Non-routable Internet addresses

0.0.0.0/8

The range is described in RFC 1122, RFC 3330 and RFC 1700 as "this host on this network", although given the usage scenarios, it would be more correct to call it "any address". 0.0.0.0 is used for:

  • In IPv4-based routing, 0.0.0.0 serves as a default route. This means no particular address has been designated in the routing table as the next hop in the packet's path to its final destination. When the default route is used with a subnet mask of 0.0.0.0, it matches any address. When used with a 255.255.255.255 mask, it matches none.
  • Within a LAN, 0.0.0.0 can be used as a source address in IPv4 broadcasting, which is used to transmit data to all devices on a LAN.
  • IP address 0.0.0.0 is used on servers to designate a service may bind to all network interfaces. It tells a server to "listen" for and accept connections from any IP address.
  • A 0.0.0.0 address indicates the client isn't connected to a TCP/IP network, and a device may give itself a 0.0.0.0 address when it is offline.

10.0.0.0/8

172.16.0.0/12

192.168.0.0/16

The three ranges described above are not routed to the Internet, as they are reserved for the organization of private local networks of IT infrastructure of companies (used for internal networks). 192.168.0.0/24 is the most commonly used private IP range for home networks. To interact with external resources and partners, NAT must be used to avoid address space overlap. The range are described in RFC 1918. For example:

  • A company might assign IPs like 10.1.1.1, 10.1.1.2 to devices within its LAN.
  • A school might use addresses like 172.16.5.1 for its networked computers.
  • Home routers often use addresses like 192.168.0.1 for the router and 192.168.0.x for connected devices.

100.64.0.0/10

In accordance with RFC 6598, it is used as a translated address block for inter-provider interactions and Carrier Grade NAT (CGNAT). It is especially useful as a common free IPv4 address space, necessary for the integration of provider resources, as well as for the allocation of non-routable addresses to subscribers.

127.0.0.0/8

In cases where a service requires a functioning network stack that will not fail when disconnected from the network, loopback addresses are used. The allocation of 127.0.0.0/8 for internal loopback addresses is defined in RFC 1122. Loopback addresses do not have to be present or processed in any network, only in the host's internal routing table.

169.254.0.0/16

According to RFC 3927, it is defined as Link-Local for automatic configuration. Link-local addresses used when a device cannot obtain an IP address from DHCP. PC, with can't get an IP address from a DHCP server, assigns itself an incomprehensible and previously unregistered IP starting with 169.254.xxx.xxx. This is the implementation of recommendations from RFC.

192.0.0.0/24

Used in various IETF protocols but not commonly assigned to end-user devices. This range is reserved for IETF protocol assignments according to RFC 6890.

192.0.2.0/24 198.51.100.0/24 203.0.113.0/24

These three subnets are, according to RFC 5737, reserved for description in documents. Reserved for documentation and examples (TEST-NET).

Often used in tutorials and technical documentation:

  • ping 192.0.2.5
  • exec curl http://203.0.113.7

192.88.99.0/24

A special case from the 192.0.0.0/24 subnet described above, but deserves a separate description for technological interest. The net has been reserved as the 6to4 relay anycast address prefix by the IETF according to RFC 6219.

198.18.0.0/15

The range is allocated for for benchmark testing of inter-network communications in accordance with RFC 2544 and the clarification in RFC 6815 that this range should not be accessible to the Internet to avoid conflicts. Used in testing scenarios to simulate network traffic without affecting real networks.

224.0.0.0/4

This range is also called Class D in the historical classification. It is allocated for Multicast, the clarification of the specifics of its operation is also a separate note. RFC 5771 describes in detail the use of subnets within the block, but the essence remains the same: these addresses are not assigned to any provider, and, accordingly, should not be visible via the Internet.

240.0.0.0/4

According to RFC 1112, this range of IP addresses, historically also known as Class E, is reserved for future use. Not commonly used or referenced in practice.

These ranges cover a variety of uses in networking, from private communications to documentation and testing scenarios, each serving a specific purpose defined by IETF standards and RFCs.