IPv6 uses 128-bit addresses, written as hexadecimal groups separated by colons, rather than IPv4's 32-bit dotted-decimal addresses. Leading zeros within a group can be omitted, and one consecutive sequence of all-zero groups can be compressed with a double colon. For example, 2001:db8:10::25 is an IPv6 address from a prefix reserved for documentation. Prefix notation, such as /64, identifies how many leading bits belong to the network prefix. The larger address space supports extensive subnetting and reduces the need for address conservation through network address translation.
For DNS, the central distinction is that an A record maps a name to an IPv4 address, whereas an AAAA record maps a name to an IPv6 address. A dual-stack application can publish both record types for the same hostname. For example, api.example.com might have an A record containing 192.0.2.25 and an AAAA record containing 2001:db8:10::25. Clients select an address using their networking capabilities and connection-selection behavior; many implement Happy Eyeballs to reduce delays when one address family is unusable. Publishing an AAAA record does not make an IPv4-only application or network IPv6-capable.
DNS record types and DNS transport are independent. A client can request and receive an AAAA record through a DNS connection carried over IPv4, or retrieve an A record over IPv6. This distinction matters in hybrid networks: an on-premises resolver can forward an AAAA query to a cloud resolver without requiring the forwarding connection itself to use IPv6. However, the client still needs a working IPv6 path to connect to the returned IPv6 address.
Reverse DNS uses PTR records. IPv6 reverse names are placed under ip6.arpa and represent the fully expanded address as individual hexadecimal digits in reverse order, separated by dots. This differs from IPv4 reverse DNS under in-addr.arpa. Creating a forward AAAA record does not automatically establish the corresponding reverse record. Reverse-zone delegation or a provider-controlled reverse-DNS configuration is needed, and a PTR response alone does not prove the identity or trustworthiness of a host.
Other record types have distinct roles. A CNAME redirects DNS resolution to another hostname, whose records determine the eventual addresses; it does not itself contain an IPv6 address. TXT records carry text such as domain-verification values or email policy data and do not provide IPv6 address resolution. An Amazon Route 53 alias is a provider-specific DNS feature rather than a separate standard DNS record type. For an eligible IPv6-capable target, an AAAA alias can return IPv6 addresses and can be used at the zone apex, where a conventional CNAME is not permitted.
In hybrid and multi-account environments, ensure that private hosted-zone associations, resolver forwarding rules, and reverse-zone ownership produce consistent answers for the intended clients. Avoid forwarding loops and distinguish an authoritative answer containing no AAAA data from an actual resolution failure. DNS64 can synthesize an AAAA answer from an IPv4 A record for an IPv4-only destination when no native AAAA answer exists, but usable connectivity also requires a suitable NAT64 path. DNS64 alone does not translate application traffic.
Operationally, IPv6 requires its own routes, firewall rules, and application listeners. A global IPv6 address does not automatically make a workload reachable from the internet, and eliminating NAT does not eliminate the need for security controls. Permit required ICMPv6 traffic, including Packet Too Big messages used for path MTU discovery. Before publishing AAAA records, test reachability from representative clients, inspect both address families, and account for DNS caching during deployment or rollback. Dual stack improves compatibility but increases the number of network paths that engineers must secure and troubleshoot.
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