Domains and DNS

What is the difference between IPv4 and IPv6?

IPv6 was finished in 1998 and IPv4 still has not gone away, which tells you everything about how migrations at internet scale actually happen.

IPv4 addresses are 32 bits, written as four numbers 0-255 separated by dots (203.0.113.7), giving about 4.3 billion possible addresses - a number IANA finished handing out to regional registries on 3 February 2011. IPv6 addresses are 128 bits, written as eight groups of hexadecimal digits (2001:0db8:85a3::8a2e:0370:7334), giving roughly 340 undecillion addresses - enough that address exhaustion is not a realistic constraint for the foreseeable future. A domain can publish an A record for its IPv4 address and an AAAA record for its IPv6 address at the same time, and most major sites do exactly that.

Worked out 2026-09-18 (IST) · dual-stack networking as commonly deployed in 2026

Side by side

IPv4 vs IPv6
	IPv4	IPv6
Address length	32 bits	128 bits
Written as	Four decimal numbers, dotted (203.0.113.7)	Eight hex groups, colon-separated (2001:0db8::7334)
Total address space	~4.3 billion	~340 undecillion
DNS record type	A	AAAA
Free pool exhausted	3 Feb 2011 (IANA)	Not applicable
Typical home-network reality	Shared via NAT, one public address per household	Often one address per device, no NAT required

Why IPv4 never actually disappeared

IPv6 finished standardisation in 1998, thirteen years before IPv4 exhaustion, and the expectation at the time was a clean cut-over. That did not happen, for the same reason large infrastructure migrations rarely happen cleanly anywhere: replacing an addressing scheme means upgrading every router, every piece of network hardware and every server along the path, and the interim workaround - NAT - turned out to be good enough to remove the urgency. The result is dual-stack: the great majority of significant sites answer on both protocols simultaneously, and will keep doing so for years yet.

What this means for a DNS setup in practice

Practical checklist
Situation	What to do
Standard website on shared or cloud hosting	Publish an A record; add an AAAA record if the host provides an IPv6 address - no downside either way
Running your own mail server	Make sure both A and AAAA (if published) have a matching PTR record, since IPv6-connecting mail servers check reverse DNS on IPv6 too
Diagnosing "works for me, not for them"	Check whether the two of you are resolving different record types - one connection on IPv4, the other on IPv6, hitting different infrastructure

See the address a domain actually publishes, on both protocols, with how to check DNS records for a domain.

Sources: IETF RFC 791 (Internet Protocol, IPv4), RFC 8200 (Internet Protocol, Version 6), and the IANA IPv4 Address Space Registry, which recorded the exhaustion of the free IPv4 pool on 3 February 2011.

Check your own numbers

See both the IPv4 and IPv6 address a domain resolves to, and which one your own connection is using.

What Is My IPYour public IP address, and what a server can infer from it.

Frequently asked

If IPv4 ran out in 2011, why does it still work?

Because "ran out" describes IANA’s free pool, not every address in use. Existing allocations kept working, and the shortage was absorbed with NAT (many devices sharing one public IPv4 address, which is how almost every home network already operates) and a secondary market where organisations buy and sell unused IPv4 blocks.

Do I need to do anything about IPv6 for my website?

Not urgently in most markets, but it is worth checking: publish an AAAA record alongside your A record if your host supports it, and nothing changes for visitors on IPv4 - they simply keep using the A record. Visitors on IPv6-only networks, which is common on mobile carriers, get a faster path with one less NAT hop.

Can a website work over IPv6 only, with no A record?

Technically yes, but it will be unreachable to any visitor or network that has no IPv6 connectivity, which is still a meaningful share of the internet in 2026. Dual-stack - publishing both A and AAAA - is the practical default, not IPv6-only.

Why do IPv6 addresses look so much longer?

Because they encode four times as many bits. 128 bits written in hexadecimal groups of four, separated by colons, is the shortest practical notation - and even then the standard allows one run of consecutive all-zero groups to be collapsed to "::" to keep addresses readable.

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