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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
12
3
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

Description

0.0.0.0

0.255.255.255

Class A network 0.x.x.x

0/8

Reserved.

10.0.0.0

10.255.255.255

Class A network 10.x.x.x

10/8

Class A private address block.

127.0.0.0

127.255.255.255

Class A network 127.x.x.x

127/8

Loopback address block.

128.0.0.0

128.0.255.255

Class B network 128.0.x.x

128.0/16

Reserved.

169.254.0.0

169.254.255.255

Class B network 169.254.x.x

169.254/16

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

172.16.0.0

172.31.255.255

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

172.16/12

Class B private address blocks.

191.255.0.0

191.255.255.255

Class B network 191.255.x.x

191.255/16

Reserved.

192.0.0.0

192.0.0.255

Class C network 192.0.0.x

192.0.0/24

Reserved.

192.168.0.0

192.168.255.255

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

192.168/16

Class C private address blocks.

223.255.255.0

223.255.255.255

Class C network 223.255.255.x

223.255.255/24

Reserved.


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 192.168.0.0 to 192.168.255.255. 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
12
3
Next Page
IP Multicast Addressing
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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