ipv6

IPv6 support

iprange supports IPv6 with the -6 / --ipv6 flag. One invocation operates on one address family — there is no mixed-family mode.

Address family selection

Flag	Behavior
(none)	IPv4 mode (default for text input)
-4 / --ipv4	Explicit IPv4 mode
-6 / --ipv6	IPv6 mode

Feature detection for scripts:

iprange --has-ipv6 && echo "IPv6 supported"

Normalization rules

IPv6 mode

• IPv6 input is parsed directly via inet_pton(AF_INET6).
• Plain IPv4 input is accepted and normalized to IPv4-mapped IPv6 (::ffff:x.x.x.x).
• Hostnames are resolved for both AAAA and A records. A-record results are normalized to ::ffff:x.x.x.x.
• The default prefix for bare IPv6 addresses is /128.

IPv4 mode

• IPv4 input is parsed normally.
• IPv4-mapped IPv6 (::ffff:x.x.x.x) is recognized and converted back to the IPv4 address.
• All other IPv6 input is dropped. A single summary warning is printed per file: N IPv6 entries dropped (use -6 for IPv6 mode).
• Hostnames are resolved for A records only.

Cross-family rules

• Operations between IPv4 and IPv6 datasets are not supported. Each invocation works with one family.
• Mixed-family range endpoints (e.g., 10.0.0.1 - 2001:db8::1) are rejected.
• Binary files declare their family in the header. Loading a binary file of the wrong family is an error.

Supported operations

All operations available in IPv4 mode work identically in IPv6 mode:

• Merge / union
• Intersection
• Complement / exclude
• Symmetric difference
• Prefix reduction (--ipset-reduce)
• All comparison and counting modes
• All output formats (CIDR, ranges, single IPs, binary, prefix/suffix)

Prefix control for IPv6

• --min-prefix N: restrict to prefixes N through 128
• --prefixes N,N,N,...: allow only specific prefix lengths (128 always enabled)

Single IP cap

The --print-single-ips safety cap (16,777,216 IPs) applies in IPv6 mode too. Ranges exceeding this are skipped with a warning.

Binary format

IPv6 uses binary format v2.0 (IPv4 uses v1.0). The formats are not interchangeable:

Format	Family	Address size	Header
v1.0	IPv4	4 bytes per address	iprange binary format v1.0
v2.0	IPv6	16 bytes per address	iprange binary format v2.0

Binary files are auto-detected by their header. Same-architecture only (no endianness conversion).

Examples

# Merge IPv6 blocklists
iprange -6 v6-list1.txt v6-list2.txt

# IPv4 input normalized to mapped IPv6
echo "10.0.0.1" | iprange -6
# output: ::ffff:a00:1/128

# Count unique IPv6 addresses
iprange -6 -C --header v6-list.txt

# Find common IPs between IPv6 lists
iprange -6 --common list1-v6.txt list2-v6.txt

# Binary cache for IPv6
iprange -6 --print-binary large-v6.txt > cache.bin
iprange -6 cache.bin

# Compare IPv6 blocklists
iprange -6 --compare --header v6-a.txt v6-b.txt v6-c.txt

Internal representation

IPv6 addresses are stored as __uint128_t (128-bit unsigned integer). This requires GCC or Clang with __uint128_t support. The configure script checks for this at build time.

All set operations (merge, common, exclude, diff, optimize) have dedicated IPv6 implementations that operate on 128-bit address pairs, following the same algorithms as the IPv4 versions.