What is an RFC 4193 Unique Local Address (ULA)?

Unique Local Addresses (ULA) are the IPv6 equivalent of IPv4 private addresses (RFC 1918). They use the prefix fd00::/8 followed by a 40-bit pseudo-random global ID to prevent address collisions when internal corporate networks merge.

How does RFC 5952 canonical IPv6 compression work?

RFC 5952 specifies that leading zeros within each 16-bit block must be suppressed, the longest consecutive run of multiple zero blocks must be shortened with :: (applied only once), and all hexadecimal letters must be lowercase.

IPv6 Subnet Calculator & ULA Generator

Expand and compress IPv6 addresses to standard RFC 5952 canonical format, calculate subnet prefixes and reverse DNS PTR pointers, and generate RFC 4193 Unique Local Addresses. 100% private in-browser.

RFC 5952 Canonical Compressed

2001:db8::1

Full Expanded (32 Hex Digits)

2001:0db8:0000:0000:0000:0000:0000:0001

Network Prefix

2001:db8::

Host Range (First - Last)

2001:db8::1 → 2001:db8::ffff:ffff:ffff:ffff

Reverse DNS PTR Record (ip6.arpa)

1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa

🔒 RFC 4193 Unique Local Address (ULA) Generator

Generate cryptographically uncolliding private IPv6 address blocks for internal LANs and enterprise VPNs with pseudo-random 40-bit Global IDs.

Generated /48 Prefix

fd00::/48

Subnet 1 (/64)

fd00::/64

IPv6 Addressing Standards

128-Bit Address Space

IPv6 provides $3.4 \times 10^{38}$ distinct addresses, eliminating the need for NAT (Network Address Translation) and allowing every connected IoT and server node an end-to-end routable IP.

Standard /64 Subnetting

SLAAC (Stateless Address Autoconfiguration) requires exactly /64 subnets where the high 64 bits denote the routing network and the low 64 bits denote the node interface ID.

Nibble-Based Reverse DNS

Each hex digit forms one dot-separated delegation domain under .ip6.arpa in reverse order, enabling granular delegated DNS resolution across ISPs.