Build a synthesized HINFO only in its allowed context
03Host Information (HINFO) is a DNS record with CPU (processor) and OS (operating system) character-string fields. RFC 8482 can use a small synthesized HINFO answer when the queried owner has no CNAME alias.
Separate owner with a CNAME alias: do not substitute the synthesized HINFO for that alias path. Follow the standard DNS algorithm. No HINFO answer is delivered by this stopped branch.
Source for this drawing: RFC 8482 · Read RFC section 4.2 ↗
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The CPU marker is ordinary record data, not authenticated policy negotiation.
- If no CNAME exists at the owner matching QNAME, the returned record MAY be synthesized. A single HINFO SHOULD be returned, CPU SHOULD be RFC8482, and OS SHOULD be the empty string.
- HINFO RDATA has two length-prefixed character strings (RFC 1035 §3.3.2). RFC8482 is seven ASCII octets; the complete default RDATA is 07 52 46 43 38 34 38 32 00, nine octets. The final zero is the OS length, not a terminator.
- For a known signed zone with DO=1, a valid RRSIG for the answer RRsets (or authority if the answer is empty) MUST be returned. With DO=0, RRSIG SHOULD be omitted (§4.2).
- A receiver SHOULD NOT infer synthesis or apply special processing just because an HINFO has these fields. A genuine HINFO can look the same. If CNAME is present, the synthesized-HINFO branch is unavailable; ordinary DNS processing still applies.
These are separate cases, not an alias followed by a contradictory successful HINFO. ASCII codecs teach only HINFO RDATA framing, not full DNS names, messages or signatures. A matching marker is not proof of server identity or synthesis.
Read the RFC section ↗