In the Internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 addressing architecture, certain IP address

IP address

An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

es are reserved by the Internet Assigned Numbers Authority

Internet Assigned Numbers Authority

The Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...

 (IANA) for special use. These addresses may be necessary for maintenance of routing table

Routing table

In computer networking a routing table, or Routing Information Base , is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics associated with those routes. The routing table contains information about the...

s, multicast

Multicast

In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...

, or operation under failure mode

Failure mode

Failure causes are defects in design, process, quality, or part application, which are the underlying cause of a failure or which initiate a process which leads to failure. Where failure depends on the user of the product or process, then human error must be considered.-Component failure:A part...

s.

The Internet Engineering Task Force

Internet Engineering Task Force

The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...

 (IETF) specified these reserved IP address ranges in various RFCs

Request for Comments

In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

. The addresses tend to be members of three categories: addresses that are globally unique, addresses that are unique to the subnet

Subnetwork

A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....

, and addresses that are only relevant to the host

Host (network)

A network host is a computer connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network layer host address....

 using the address.

Reserved IPv4 addresses

These addresses are listed in RFC 5735.

CIDR	IP Range	Number of Unique Addresses	Locality	Purpose
0.0.0.0/8	0.0.0.0–0.255.255.255	16777216		Used for broadcast messages to the current ("this") network as specified by RFC 1700, page 4.
10.0.0.0/8	10.0.0.0–10.255.255.255	16777216		Used for local communications within a private network Private network In the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...  as specified by RFC 1918.
127.0.0.0/8	127.0.0.0–127.255.255.255	16777216		Used for loopback addresses to the local host.
169.254.0.0/16	169.254.0.0–169.254.255.255	65536		Used for autoconfiguration 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	1048576		Used for local communications within a private network as specified by RFC 1918
192.0.2.0/24	192.0.2.0–192.0.2.255	256		Assigned as "TEST-NET" for use solely in documentation Documentation Documentation is a term used in several different ways. Generally, documentation refers to the process of providing evidence.Modules of Documentation are Helpful...  and example source code Source code In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...  and should not be used publicly.
192.88.99.0/24	192.88.99.0–192.88.99.255	256		Used by 6to4 6to4 6to4 is an Internet transition mechanism for migrating from IPv4 to IPv6, a system that allows IPv6 packets to be transmitted over an IPv4 network without the need to configure explicit tunnels...  anycast Anycast Anycast is a network addressing and routing methodology in which datagrams from a single sender are routed to the topologically nearest node in a group of potential receivers all identified by the same destination address.-Addressing methodologies:...  relays as specified by RFC 3068.
192.168.0.0/16	192.168.0.0–192.168.255.255	65536		Used for local communications within a private network as specified by RFC 1918.
198.18.0.0/15	198.18.0.0–198.19.255.255	131072		Used for testing of inter-network communications between two separate subnets as specified in RFC 2544.
198.51.100.0/24	198.51.100.0–198.51.100.255	256		Assigned as "TEST-NET-2" for use solely in documentation Documentation Documentation is a term used in several different ways. Generally, documentation refers to the process of providing evidence.Modules of Documentation are Helpful...  and example source code Source code In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...  and should not be used publicly.
203.0.113.0/24	203.0.113.0–203.0.113.255	256		Assigned as "TEST-NET-3" for use solely in documentation Documentation Documentation is a term used in several different ways. Generally, documentation refers to the process of providing evidence.Modules of Documentation are Helpful...  and example source code Source code In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...  and should not be used publicly.
224.0.0.0/4	224.0.0.0–239.255.255.255	268435456		Reserved for multicast Multicast In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...  assignments as specified in RFC 3171
240.0.0.0/4	240.0.0.0–255.255.255.255	268435456		255.255.255.255 is reserved for the "limited broadcast" destination address. All others in this block are reserved for future allocation by the IANA.

Reserved IPv6 addresses

These addresses are listed in RFC 5156.

CIDR	IP Range	Number of Unique Addresses	Locality	Purpose
::/128	::	1		Unspecified address
::1/128	::1	1		Used for loopback address to the local host.
::ffff:0:0/96	::ffff:0:0–::ffff:ffff:ffff	4294967296		IPv4 mapped addresses
2001::/32	2001::–2001::ffff:ffff:ffff:ffff:ffff:ffff	296		Teredo tunneling Teredo tunneling In computer networking, Teredo is a transition technology that gives full IPv6 connectivity for IPv6-capable hosts which are on the IPv4 Internet but which have no direct native connection to an IPv6 network...
2001:10::/28	2001:10::–2001:1f:ffff:ffff:ffff:ffff:ffff:ffff	2100		Overlay Routable Cryptographic Hash Identifiers (ORCHID)
2001:db8::/32	2001:db8::–2001:db8:ffff:ffff:ffff:ffff:ffff:ffff	296		Addresses used in documentation
2002::/16	2002::–2002:ffff:ffff:ffff:ffff:ffff:ffff:ffff	2112		6to4 6to4 6to4 is an Internet transition mechanism for migrating from IPv4 to IPv6, a system that allows IPv6 packets to be transmitted over an IPv4 network without the need to configure explicit tunnels...
fc00::/7	fc00::–fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff	2121		Unique local address Unique local address A unique local address is an IPv6 address in the block fc00::/7, defined in RFC 4193. It is the IPv6 counterpart of the IPv4 private address. Unique local addresses are available for use in private networks, e.g. inside a single site or organization, or spanning a limited number of sites or...
ff00::/8	ff00::–ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff	2120		Multicast Multicast In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...