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RFC 8106 / START HERE

IPv6 DNS advertisements, before the details

IPv6 is Internet Protocol version 6. RA means Router Advertisement; DNS means Domain Name System. These RA options tell a host which recursive DNS servers and search suffixes it can use.

A router can advertise DNS server IPv6 addresses and a DNS search list on its link. The host keeps that configuration for its own lifetime, then makes separate DNS queries when it needs an answer.

Start the guide See the 5 chapters ↓

The idea in one picture

  1. Advertise DNS information

  2. Keep scoped configuration

  3. Make a later DNS query

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

Why it exists

This March 2017 Proposed Standard replaces RFC 6106. It raises the recommended default DNS-option lifetime for lossy links and clarifies processing, link-local scope, source preference and security limits.

A familiar example

Imagine a welcome desk giving you a directory service’s address and a suggested neighborhood to search. That is contact information, not an answer or proof the desk is trustworthy; it can also expire or be withdrawn.

Helpful background

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

Neighbor DiscoveryRFC 4861 · beginner overview ↗SLAACRFC 4862 · beginner overview ↗DNS wireRFC 1035 · beginner overview ↗

What you’ll learn next

Begin with chapter one, or choose a topic.

  1. Carry DNS configuration in Router AdvertisementsLearning how to contact a resolver is separate from getting an IPv6 address or a DNS answer.
  2. Decode RDNSS addresses and keep their link scopeType 25 carries whole 128-bit addresses and a shared lifetime; a link-local address also needs its link.
  3. Encode search suffixes without DNS compressionType 31 concatenates zero-terminated domain names and zero padding; the suffix is not itself an answer.
  4. Refresh and withdraw DNS data using its own lifetimeReceipt-relative DNS lifetimes survive router-lifetime expiry and require synchronized removal from both repositories.
  5. Merge sources without mistaking configuration for trustAn ordered resolver list needs source-aware preference, while well-formed advertisements can still be malicious.
Start with chapter one →

This introduction explains RFC 8106 (2017). Read the original RFC ↗