Subnet Addressing ("Subnetting") Concepts

Previous Topic/Section
IP Subnet Addressing ("Subnetting") Concepts
Previous Page
Pages in Current Topic/Section
1
23
Next Page
IP Subnetting: "Three-Level" Hierarchical IP Subnet Addressing
Next Topic/Section

IP Subnet Addressing Overview, Motivation, and Advantages
(Page 1 of 3)

IP addressing was originally designed around the assumption of a strict two-level hierarchy for internetworks. The first level was the network, and the second level the host. Each organization was usually represented by a single network identifier that indicated a Class A, B or C block dedicated to them. Within that network they had to put all of the devices they wanted to connect to the public IP network.

The Motivation for Subnet Addressing

It did not take long after the “classful” scheme was developed for serious inadequacies in it to be noticed, especially by larger organizations. The reason is that while dividing a large internetwork into networks that contain hosts is conceptually simple, it doesn't always match well the structure of each of the networks that comprises the internet. A big company with thousands of computers doesn't structure them as one big whomping physical network. Trying to assign and administer IP addresses to an organization's entire network without any form of internal logical structure is very difficult.

Unfortunately, under the original “classful” addressing scheme, there was no good solution to this problem. The most commonly-chosen alternative at the time was to trade a single large block of addresses such as a Class B for a bunch of Class Cs. However, this caused additional problems:

  • It contributed to the explosion in size of IP routing tables.

  • Every time more address space was needed, the administrator would have to apply for a new block of addresses.

  • Any changes to the internal structure of a company's network would potentially affect devices and sites outside the organization.

  • Keeping track of all those different Class C networks would be a bit of a headache in its own right.

Related Information: I fully explain the problems with “classful” addressing within the section on “classful” addressing.



Previous Topic/Section
IP Subnet Addressing ("Subnetting") Concepts
Previous Page
Pages in Current Topic/Section
1
23
Next Page
IP Subnetting: "Three-Level" Hierarchical IP Subnet Addressing
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.