Reserved IP Address
Address range set aside by IANA or an RFC for a specific purpose and excluded from normal public routing.
A reserved IP address belongs to a range that IANA and various RFCs have removed from general allocation. The address is technically valid but routers, registries and operating systems treat it as having a fixed meaning, so it is never assigned to an arbitrary host on the public Internet.
In IPv4 the main reservations are 0.0.0.0/8 (this network, RFC 1122), 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (private use, RFC 1918), 100.64.0.0/10 (carrier-grade NAT, RFC 6598), 127.0.0.0/8 (loopback), 169.254.0.0/16 (link-local, RFC 3927), 192.0.2.0/24, 198.51.100.0/24 and 203.0.113.0/24 (documentation, RFC 5737), 198.18.0.0/15 (network benchmarking, RFC 2544), 224.0.0.0/4 (multicast), 240.0.0.0/4 (future use) and 255.255.255.255/32 (limited broadcast).
In IPv6 the equivalents are ::/128 (unspecified), ::1/128 (loopback), 64:ff9b::/96 (NAT64), 100::/64 (discard), 2001:db8::/32 (documentation), fc00::/7 (unique local), fe80::/10 (link-local) and ff00::/8 (multicast).
Reserved ranges should never appear as the source of public Internet traffic. Operators filter them at the network edge with bogon lists, and seeing one as a public source typically means a misconfiguration, a leaked private prefix, or spoofed traffic. Documentation ranges in particular are useful in examples and test environments because they will not collide with any real allocation.
Key Points
- Defined by IANA and RFCs, excluded from public allocation
- IPv4 reserved blocks include private (RFC 1918), CGNAT (RFC 6598), loopback, link-local, documentation, benchmarking and multicast
- IPv6 reserved blocks include
::,::1,2001:db8::/32,fc00::/7,fe80::/10,ff00::/8 - Documentation ranges are safe to use in examples and tests
- A reserved source on public traffic indicates misconfiguration or spoofing
- Operators commonly filter bogon ranges at the edge