Which of the Following DNS Record Types is Used to Resolve IPv6 Addresses?

The Short Answer: AAAA Records Resolve IPv6 Addresses

The Domain Name System (DNS) is the backbone of the internet, translating human-readable domain names into the numerical IP addresses that computers use to communicate. When the question asks which DNS record type is used to resolve IPv6 addresses, the answer is the AAAA record — pronounced "quad-A." As the internet transitions towards IPv6, the next generation of IP addressing, DNS has been updated to accommodate these longer and more complex addresses. The specific DNS record type designed to map domain names to IPv6 addresses is the AAAA record. IPv6 replaces ARP for address resolution - see the two types of messages used in place of ARP in IPv6.

Why "quad-A"? An A record holds a 32-bit IPv4 address. An IPv6 address is 128 bits — exactly four times as long — so the record that carries it gets four A's. That one naming detail answers a surprising number of exam questions on its own.

While other DNS record types like A records (for IPv4), CNAME records (for aliases), and MX records (for mail exchange servers) play vital roles in the DNS system, they are not used for IPv6 address resolution. Understanding the function of each DNS record type is a fundamental aspect of networking knowledge, and a concept you'll undoubtedly encounter in your Cisco 200-301 exam preparation.

The DNS Record Family at a Glance

AAAA never appears alone on an exam for long. Expect it alongside the rest of the common record types, so it pays to know the whole family and what each one is actually for:

• A — maps a hostname to a 32-bit IPv4 address. The original address record.
• AAAA — maps a hostname to a 128-bit IPv6 address. Same job as A, four times the address.
• CNAME — maps a hostname to another hostname (an alias). The canonical name is then resolved to its A or AAAA record. A CNAME cannot coexist with other record types for the same name.
• MX — identifies the mail servers that accept email for a domain, with a preference value to rank them. MX records point to hostnames, never directly to IP addresses.
• TXT — carries arbitrary text, used in practice for verification and email authentication frameworks such as SPF, DKIM, and DMARC.
• PTR — the reverse of A and AAAA: maps an IP address back to a hostname. IPv4 reverse lookups live under in-addr.arpa; IPv6 reverse lookups live under ip6.arpa.
• NS and SOA — NS records name the authoritative servers for a zone, and the SOA record holds the zone's administrative data. You will meet these whenever a question turns to how a zone is delegated.

Notice the direction of travel. A and AAAA go from name to address; PTR goes from address to name. A classic exam trap swaps those directions, so fix it in your mind now: if the question starts with a hostname and wants an IPv6 address, it is asking about AAAA.

How a Resolver Uses AAAA Records in Practice

Suppose your laptop needs to reach www.example.com and the network is dual-stack, running IPv4 and IPv6 side by side. Your operating system does not simply pick one protocol. The stub resolver on the host asks the recursive resolver for both the A and the AAAA records for the name — typically in parallel. If a AAAA record comes back, the host now has an IPv6 address to try; if only an A record exists, IPv4 is the only option.

The recursive resolver does the legwork you learned about in DNS fundamentals: it asks a root server, gets referred to the TLD servers, then to the domain's authoritative server, and caches the answer for the record's TTL so the next lookup is instant. The record type requested flows through that whole chain unchanged — ask for AAAA and every server in the path understands you want the IPv6 mapping.

Having an address is not the same as using it successfully. Modern systems apply the Happy Eyeballs approach (RFC 8305): the host attempts the IPv6 connection first, but races it against IPv4 with a short head start for IPv6. If the IPv6 path is broken — a tunnel that goes nowhere, a router that drops the traffic — the connection falls back to IPv4 almost immediately instead of hanging. This is why a host can hold a perfectly valid AAAA record yet still end up talking over IPv4, and why "the site has a AAAA record" and "my traffic used IPv6" are two different statements.

Checking AAAA Records with dig and nslookup

You can watch all of this happen from the command line. On Linux or macOS, use dig and name the record type explicitly:

dig AAAA www.example.com

The ANSWER SECTION of the output shows the AAAA record with its TTL and the full 128-bit address. Compare it with the IPv4 equivalent:

dig A www.example.com

On Windows, nslookup does the same job once you set the query type:

nslookup
> set type=AAAA
> www.example.com

Or in a single line: nslookup -type=AAAA www.example.com. If the AAAA query returns no answer section while the A query succeeds, the name is IPv4-only — a normal and common result, not an error. If both come back empty, the name itself does not resolve, and your troubleshooting belongs at the DNS level rather than the IPv6 level.

Common Exam Traps

• A vs AAAA: Both resolve names to addresses. The only difference is address length — 32-bit IPv4 for A, 128-bit IPv6 for AAAA. Any option suggesting AAAA is "a more secure A record" or "an alias record" is wrong.
• The quad-A name: AAAA is not a version number or a quality grade. It is four A's because the address is four times longer than the 32 bits an A record holds.
• AAAA does not do reverse lookups: Turning an IPv6 address back into a hostname is PTR's job, under ip6.arpa. AAAA only goes name-to-address.
• CNAME plus AAAA: A name that is a CNAME cannot also hold its own AAAA record. The resolver follows the alias to the canonical name and returns that name's AAAA record instead.
• Dual-stack behavior: When both A and AAAA exist, hosts generally prefer IPv6 but fall back to IPv4 when the IPv6 path fails (Happy Eyeballs). "Prefers IPv6" does not mean "IPv6 only."
• MX confusion: MX records look like they belong in an addressing question, but they only ever identify mail servers. They never resolve a hostname to an IPv6 address for general traffic.

Sample Questions for Cisco 200-301 Exam Prep Practice Test

Which DNS record type is used to resolve a hostname to an IPv6 address?

A. A

B. AAAA

C. CNAME

D. MX

Why is the IPv6 address record called a "quad-A" record?

A. It is the fourth version of the A record

B. It stores an address four times longer than the 32-bit address in an A record

C. It must be configured on four DNS servers

D. It supports four addresses per hostname

A dual-stack host receives both an A record and a AAAA record for a website, but the IPv6 path to the site is broken. What does the host typically do?

A. It refuses to connect until IPv6 is repaired

B. It falls back to the IPv4 address from the A record

C. It converts the IPv6 address into an IPv4 address

D. It asks the DNS server to delete the AAAA record

Which record type would you query to find the hostname associated with a known IPv6 address?

A. AAAA

B. TXT

C. PTR

D. MX

Which statement about a hostname that has a CNAME record is correct?

A. It can also hold its own AAAA record

B. It points to a canonical name whose A or AAAA record is returned instead

C. It is used only for IPv6 networks

D. It identifies the mail servers for the domain

Related guides

• What are two types of IPv6 unicast addresses?
• Two methods to shorten IPv6 address notation
• What is used in the EUI-64 process to create an IPv6 interface ID?
• Which DNS Record Type Resolves IPv6 Addresses? The AAAA Record

Official source: Cisco Learning Network - CCNA.

Drilling DNS and IPv6 for the CCNA? Put it all together — record types, dual-stack behavior, and the rest of IP services — with the CCNA study material at Study4Pass, and make sure the next DNS question on the exam is an easy one.