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RFC 3596 / DNS FOR IPv6

Ask for AAAA over either IP version

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An IPv6 address answer can travel over IPv4. Conversely, an IPv4 address answer can travel over IPv6.

DIAGRAMRead RFC section 2.3 ↗
RFC 3596 · § 2.3EXAMPLE
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Ask for AAAA over either IP versionTwo separate exchanges use requester and DNS server. First, IN AAAA question over IPv4 returns chosen IPv6 AAAA records in Answer and no Additional entries. Second, an IN A question over IPv6 returns an IPv4 A record. Arrows reverse with request and reply. No packet format, transport migration, application connection or address-order selection is inferred.Separate exchange 2 · DNS over IPv6RequesterDNS serverDNS response over IPv6Answer: A 192.0.2.1IPv4 address data over IPv6 transportRecord family and transport remain independent
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Return the A record over IPv6.

The chosen IPv4 address 192.0.2.1 travels inside a DNS answer over IPv6. DNS transport and record address family remain separate.

Source for this drawing: RFC 3596 · Read RFC section 2.3 ↗

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A message needs an address.

Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.

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RFC 1034 DNS RFC 8200 IPv6 RFC 5952 IPv6 text

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KEY POINT

The question chooses the record type; transport carries the message.

  • An Internet-class AAAA query asks for the associated AAAA records in the answer section. QNAME is the queried name, QCLASS the record class (here IN), and QTYPE the requested type (AAAA or A).
  • A type AAAA query does not trigger additional-section processing. Do not automatically add A records just because the response contains IPv6 addresses.
  • The IP version used to query DNS is independent of the IP version stored in records. RFC 3596 does not choose which application address to connect to.
DETAILS

Shown exchanges assume a successful, untruncated response and locally available data; the requester can be a DNS lookup service. Generic DNS alias, negative-answer, retry and truncation behavior is separate. Transport examples do not promise working connectivity or a particular UDP/TCP choice.

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