Editing IPv4 (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 networks. Packets addresses in these ranges are not routable in 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 RFC|1918}}
|-
!Name!![[CIDR]] block!!Address range!!Number of<br>addresses!!''[[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 interoperate via the public Internet, the two networks must be bridged across the Internet via a [[virtual private network]] (VPN) or an [[IP tunnel]], which [[Encapsulation (networking)|encapsulates]] packets, including their headers containing the private addresses, in a protocol layer during transmission across the public network. Additionally, encapsulated packets may be encrypted for transmission across public networks to secure the data.