Private and Reserved IP Addresses

• 0.0.0.0/8 - local network. Addresses in this block refer to source hosts on "this" network.
• 127.0.0.0/8 - host loopback addresses.
• ::1/128 (0:0:0:0:0:0:0:1) - IPv6 loopback address.

The following blocks of IP addresses are reserved for private or local area (LAN) networks (RFC 1918):

• 10.0.0.0/8   (10.0.0.0 – 10.255.255.255)
• 172.16.0.0/12   (172.16.0.0 – 172.31.255.255)
• 192.168.0.0/16   (192.168.0.0 – 192.168.255.255)

IP addresses from these ranges are called “Private IP Addresses” and used by companies and organizations within their private networks. Private IP addresses should not appear on the public Internet.

Sometimes private IP addresses are recorded in a header of an e-mail message. This indicates that the message has passed through e-mail forwarding hosts on the local network before reaching the Internet.

The fc00::/7 addresses, called “Unique Local IPv6 Unicast Addresses“, are globally unique but intended for use only within local sites (RFC 4193).

The 100.64.0.0/10   (100.64.0.0 – 100.127.255.255) block is allocated for use by service providers deploying carrier-grade NAT (CGN) to provide Internet connectivity for multiple customer devices or network (RFC 6598). Shared address space is not-globally routable and could be sometimes used in a similar way as the private IP address ranges (RFC 1918).

The 169.254.0.0/16 block is called “Link-local“ addresses (RFC 3927). Hosts obtain these addresses through the auto-configuration future named “Automatic Private IP Addressing“ (APIPA) in a situation when a DHCP server is not available on the network.

Other known usage for the IPs from the link-local block:

• In Google Cloud Platform (GCP) 169.254.169.254 is assigned to the Compute Engine metadata server which also acts as NTP server, DHCP server, and DNS resolver. Also, Cloud Router BGP peering IP addresses are selected from the link-local IP address space.
• In Amazon Web Services (AWS) 169.254.169.254 is allocated to the EC2 instance metadata service, 169.254.169.123 - to the Amazon Time Sync Service, and 169.254.169.253 - to the Amazon DNS server.

The link-local IPv6 unicast addresses fe80::/10 are designed for use on a single link and support automatic address configuration and neighbor discovery.

The following address blocks are reserved for use in documentation and examples (RFC 5737, RFC 6676, RFC 3849):

• 192.0.2.0/24 - TEST-NET-1.
• 198.51.100.0/24 - TEST-NET-2.
• 203.0.113.0/24 - TEST-NET-3.
• 233.252.0.0/24 - MCAST-TEST-NET (IPv4 multicast addresses).
• 2001:db8::/32 - IPv6 unicast.
• ff0X::db8:0:0/96 - IPv6 multicast (the value of X defines the scope of the address).

The 198.18.0.0/15   (192.18.0.0 – 198.19.255.255) IPv4 block and the 2001:2::/48 IPv6 block are allocated for benchmarking and testing (RFC 2544, RFC 5180).

• 224.0.0.0/4   (224.0.0.0 – 239.255.255.255) - IP multicast (former Class D IP addresses).
• 255.255.255.255/32 - "limited broadcast" destination address.
• ff00::/8 - IPv6 multicast addresses.

• 192.0.0.0/24 - reserved for IETF protocol assignments (RFC 5736).
• 192.88.99.0/24 - the block was reserved for anycast 6to4 transition mechanism which is deprecated by RFC 7526.
• 240.0.0.0/4 - formerly known as Class E IP addresses. It is reserved for future use (RFC 1112, Section 4).

IANA IPv4 Special-Purpose Address Registry
IANA IPv6 Special-Purpose Address Registry
RFC 6890 - Special-Purpose IP Address Registries
RFC 4291 - IP Version 6 Addressing Architecture
IPv6 Addressing Cheat Sheet