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technology/internet/Internet Protocol.md
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@ -32,7 +32,7 @@ IPv4 reserves special address blocks for private networks (224 + 220 + 2
IPv4 addresses may be represented in any notation expressing a 32-bit integer value. They are most often written in dot-decimal notation, which consists of four octets of the address expressed individually in decimal numbers and separated by periods.
For example, the quad-dotted IP address in the illustration (`172.16.254.1`) represents the 32-bit decimal number 2886794753, which in hexadecimal format is 0xAC10FE01.
For example, the quad-dotted IP address in the illustration (`172.16.254.1`) represents the 32-bit decimal number `2886794753`, which in hexadecimal format is ` 0xAC10FE01`.
CIDR notation combines the address with its routing prefix in a compact format, in which the address is followed by a slash character (/) and the count of leading consecutive 1 bits in the routing prefix (subnet mask).
@ -40,25 +40,25 @@ CIDR notation combines the address with its routing prefix in a compact format,
The Internet Engineering Task Force (IETF) and IANA have restricted from general use various reserved IP addresses for special purposes. Notably these addresses are used for multicast traffic and to provide addressing space for unrestricted uses on private networks.
**Special address blocks**:
| Address block | Address range | Number of <br>addresses | Scope | Description |
| ------------------ | --------------------------- | ------------------------ | --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 0.0.0.0/8 | 0.0.0.0–0.255.255.255 | 16777216 | Software | Current (local, "this") network |
| 10.0.0.0/8 | 10.0.0.0–10.255.255.255 | 16777216 | Private network | Used for local communications within a private network |
| 100.64.0.0/10 | 100.64.0.0–100.127.255.255 | 4194304 | Private network | Shared address space 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 | 16777216 | Host | Used for loopback addresses to the local host |
| Address block | Address range | Number of <br>addresses | Scope | Description |
| ------------------ | --------------------------- | ------------------------ | --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| 0.0.0.0/8 | 0.0.0.0–0.255.255.255 | 16777216 | Software | Current (local, "this") network |
| 10.0.0.0/8 | 10.0.0.0–10.255.255.255 | 16777216 | Private network | Used for local communications within a private network |
| 100.64.0.0/10 | 100.64.0.0–100.127.255.255 | 4194304 | Private network | Shared address space 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 | 16777216 | Host | Used for loopback addresses to the local host |
| 169.254.0.0/16 | 169.254.0.0–169.254.255.255 | 65536 | Subnet | Used for link-local addresses between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a [DHCP](DHCP.md) server |
| 172.16.0.0/12 | 172.16.0.0–172.31.255.255 | 1048576 | Private network | Used for local communications within a private network |
| 192.0.0.0/24 | 192.0.0.0–192.0.0.255 | 256 | Private network | IETF Protocol Assignments, DS-Lite (/29) |
| 192.0.2.0/24 | 192.0.2.0–192.0.2.255 | 256 | Documentation | Assigned as TEST-NET-1, documentation and examples |
| 192.88.99.0/24 | 192.88.99.0–192.88.99.255 | 256 | Internet | Reserved. Formerly used for IPv6 to IPv4 relay (included IPv6 address block `2002::/16`). |
| 192.168.0.0/16 | 192.168.0.0–192.168.255.255 | 65536 | Private network | Used for local communications within a private network |
| 198.18.0.0/15 | 198.18.0.0–198.19.255.255 | 131072 | Private network | Used for benchmark testing of inter-network communications between two separate subnets |
| 198.51.100.0/24 | 198.51.100.0–198.51.100.255 | 256 | Documentation | Assigned as TEST-NET-2, documentation and examples |
| 203.0.113.0/24 | 203.0.113.0–203.0.113.255 | 256 | Documentation | Assigned as TEST-NET-3, documentation and examples |
| 224.0.0.0/4 | 224.0.0.0–239.255.255.255 | 268435456 | Internet | In use for multicast (former Class D network) |
| 233.252.0.0/24 | 233.252.0.0–233.252.0.255 | 256 | Documentation | Assigned as MCAST-TEST-NET, documentation and examples (Note that this is part of the above multicast space.) |
| 240.0.0.0/4 | 240.0.0.0–255.255.255.254 | 268435455 | Internet | Reserved for future use (former Class E network) |
| 255.255.255.255/32 | 255.255.255.255 | 1 | Subnet | Reserved for the "limited broadcast" destination address |
| 172.16.0.0/12 | 172.16.0.0–172.31.255.255 | 1048576 | Private network | Used for local communications within a private network |
| 192.0.0.0/24 | 192.0.0.0–192.0.0.255 | 256 | Private network | IETF Protocol Assignments, DS-Lite (/29) |
| 192.0.2.0/24 | 192.0.2.0–192.0.2.255 | 256 | Documentation | Assigned as TEST-NET-1, documentation and examples |
| 192.88.99.0/24 | 192.88.99.0–192.88.99.255 | 256 | Internet | Reserved. Formerly used for IPv6 to IPv4 relay (included IPv6 address block `2002::/16`). |
| 192.168.0.0/16 | 192.168.0.0–192.168.255.255 | 65536 | Private network | Used for local communications within a private network |
| 198.18.0.0/15 | 198.18.0.0–198.19.255.255 | 131072 | Private network | Used for benchmark testing of inter-network communications between two separate subnets |
| 198.51.100.0/24 | 198.51.100.0–198.51.100.255 | 256 | Documentation | Assigned as TEST-NET-2, documentation and examples |
| 203.0.113.0/24 | 203.0.113.0–203.0.113.255 | 256 | Documentation | Assigned as TEST-NET-3, documentation and examples |
| 224.0.0.0/4 | 224.0.0.0–239.255.255.255 | 268435456 | Internet | In use for multicast (former Class D network) |
| 233.252.0.0/24 | 233.252.0.0–233.252.0.255 | 256 | Documentation | Assigned as MCAST-TEST-NET, documentation and examples (Note that this is part of the above multicast space.) |
| 240.0.0.0/4 | 240.0.0.0–255.255.255.254 | 268435455 | Internet | Reserved for future use (former Class E network) |
| 255.255.255.255/32 | 255.255.255.255 | 1 | Subnet | Reserved for the "limited broadcast" destination address |
### 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.