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Encyclopedia > RFC 1918

Private IP address space has been allocated via RFC 1918. This means the addresses are available for any use by anyone and therefore the same private IP addresses can be reused. However they are defined as not routable on the public Internet. They are used extensively in private networks due to the shortage of publicly registerable IP addresses and therefore network address translation is required to connect those networks to the Internet.


Private IP addresses also provide a basic form of security as in a typical network configuration of this type it is not possible for the outside world (Internet) to establish a connection directly to a host using these addresses.


Specifically the networks are:

Name start IP address end IP address classful description largest CIDR block
24-bit block 10.0.0.0 10.255.255.255 single class A 10.0.0.0/8
20-bit block 172.16.0.0 172.31.255.255 16 contiguous class Bs 172.16.0.0/12
16-bit block 192.168.0.0 192.168.255.255 256 contiguous class Cs 192.168.0.0/16

RFC 1597 was the original specification but is now for historical purposes only.


To reduce load on the root nameservers caused by reverse DNS lookups for these IP addresses, a system of "black-hole" nameservers is provided by anycast network AS112. [1] (http://www.as112.net/)


See also

External links


  Results from FactBites:
 
RFC 1918 (rfc1918) - Address Allocation for Private Internets (3106 words)
RFC 1918: Is IP addresses starting with 169.254.0.0 considered in IP address space for...
RFC 1918: If a public IP(64.27.12.150 for http://odissei.atspace com) is hit from a...
RFC 1918: There should be a reference to the other non globally routable IP addresses used...
BCP5 (2679 words)
RFC 1918 Address Allocation for Private Internets February 1996 Moving a host from private to public or vice versa involves a change of IP address, changes to the appropriate DNS entries, and changes to configuration files on other hosts that reference the host by IP address.
RFC 1918 Address Allocation for Private Internets February 1996 A major drawback to the use of private address space is that it may actually reduce an enterprise's flexibility to access the Internet.
RFC 1918 Address Allocation for Private Internets February 1996 If a suitable subnetting scheme can be designed and is supported by the equipment concerned, it is advisable to use the 24-bit block (class A network) of private address space and make an addressing plan with a good growth path.
  More results at FactBites »

 

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