Test IP Address Ranges: IPv4, IPv6 and Private Networks

Test IP address ranges depend on the task. Use documentation prefixes for addresses displayed in tutorials, screenshots and stored fixtures. Use an assigned address on a network you control for a working test endpoint. Private IPs may reach real equipment; documentation allocations describe intended use, not an automatic firewall ^{[rfc5737][rfc1918]}.

Documentation IP ranges to copy into examples

RFC 9637 expanded the IPv6 documentation space in 2024; it did not replace 2001:db8::/32. A validator or example allowlist that recognizes only the older prefix misses the newer allocation. Keep the allowed prefixes explicit instead of relying on a loosely named isPrivate helper.

Private, loopback and documentation addresses do different jobs

A webhook fixture containing 10.0.0.1 can contact a company service when a developer connects to a VPN. Changing it to a documentation IP improves the example, but the test harness should still intercept the HTTP call or allow connections only to its test server. Do not assign TEST-NET addresses as a substitute for a private network plan.

How to generate a small deterministic fixture

For 100 unique display values, this JavaScript expression is sufficient: Array.from({ length: 100 }, (_, i) => "192.0.2." + (i + 1)). It emits 192.0.2.1 through 192.0.2.100, requires no random library, and repeats on every run. These are strings for a fixture, not endpoints to probe.

For a larger file, enumerate across all three IPv4 documentation blocks and decide whether .0 and .255 belong in your test. The full space is 3 × 256 = 768 values. Excluding those two values per block leaves 3 × 254 = 762. A request for 10,000 unique IPv4 documentation strings is impossible within these blocks; permit repeats if uniqueness is irrelevant, or use IPv6 documentation space.

The bulk identity exporter currently exports person and address fields, not IP addresses. Add the IP fixture column in your own script.

Parser cases: syntax, normalization and purpose

IPv6 has multiple valid textual representations. RFC 5952 gives a canonical output form: lowercase hexadecimal, omit leading zeros, compress the longest run of zero groups and use the first run when tied. Do not compress a single zero group. Accept valid input forms, parse them, then compare normalized values ^[rfc5952].

Checks before committing an IP fixture

• Validate syntax and CIDR membership separately. A valid address can still be outside your approved example ranges.
• State whether the test stores a string or opens a connection. Configure network isolation for the latter.
• Check uniqueness only when the test requires it; documentation IPv4 space is finite.
• For related device fields, use the MAC format guide and User-Agent parser cases.