Negotiate EDNS UDP size and extended fields through the OPT pseudo-record

Use this document to connect an official requirement or behavior to observable evidence: Negotiate EDNS UDP size and extended fields through the OPT pseudo-record. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 6891 — Extension Mechanisms for DNS (EDNS(0)) from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• EDNS uses an OPT pseudo-record to carry the sender’s UDP payload size plus extended response-code, version, flag, and option fields. The research record locates this support at Section 6.1 (OPT Record Definition).
• A requestor advertises the maximum UDP payload it can reassemble in the OPT CLASS field, and responders must limit replies to that advertised size. The research record locates this support at Section 6.2.3 (OPT Record TTL Field Use), requestor payload size.
• A responder that implements EDNS includes OPT in a response only when the request contained OPT. The research record locates this support at Section 6.1.1 (Basic Elements), request-response rule.

These statements are the factual basis for this document. Do not extend them into a broader assurance. Review authoritative zones, delegations, resolvers, caches, record owners, and the clients that consume the resulting answers only where the source and recorded environment align.

What the source does not establish

This RFC evidence supports only the named DNS protocol decision; it does not prove Windows implementation support or a safe production configuration. No current deployment state or change approval follows from the source alone. Validate Windows DNS roles, Active Directory-integrated data, forwarding paths, time, routing, firewalls, and registrar or registry state, and treat examples or options as conditional inputs rather than defaults.

Applicability questions

• For source statement 1 at Section 6.1 (OPT Record Definition), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 6.2.3 (OPT Record TTL Field Use), requestor payload size, which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 6.1.1 (Basic Elements), request-response rule, which observable configuration, record, or test can confirm applicability here?
• Within authoritative zones, delegations, resolvers, caches, record owners, and the clients that consume the resulting answers, which versions, roles, and configuration states define the review population?
• Could Windows DNS roles, Active Directory-integrated data, forwarding paths, time, routing, firewalls, and registrar or registry state invalidate the test, hide a failure, or change applicability?
• Who owns the decision, and which observation requires stopping, escalation, or rollback?

DSE recommendation:

DSE recommends using the cited source as the evidence anchor for this decision. Start with applicability, then compare the observed state with the cited source. Record the source location, examined part of authoritative zones, delegations, resolvers, caches, record owners, and the clients that consume the resulting answers, observed and expected states, owner, and reason for deviation.

Do not move from citation to production in one step. Pilot the decision where practical, observe agreed signals, retain a reversal point, and verify Windows DNS roles, Active Directory-integrated data, forwarding paths, time, routing, firewalls, and registrar or registry state. Handle credentials, keys, recovery data, and personal information through approved secure channels.

Verification and evidence

Evidence should let another reviewer reproduce this decision. Retain observations beside the traced locations Section 6.1 (OPT Record Definition); Section 6.2.3 (OPT Record TTL Field Use), requestor payload size; Section 6.1.1 (Basic Elements), request-response rule. Favor zone data, packet captures, query transcripts, delegation checks, resolver configuration, and negative-answer behavior, linked to stable identifiers, time, and operator.

Record the decision even when no change is made, including uncertainty and the next trigger. Use safe testing conditions for disruptive work, preserve rollback proof, and revisit the conclusion after relevant platform, dependency, vendor, or ownership changes.

Official references

• RFC 6891 — Extension Mechanisms for DNS (EDNS(0)) — RFC Editor / Internet Engineering Task Force