IPv6 Shorthand Calculator

What IPv6 shorthand means

An IPv6 address is 128 bits, written as eight hextets (groups of 4 hex digits) separated by colons, e.g. 2001:0db8:0000:0000:0000:ff00:0042:8329. Shorthand (compressed form) is the same value written shorter per RFC 5952: no unnecessary leading zeros, and at most one :: replacing the longest run of zero hextets.

This calculator accepts any valid form (full, partially shortened, mixed case) and returns the canonical compressed form plus the expanded form — useful when comparing logs, ACLs, AAAA records, and host configs.

Compression rules (RFC 5952)

• Leading zeros in hextets — drop them: 0db8 → db8, 0042 → 42. A zero hextet is 0, not an empty field.
• :: only once — it replaces the longest run of at least two consecutive zero hextets. A second :: makes the address ambiguous.
• Length ties — if two zero runs are equally long, compress the leftmost one.
• Lowercase — recommended output uses a–f, not A–F.
• Do not use :: for a single zero — a lone 0 hextet stays as 0 (unless it is part of a longer zero run).

Expanded vs compressed

• Expanded — always 8×4 hex digits: easier sorting, diffs, and naive string matches in firewalls.
• Compressed — clearer in DNS AAAA, interface configs, and docs.
• Partial shorthand — e.g. leading zeros removed but no ::; valid but not canonical. The calculator normalizes to RFC 5952.

Same 128 bits: 2001:0db8:0000:0000:0000:ff00:0042:8329 = 2001:db8::ff00:42:8329.

Common mistakes

• Using :: twice in one address.
• Leaving leading zeros in “compressed” form (2001:0db8::1 — prefer 2001:db8::1).
• Confusing hextets with bytes — IPv6 groups 16-bit chunks, not IPv4-style octets.
• Pasting dotted IPv4 without mapping (::ffff:192.0.2.1 is the IPv4-mapped form).
• Assuming “most zeros on the right” always wins — ties go to the left.

Worked examples

1) Documentation prefix

Full input: 2001:0db8:0000:0000:0000:ff00:0042:8329

• Drop leading zeros → 2001:db8:0:0:0:ff00:42:8329
• Longest zero run: three hextets 0:0:0 → ::
• Compressed: 2001:db8::ff00:42:8329

2) Leading zeros only (no ::)

2001:0db8:0001:0002:0003:0004:0005:0006 → 2001:db8:1:2:3:4:5:6 (no two consecutive zero hextets, so no ::).

3) :: only once

2001:db8:0:0:1:0:0:1 — two runs of two zeros; compress the left: 2001:db8::1:0:0:1 (RFC 5952 leftmost on a tie).

4) Loopback

0000:0000:0000:0000:0000:0000:0000:0001 → ::1.

5) Link-local

fe80:0000:0000:0000:0202:b3ff:fe1e:8329 → fe80::202:b3ff:fe1e:8329. The fe80::/10 prefix stays; compression only collapses the zero run after it.

6) Leading-zero cleanup only

Input 2001:0db8:0:0:0:0:0:1 is already partly shortened. Canonical: 2001:db8::1 — the calculator finishes RFC 5952 (lowercase + a single ::).

When to use shorthand in practice

• AAAA records / docs — compressed form is easier for humans; tools normalize anyway.
• ACL / SIEM logs — expanded form can make naive text sorts predictable; or normalize before compare.
• Router configs — IOS/FRR/Linux usually accept both; pick one team convention.
• Debug — if a client “won’t connect”, expand in the calculator and compare bit-for-bit with the interface address (ip -6 addr).

Remember: shorthand does not change the address value — only the notation. A typo still compresses into a “pretty” wrong address — always verify against the source (SLAAC, DHCPv6, VLAN docs).