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". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||^$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 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 "Classful" (Conventional) Addressing

Previous Topic/Section
IP Addresses With Special Meanings
Previous Page
Pages in Current Topic/Section
Next Page
IP Multicast Addressing
Next Topic/Section

IP Reserved, Loopback and Private Addresses
(Page 3 of 3)

Reserved, Loopback and Private Addressing Blocks

Table 47 shows all of the special blocks set aside from the normal IP address space in numerical order, with a brief explanation of how each is used:

Table 47: Reserved, Loopback and Private IP Addresses

Range Start Address

Range End Address

“Classful” Address Equivalent

Classless Address Equivalent


Class A network 0.x.x.x



Class A network 10.x.x.x


Class A private address block.

Class A network 127.x.x.x


Loopback address block.

Class B network 128.0.x.x



Class B network 169.254.x.x


Class B private address block reserved for automatic private address allocation. See the section on DHCP for details.

16 contiguous Class B networks from 172.16.x.x through 172.31.x.x


Class B private address blocks.

Class B network 191.255.x.x



Class C network 192.0.0.x



256 contiguous Class C networks from 192.168.0.x through 192.168.255.x


Class C private address blocks.

Class C network 223.255.255.x



I have shown both the “classful” and classless notation representing each of these blocks. This is both because the Internet now uses classless addressing, and because some of the private blocks don't correspond to single class A, B or C networks. Note especially the private address block from to This is the size of a class B network, but it isn't class B in the “classful” scheme, because the first octet of “192” puts it in the class C part of the address space. It is in fact 256 contiguous class C networks.

You may also notice the special class B (/16) block 169.254.x.x. This is reserved for Automatic Private IP Addressing (APIPA). Systems that are configured to use this feature will automatically assign systems addresses from this block to enable them to communicate even if no server can be found for “proper” IP address assignment using DHCP. This is described in a special topic in the section describing DHCP.

Previous Topic/Section
IP Addresses With Special Meanings
Previous Page
Pages in Current Topic/Section
Next Page
IP Multicast 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 (
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.