IP
Internet Protocol (IP) is a foundational network protocol for routing across networks. Machines are assigned an Internet Protocol Address (IP address) to which packets are addressed.
Contents
Addresses
An IP address is a unique 32-bit or 128-bit number, for IPv4 and IPv6 respectively.
Addresses can either be static or dynamically assigned. The predominant method for assigning dynamic addresses is DHCP.
Reserved Addresses
A set of addresses are reserved for local networking:
IP Block |
IP Range |
Reserved for |
127.0.0.0/8 |
127.0.0.0 - 127.255.255.255 |
Loopback |
10.0.0.0/8 |
10.0.0.0 - 10.255.255.255 |
Local network |
172.16.0.0/12 |
172.16.0.0 - 172.31.255.255 |
Local network |
192.0.0.0/24 |
192.0.0.0 - 192.0.0.255 |
Local network |
192.168.0.0/16 |
192.168.0.0 - 192.168.255.255 |
Local network |
::1/128 |
::1 (yes, just one address) |
Loopback |
fc00::/7 |
fc00:: - fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff |
Local network |
There are also a number of reservations for infrastructure and future use. The remainder are mapped to the public internet.
Networks
Most networks are Local Area Networks (LAN). A LAN should restrict itself to the set of addresses reserved for local addressing, but there is no reason for local addresses to be globally unique.
A gateway stands between the LAN and the Wide Area Network (WAN). The Internet Assigned Numbers Authority (IANA) manages the assignment of addresses in this space.
Design
Apart from the standardization of addresses, IP also lays out how packets should be formed and routed.
IP packets are assumed to be unreliable, for reasons including data corruption, out-of-order delivery, and disappearance. This is only mitigated by a checksum included in the IP packet. If any relaying node finds fault in a checksum, however, the packet is discarded without notification. All issues of the IP network are expected to be solved in higher-level protocols.