Reserved and special-use IP addresses
Not every IP address is an ordinary, routable address that can be handed out to a device on the public internet. The IETF and IANA set aside certain ranges for special purposes — loopback traffic, private networks, documentation examples, multicast, and future use. These blocks are documented in RFCs and collected in IANA's Special-Purpose Address Registries. Because they are reserved, they behave differently from the public addresses your ISP assigns, and most of them are never routed across the open internet.
This page lists the most important reserved ranges for both IPv4 and IPv6, with their CIDR notation, common name, and purpose. Knowing these blocks helps you read network configs, recognize placeholder addresses in documentation, and understand why some addresses never show up as a real public IP.
IPv4 special-use ranges
| Range (CIDR) | Name | Purpose |
|---|---|---|
0.0.0.0/8 | "This network" | The unspecified address and this-network source; not a valid destination (RFC 1122) |
10.0.0.0/8 | Private (RFC 1918) | Private use inside home and corporate networks — see private IP ranges |
100.64.0.0/10 | Carrier-grade NAT | Shared address space for CGNAT between subscribers and the ISP (RFC 6598) |
127.0.0.0/8 | Loopback | Refers back to the local host — see what is localhost |
169.254.0.0/16 | Link-local (APIPA) | Self-assigned when no DHCP server is available (RFC 3927) |
172.16.0.0/12 | Private (RFC 1918) | Private use — a common range for business networks |
192.0.2.0/24 | Documentation (TEST-NET-1) | Reserved for examples and documentation (RFC 5737) |
192.88.99.0/24 | 6to4 relay anycast | Former IPv6 6to4 relay anycast prefix; now deprecated (RFC 7526) |
192.168.0.0/16 | Private (RFC 1918) | Private use — the most common home-router range |
198.18.0.0/15 | Benchmarking | Reserved for network device benchmark testing (RFC 2544) |
198.51.100.0/24 | Documentation (TEST-NET-2) | Reserved for examples and documentation (RFC 5737) |
203.0.113.0/24 | Documentation (TEST-NET-3) | Reserved for examples and documentation (RFC 5737) |
224.0.0.0/4 | Multicast | Class D multicast group addresses (RFC 5771) |
240.0.0.0/4 | Reserved (future use) | Former Class E, reserved for future use (RFC 1112) |
255.255.255.255/32 | Limited broadcast | Broadcast to all hosts on the local link (RFC 919) |
IPv6 special-use ranges
IPv6 has its own set of reserved prefixes. If you are new to the longer addresses and hexadecimal notation, the IPv4 vs IPv6 comparison covers the background. The table below lists the key special-use IPv6 blocks.
| Range | Name | Purpose |
|---|---|---|
::/128 | Unspecified | The all-zeros address, used as a source before an address is assigned |
::1/128 | Loopback | The IPv6 loopback, equivalent to localhost |
::ffff:0:0/96 | IPv4-mapped | Represents IPv4 addresses inside an IPv6 address (RFC 4291) |
64:ff9b::/96 | IPv4/IPv6 translation | Well-known prefix for NAT64 translation (RFC 6052) |
2001:db8::/32 | Documentation | Reserved for examples and documentation (RFC 3849) |
fc00::/7 | Unique local (private) | Private addressing within a site, not globally routed (RFC 4193) |
fe80::/10 | Link-local | Valid only on a single link, auto-configured on every interface (RFC 4291) |
ff00::/8 | Multicast | All IPv6 multicast group addresses (RFC 4291) |
Why this matters
None of these reserved ranges will ever appear as a normal public address on the home page when you check your IP. If a tool reports one of them as your "public" IP, something is misconfigured or you are seeing a private, loopback, or link-local address instead.
These blocks are also useful to recognize in everyday work. When you read a tutorial and see an address like 203.0.113.10 or 2001:db8::1, it is a documentation placeholder — not a real host — so you can safely substitute your own values. When you plan network segments and calculate ranges with the subnet calculator, keeping the reserved blocks in mind helps you avoid overlapping them with your own allocations. And when a device suddenly shows a 169.254.x.x address, that link-local range is a strong hint that DHCP failed. Treat this list as a quick reference the next time an unfamiliar address turns up in a config file or log.