Keep optional extras and type categories separate
06Additional-section processing can attach helpful extra records to a DNS reply. A server cannot invent type-specific extras for a record whose format it does not know.
Separate classification examples: ANY255 is a query-only type and OPT41 is a message Meta-TYPE. They do not enter this stored-unknown-data path. The gate does not discard a valid message OPT; its own protocol rules apply.
Source for this drawing: RFC 3597 · Read RFC section 8 ↗
New to this? Start hereA quick picture + helpful background
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.
Unknown types cause no additional-section processing. A future RR definition MAY specify such processing, but it MUST be optional because an unaware server cannot perform it.
- Unknown types cause no additional-section processing. A future RR definition MAY specify such processing, but it MUST be optional because an unaware server cannot perform it.
- A knowledgeable server may supply useful extras according to that type’s definition; the absence of optional extras does not by itself invalidate the new type’s answer. This does not override rules for unrelated existing record types.
- RFC6895 §3.1 distinguishes stored data TYPEs, query-only QTYPEs and message Meta-TYPEs. ANY (255) and OPT (41) are not ordinary opaque stored data records under RFC3597 §2.
- Registration updates5395/6195 were succeeded by6895. Its §§3.1–3.2 protect generic TYPE/CLASS naming and the allocation framework; this guide does not reproduce a live IANA registry. RFC3597 §10 adds neither authentication nor encryption.
Offline bounded examples, not a complete DNS server, master-file parser or DNSSEC validator. Hexadecimal pairs represent octets (eight-bit bytes). Layouts are schematic unless marked otherwise. Generic data transport neither understands an application nor authenticates it.
Read the RFC section ↗