Visual RFC.
ALL RFCs / RFC 9471
Read the RFC ↗

RFC 9471 / START HERE

DNS referral glue, before the details

DNS means Domain Name System. Glue is a name for address records that help a resolver reach the name servers named in a referral.

A DNS parent can point a resolver to a child zone’s name servers. When their names lie inside that child, the parent’s available IPv4 (A) and IPv6 (AAAA) address records help the resolver make its first contact instead of going in a circle.

Start the guide See the 5 chapters ↓

The idea in one picture

  1. Refer to child servers

  2. Supply their addresses

  3. Signal incomplete glue

A simplified picture of the idea; the chapters explain the actual mechanisms.

Why it exists

This September 2023 Proposed Standard updates RFC 1034. It clarifies that a referral must include all available in-domain glue or signal truncation when size prevents that. Sibling glue has different recommendation and truncation rules.

A familiar example

Imagine a directory saying “ask the office inside that building” while also supplying the office’s street address. The address lets you start, but it is not the final answer to your question or proof that the office is trustworthy.

Helpful background

You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.

DNSRFC 1034 · beginner overview ↗DNS wireRFC 1035 · beginner overview ↗DNS over TCPRFC 7766 · beginner overview ↗

What you’ll learn next

Begin with chapter one, or choose a topic.

  1. Read a referral without confusing it with an answerA parent points the resolver to child name servers and supplies addresses needed to reach them.
  2. Set truncation when any required glue cannot fitAll available in-domain glue matters, even when some of it already fits.
  3. Distinguish sibling glue and its optional truncationGlue type is relative to the delegated child selected by the question, not a permanent label on an address.
  4. Break a closed sibling dependency cycleTwo sibling zones can depend on each other before the resolver has any usable address.
  5. Separate missing zone data from response-size handlingA truncation rule cannot create unavailable records or replace DNS security and operational work.
Start with chapter one →

This introduction explains RFC 9471 (2023). Read the original RFC ↗