Private and reserved IP ranges

Definition and scope

Distinguish private, loopback, link-local, documentation and globally routable addresses.

Use this reference to establish the meaning and limits of the result before changing production configuration.

How it works

RFC 1918 defines 10/8, 172.16/12 and 192.168/16 for private IPv4. Other special ranges include loopback 127/8, link-local 169.254/16, CGNAT 100.64/10 and documentation networks such as 192.0.2/24. IPv6 has ::1, fe80::/10 and fc00::/7.

How to read it

Private does not mean anonymous or secure; it only describes routing scope. Reserved and documentation ranges have different purposes. A library’s is_private flag may group several non-global categories, so show the precise classification.

Correct and incorrect examples

Compare the normalized examples. Technical values are illustrative and use documentation ranges or reserved names.

Correct

192.0.2.0/24 is documentation space, not a private LAN range

Incorrect or misleading

192.0.2.10 ∈ RFC1918

Element	Role	Example
10.0.0.0/8	RFC1918	is_global=false
172.16.0.0/12	RFC1918	is_global=false
192.168.0.0/16	RFC1918	is_global=false
100.64.0.0/10	CGNAT	shared
127.0.0.0/8	loopback	is_loopback=true
169.254.0.0/16	link-local	is_link_local=true
192.0.2.0/24	documentation	TEST-NET-1
fc00::/7	ULA	is_global=false
fe80::/10	link-local	is_link_local=true
2001:db8::/32	documentation	IPv6

Common problems

Publishing private addresses in public DNS, confusing CGNAT with an internal LAN, or filtering all IPv6 special ranges as one category leads to broken diagnostics and unsafe access controls.

Practical checklist

Classify both the literal address and embedded IPv4 forms, deny internal ranges for server-side probes, and use documentation prefixes—not real customer addresses—in examples.

Standards and primary references

These primary specifications define the protocol behavior. Provider documentation may add operational requirements but cannot replace the standard.