# A record vs AAAA record: what's the difference?

> A record vs AAAA record: an A record maps a hostname to an IPv4 address, an AAAA record maps it to an IPv6 address. See the difference and when you need each.

**An A record maps a hostname to a 32-bit IPv4 address; an AAAA record maps the same hostname to a 128-bit IPv6 address. They are the same kind of DNS record — a direct address answer — for two different versions of the Internet Protocol.** You publish an A record so IPv4 clients can reach your host, and an AAAA record so IPv6 clients can. Most production names carry both.

## Quick Takeaways

- An A record answers "what IPv4 address is this name?"; an AAAA record answers "what IPv6 address is this name?"
- Both are address records that resolve in a single lookup — the only difference is the address family they return.
- "AAAA" (quad-A) is four times the letters of "A" because an IPv6 address is 128 bits, four times the 32 bits of IPv4.
- A resolver asks for whichever family the client needs: an IPv6-capable client requests AAAA first and falls back to A.
- For email, a sending host that connects over IPv6 needs a matching AAAA and a reverse DNS ([PTR](/learning/what-is-a-ptr-record)) record, or Gmail and Yahoo may reject it.
- You do not choose one *instead* of the other — publish both when your host has both an IPv4 and an IPv6 address.

| | A record | AAAA record |
|---|---|---|
| **Points to** | An IPv4 address (e.g. `203.0.113.10`) | An IPv6 address (e.g. `2001:db8::1`) |
| **Address size** | 32-bit | 128-bit |
| **Protocol** | IPv4 | IPv6 |
| **Resolves in** | One lookup | One lookup |
| **Coexists at same name** | Yes — with AAAA and other records | Yes — with A and other records |
| **Needed when** | Any client still on IPv4 (nearly all) | Clients and mail servers reaching you over IPv6 |

## What is an A record?

An [A record](/learning/what-is-an-a-record) ("address" record) maps a hostname to a single IPv4 address — the familiar dotted-quad numbers like `203.0.113.10`. When a resolver looks up `example.com` and finds an A record, it has the final answer in one step and can open a connection. A records are the oldest and most common record type in [DNS](/learning/what-is-a-dns): almost every hostname on the internet has one, because IPv4 is still the default path for the vast majority of clients.

Because an A record returns an address directly, it is a valid answer at the zone apex (the bare root domain) and coexists with other record types at the same name. A single `example.com` can hold an A record, an [MX record](/learning/what-is-an-mx-record) for mail, and [TXT records](/learning/what-is-a-txt-record) for SPF and DMARC all at once.

## What is an AAAA record?

An AAAA record — said "quad-A" — does exactly the same job as an A record, but for IPv6. It maps a hostname to a 128-bit IPv6 address, written as eight groups of hexadecimal separated by colons, like `2001:db8::1`. We cover the format in depth in [what is an AAAA DNS record](/learning/what-is-an-aaaa-dns-record-quad-a-explained).

The name is the clearest mnemonic for the difference. An IPv4 address is 32 bits; an IPv6 address is 128 bits — four times as large — so the record type gets four A's. IPv6 exists because the roughly 4.3 billion IPv4 addresses ran out; its vastly larger space (about 340 undecillion addresses) removes that ceiling. An AAAA record is how a name advertises its IPv6 address so that IPv6-capable clients can connect natively instead of falling back to IPv4.

## A record vs AAAA record: what's the actual difference?

The only real difference is the address family each record returns. Everything else — how it is queried, that it resolves in one hop, that it can share a name with other records — is identical. Three practical points follow from that single distinction.

**Address family.** An A record returns an IPv4 address; an AAAA record returns an IPv6 address. A resolver does not "convert" between them — it asks specifically for the type the client needs.

**Which one gets used.** A dual-stack client (one with both IPv4 and IPv6 connectivity) typically requests the AAAA record first and prefers IPv6, falling back to the A record if no IPv6 route works. This behaviour, often called Happy Eyeballs, is why a host with a broken AAAA record can feel slow or unreachable for some users even though its A record is perfect.

**Coexistence.** A and AAAA are not mutually exclusive and never conflict. The standard practice for a public host is to publish both, so IPv4-only and IPv6-capable clients can each reach it. Unlike a [CNAME, which cannot share a name with any other record](/learning/cname-vs-a-record-whats-the-difference), address records stack freely.

## When do you need an AAAA record?

You need an AAAA record whenever a host has an IPv6 address that you want clients to reach over IPv6. In practice:

- **Public websites and services** should publish both A and AAAA if their server or load balancer has IPv6 connectivity — it lets IPv6 users connect without translation and future-proofs the name.
- **You do not need AAAA if your host has no IPv6 address.** Publishing an AAAA that points to an unreachable address is worse than having none, because dual-stack clients try IPv6 first and stall when it fails.
- **Keep A and AAAA in sync.** If a host moves, update both records. A stale AAAA pointing at an old or dead address is a classic cause of "works for me, broken for them" reports.

If you only ever publish an A record, IPv6-only clients reach you through their provider's translation layer or not at all. As IPv6 adoption climbs, a matching AAAA increasingly matters for reachability and performance.

## How do A and AAAA records affect email?

For mail, address records matter in two directions, and both are easy to overlook.

First, an **MX record must point at a hostname that resolves via A or AAAA** — never at a [CNAME](/learning/cname-vs-a-record-whats-the-difference). When a sending server looks up your MX host, it needs a real address answer; an IPv6-capable sender will happily use your AAAA record to connect over IPv6 if one exists.

Second, and more consequential for [deliverability](/learning/how-can-you-check-and-improve-your-email-domain-reputation): if *your* outbound mail server sends over IPv6, the major mailbox providers apply stricter rules. Both Gmail and Yahoo require an IPv6 sending host to have a valid reverse DNS ([PTR](/learning/what-is-a-ptr-record)) record whose name resolves back — via an A or AAAA record — to the sending IP, and to pass [SPF](/tools/spf) or DKIM alignment. A mismatched or missing PTR on an IPv6 sender is a common reason otherwise-authenticated mail gets rejected. If you are not sure whether your sending IPs (v4 and v6) line up with their DNS, Palisade's [Email Security Score](/tools/email-security-score) checks the records that mailbox providers actually look at before deliverability suffers.

## Common issues with A and AAAA records

A few failure modes come up again and again.

**A stale or wrong AAAA record.** The most painful one: a host has a broken IPv6 path but still advertises an AAAA. Dual-stack clients try IPv6 first, time out, and only then fall back — so the site loads slowly or intermittently for a subset of users while looking fine to everyone else. Fix the IPv6 route or remove the AAAA.

**Publishing AAAA for a host with no IPv6.** If your server genuinely has no IPv6 address, do not invent an AAAA record. An address record must point at a reachable address.

**Forgetting to update one of the pair.** When you renumber a host, update both the A and the AAAA. Editing only one leaves half your users pointed at a dead address.

**Confusing AAAA with a different record type.** AAAA is strictly IPv6 addressing. It is unrelated to [MX](/learning/what-is-an-mx-record), TXT, or [PTR](/learning/what-is-a-ptr-record) records, even though those can all live at related names.

## Frequently asked questions

### Is an AAAA record just a bigger A record?

Functionally, yes — same job, different address family. An A record carries a 32-bit IPv4 address and an AAAA record carries a 128-bit IPv6 address. The resolution process is otherwise identical.

### Do I need both an A and an AAAA record?

Publish both when your host has both an IPv4 and an IPv6 address — that lets every client reach you natively. Publish only an A record if the host has no working IPv6 address; a broken AAAA is worse than none.

### Which record does a browser use if both exist?

A dual-stack client generally requests the AAAA record first and prefers IPv6, falling back to the A record if the IPv6 connection fails. That is why a broken AAAA can degrade the experience even when the A record is correct.

### Does IPv6 affect whether my email gets delivered?

It can. If your mail server sends over IPv6, Gmail and Yahoo require a valid reverse DNS (PTR) record for that IPv6 address plus passing authentication, or they may reject the message. Sending over IPv4 with correct records avoids that specific pitfall.

## Related reading

- [What is an A record?](/learning/what-is-an-a-record)
- [What is an AAAA DNS record (Quad-A explained)?](/learning/what-is-an-aaaa-dns-record-quad-a-explained)
- [CNAME vs A record: what's the difference?](/learning/cname-vs-a-record-whats-the-difference)