Editing IPv4 (section)

===Special-use addresses===
The [[Internet Engineering Task Force]] (IETF) and IANA have restricted from general use various [[reserved IP addresses]] for special purposes.{{Ref RFC|6890}} Notably these addresses are used for [[multicast]] traffic and to provide addressing space for unrestricted uses on private networks.
<section begin=IPv4-special-address-blocks/><!--This table is transcluded to other pages, such as [[Reserved IP addresses]]. (see: [[Wikipedia:transclusion]])-->
:{|class="wikitable sortable"
|+Special address blocks
!Address block
!Address range
!Number of addresses
!Scope
!Description
|-
|0.0.0.0/8
|0.0.0.0–0.255.255.255
|align=right|{{val|16,777,216}}
|Software
|Current (local, "this") network{{Ref RFC|6890}}
|-
|10.0.0.0/8
|10.0.0.0–10.255.255.255
|align=right|{{val|16,777,216}}
|Private&nbsp;network
|Used for local communications within a private network{{Ref RFC|1918}}
|-
<!--Note: 14.0.0.0/8, 24.0.0.0/8 and 39.0.0.0/8 are outdated and irrelevant. Do not add them.-->
|100.64.0.0/10
|100.64.0.0–100.127.255.255
|align=right|{{val|4,194,304}}
|Private&nbsp;network
|[[IPv4 shared address space|Shared address space]]{{Ref RFC|6598}} for communications between a service provider and its subscribers when using a [[carrier-grade NAT]]
|-
|127.0.0.0/8
|127.0.0.0–127.255.255.255
|align=right|{{val|16,777,216}}
|Host
|Used for [[loopback address]]es to the local host<ref name=rfc6890/>
|-
<!--Note: 128.0.0.0/16 is "no longer needed" and "subject to future allocation" so it is not relevant here.-->
<!--"Note that 128.66.0.0/24 has been used for some examples in the past. However, this block did not appear in the list of special prefixes in RFC 3330 or its successors, and the block is therefore not reserved for any special purpose. The block can be used for regular address assignments with caution." excerpt from RFC 5737.-->
|169.254.0.0/16
|169.254.0.0–169.254.255.255
|align=right|{{val|65,536}}
|Subnet
|Used for [[link-local address]]es{{Ref RFC|3927}} between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a [[DHCP]] server
|-
|172.16.0.0/12
|172.16.0.0–172.31.255.255
|align=right|{{val|1,048,576}}
|Private&nbsp;network
|Used for local communications within a private network<ref name=rfc1918/>
|-
<!--Note: 191.255.0.0/16 and 192.0.0.0/24 is "no longer needed" and "subject to future allocation" so it is not relevant here.-->
|-
|192.0.0.0/24
|192.0.0.0–192.0.0.255
|align=right|{{val|256}}
|Private&nbsp;network
|IETF Protocol Assignments, [[DS-Lite]] (/29)<ref name=rfc6890/>
|-
|192.0.2.0/24
|192.0.2.0–192.0.2.255
|align=right|{{val|256}}
|Documentation
|Assigned as TEST-NET-1, documentation and examples{{Ref RFC|5737}}
|-
|192.88.99.0/24
|192.88.99.0–192.88.99.255
|align=right|{{val|256}}
|Internet
|Reserved.{{Ref RFC|7526}} Formerly used for [[6to4|IPv6 to IPv4]] relay{{Ref RFC|3068}} (included [[IPv6]] address block [[IPv6 address#Special addresses|2002::/16]]).
|-
|192.168.0.0/16
|192.168.0.0–192.168.255.255
|align=right|{{val|65,536}}
|Private network
|Used for local communications within a private network<ref name=rfc1918/>
|-
|198.18.0.0/15
|198.18.0.0–198.19.255.255
|align=right|{{val|131,072}}
|Private&nbsp;network
|Used for benchmark testing of inter-network communications between two separate subnets{{Ref RFC|2544}}
|-
|198.51.100.0/24
|198.51.100.0–198.51.100.255
|align=right|{{val|256}}
|Documentation
|Assigned as TEST-NET-2, documentation and examples<ref name=rfc5737/>
|-
|203.0.113.0/24
|203.0.113.0–203.0.113.255
|align=right|{{val|256}}
|Documentation
|Assigned as TEST-NET-3, documentation and examples<ref name=rfc5737/>
|-
<!--223.255.255.0/24 presently unused, but subject to future allocation-->
|224.0.0.0/4
|224.0.0.0–239.255.255.255
|align=right|{{val|268,435,456}}
|Internet
|In use for [[IP multicast|multicast]]{{Ref RFC|5771}} (former Class D network)
|-
|233.252.0.0/24
|233.252.0.0–233.252.0.255
|align=right|{{val|256}}
|Documentation
|Assigned as MCAST-TEST-NET, documentation and examples (This is part of the above multicast space.)<ref name="rfc5771"/>{{Ref RFC|6676}}
|-
|240.0.0.0/4
|240.0.0.0–255.255.255.254
|align=right|{{val|268,435,455}}
|Internet
|Reserved for future use{{Ref RFC|3232}} (former Class E network)
|-
|255.255.255.255/32
|255.255.255.255
|align=right|{{val|1}}
|Subnet
|Reserved for the "limited [[Broadcast address|broadcast]]" destination address{{Ref RFC|6890}}
|}<section end=IPv4-special-address-blocks/>

====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.