Editing Wide area network (section)

==Private networks==
Of the approximately four billion addresses defined in IPv4, about 18 million addresses in three ranges are reserved for use in [[private network]]s. Packets addressed in these ranges are not routable on the public Internet; they are ignored by all public routers. Therefore, private hosts cannot directly communicate with public networks, but require [[network address translation]] at a routing gateway for this purpose.
<section begin=IPv4-private-networks/><!-- This table is transcluded to other pages, such as [[Blackhole server]]. (see: [[Wikipedia:transclusion]]) -->
:{| class="wikitable"
|+ Reserved private IPv4 network ranges<ref name=rfc1918>{{cite IETF|rfc=1918|bcp=5|title=Address Allocation for Private Internets|publisher=Network Working Group [[IETF]]|author1=Y. Rekhter|author2=B. Moskowitz|author3=D. Karrenberg|author4=G. J. de Groot|author5=E. Lear|date=February 1996}}</ref>
|-
!Name!![[CIDR]] block!!Address range!!Number of addresses!!''Obsolete [[classful]]'' description
|-
|24-bit block||10.0.0.0/8||10.0.0.0 – 10.255.255.255||align="right"|{{val|16777216}}||Single Class A.                         
|-
|20-bit block|||172.16.0.0/12||172.16.0.0 – 172.31.255.255||align="right"|{{val|1048576}}||Contiguous range of 16 Class B blocks.  
|-
|16-bit block||192.168.0.0/16||192.168.0.0 – 192.168.255.255||align="right"|{{val|65536}}||Contiguous range of 256 Class C blocks. 
|}<section end=IPv4-private-networks/>

Since two private networks, e.g., two branch offices, cannot directly communicate via the public Internet, the two networks must be bridged across the Internet via a [[virtual private network]] (VPN) or other form of [[IP tunnel]] that [[Encapsulation (networking)|encapsulates]] packets, including their headers containing the private addresses, for transmission across the public network. Additionally, encapsulated packets may be encrypted to secure their data.