Carry DNS configuration in Router Advertisements
01Learning how to contact a resolver is separate from getting an IPv6 address or a DNS answer.
The host can later query the advertised recursive server. The server is distinct from the advertising router in this example; no completed answer, reachability guarantee or trusted identity is invented.
Source for this drawing: RFC 8106 · Read RFC section 4 ↗
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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.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
RA means Router Advertisement, a Neighbor Discovery message. DNS means Domain Name System. RDNSS means Recursive DNS Server; DNSSL means DNS Search List. A router can advertise recursive-server IPv6 addresses and search suffixes to hosts on its link (§§1,3–4).
- RA means Router Advertisement, a Neighbor Discovery message. DNS means Domain Name System. RDNSS means Recursive DNS Server; DNSSL means DNS Search List. A router can advertise recursive-server IPv6 addresses and search suffixes to hosts on its link (§§1,3–4).
- An RDNSS address identifies a DNS server the host can query. A DNSSL entry is a suffix a resolver can use when searching for a short, unqualified name. Neither entry is a completed DNS answer, a website address for that short name, or an assignment of the host’s own address (§3).
- The advertising router is assumed already configured with DNS information; how the router obtains it is out of scope. The RDNSS can be a different node from that router (§4). Our example advertises 2001:db8::53 and picnic.example.; these are fictional documentation values.
- Hosts conforming to this specification MUST extract DNS information from RAs unless the user has specified static DNS configuration. RA and DHCPv6 DNS information can coexist, and information from multiple sources MUST be maintained in an ordered list (§1.2). No actual host setting is changed by this guide.
- The host still validates the RA under Neighbor Discovery rules, then checks the DNS options. Valid DNS options SHOULD be copied into the DNS and Resolver Repositories in order; invalid options MUST be discarded (§5.3.1). Option syntax does not authenticate a router.
Fictional documentation addresses/domains and chosen seconds. The isolated-option codecs and repository snapshots are bounded teaching models; no real RA, DNS query, operating-system configuration or security validation occurs.
Read the RFC section ↗