In the Internet addressing architecture, certain IP addresses are reserved by the Internet Assigned Numbers Authority (IANA) for special use. These addresses may be necessary for maintenance of routing tables, multicast, or operation under failure modes.
The Internet Engineering Task Force (IETF) specified these reserved IP address ranges in various RFCs. The addresses tend to be members of three categories: addresses that are globally unique, addresses that are unique to the subnet, and addresses that are only relevant to the host using the address.
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 | Subnet | 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 | Subnet | Used for local communications within a private network as specified by RFC 1918. |
| 127.0.0.0/8 | 127.0.0.0–127.255.255.255 | 16777216 | Local | 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 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 | Subnet | 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 | Subnet | Assigned as "TEST-NET" for use solely in documentation and example source code and should not be used publicly. |
| 192.88.99.0/24 | 192.88.99.0–192.88.99.255 | 256 | Global | Used by 6to4 anycast relays as specified by RFC 3068. |
| 192.168.0.0/16 | 192.168.0.0–192.168.255.255 | 65536 | Subnet | 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 | Private network | 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 | Subnet | Assigned as "TEST-NET-2" for use solely in documentation and example source code and should not be used publicly. |
| 203.0.113.0/24 | 203.0.113.0–203.0.113.255 | 256 | Subnet | Assigned as "TEST-NET-3" for use solely in documentation and example source code and should not be used publicly. |
| 224.0.0.0/4 | 224.0.0.0–239.255.255.255 | 268435456 | Global | Reserved for multicast assignments as specified in RFC 3171 |
| 240.0.0.0/4 | 240.0.0.0–255.255.255.255 | 268435456 | Global | 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. |
These addresses are listed in RFC 5156.
| CIDR | IP Range | Number of Unique Addresses | Locality | Purpose |
|---|---|---|---|---|
| ::/128 | :: | 1 | Unspecified address | |
| ::1/128 | ::1 | 1 | Local | Used for loopback address to the local host. |
| ::ffff:0:0/96 | ::ffff:0:0–::ffff:ffff:ffff | 4294967296 | Local | IPv4 mapped addresses |
| 2001::/32 | 2001::–2001::ffff:ffff:ffff:ffff:ffff:ffff | 296 | Global | Teredo tunneling |
| 2001:10::/28 | 2001:10::–2001:1f:ffff:ffff:ffff:ffff:ffff:ffff | 2100 | Local | Overlay Routable Cryptographic Hash Identifiers (ORCHID) |
| 2001:db8::/32 | 2001:db8::–2001:db8:ffff:ffff:ffff:ffff:ffff:ffff | 296 | Subnet | Addresses used in documentation |
| 2002::/16 | 2002::–2002:ffff:ffff:ffff:ffff:ffff:ffff:ffff | 2112 | Global | 6to4 |
| fc00::/7 | fc00::–fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff | 2121 | Subnet | Unique local address |
| ff00::/8 | ff00::–ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff | 2120 | Global | Multicast |