Network Working Group B. Morrison Internet-Draft Alter Meridian Pty Ltd Intended status: Informational 9 October 2026 Expires: 12 April 2027 Discovery of Model Context Protocol Servers via DNS TXT Records draft-morrison-mcp-dns-discovery-08 Abstract This document defines a DNS-based mechanism for discovering Model Context Protocol (MCP) servers, the identity of the organisations that operate them, and a cryptographic identity envelope bound to an individual Sovereign-tier ~handle published under the same zone. Three TXT records are defined. _mcp. advertises an MCP server's endpoint URL, agent protocol family, transport binding, cryptographic identity, and capability profile. _org-alter. advertises the operator's canonical organisational identity, including its legal entity, registry identifier, regions of operation, and any regulatory framework under which it must refuse external automated access. _alter. publishes an Ed25519-signed envelope binding a ~handle to a public key, an IdentityLog root reference, and a revocation commitment. DNSSEC validation is REQUIRED for the envelope record, and a DANE TLSA pin on the MCP endpoint is REQUIRED where resolving an envelope and opening an MCP session are one recognition transaction. The mechanism complements HTTPS-based discovery, and follows the precedent set by DKIM, SPF, DMARC, and MTA-STS. A companion alter: URI scheme is provisionally registered with IANA. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Morrison Expires 12 April 2027 [Page 1] Internet-Draft MCP DNS Discovery October 2026 This Internet-Draft will expire on 12 April 2027. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Related Work . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Why TXT rather than SVCB . . . . . . . . . . . . . . . . . . 9 5. Record Format: _mcp. (Service Discovery) . . . . . . 10 5.1. DNS Location . . . . . . . . . . . . . . . . . . . . . . 10 5.2. ABNF Grammar . . . . . . . . . . . . . . . . . . . . . . 10 5.3. Field Definitions . . . . . . . . . . . . . . . . . . . . 12 5.3.1. v (REQUIRED) . . . . . . . . . . . . . . . . . . . . 12 5.3.2. url (REQUIRED) . . . . . . . . . . . . . . . . . . . 12 5.3.3. proto (OPTIONAL) . . . . . . . . . . . . . . . . . . 13 5.3.4. transport (OPTIONAL) . . . . . . . . . . . . . . . . 13 5.3.5. Reading a record published before this revision . . . 14 5.3.6. pk (OPTIONAL) . . . . . . . . . . . . . . . . . . . . 15 5.3.7. epoch (OPTIONAL) . . . . . . . . . . . . . . . . . . 16 5.3.8. cap (OPTIONAL) . . . . . . . . . . . . . . . . . . . 16 5.3.9. attest (OPTIONAL) . . . . . . . . . . . . . . . . . . 17 5.3.10. scope (OPTIONAL) . . . . . . . . . . . . . . . . . . 17 5.3.11. priority (OPTIONAL) . . . . . . . . . . . . . . . . . 18 5.3.12. ttl (OPTIONAL) . . . . . . . . . . . . . . . . . . . 18 5.3.13. ext (OPTIONAL) . . . . . . . . . . . . . . . . . . . 18 5.4. Forward Compatibility . . . . . . . . . . . . . . . . . . 18 5.5. Multi-String Concatenation . . . . . . . . . . . . . . . 19 6. Record Format: _org-alter. (Identity Bootstrap) . . . 19 6.1. DNS Location . . . . . . . . . . . . . . . . . . . . . . 19 6.2. ABNF Grammar . . . . . . . . . . . . . . . . . . . . . . 20 6.3. Field Definitions . . . . . . . . . . . . . . . . . . . . 22 6.3.1. v (REQUIRED) . . . . . . . . . . . . . . . . . . . . 22 6.3.2. org (REQUIRED) . . . . . . . . . . . . . . . . . . . 22 6.3.3. entity (RECOMMENDED) . . . . . . . . . . . . . . . . 22 6.3.4. entity-type (OPTIONAL) . . . . . . . . . . . . . . . 23 6.3.5. founded (OPTIONAL) . . . . . . . . . . . . . . . . . 23 Morrison Expires 12 April 2027 [Page 2] Internet-Draft MCP DNS Discovery October 2026 6.3.6. regions (OPTIONAL) . . . . . . . . . . . . . . . . . 23 6.3.7. regulated (OPTIONAL) . . . . . . . . . . . . . . . . 24 6.3.8. bootstrap (OPTIONAL) . . . . . . . . . . . . . . . . 24 6.3.9. mcp-policy (OPTIONAL) . . . . . . . . . . . . . . . . 25 6.3.10. epoch (OPTIONAL) . . . . . . . . . . . . . . . . . . 25 6.3.11. pk (OPTIONAL) . . . . . . . . . . . . . . . . . . . . 25 6.3.12. attest (OPTIONAL) . . . . . . . . . . . . . . . . . . 26 6.3.13. ext (OPTIONAL) . . . . . . . . . . . . . . . . . . . 26 6.4. Forward Compatibility . . . . . . . . . . . . . . . . . . 26 7. Record Format: _alter. (Envelope Publication) . . . . 26 7.1. DNS Location . . . . . . . . . . . . . . . . . . . . . . 26 7.1.1. Applicability of the Envelope Record . . . . . . . . 27 7.2. ABNF Grammar . . . . . . . . . . . . . . . . . . . . . . 28 7.3. Field Definitions . . . . . . . . . . . . . . . . . . . . 30 7.3.1. v (REQUIRED) . . . . . . . . . . . . . . . . . . . . 30 7.3.2. h (REQUIRED) . . . . . . . . . . . . . . . . . . . . 31 7.3.3. pk (REQUIRED) . . . . . . . . . . . . . . . . . . . . 31 7.3.4. ilr (REQUIRED) . . . . . . . . . . . . . . . . . . . 31 7.3.5. ts (REQUIRED) . . . . . . . . . . . . . . . . . . . . 31 7.3.6. rev (REQUIRED) . . . . . . . . . . . . . . . . . . . 32 7.3.7. sig (REQUIRED) . . . . . . . . . . . . . . . . . . . 32 7.3.8. Unknown fields . . . . . . . . . . . . . . . . . . . 32 7.4. Canonical Serialisation . . . . . . . . . . . . . . . . . 32 7.5. Forward Compatibility . . . . . . . . . . . . . . . . . . 34 7.6. Multi-String Reassembly . . . . . . . . . . . . . . . . . 34 8. DNSSEC Requirement . . . . . . . . . . . . . . . . . . . . . 34 9. DANE TLSA Pin . . . . . . . . . . . . . . . . . . . . . . . . 35 10. IdentityLog Cross-Reference . . . . . . . . . . . . . . . . . 36 11. alter: URI Scheme Cross-Reference . . . . . . . . . . . . . . 36 12. Discovery and Bootstrap Procedures . . . . . . . . . . . . . 37 12.1. Discovery Procedure: _mcp. . . . . . . . . . . . 37 12.1.1. Input . . . . . . . . . . . . . . . . . . . . . . . 37 12.1.2. Algorithm . . . . . . . . . . . . . . . . . . . . . 37 12.2. Identity Bootstrap Procedure: _org-alter. . . . 39 12.2.1. Input . . . . . . . . . . . . . . . . . . . . . . . 39 12.2.2. Algorithm . . . . . . . . . . . . . . . . . . . . . 39 12.2.3. First-Run Cold Start . . . . . . . . . . . . . . . . 40 12.3. Envelope Recognition Procedure: _alter. . . . . 41 13. Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 13.1. Key Continuity . . . . . . . . . . . . . . . . . . . . . 43 13.1.1. Absence Is Not Revocation . . . . . . . . . . . . . 45 13.1.2. Change-of-Control Signals . . . . . . . . . . . . . 45 14. Security Considerations . . . . . . . . . . . . . . . . . . . 46 14.1. DNSSEC Downgrade . . . . . . . . . . . . . . . . . . . . 46 14.2. TLSA Pin Rotation . . . . . . . . . . . . . . . . . . . 46 14.3. Envelope Substitution . . . . . . . . . . . . . . . . . 47 14.4. Revocation Opacity . . . . . . . . . . . . . . . . . . . 47 14.5. Clock Skew and ts= . . . . . . . . . . . . . . . . . . . 48 Morrison Expires 12 April 2027 [Page 3] Internet-Draft MCP DNS Discovery October 2026 14.6. Cross-Record Key Consistency . . . . . . . . . . . . . . 48 14.7. Passive-Stream Coupling . . . . . . . . . . . . . . . . 48 14.8. Change of Control . . . . . . . . . . . . . . . . . . . 49 15. Privacy Considerations . . . . . . . . . . . . . . . . . . . 49 15.1. Public Handle Disclosure . . . . . . . . . . . . . . . . 50 15.2. DNS Query Metadata . . . . . . . . . . . . . . . . . . . 50 15.3. Revocation Unlinkability . . . . . . . . . . . . . . . . 50 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 16.1. Underscored DNS Node Name Registration . . . . . . . . . 50 16.2. alter: URI Scheme Registration . . . . . . . . . . . . . 51 16.3. Envelope Version Registry . . . . . . . . . . . . . . . 51 16.4. Org-Alter Version Registry (unchanged from revision 02) . . . . . . . . . . . . . . . . . . . . . . . . . . 51 16.5. Registry Namespace Registry (unchanged from revision 02) . . . . . . . . . . . . . . . . . . . . . . . . . . 51 16.6. Framework Token Registry (unchanged from revision 02) . 52 16.7. Signature Algorithm Registry . . . . . . . . . . . . . . 52 17. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 52 17.1. Minimal Envelope for a Single Handle (NOT RECOMMENDED) . . . . . . . . . . . . . . . . . . . . . . 52 17.2. Zone Hosting Multiple Handles (a publisher MUST NOT do this) . . . . . . . . . . . . . . . . . . . . . . . . . 52 17.3. Full Zone (All Three Records; the _alter record is NOT RECOMMENDED) . . . . . . . . . . . . . . . . . . . . . . 53 18. Interoperability with Earlier Record Generations . . . . . . 53 19. Implementation Status . . . . . . . . . . . . . . . . . . . . 54 20. Normative References . . . . . . . . . . . . . . . . . . . . 55 21. Informative References . . . . . . . . . . . . . . . . . . . 57 Appendix A. Recognition Pseudocode . . . . . . . . . . . . . . . 59 Appendix B. Document History . . . . . . . . . . . . . . . . . . 61 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 69 1. Introduction Model Context Protocol (MCP) [MCP] is an open protocol for structured interaction between AI agents and tool-providing servers. A complete agent-to-organisation-to-individual interaction chain has three distinct discovery requirements: 1. *Service discovery.* Where is the MCP server endpoint? What transport does it speak? What cryptographic key authenticates it? The _mcp. record answers this. Morrison Expires 12 April 2027 [Page 4] Internet-Draft MCP DNS Discovery October 2026 2. *Organisational identity bootstrap.* Who is the organisation operating the server? What is its legal entity? Where is it registered? Under what regulatory frameworks does it operate, and which automated access pathways must it refuse to participate in? The _org-alter. record answers this. 3. *Individual identity recognition.* Who is the Sovereign-tier person bound to a ~handle hosted under the domain? What public key signs their statements? What append-only log anchors the lifecycle of their identity? How may their envelope be revoked? The _alter. record answers this. The three questions are distinct. An MCP client may need to discover an endpoint without caring about the operator's identity or any individual handle. An onboarding wizard installing an org-alter instance may need to read the operator's identity without caring (yet) about the MCP endpoint. A recognition verifier (resolving an alter:~alice URI) needs the individual envelope without necessarily invoking an MCP session. Conflating any two of these into a single TXT record would force every consumer to parse fields it does not need and would crowd the 255-octet character-string limit. Splitting them across three underscore-prefixed labels mirrors the pattern established by DKIM [RFC6376] (._domainkey.) and DMARC [RFC9989] (_dmarc.), where each record serves a single semantic purpose. SPF [RFC7208] and MTA-STS [RFC8461] set the same precedent for carrying policy in a TXT record under a reserved label. This revision is fully backward-compatible with revisions 01 and 02. Implementations that consume only the _mcp. record continue to work unchanged. Implementations that wish to bootstrap an org- alter identity may additionally query _org-alter.. Implementations that wish to recognise an individual ~handle may additionally query _alter.. This document stands alone. All three record formats (Section 5, Section 6, Section 7), all three procedures (Section 12.1, Section 12.2, Section 12.3), the signing input (Section 7.4) and the caching rules (Section 13) are given here in full. An implementer needs no other document in this series. Revisions 01 and 02 are cited where this document records what they said, and are cited informatively, because nothing here depends on fetching them. The envelope published at _alter. is the handle-holder's own declaration, signed by their Ed25519 key and verifiable by any client with access to a DNSSEC-validating recursive resolver. It also carries a reference to an IdentityLog root, and Section 10 sets out what that reference does and does not establish. Morrison Expires 12 April 2027 [Page 5] Internet-Draft MCP DNS Discovery October 2026 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Terminology Envelope An Ed25519-signed JSON object binding a ~handle to a public key, an IdentityLog root reference, an inception timestamp, a revocation hash commitment, a signature algorithm tag, a detached signature, and a caveats array. The TXT grammar that carries the seven required envelope fields across DNS, and the signing input over which they are verified, are specified in Section 7 of this document. ~handle A Sovereign-tier identifier, leading tilde mandatory (e.g. ~alice). Bot-tier handles carry a .bot suffix (e.g. ~example- bot.bot); Instrument-tier handles use the prefix ~cc- (e.g. ~cc- example-model). An Instrument-tier handle identifies an instrument whose acts are attributed to the Sovereign that operates it; it is not an independent handle (Section 8.5 of [MORRISON-IFT]). After the tilde, a handle begins with a letter and continues with letters, digits, "-" and "."; it never contains "_". An organisation's handle may therefore be dotted, as in ~example.com. The grammar is the handle-name of [ALTER-URI], restated in Section 7.2, and the tier is read from the lexical form alone. A dotted handle is not a domain name, and the Handle- Domain Confusion consideration of [ALTER-URI] applies. IdentityLog An append-only transparency log recording envelope lifecycle events (mint, caveat-add, revocation, key-rotation), whose root the ilr= field of Section 7 references. The log's cadence, its witness protocol, and the client profile for checking it are NOT specified by this document and are not yet specified anywhere a reader can fetch. Section 10 states what a resolver may and may not conclude from ilr= in the meantime. Recognition The act of a resolver observing and verifying an envelope on cryptographic merit. A published record is an assertion the resolver may verify or reject. DNSSEC Validation The act of an authenticating DNS resolver verifying the RRSIG chain from the root trust anchor to the TXT RRset, per [RFC4033], [RFC4034], and [RFC4035], and setting the AD bit on the response delivered to the stub client. Morrison Expires 12 April 2027 [Page 6] Internet-Draft MCP DNS Discovery October 2026 DANE TLSA Pin A DNS TLSA resource record [RFC6698] binding a server's leaf TLS certificate (or the public key therein) to the zone that hosts the envelope. In this document, the pin applies to the MCP endpoint at mcp.. alter: URI A URI scheme for dispatchable ~handle references, specified in [ALTER-URI] and provisionally registered with IANA on 5 October 2026 per [RFC7595] Section 4. Handler guidance is given in Section 11 of this document. Where this document names a ~handle in prose as a reference, it is written as an alter: URI, for example alter:~alice. The h field of Section 7.3.2 carries the bare form its grammar defines, and the value ~alice corresponds to the URI alter:~alice. The terms Org-Identity Record, Identity Bootstrap, Canonical Entity Identifier and Regulatory Refusal Marker carry the meanings given by Section 6 and Section 12.2. 3. Related Work Several drafts now publish agent discovery data in DNS, with overlapping vocabularies. Two of them are called AID and they are different documents. [AGENT-AID] is "Agent Identity and Discovery", and [DNS-AID] is "DNS for AI Discovery". [AGENT-AID] is the closest neighbour to the service-discovery record of this document, and it came first. It publishes a TXT record at _agent. carrying a leading v=aid2 version tag and semicolon- delimited key=value pairs, which give the endpoint URI (u), a protocol token (p), an authentication hint (a), and optionally an Ed25519 public key for endpoint proof (k), carried as an unpadded base64url JWK x value whose JWK thumbprint [RFC7638] is the HTTP Message Signature [RFC9421] keyid. The earlier v=aid1 format, with its i rotation identifier, stays valid through [AGENT-AID]'s compatibility window. The _mcp record of Section 5 reaches the same three facts, an endpoint, a protocol, and a key, in an underscore- prefixed TXT record with a leading version tag and semicolon- delimited pairs. The _mcp record derives its pattern from DKIM [RFC6376]. [AGENT-AID] published its record first, in March 2026. Morrison Expires 12 April 2027 [Page 7] Internet-Draft MCP DNS Discovery October 2026 The two can be published together. [AGENT-AID] gives where an agent is and which protocol to speak to it. The _mcp record gives an MCP endpoint's transport, authentication, capability scope and key epoch, and the _org-alter record of Section 6 gives the legal entity behind the endpoint, its registry identifier, operating regions and regulatory refusal markers. A client that learns p=mcp from _agent. may also look up _mcp.. The keys bind different things, so publishing both is not a duplication. The k of [AGENT-AID] binds a key to an endpoint, and proves control of the server that answers. The _alter and _org-alter records bind a key to a ~handle or to a legal entity, with a log root and a revocation commitment. [DNS-AID] specifies discovery of AI agents through DNS. It carries connectivity in SVCB records with TXT as a fallback, an alpn parameter that may hold the transport, an application-layer agent protocol, or both (alpn=mcp,h2,h3), and an optional bap parameter for the agent protocol alone, so that consumers can match on the agent protocol without parsing transports out of alpn. It predates this document's treatment of the same question. Both operate over unicast DNS. DNS-AID addresses agent discovery generally, while this document addresses one protocol family and adds the identity records that carry a signed envelope. [MDNS-AGENT] specifies zero-configuration discovery over mDNS and DNS-SD. Its proto parameter names the agent protocol family, and it defines exactly one value for it, proto=a2a, saying that A2A is the only instantiation included in that document and leaving other agent protocols to future work. It defines no registry for the key. This document uses proto with the same meaning. The owner names and service types of the two documents differ, so no record is shared between them. [MDNS-ARCHITECT] publishes registered agents through standard A, SVCB, and SRV records at a registry, with a worked SVCB example that puts the agent protocol and the transport side by side (SVCB 0 mcp ... alpn=h2). [SAIP] is a neighbour to the identity records of this document rather than to its service-discovery record. It publishes an agent's Ed25519 public key in an underscore-prefixed TXT record at _saip., with a leading v= version tag, deriving its pattern, as this document does, from DKIM [RFC6376] and SPF [RFC7208]. Its Section 10, "Trust and Attestation Discovery", specifies that publication and the discovery of the key from it. The bindings differ. The _saip record binds a key to a vendor's declared network footprint, carrying authorised ASNs, authorised IP prefixes, and an Morrison Expires 12 April 2027 [Page 8] Internet-Draft MCP DNS Discovery October 2026 expiry. The _alter record of Section 7 binds a key to a ~handle, with a log root and a revocation commitment. A deployment that wanted both could publish both, and nothing in either record's owner name or field set collides with the other. The neighbouring drafts keep the agent protocol and the transport apart, each in its own way. [MDNS-AGENT] defines proto as the agent protocol identifier and never as a transport, and carries the connection data in the SRV record instead. [MDNS-ARCHITECT] defines no proto key at all, and keeps the agent protocol distinct from the wire protocol inside its SVCB record, the one in the mcp position and the other in alpn. Neither of them puts a transport where the agent protocol belongs. Revision 01 of this document did, and this document no longer does. This document uses one parameter for the agent protocol family and a second, separate parameter for the transport or binding. The transport parameter is named transport because the Model Context Protocol specification already calls this axis by that name, so an MCP implementer meets one term, not two. This document keeps a third axis separate again. transport names the binding (streamable-http, sse), and the wire protocol underneath it (h2, h3) is left to the alpn service parameter of SVCB and HTTPS records [RFC9460], where DNS already carries it. [DNS-AID] permits alpn to hold the transport, the agent protocol, or both. This document does not overload alpn in that way. 4. Why TXT rather than SVCB [DNS-AID] carries its connectivity data in SVCB records, with TXT as a fallback, and [MDNS-ARCHITECT] uses SVCB. This document is the reverse, TXT is the primary carrier. The reason is the payload. An _mcp record's value is almost entirely opaque tokens the resolver does not interpret, an endpoint URL, a public key, a capability list, an attestation scope. SVCB is useful when a resolver or a connection library acts on the parameters directly, selecting a transport, following an alpn, choosing a port. It adds a registered SvcParamKey per field and a priority-ordered target list. For a record whose fields are consumed by an MCP client after resolution, and not by the resolver, that machinery is overhead without a matching benefit, and a TXT string is the lighter carrier. Morrison Expires 12 April 2027 [Page 9] Internet-Draft MCP DNS Discovery October 2026 Where a field IS resolver-actionable, this document defers to SVCB rather than duplicating it. The wire protocol lives in the SVCB or HTTPS alpn parameter [RFC9460], never in this TXT record, for that reason. An operator who wants SVCB-based transport selection publishes an HTTPS record for the endpoint host in the ordinary way, and the two records coexist. 5. Record Format: _mcp. (Service Discovery) This section defines the Discovery Record introduced in revision 00, in full. 5.1. DNS Location The Discovery Record is a DNS TXT resource record [RFC1035] published at the label _mcp prepended to the Policy Domain: _mcp.. IN TXT "" The underscore prefix conforms to the conventions established in [RFC8552] for globally scoped, underscore-prefixed DNS node names. Multiple TXT resource records MAY be published at the same DNS name. Where multiple records exist, each MUST independently conform to the syntax defined in this section. Clients MUST evaluate all returned records and select among them using the priority field as described below. 5.2. ABNF Grammar The record value is a semicolon-delimited sequence of key-value pairs. The following ABNF [RFC5234] defines the syntax: Morrison Expires 12 April 2027 [Page 10] Internet-Draft MCP DNS Discovery October 2026 mcp-record = version *( ";" SP field ) version = "v=mcp1" field = url-field / proto-field / transport-field / pk-field / epoch-field / cap-field / attest-field / scope-field / priority-field / ttl-field / ext-field / unknown-field url-field = "url=" https-uri proto-field = "proto=" proto-value transport-field = "transport=" transport-value pk-field = "pk=" algo ":" base64url epoch-field = "epoch=" 1*DIGIT cap-field = "cap=" cap-csv attest-field = "attest=" attest-csv scope-field = "scope=" scope-csv priority-field = "priority=" 1*DIGIT ttl-field = "ttl=" 1*DIGIT ext-field = "ext=" https-uri unknown-field = token "=" *qtext https-uri = "https://" *uri-char uri-char = %x21-3A / %x3C-7E ; printable ASCII, excluding ";" (%x3B) and SP. ; A URI carries no raw space, so admitting one here ; would let a url= value swallow the field after it. qtext = %x20-3A / %x3C-7E ; printable ASCII and SP, excluding ";" (%x3B), ; which delimits one field from the next. A value ; that could contain ";" could swallow the delimiter. algo = "ed25519" base64url = 1*( ALPHA / DIGIT / "-" / "_" ) proto-value = token transport-value = token cap-csv = cap-token *( "," cap-token ) cap-token = token attest-csv = attest-token *( "," attest-token ) attest-token = token scope-csv = scope-token *( "," scope-token ) scope-token = "tools" / "resources" / "prompts" / "sampling" / "identity" / token token = 1*( ALPHA / DIGIT / "-" / "_" ) unknown-field matches ONLY a field name this document does not define. ABNF has no way to say "any token except these", so the exclusion is stated here, and it is normative. Where a field name IS defined above, the field MUST be parsed by that field's own rule. A record in which a defined field's value does not satisfy its own rule is MALFORMED, and a client MUST discard it, exactly as Section 12.1 Morrison Expires 12 April 2027 [Page 11] Internet-Draft MCP DNS Discovery October 2026 discards a record whose url is not a valid HTTPS URI. A client MUST NOT re-read such a field as an unknown-field. Without this rule the alternation would swallow every defect it was written to exclude: url=https://x.com priority=5 would parse as an unknown field named url rather than as the malformed url field it is. The grammar admits any token in proto and in transport. Revision 01 admitted any token in proto and records in the wild carry transport values there, so a resolver MUST be able to PARSE such a record before it can decide what to do with it, and the reading rule of Section 5.3.5 is what decides. The values this document DEFINES are enumerated in the field definitions below. proto has exactly one defined value, mcp. transport has exactly three, streamable-http, sse, and stdio-url. Those two sets are disjoint, so no value is defined for both fields. A transport value appearing in proto is RECOGNISED there, under Section 5.3.5, and is not DEFINED there. 5.3. Field Definitions 5.3.1. v (REQUIRED) Protocol version identifier. MUST be the literal string mcp1. MUST appear as the first field in the record. Clients MUST reject any record whose v field is absent, is not the first field, or contains a value other than mcp1. This version gate enables future incompatible revisions of the record format. A future version mcp2 would indicate breaking changes to field semantics or discovery flow. 5.3.2. url (REQUIRED) The HTTPS URL of the MCP server endpoint. MUST use the https scheme. MUST be a syntactically valid URI per RFC 3986. This is the entry point for MCP session establishment. Clients MUST NOT attempt to connect to URLs using schemes other than https. Servers MUST present a valid TLS certificate for the hostname in the URL. Morrison Expires 12 April 2027 [Page 12] Internet-Draft MCP DNS Discovery October 2026 5.3.3. proto (OPTIONAL) The agent protocol family the endpoint speaks. Default value: mcp. For a record published at _mcp. the only value defined by this document is mcp; the field is retained because the same key, with the same meaning, is used by [MDNS-AGENT] (see Section 3) and a client that reads several of them should not have to special-case this one. proto does not name a transport. It does not carry streamable-http, sse, h2, h3, or any other binding. The transport is carried by the transport field below. A record published under revision 01 may still carry a transport value here, and Section 5.3.5 says how to read one. The field is OPTIONAL, but not unconditionally. A publisher that emits a transport field MUST also emit proto=mcp, for the interoperability reason given in Section 5.3.5. Omitting proto is permitted only where transport is also omitted. 5.3.4. transport (OPTIONAL) The MCP transport binding used by the server. Default value: streamable-http. Defined values: * streamable-http, the HTTP-based streaming transport (default). * sse, the HTTP+SSE transport of MCP protocol version 2024-11-05, retained for deployed servers. The Model Context Protocol specification marks this transport superseded by streamable-http. It is listed so an existing server stays discoverable, not as a recommendation for new deployments. * stdio-url, a URL pointing to a signed launch descriptor for a stdio-based server (descriptor format out of scope). This is a discovery convenience defined by this document, not one of the MCP specification's own transport names. The field is named transport because that is the term the Model Context Protocol specification itself uses for this axis, so an _mcp record and an MCP client configuration name the transport the same way. Implementations SHOULD support at least streamable-http. A client that meets a transport value it does not recognise MUST skip the record and proceed to the next record by priority, or to HTTPS fallback. Morrison Expires 12 April 2027 [Page 13] Internet-Draft MCP DNS Discovery October 2026 The wire protocol beneath the transport (h2, h3, http/1.1) is NOT carried in this record. It is already expressible as the alpn service parameter of an SVCB or HTTPS resource record [RFC9460], and duplicating it in TXT would create two sources of truth for one fact. 5.3.5. Reading a record published before this revision Revision 01 of this document defined proto as the transport, so records in the wild carry proto=streamable-http, proto=sse, or proto=stdio-url. Revision 01 also admitted ANY token in that field, and required a client that met a proto value it did not recognise to SKIP the record. Both of those behaviours are preserved here. Such records remain valid and MUST be read as follows. A client reading an _mcp record determines two things, the protocol family first and the transport second. Taking them in the other order is what makes an unrecognised value look harmless, so the order is normative. *Step A, the protocol family.* The family is mcp where any one of the following holds: * proto is absent; * proto carries mcp; * proto carries one of the three values defined for transport in Section 5.3.4. This is the revision 01 form, in which the transport was written into proto. Where proto carries any other value, it names a protocol family this document does not define. The client MUST skip the record and proceed to the next record by priority, or to HTTPS fallback. It MUST NOT treat the value as a transport, and it MUST NOT apply a default transport to the record. This holds whether or not a transport field is also present: a record reading transport=streamable-http; proto=websocket is skipped, because the family is unknown, and the presence of a readable transport does not make an unknown family speakable. *Step B, the transport.* A client reaches this step only where Step A yielded the family mcp. * Where transport is present and carries one of the three values defined in Section 5.3.4, that value is the transport, and any transport value carried in proto MUST be ignored. Morrison Expires 12 April 2027 [Page 14] Internet-Draft MCP DNS Discovery October 2026 * Where transport is present and carries any other value, the client MUST skip the record, and MUST proceed to the next record by priority or to HTTPS fallback (Section 5.3.4). * Where transport is absent and proto carries one of the three defined transport values, that value is the transport. This is the revision 01 form. * Where transport is absent and proto is absent or carries mcp, the transport is streamable-http. Revision 01 admitted any token in proto, so proto=websocket was a syntactically legal record, and every conformant revision 01 client SKIPPED it, because revision 01 required a skip on an unrecognised proto value. A client that instead read an unrecognised proto value as a protocol family, and then applied the default transport, would open a streamable-http session against a server that never offered one. That record was unusable under revision 01 and it stays unusable here, which keeps the two revisions interoperable. A publisher that emits a transport field MUST also emit proto=mcp. A revision 01 client does not know the transport field, and its own forward-compatibility rule tells it to IGNORE any field it does not know, so it reads only proto. A record carrying transport=streamable-http beside proto=sse would therefore resolve to streamable-http under this revision and to sse under revision 01, which is one record and two transports. Setting proto=mcp alongside transport removes the divergence, because a revision 01 client then finds no transport it recognises in proto and skips the record rather than reaching a different endpoint state than a current client would. Publishers SHOULD move to the two-field form. No flag day is required, because the two forms are distinguishable by inspection, and because no value is defined for both fields (Section 5.2). 5.3.6. pk (OPTIONAL) Ed25519 public key for endpoint verification, encoded as ed25519: where is the raw 32-byte public key encoded per [RFC4648] Section 5, without padding. Where present, the pk field provides a cryptographic binding between the DNS record and the MCP server. Clients MUST verify that the key matches at least one of the following: 1. A key in the server's TLS certificate SubjectPublicKeyInfo. Morrison Expires 12 April 2027 [Page 15] Internet-Draft MCP DNS Discovery October 2026 2. The signing key used in HTTP Message Signatures [RFC9421] on MCP responses. 3. The key declared in the Server Card [SEP-1649] served by the endpoint. If verification fails, the client MUST treat the server as untrusted and SHOULD NOT proceed with the MCP session. 5.3.7. epoch (OPTIONAL) A monotonic non-negative integer that increments on every key rotation. Default value: 0. Signed claims or attestations issued by the MCP server carry a key identifier (kid) of the form :#. Verifiers resolve the Discovery Record, extract the current epoch, and apply the following rules: * Claims with epoch == current are valid, subject to temporal checks. * Claims with epoch < current are revoked unless the claim's expiry timestamp predates the rotation event. * Claims with epoch > current MUST be rejected as either forgeries or evidence of a stale verifier DNS cache. The epoch field enables epoch-based revocation without external Certificate Revocation Lists (CRLs) or Online Certificate Status Protocol (OCSP) infrastructure. Incrementing the epoch revokes all outstanding claims issued under prior epochs, subject to the grace period defined by each claim's expiry. The rules above compare a claim against the record. They do not compare the record against itself over time. A publisher never lowers the epoch, because the field is monotonic, so a record whose epoch is lower than one a client has already observed is not a state a conformant publisher produces. Section 13.1 states what a client does when it observes one, and what it does when the pk changes. 5.3.8. cap (OPTIONAL) Capability tier advertised by the server, expressed as a comma- separated list of tokens. This field provides a coarse hint to clients about the functional scope of the server. Morrison Expires 12 April 2027 [Page 16] Internet-Draft MCP DNS Discovery October 2026 No normative semantics are defined for specific capability values in this document. Protocol extensions MAY define capability tokens and their semantics. Clients that do not recognise a capability token MUST ignore it. 5.3.9. attest (OPTIONAL) A comma-separated list of attestation types that the MCP server declares it is authorised to issue. The value enumerates claim types that downstream verifiers will accept from this issuer. Defined values, extensible: * employ, current employment affiliation. * contract, contractual or freelance engagement. * alumnus, former affiliation. * director, board or directorial role. * member, generic membership (professional body, association). * contrib, verified contribution without formal affiliation. Verifiers MUST reject any attestation claim whose type is not present in the issuer's attest field. This provides a structural defence against capability creep: the domain's published attestation scope is the upper bound on what its claims can assert. Forward compatibility: unknown attestation values MUST be ignored, not rejected. A verifier encountering attest=employ,fellow where fellow is undefined treats the record as attest=employ and proceeds. 5.3.10. scope (OPTIONAL) Comma-separated list of MCP primitives supported by the server. Defined values: * tools, the server exposes callable tools. * resources, the server exposes readable resources. * prompts, the server exposes prompt templates. * sampling, the server supports LLM sampling requests. * identity, the server supports identity resolution queries. Morrison Expires 12 April 2027 [Page 17] Internet-Draft MCP DNS Discovery October 2026 Unknown values MUST be ignored. This field is advisory; the authoritative capability set is declared during the MCP initialize handshake. 5.3.11. priority (OPTIONAL) A non-negative integer. Default value: 10. Where multiple Discovery Records exist at the same DNS name, clients MUST sort records by priority in ascending order and attempt connection to lower-valued records first. This field enables multi-server failover without external load balancing. If connection to the highest-priority server fails, the client proceeds to the next record. 5.3.12. ttl (OPTIONAL) Advisory TTL in seconds for client-side caching of the parsed Discovery Record metadata. Clients MAY use this value to avoid repeated DNS lookups when the DNS TTL is shorter than desired. The DNS TTL itself remains authoritative for cache expiry of the raw DNS response; the ttl field applies to post-parse metadata caching only. 5.3.13. ext (OPTIONAL) An HTTPS URL pointing to a protocol-extension document. The format and semantics of the extension document are defined by the protocol extension, not by this specification. This field enables protocol-specific extensions (identity protocols, payment protocols, agent-to-agent negotiation) to attach additional metadata without consuming space in the DNS TXT record. The extension document MUST be served over HTTPS. Clients that do not recognise or support the extension MUST ignore this field. 5.4. Forward Compatibility Implementations MUST ignore unknown fields. A parser encountering a field name that it does not recognise MUST skip that field and continue parsing the remaining fields. This rule ensures that future extensions to the record format do not break existing implementations. Ignoring an unknown FIELD is not the same act as skipping a record on an unrecognised VALUE in a field this document defines. The first is required here; the second is required by Section 5.3.4 and Section 5.3.5. Morrison Expires 12 April 2027 [Page 18] Internet-Draft MCP DNS Discovery October 2026 Breaking changes to the semantics of existing fields require a version bump, for example v=mcp2. 5.5. Multi-String Concatenation DNS TXT resource records are limited to 255 bytes per character- string [RFC1035]. Where a Discovery Record exceeds 255 bytes, the record MUST be split across multiple character-strings within a single TXT RDATA, which the client concatenates, as [RFC7208] Section 3.3 does for SPF. Example of a multi-string record: _mcp.example.com. IN TXT ( "v=mcp1; url=https://mcp.example.com; " "pk=ed25519:LongBase64UrlEncodedPublicKeyValueHere; " "epoch=3; attest=employ,contract,alumnus; scope=tools,identity" ) Parsers MUST concatenate all character-strings within a single TXT RDATA before parsing the semicolon-delimited fields. Parsers MUST NOT treat each character-string as an independent record. 6. Record Format: _org-alter. (Identity Bootstrap) This section defines the Org-Identity Record introduced in revision 02. It is given here in full. 6.1. DNS Location The Org-Identity Record is a DNS TXT resource record [RFC1035] published at the label _org-alter prepended to the Policy Domain: _org-alter.. IN TXT "" The underscore prefix conforms to the conventions established in [RFC8552] for globally scoped, underscore-prefixed DNS node names. A domain MAY publish a _mcp. record without an _org- alter. record (service-only deployment), or an _org- alter. record without a _mcp. record (identity-only deployment), or both (full deployment). The recommended pattern for any operator running an org-alter instance is to publish both. Multiple TXT resource records MAY be published at the same DNS name (e.g., for staged identity rotation). Clients MUST evaluate all returned records and select the one with the highest epoch field. Morrison Expires 12 April 2027 [Page 19] Internet-Draft MCP DNS Discovery October 2026 6.2. ABNF Grammar The record value is a semicolon-delimited sequence of key-value pairs. The following ABNF [RFC5234] defines the syntax: Morrison Expires 12 April 2027 [Page 20] Internet-Draft MCP DNS Discovery October 2026 orgalter-record = version *( ";" SP field ) version = "v=alter1" field = org-field / entity-field / entity-type-field / founded-field / regions-field / regulated-field / bootstrap-field / mcp-policy-field / epoch-field / pk-field / attest-field / ext-field / unknown-field org-field = "org=" text-value entity-field = "entity=" registry ":" text-value entity-type-field = "entity-type=" text-value founded-field = "founded=" date-fullyear regions-field = "regions=" region-csv regulated-field = "regulated=" framework-csv bootstrap-field = "bootstrap=" https-uri mcp-policy-field = "mcp-policy=" policy-token epoch-field = "epoch=" 1*DIGIT pk-field = "pk=" algo ":" base64url attest-field = "attest=" attest-csv ext-field = "ext=" https-uri unknown-field = token "=" *qtext registry = "abn" / "acn" / "ein" / "ch" / "cro" / "lei" / token text-value = 1*qtext qtext = %x20-3A / %x3C-7E ; printable ASCII and SP, excluding ";" (%x3B), ; which delimits fields. A legal entity name carries ; spaces, so VCHAR alone cannot express one. region-csv = region-token *( "," region-token ) region-token = 2ALPHA ; ISO 3166-1 alpha-2 framework-csv = framework-token *( "," framework-token ) framework-token = "disp" / "itar" / "ear" / "hipaa" / "gdpr" / "soc2" / "iso27001" / "iso42001" / "essential8" / "aprs" / token policy-token = "open" / "refuse-automated" / "refuse-tenant" / "refuse-all" / token date-fullyear = 4DIGIT [ "-" 2DIGIT [ "-" 2DIGIT ] ] algo = "ed25519" base64url = 1*( ALPHA / DIGIT / "-" / "_" ) https-uri = "https://" *uri-char uri-char = %x21-3A / %x3C-7E ; printable ASCII, excluding ";" (%x3B) and SP. ; A URI carries no raw space. token = 1*( ALPHA / DIGIT / "-" / "_" ) Morrison Expires 12 April 2027 [Page 21] Internet-Draft MCP DNS Discovery October 2026 A legal entity name carries spaces, so text-value admits them and excludes only the semicolon that separates one field from the next. Revision 02 defined org, entity and entity-type over 1*VCHAR, which excludes the space. A URI does not carry a raw space, so bootstrap and ext are defined over uri-char rather than text-value. Admitting SP in a URI value would let it run past its own end and consume the field after it. As in Section 5.2, unknown-field matches ONLY a field name this document does not define. Where a field name IS defined above, the field MUST be parsed by that field's own rule, and a record in which a defined field's value does not satisfy its rule is MALFORMED and MUST be discarded rather than re-read as an unknown field. 6.3. Field Definitions 6.3.1. v (REQUIRED) Protocol version identifier. MUST be the literal string alter1. MUST appear as the first field in the record. Clients MUST reject any record whose v field is absent, is not the first field, or contains a value other than alter1. The version namespace is independent of the _mcp record's v=mcp1 namespace. This allows the two record types to evolve independently. 6.3.2. org (REQUIRED) The canonical legal name of the organisation operating the domain. MUST be the registered legal entity name as it appears in the operator's primary corporate registry, not a trading name or brand. For trading names, see the optional entity-type field. Examples: org=Example Pty Ltd org=Example Corporation 6.3.3. entity (RECOMMENDED) A globally-disambiguating canonical entity identifier, prefixed by its registry namespace. Defined registries: * abn:, Australian Business Number (11 digits, no spaces). * acn:, Australian Company Number (9 digits, no spaces). Morrison Expires 12 April 2027 [Page 22] Internet-Draft MCP DNS Discovery October 2026 * ein:, US Employer Identification Number (NN-NNNNNNN). * ch:, UK Companies House number (8 alphanumeric). * cro:, Irish Companies Registration Office number. * lei:, Legal Entity Identifier (20 alphanumeric per ISO 17442). Additional registries MAY be defined; clients MUST treat unknown registry namespaces as opaque identifiers. Example: entity=abn:12345678901 The entity field lets a verifier check the declared name against the public registry. A domain claiming to be Example Pty Ltd without an ABN that resolves to that name in ABR Lookup shows as a mismatch to any verifier with access to that registry. 6.3.4. entity-type (OPTIONAL) A short human-readable label for the entity's type, drawn from its jurisdiction's vocabulary. Examples: Pty Ltd, LLC, GmbH, SAS, non- profit. This field is advisory and is intended for display to humans; it is not a structured taxonomy. 6.3.5. founded (OPTIONAL) The date the legal entity was founded or registered, as YYYY or YYYY- MM or YYYY-MM-DD per ISO 8601. This field is advisory and is used by onboarding wizards and identity verifiers to display "Founded N years ago" or to detect implausibly young entities making strong claims. 6.3.6. regions (OPTIONAL) A comma-separated list of ISO 3166-1 alpha-2 country codes indicating the operator's primary regions of operation. This field is advisory. It is used by onboarding wizards to set sane defaults for jurisdiction-specific behaviour (e.g., currency, locale, public registry preference). Example: regions=AU,NZ,SG Morrison Expires 12 April 2027 [Page 23] Internet-Draft MCP DNS Discovery October 2026 6.3.7. regulated (OPTIONAL) A comma-separated list of regulatory framework tokens under which the operator is bound. Defined values (extensible): * disp, Australian Defence Industry Security Program. * itar, US International Traffic in Arms Regulations. * ear, US Export Administration Regulations. * hipaa, US Health Insurance Portability and Accountability Act. * gdpr, EU General Data Protection Regulation. * soc2, AICPA SOC 2 Type II. * iso27001, ISO/IEC 27001 information security management. * iso42001, ISO/IEC 42001 AI management systems. * essential8, ASD Essential Eight (ML2 or higher). * aprs, Australian Privacy Principles / Privacy Act. A token in this field declares that the operator is bound by the named framework and that automated access crossing the regulated boundary MUST be refused. Onboarding wizards reading this field MUST refuse to attempt authenticated access to data stores covered by the declared framework, regardless of whether credentials are available. A remote agent can read the declaration before it attempts a connection. Forward compatibility: an unknown framework token MUST NOT be ignored. It has the effect that step 4 of Section 12.2 gives any framework token. 6.3.8. bootstrap (OPTIONAL) An HTTPS URL pointing to a JSON document containing additional identity bootstrap metadata: a directory of public roster members (if the org chooses to publish one), an organisational logo URL, a canonical public website URL, an attest profile beyond what fits in DNS, and any operator-defined extensions. The bootstrap document MUST be served over HTTPS with a valid TLS certificate for the Policy Domain. The document format is operator- defined. Morrison Expires 12 April 2027 [Page 24] Internet-Draft MCP DNS Discovery October 2026 6.3.9. mcp-policy (OPTIONAL) A single token declaring how the operator's MCP endpoint relates to external automated access: * open, the MCP endpoint accepts queries from any agent with appropriate authentication. * refuse-automated, the MCP endpoint exists for human-mediated access only. Automated agents SHOULD NOT initiate sessions. * refuse-tenant, the MCP endpoint exists, but the operator runs one or more tenants (e.g., an M365 tenant) into which automated access is forbidden. This is the typical declaration for an org-alter instance run by an operator who has DISP-accredited or ITAR-bound systems alongside their public meta-layer. * refuse-all, the MCP endpoint exists for the operator's own internal use only. External agents MUST NOT attempt connection. Default value, if absent: open. The mcp-policy field complements the regulated field. regulated=disp; mcp-policy=refuse-tenant is the canonical declaration for a defence contractor running an org-alter at the unclassified meta-layer alongside a regulated tenant they will not allow automated agents to enter. 6.3.10. epoch (OPTIONAL) A monotonic non-negative integer that increments on every identity rotation event (e.g., legal entity restructure, change of control, move to a new jurisdiction). Default value: 0. Semantics mirror the epoch field of the _mcp record (Section 5.3.7). A wizard that has persisted this record's pk and epoch applies the rules of Section 13.1 when it re-reads the record. 6.3.11. pk (OPTIONAL) Ed25519 public key for endpoint verification, encoded identically to the _mcp record's pk field (Section 5.3.6). When present, the same key provides cryptographic binding for both endpoint discovery and identity bootstrap. Morrison Expires 12 April 2027 [Page 25] Internet-Draft MCP DNS Discovery October 2026 6.3.12. attest (OPTIONAL) A comma-separated list of attestation types the operator declares it is authorised to issue, identical in semantics to the _mcp record attest field (Section 5.3.9). Where both records publish an attest field, the values MUST be consistent. An onboarding wizard SHOULD use the union of the two. 6.3.13. ext (OPTIONAL) An HTTPS URL pointing to a protocol-extension document, identical in semantics to the _mcp record ext field (Section 5.3.13). This field is distinct from bootstrap: ext is for protocol-level extensions to the discovery format itself; bootstrap is for operator-level identity metadata. 6.4. Forward Compatibility Implementations MUST ignore unknown fields. This rule, identical to that of the _mcp record (Section 5.4), ensures that future extensions to the _org-alter record format do not break existing implementations. 7. Record Format: _alter. (Envelope Publication) This section defines the Envelope Publication record introduced in revision 03. The record publishes the seven required fields of the identity envelope (binding a ~handle to its public key, IdentityLog root, inception timestamp, revocation commitment, and detached signature, under a protocol version) at an underscore-prefixed label under the handle's hosting zone. The envelope schema admits an optional caveats array which is never carried in DNS; this document specifies no transport and no vocabulary for it, so under this document the array is always empty and the signature is computed over an empty array (Section 7.4). The signature algorithm is not a separate field. It is derived from the pk= prefix via the registry of Section 16.7, and enters the signing input under that derivation. 7.1. DNS Location The Envelope Record is a DNS TXT resource record [RFC1035] published at the label _alter prepended to the hosting zone: _alter.. IN TXT "" The underscore prefix conforms to the conventions established in [RFC8552] for globally scoped, underscore-prefixed DNS node names. Morrison Expires 12 April 2027 [Page 26] Internet-Draft MCP DNS Discovery October 2026 Publication of a per-individual envelope at this label is *NOT RECOMMENDED*, for the reasons in Section 7.1.1. That applies to any number of handles. A zone MUST NOT publish envelopes for more than one ~handle at this owner name, because a single query there returns every handle the zone hosts (Section 7.1.1). A domain MAY publish any combination of _mcp., _org- alter., and _alter. records independently (service- only, identity-only, envelope-only, or any intersection). 7.1.1. Applicability of the Envelope Record Publication of a per-individual envelope in DNS is *NOT RECOMMENDED* for new deployments. Three properties of DNS are the reason. *Enumeration.* Where a zone co-hosts several handles at one owner name, a single query returns the entire set, and the individuals listed in it cannot each consent to the disclosure of the others. Even with one handle per zone, DNSSEC's authenticated denial of existence permits zone walking unless NSEC3 or a compact denial scheme is deployed, and this document does not require one. *Size.* A conformant envelope does not fit in a single 255-octet character-string, and no conformant envelope is smaller than the limit. Co-hosting a handful of handles at one owner name exceeds the 1232-octet fragmentation budget that current DNS operational guidance assumes, and the RRset grows without bound in the number of handles. The resolution algorithm of Section 12.3 retrieves the whole RRset and filters client-side, so the cost of resolving one handle grows with the number of handles the zone hosts. *Erasure.* A DNS record, once published and cached, cannot be recalled. A mechanism that binds a natural person's identifier to a key in public DNS offers that person no way to withdraw the binding from the caches and passive collectors that have already taken it. Revocation, where this document specifies it at all, marks a binding dead from the moment of reveal, along with every claim signed under its key (Section 7.3.6); it does not unpublish it. These properties come from publishing in DNS. They do not apply to the envelope format, its signing input (Section 7.4), or the verification procedure (Section 12.3). Morrison Expires 12 April 2027 [Page 27] Internet-Draft MCP DNS Discovery October 2026 7.2. ABNF Grammar The record value is a semicolon-delimited sequence of key-value pairs. Two grammars are given, because a publisher and a resolver are held to different rules. alter-record is what a conformant publisher MUST emit. alter-accepted is what a conformant resolver MUST accept. Every alter-record is an alter-accepted; the converse does not hold. The following ABNF (per [RFC5234]) defines the syntax: Morrison Expires 12 April 2027 [Page 28] Internet-Draft MCP DNS Discovery October 2026 ; Publisher emission. A conformant publisher MUST emit this form. alter-record = version ";" SP handle-field ";" SP pubkey-field ";" SP ilr-field ";" SP ts-field ";" SP rev-field ";" SP sig-field *( ";" SP unknown-field ) ; Resolver acceptance. A conformant resolver MUST accept this form. ; The version field stays first. The remaining six required fields ; may arrive in any order, each exactly once, interleaved with any ; number of unknown fields. alter-accepted = version *( ";" SP accepted-field ) accepted-field = handle-field / pubkey-field / ilr-field / ts-field / rev-field / sig-field / unknown-field version = "v=alter1" handle-field = "h=" handle pubkey-field = "pk=" algo ":" base64url ilr-field = "ilr=" base64url ; SHA-256 of IdentityLog root ts-field = "ts=" 1*DIGIT ; inception_ts, Unix seconds rev-field = "rev=" base64url ; SHA-256 of revocation pre-image sig-field = "sig=" base64url ; Ed25519 detached signature unknown-field = token "=" *qtext handle = "~" handle-name handle-name = sovereign-name / bot-name / instrument-name sovereign-name = ALPHA *( ALPHA / DIGIT / "-" / "." ) ; Sovereign tier bot-name = ALPHA *( ALPHA / DIGIT / "-" / "." ) ".bot" ; Bot tier instrument-name = "cc-" 1*( ALPHA / DIGIT / "-" / "." ) ; Instrument tier algo = "ed25519" base64url = 1*( ALPHA / DIGIT / "-" / "_" ) token = 1*( ALPHA / DIGIT / "-" / "_" ) qtext = %x20-3A / %x3C-7E ; printable ASCII and SP, excluding ";" (%x3B), ; which delimits one field from the next. ABNF alone cannot express "each of these six exactly once, in any order", so the cardinality rule is stated here and is normative. A resolver MUST reject any record in which a required field is absent, or in which any field name appears more than once. Morrison Expires 12 April 2027 [Page 29] Internet-Draft MCP DNS Discovery October 2026 ABNF cannot express the exclusion either. As in Section 5.2, unknown-field matches ONLY a field name this document does not define. Where a field name IS defined above, the field MUST be parsed by that field's own rule, and a record in which a defined field's value does not satisfy its rule is MALFORMED and MUST be rejected rather than re-read as an unknown field. The seven keys are REQUIRED. Publishers MUST NOT omit or reorder them, and MUST emit them in the order shown in alter-record. The v field is first for publisher and resolver alike. A resolver MUST reject a record whose v field is absent or is not the first field (Section 7.3.1), so the ordering freedom above extends to the remaining six required fields and to unknown fields, and never to v. Ordering among those six carries no meaning, and a resolver MUST NOT derive any from it. Resolvers MUST tolerate unknown fields wherever they appear, and MUST ignore them, per the forward-compatibility rule of Section 7.5. Field order on the wire has no part in signature computation. The signed bytes are the JCS serialisation specified in Section 7.4, which sorts member names in code-point order and is therefore blind to the order the TXT record used. 7.3. Field Definitions 7.3.1. v (REQUIRED) Protocol version identifier. MUST be the literal string alter1. MUST appear as the first field in the record. Resolvers MUST reject any record whose v field is absent, is not the first field, or contains a value other than alter1. The version namespace v=alter1 on _alter. is independent of the identically-named v=alter1 on _org-alter.. The two namespaces are disambiguated by the enclosing record label and MUST NOT be conflated. Future versions of either record may advance independently (e.g. _alter. may progress to v=alter2 while _org-alter. remains at v=alter1, or the reverse). Morrison Expires 12 April 2027 [Page 30] Internet-Draft MCP DNS Discovery October 2026 7.3.2. h (REQUIRED) The Sovereign-, Bot-, or Instrument-tier ~handle to which the envelope binds. The leading tilde is mandatory. Where a resolver encounters multiple envelope TXT RRs sharing an owner name, h= is the sole field it MAY use to disambiguate them. Publishers MUST NOT create that arrangement (Section 7.1); the rule is retained for resolvers only, so that a record published under revision 04 can still be read. An Instrument-tier handle has no envelope of its own (Section 2); a publisher SHOULD NOT publish an envelope whose h is an Instrument-tier handle. 7.3.3. pk (REQUIRED) An Ed25519 public key prefixed by its algorithm namespace and encoded in base64url without padding per [RFC4648] Section 5: pk=ed25519: Resolvers MUST reject records whose algorithm prefix is not ed25519 until a future revision registers additional algorithms. The pk value is the verification key for the detached signature in the sig field. 7.3.4. ilr (REQUIRED) Base64url-no-pad SHA-256 digest of an IdentityLog root that the publisher claims was witnessed at envelope creation. The field carries a root and nothing more, so it cannot establish that this envelope is recorded in that log, and a resolver MUST NOT rely on it to detect substitution. Section 10 states what it can and cannot establish, and Section 14.3 sets out the forgery it permits. 7.3.5. ts (REQUIRED) Envelope inception timestamp, expressed on the wire as decimal Unix seconds. Resolvers MAY use this field to detect clock skew, evaluate caveat maturity, or reject envelopes with implausibly future inception. In the signing input of Section 7.4 the value is carried as a JSON string of those same decimal digits, never as a JSON number. A resolver that re-types it as a number canonicalises different bytes and every signature fails against it. Morrison Expires 12 April 2027 [Page 31] Internet-Draft MCP DNS Discovery October 2026 7.3.6. rev (REQUIRED) Base64url-no-pad SHA-256 digest of the revocation pre-image. Revocation is effected by revealing the pre-image to the IdentityLog; upon reveal, the envelope is considered revoked and MUST NOT be honoured by resolvers. The rev field is a hash commitment: the pre- image is never published in DNS and is released only at revocation time to the log. Revocation takes effect at once and has no grace period. From the moment the pre-image is revealed, every claim signed under the envelope's pk is invalid, whenever it was signed, and a verifier MUST NOT honour a claim signed under the key of a revoked envelope. The epoch rotation of the _mcp record differs: a claim issued under an earlier epoch keeps the grace of its own expiry (Section 5.3.7), because rotation is routine and revocation signals compromise. Publishers MUST NOT treat removal of the TXT record as revocation. Absence of a record is indistinguishable from misconfiguration; only pre-image reveal is authoritative. 7.3.7. sig (REQUIRED) Base64url-no-pad detached signature over the JCS-canonicalised envelope JSON with the sig field absent. Canonicalisation is specified by [RFC8785]. The signing input is the envelope JSON reconstructed from the parsed TXT fields, plus a signature_alg member derived from the pk= algorithm prefix per the registry of Section 16.7, plus an EMPTY caveats array. The signature algorithm itself is the one named by the pk= prefix. The exact signing input is normative and appears in Section 7.4; it is not restated by reference elsewhere. 7.3.8. Unknown fields Fields not enumerated above MUST be ignored by resolvers per the forward-compatibility rule (Section 7.5), as the unknown-field rule of Section 7.2 provides. Future revisions of this document MAY define additional envelope fields, and MUST introduce a new field only together with a new envelope version registered under Section 16.3. This document defines no registry of envelope fields. 7.4. Canonical Serialisation The sig input is constructed as follows. This construction is normative and exhaustive. An implementation that deviates in a key name, a value type, or the membership of the object will produce bytes that no other implementation can verify. Morrison Expires 12 April 2027 [Page 32] Internet-Draft MCP DNS Discovery October 2026 1. Parse the TXT RR character-strings into key-value pairs. 2. Derive signature_alg from the algorithm prefix of the pk value via the Signature Algorithm Registry of Section 16.7. For pk=ed25519:... the derivation yields the string Ed25519. 3. Construct the envelope JSON object, whose members are exactly the six parsed fields that are not sig, plus the derived signature_alg, plus caveats: { "v": "", "h": "", "pk": "", "ilr": "", "ts": "", "rev": "", "caveats": [], "signature_alg": "" } The keys are the TXT field names, not expanded synonyms. Every value is a JSON string, ts included, which carries the decimal digits of the TXT field verbatim and is NOT converted to a JSON number. caveats is a JSON array and, for any envelope resolved from DNS under this document, it MUST be the EMPTY array. This document defines no caveat transport and no caveat vocabulary, so a non-empty array has no interoperable meaning and an implementation MUST NOT construct one. sig MUST be absent from the signing input, and no other member may be present. These rules make the signed bytes a total function of the TXT record. 4. Apply [RFC8785] JSON Canonicalisation Scheme to the object, which sorts the member names in code-point order. The member order shown above is illustrative and has no effect on the canonical bytes. 5. The resulting byte stream is the signing input for the algorithm named in step 2. Verification reverses this construction and checks the detached signature in the sig field against the derived byte stream. v is inside the signing input. A resolver that accepted an envelope whose version was unsigned could be walked down to a weaker version namespace by an on-path rewrite of the v field alone, so the version is signed with everything else. Morrison Expires 12 April 2027 [Page 33] Internet-Draft MCP DNS Discovery October 2026 Publishers MUST emit TXT fields in the order given in Section 7.2, but the DNS key=value ordering has no role in signature computation: the signed bytes are always the JCS serialisation of the JSON object. 7.5. Forward Compatibility Resolvers MUST ignore unknown fields in the _alter. record. This rule, identical to that of the _mcp and _org-alter records (Section 5.4, Section 6.4), ensures that future extensions do not break existing implementations. Publishers MUST NOT introduce new fields that repurpose or overload the seven required field names; a new field MUST use a new name, and is introduced only together with a new envelope version registered under Section 16.3 (Section 7.3.8). 7.6. Multi-String Reassembly Where the serialised envelope exceeds the 255-octet character-string limit of [RFC1035] Section 3.3.14, publishers SHOULD split at ; boundaries between complete key-value pairs where the pair fits. A publisher MAY split within a key-value pair, and MUST do so where a single pair exceeds 255 octets on its own, which any signature algorithm with a large signature will require. Resolvers MUST concatenate the character-strings of a TXT RR in the order returned by the DNS library (i.e. the RR wire order) BEFORE parsing, so the split point is not observable to the parser and carries no meaning. 8. DNSSEC Requirement The zone publishing an _alter. envelope record MUST be DNSSEC-signed per [RFC4033], [RFC4034], and [RFC4035]. Authoritative servers MUST respond with valid RRSIG coverage for the TXT RRset. Recursive resolvers handling queries for the envelope RRset MUST perform DNSSEC validation and MUST set the AD (Authenticated Data) bit on the response delivered to the stub client. Stub clients (MCP clients, alter-runtime daemons, onboarding wizards, recognition verifiers) consuming _alter. envelope records MUST reject any response that lacks a set AD bit or that fails local RRSIG verification when operating in validating-stub mode. A record obtained over an unvalidated DNS path MUST be treated as unauthenticated TXT content. Treating it as an envelope is a downgrade vulnerability (Section 14.1). This requirement is specific to _alter. records. DNSSEC is RECOMMENDED but not REQUIRED for _mcp. and _org- alter. records in this revision, for backward compatibility Morrison Expires 12 April 2027 [Page 34] Internet-Draft MCP DNS Discovery October 2026 with revision 01 and revision 02 deployments. Future revisions of this document MAY promote DNSSEC to REQUIRED for the other two records once deployment data justifies the promotion. 9. DANE TLSA Pin The MCP endpoint associated with a published envelope MUST carry a DANE TLSA resource record [RFC6698] binding the endpoint's leaf TLS certificate or SubjectPublicKeyInfo to the zone. The TLSA record MUST be published at: _443._tcp.mcp.. IN TLSA Recommended parameters: * *Usage field.* 3 (DANE-EE), pin the end-entity certificate directly, with no CA chain reliance. A publisher that explicitly requires CA-chain validation MAY use 1 (PKIX-EE) instead. Publishers MUST NOT use 0 (PKIX-TA) or 2 (DANE-TA) for the envelope record; the trust basis of the envelope is the end-entity leaf. * *Selector field.* 1 (SPKI), pin the SubjectPublicKeyInfo so that certificate rotations preserving the keypair do not invalidate the record. Selector 0 (full certificate) MAY be used but requires more frequent TLSA republication. * *Matching-type field.* 1 (SHA-256). Matching type 2 (SHA-512) is reserved for future revisions. Clients establishing an MCP session at https://mcp./ in conjunction with a resolved envelope MUST fetch and validate the TLSA record, MUST abort the TLS handshake on mismatch, and MUST NOT fall back to PKIX-only validation on TLSA failure. The TLSA requirement is scoped to envelopes whose MCP session establishment is triggered by the resolved envelope (i.e. when the envelope resolution and the subsequent MCP session are part of a single recognition transaction). MCP clients that do not resolve an envelope (e.g. revision 01 clients consuming only _mcp.) are out of scope for this requirement and continue to operate under revision 01 rules. Morrison Expires 12 April 2027 [Page 35] Internet-Draft MCP DNS Discovery October 2026 10. IdentityLog Cross-Reference The ilr= field of the _alter. record carries a base64url-no- pad SHA-256 digest of an IdentityLog root claimed by the publisher to have been witnessed at envelope creation. What ilr= can and cannot establish: * A resolver that has an independent view of the log MAY confirm that the root named in ilr= is one the log actually published. * A resolver MUST NOT conclude from ilr= that the envelope in front of it is recorded in that log. The field carries a root and nothing else. It carries no leaf hash, no audit path, and no proof of inclusion, so no resolver can perform that check, and Section 14.3 sets out the forgery this permits. * A resolver MUST NOT treat the presence, absence, or successful lookup of ilr= as a defence against envelope substitution. The field is advisory. It is kept so that the wire format does not change. The log's leaf hashing, tree construction, cadence, and witness protocol are not specified by this document, and a reader should not assume a specification exists. The revocation check also crosses the IdentityLog. Where a resolver has access to the log's revocation surface, it MUST treat the envelope as revoked, and MUST NOT honour it regardless of the freshness of the TXT RRset, if a pre-image whose SHA-256 equals the rev= field has been revealed there. A reader implementing from this document alone has no such access. The surface that carries reveals is not specified here and is not published anywhere a reader can fetch, so revocation status cannot presently be established from DNS alone. 11. alter: URI Scheme Cross-Reference The URI scheme alter: provides a dispatchable surface for ~handle references: operating-system URI handlers (xdg-mime, LSHandlers, Windows registry, Android intent-filter) invoke a resolver that retrieves the envelope from DNS and verifies it per Section 12.3. The scheme is specified in [ALTER-URI]. The registration sought is provisional, per [RFC7595] Section 4, under the procedure of [RFC7595] Section 7.2. The full registration body, scheme syntax, Morrison Expires 12 April 2027 [Page 36] Internet-Draft MCP DNS Discovery October 2026 semantics, encoding considerations, interoperability and security considerations, author and change controller, is submitted to IANA separately from this document. The registration reference will be substituted when IANA assigns one. Handlers invoked via alter: URIs MUST perform full envelope verification, DNSSEC validation (Section 8), and DANE TLSA binding (Section 9) when establishing any HTTPS session, before acting on any content or directive derived from the envelope. 12. Discovery and Bootstrap Procedures The formats these procedures consume are given in full in Section 5, Section 6 and Section 7. 12.1. Discovery Procedure: _mcp. This is the algorithm an MCP client follows to discover an MCP server associated with a given domain. It is the algorithm of [DNSDISC-01], restated here in full. Revision 05 added the reading rule at step 7c, and revision 06 extended step 7b to apply Section 13.1. Every other step is unchanged. 12.1.1. Input The procedure takes a single input, an Origin Domain. The Origin Domain is typically extracted from an identifier encountered during agent operation, such as an email address (user@example.com yields example.com), a URL (https://example.com/path yields example.com), a handle (~user@example.com yields example.com), or a bare domain. 12.1.2. Algorithm 1. *Normalise.* Convert the Origin Domain to its canonical form: lowercase per [RFC4343], and apply IDNA2008 processing where the domain contains non-ASCII labels. 2. *Construct query name.* Prepend the label _mcp. to the normalised Origin Domain, yielding _mcp... 3. *Query DNS.* Issue a DNS query for _mcp.. IN TXT via the client's configured recursive resolver. Clients SHOULD prefer DoH ([RFC8484]) or DoT ([RFC7858]) to protect query privacy (Section 15.2). 4. *Handle the DNS response.* a. On NOERROR with one or more TXT records, proceed to step 5. Morrison Expires 12 April 2027 [Page 37] Internet-Draft MCP DNS Discovery October 2026 b. On NXDOMAIN, or NOERROR with zero TXT records, proceed to step 8 (HTTPS fallback). c. On SERVFAIL or timeout, the client MAY retry with exponential backoff, or proceed to step 8. 5. *Parse records.* For each TXT RDATA in the response: a. Concatenate all character-strings within the RDATA. b. Split the concatenated string on the ";" delimiter, trimming leading and trailing whitespace from each field. c. Verify that the first field is v=mcp1. If it is not, discard this record. d. Extract all recognised fields. Ignore unknown fields, per the forward-compatibility rule of Section 5.4. e. Verify that the url field is present and carries a syntactically valid HTTPS URL. If it does not, discard this record. 6. *Sort by priority.* Collect all valid records and sort them by priority in ascending order, lowest value first. Records of equal priority MAY be tried in any order. 7. *Connect.* For each record in priority order: a. Establish a TLS connection to the host named in the url field. b. Where the client holds a pinned key binding for the Origin Domain, apply Section 13.1 first, and verify the endpoint against the pinned key whether or not the record carries a pk field. Otherwise, where the record carries a pk field, verify the key per Section 5.3.6. On failure, skip to the next record. c. Determine the transport by applying the reading rule of Section 5.3.5 to the record's transport and proto fields. Where that rule directs the client to SKIP the record, skip it and proceed to the next record by priority. Otherwise, initiate the MCP session over the transport the rule yields. d. If the MCP initialize handshake succeeds, discovery is complete. Morrison Expires 12 April 2027 [Page 38] Internet-Draft MCP DNS Discovery October 2026 e. If connection or handshake fails, proceed to the next record. If all records are exhausted, proceed to step 8. 8. *HTTPS fallback.* Attempt HTTPS-based discovery by fetching https:///.well-known/mcp/server-card.json per [SEP-1649], or https:///.well-known/mcp per [SEP-1960]. If fallback succeeds, proceed with the MCP session. If fallback fails, discovery has failed. This procedure does not consume the _alter. record and imposes no DNSSEC requirement. A client that resolves an envelope executes Section 12.3 instead, which does. 12.2. Identity Bootstrap Procedure: _org-alter. This is the procedure by which an org-alter implementation reads its own DNS records on first install to populate its canonical identity state. It is the algorithm of [DNSDISC-02], unchanged, restated here in full. 12.2.1. Input The procedure takes a single input, the operator's primary domain name, being the Policy Domain under which the operator publishes records. 12.2.2. Algorithm 1. *Query _org-alter. TXT.* Issue a DNS query for the Org- Identity Record. 2. *If found, parse and load.* Extract org, entity, entity-type, founded, regions, regulated, and mcp-policy into the org-alter's identity state. These become the canonical identity declaration the org-alter uses in all subsequent self-description and external attestation. 3. *If bootstrap= is present, fetch the bootstrap document* over HTTPS. Validate the document's TLS certificate against the Policy Domain. Merge the document's roster, logo, and extension fields into the identity state. Reject the bootstrap document if its TLS certificate is invalid, or if its content does not parse. 4. *Honour regulated= and mcp-policy=* as immutable structural constraints on the org-alter instance. Morrison Expires 12 April 2027 [Page 39] Internet-Draft MCP DNS Discovery October 2026 a. If regulated carries any framework token, set the org-alter's boundary policy to refuse, and disable every automated data ingestion. b. If mcp-policy=refuse-tenant, the org-alter MUST refuse to install any ingester that requires authenticated access to a tenant covered by the declared framework, even where credentials are subsequently provided. c. The wizard SHOULD display these constraints to the operator for confirmation, and MUST NOT allow the operator to override them silently. An operator who wishes to relax a constraint MUST update the DNS record first, then re-run bootstrap. 5. *Cross-check _mcp..* Query the service-discovery record of Section 5. Where both records exist and both publish a pk field, the values MUST match. A mismatch indicates either a configuration error or a key compromise; the wizard MUST refuse to bootstrap under that condition, and MUST surface the discrepancy to the operator. Section 14.6 states how this rule relates to the envelope key of Section 7, which is a distinct key and is not subject to it. 6. *Verify against public registries.* Where the entity field declares a known registry namespace (for example abn:), the wizard SHOULD query the corresponding free public registry and verify that the declared entity identifier resolves to the declared org name. A mismatch is not necessarily fatal, because names change and registries lag, but the wizard MUST surface the discrepancy and MUST require operator confirmation before proceeding. 7. *Persist canonical state.* Write the resolved identity into the org-alter's local identity state, source-citing each field to its DNS or HTTPS origin. 12.2.3. First-Run Cold Start For an operator who has not yet published an _org-alter record at the time of installation, the wizard MUST fall back to interactive seeding. It prompts for org, optionally prompts for entity, and asks whether the operator's environment is regulated. After interactive seeding, the wizard SHOULD generate a draft DNS record value for the operator to publish, which completes the bootstrap loop. Morrison Expires 12 April 2027 [Page 40] Internet-Draft MCP DNS Discovery October 2026 12.3. Envelope Recognition Procedure: _alter. The procedure takes two inputs, a zone and the ~handle to be recognised, and both are REQUIRED. An alter: URI [ALTER-URI] supplies the handle. The zone is never derived from the spelling of the handle. It is supplied by the caller, or taken as Section 3.4 of [ALTER-URI] specifies. A resolver that has only a zone, and no handle, cannot execute this procedure. Step 4 selects the record whose h= matches the requested handle, and with no requested handle there is nothing to match against. Such a resolver has not been asked a recognition question, and MUST NOT treat whatever record it finds at the owner name as the answer to one. Given those two inputs, a resolver MUST execute the following steps in order. Steps 1 through 8 and step 10 are FATAL: failure of any of them terminates recognition, and the envelope MUST be treated as unverified. Steps 9, 11 and 12 are ADVISORY: being UNABLE to perform them MUST NOT terminate recognition, because a resolver that cannot reach a surface has learned nothing either way. A POSITIVE finding is different. A revocation observed at step 12 is FATAL and MUST abort (Section 10). 1. *Query.* Issue a DNS TXT query for _alter... Use DoH or DoT in preference to UDP/53 where operationally feasible. 2. *DNSSEC validation.* Validate the RRSIG chain from the root trust anchor to the TXT RRset (Section 8). Confirm the AD bit on the response when relying on an upstream validating resolver, or locally RRSIG-validate in validating-stub mode. On failure, abort. 3. *Chunk reassembly.* Concatenate character-strings in RR order; parse ;-separated key-value pairs. 4. *Handle disambiguation.* Select the record whose h= field matches the requested ~handle. If no record matches, abort. 5. *Field extraction.* Confirm presence of the seven required fields (v, h, pk, ilr, ts, rev, sig). Reject any record missing any required field, or whose v is not alter1. 6. *Envelope reconstruction.* Build the envelope JSON exactly as Section 7.4 specifies, deriving signature_alg from the pk= prefix and supplying an empty caveats array. 7. *JCS canonicalisation.* Apply [RFC8785] JCS to the envelope with the sig field absent. Morrison Expires 12 April 2027 [Page 41] Internet-Draft MCP DNS Discovery October 2026 8. *Ed25519 verification.* Verify the detached sig over the JCS byte stream using the public key in pk. On failure, abort. 9. *IdentityLog cross-reference (ADVISORY).* A resolver with an independent view of the log MAY confirm that the root named in ilr= is one the log published. A resolver MUST NOT abort on failure, and MUST NOT treat success as evidence that this envelope is in the log, because ilr= carries no proof of inclusion (Section 10; Section 14.3). 10. *DANE TLSA validation.* When establishing an MCP session at mcp. as part of the same recognition transaction, fetch the TLSA record at _443._tcp.mcp.. and gate the TLS handshake on the binding (Section 9). On mismatch, abort. 11. *Caveats evaluation (OUT OF SCOPE for this document).* The envelope schema admits an optional caveats array, which is never carried in DNS. This document specifies neither a transport for it nor a vocabulary, so a resolver implementing this document alone MUST treat the envelope as having no caveats, and MUST verify the signature over an empty caveats array per Section 7.4. A future document may define a caveats surface, and until one does, an envelope whose signer intended caveats cannot be distinguished from one that carries none. 12. *Revocation check (ADVISORY).* Where the resolver has access to the log's revocation surface, consult it. Being UNABLE to perform this step MUST NOT terminate recognition, and Section 10 says why a resolver implementing this document alone cannot. If a pre-image whose SHA-256 equals rev= has been revealed, the envelope IS revoked, recognition MUST abort, and the envelope MUST NOT be honoured however fresh the TXT RRset. The revocation is immediate, and every claim signed under the envelope's key is invalid from that moment, whenever it was signed (Section 7.3.6). An envelope is verified when every FATAL step (1 through 8, and 10) has succeeded AND no ADVISORY step has returned a positive failure. A resolver that CANNOT reach a revocation surface proceeds, while a resolver that OBSERVES a revocation MUST abort and MUST NOT treat the envelope as verified. An unverified envelope MUST be refused upstream of any authorisation or trust decision. Morrison Expires 12 April 2027 [Page 42] Internet-Draft MCP DNS Discovery October 2026 13. Caching The rules for the first two records are those of [DNSDISC-01] and [DNSDISC-02], unchanged, with the key continuity rule of Section 13.1 added in revision 06, restated here so that a reader need not fetch either document to cache correctly. For _mcp., clients SHOULD cache the parsed record metadata for the duration of the DNS TTL. Where the record carries a ttl field, clients MAY extend the metadata cache to that duration, but MUST re-validate the underlying DNS record when the DNS TTL expires. A client that has connected to an MCP server and verified its pk SHOULD cache the verified key binding and re-validate it on subsequent connections, which is trust on first use with periodic re- verification against DNS. What the client does when that re- verification disagrees with what it cached is stated in Section 13.1. For _org-alter., records SHOULD be cached for the duration of the DNS TTL. An onboarding wizard typically reads the record once at install time and persists the resolved state locally, so the DNS record need not be re-read on every invocation. Wizards MAY re-read it on operator request, on epoch change detected by a periodic background poll, or on identity verification failure. _alter. records SHOULD be cached for the duration of the DNS TTL. Resolvers MUST NOT serve stale envelope TXT past the RRset TTL unless they are themselves validating caches and can re-confirm RRSIG coverage on each serve. Recognition verifiers MAY cache successful verification results locally for a short interval (bounded above by the RRset TTL or 3600 seconds, whichever is smaller) to amortise the cost of repeated JCS and Ed25519 operations. A resolver that is able to perform the revocation check at all (Section 10 sets out why one working from this document alone is not) MUST re-run it on each recognition event, not on each cache refresh. 13.1. Key Continuity This section states what a client does when re-validation of a cached key binding fails. The mechanism is the one SSH clients apply to host keys. A pinned key binding is the triple a client holds after a successful verification under Section 5.3.6: the Origin Domain, the pk it verified, and the epoch the record carried at the time, defaulting to 0 where the record carried none. On each later resolution of _mcp. for which it holds a pin, the client compares the record it receives with the pin, and the following rules apply in order. Morrison Expires 12 April 2027 [Page 43] Internet-Draft MCP DNS Discovery October 2026 1. *Same key, same epoch.* Continuity holds. The client proceeds under Section 12.1. 2. *Epoch lower than the pinned epoch.* The epoch is monotonic (Section 5.3.7), so a decrease is never a state a conformant publisher produces. It indicates a stale or manipulated response, a publisher restoring an old record, or a new operator of the domain that began its own count at 0. The client MUST NOT lower its pinned epoch, and MUST NOT replace its pinned key on the strength of this record. It SHOULD re-query, bypassing any local cache it controls. Where the served key equals the pinned key, the client MAY proceed, and MUST evaluate the kid of any claim against its pinned epoch rather than the lower served one. Where the served key differs, the client MUST treat the server as untrusted, exactly as a failed verification under Section 5.3.6, and SHOULD surface the discrepancy. 3. *Different key, same epoch.* The record's own contract is that the epoch increments on every key rotation, so a key that changes without it is an undeclared change. The client MUST treat the server as untrusted, MUST NOT replace its pin, and SHOULD surface the discrepancy. 4. *Different key, higher epoch.* This is a declared rotation. The client MUST verify the new key per Section 5.3.6 before replacing its pin, and on success MAY replace the pinned key and epoch. A declared rotation is also what a new operator of a lapsed and re- registered domain can publish, because the epoch is self-asserted by whoever controls the zone. A client with access to registration data SHOULD therefore apply the change-of-control signals of Section 13.1.2 before it replaces the pin. 5. *Same key, higher epoch.* The client MAY raise its pinned epoch. Claims under the lower epoch are then handled per Section 5.3.7. 6. *No key.* A record that carried a pk when the pin was made and now carries none has not released the pin. The client MUST continue to verify the endpoint against the pinned key, as step 7b of Section 12.1.2 requires. Removing the field is not a way to rotate a key. A pinned key MUST NOT be replaced automatically under rules 2, 3 or 6. It MAY be replaced by an action of the client's user or operator, taken outside this procedure and after the discrepancy has been surfaced to them. Morrison Expires 12 April 2027 [Page 44] Internet-Draft MCP DNS Discovery October 2026 13.1.1. Absence Is Not Revocation A client that holds a pin and finds no _mcp record, on NXDOMAIN or on NOERROR with no TXT records, proceeds to the HTTPS fallback of step 8 of Section 12.1.2. It MUST NOT clear the pin, and MUST NOT treat the absence as revocation of the binding or of any claim issued under it. A client that reaches an endpoint for the same Origin Domain by fallback SHOULD verify it against the pinned key. This is the position Section 14.4 takes for the envelope record, for the same reason. A zone that is briefly unreachable, through an outage, a registrar incident or a tooling error, must not become a revocation event. A second reason applies to pins alone. If absence cleared a pin, an attacker able to suppress the record for a single resolution would reset the client to first use, and could then publish its own key and have it accepted as though no pin had ever existed. This differs from [DOMAIN-SET], which holds in its Section 6.4 that removal of a record is revocation. The two records do different jobs. A domain-set record is an attestation its publisher withdraws by deleting it. An _mcp record is a pointer to an endpoint, and a key binding is revoked by rotation, under rule 4 above, never by the record going away. 13.1.2. Change-of-Control Signals The epoch cannot distinguish a rotation by the existing operator from a rotation by a new one, because both publish a higher epoch and a new key. Registration data can, in part. [DOMAIN-SET] Section 6.3 gives consumer rules for this case, graded by the strength of the signal, and this document adopts them for the pinned key binding. A client with access to registration data for the Origin Domain, for example through RDAP [RFC9083], SHOULD consume those signals in the order given there, and act on them as follows. 1. *Creation date changed.* The registry object was deleted and the name registered again, and renewal or restoration never changes it. The domain is now operated by a party the pin says nothing about. The client MUST discard the pin, MUST NOT carry the pinned binding, or any trust its user or operator attached to it, forward to whatever key the record now serves, and SHOULD surface the change. A binding made after that point is a first use, and MUST NOT be presented as a continuation of the earlier one. 2. *Lapse indicators.* A registry grace status, or an expiry earlier than the observation, means the registration lapsed. Control may have passed without deletion, because names sold on in expiry Morrison Expires 12 April 2027 [Page 45] Internet-Draft MCP DNS Discovery October 2026 auctions keep their creation date. A declared rotation under rule 4 observed while a lapse indicator is present MUST NOT replace the pin automatically, and SHOULD be surfaced for the action of the user or operator described above. 3. *Transfer indicators.* A transfer event, or a change of sponsoring registrar, SHOULD be surfaced as a warning. It does not by itself block a declared rotation. A change of control that leaves no trace in registration data, such as a sale inside one registrar with no lapse, followed by a declared rotation, is not detectable by a client following this document. [DOMAIN-SET] states the same limit for its own records. 14. Security Considerations The security considerations of [DNSDISC-01] Section 7 apply to the _mcp record, and those of [DNSDISC-02] Section 10 apply to the _org- alter record. The subsections below cover the _alter envelope record and the rules this document adds to the other two records. 14.1. DNSSEC Downgrade The mandatory DNSSEC requirement in Section 8 is the primary defence against on-path manipulation of envelope TXT content. An attacker who can inject unsigned responses, e.g. via a compromised resolver or a DNS middlebox that strips RRSIG, would otherwise be able to substitute an attacker-controlled envelope at the resolver boundary. Stub clients MUST reject any response lacking AD or failing local RRSIG verification. Operators MUST NOT downgrade the _alter. RRset to unsigned during KSK/ZSK rollover (see [RFC6781] for best-current practice on rollover). 14.2. TLSA Pin Rotation The DANE TLSA requirement in Section 9 binds the MCP endpoint's TLS leaf to a specific hash. Operators rotating certificates MUST publish the new TLSA record before the new certificate is activated on the live listener, with a grace window of at least twice the TLSA RRset TTL. Selector 1 (SPKI) survives rotations that preserve the keypair; selector 0 requires republication on every rotation. Loss of the TLS private key forces certificate reissue and republication of the TLSA record, not silent cert replacement. It does not engage the rev= reveal path, which revokes the identity envelope and has no bearing on a TLS leaf. Morrison Expires 12 April 2027 [Page 46] Internet-Draft MCP DNS Discovery October 2026 14.3. Envelope Substitution An attacker in control of a domain's DNS can publish an arbitrary envelope for any ~handle claimed to be hosted under that zone. The structural defences, and the limit of each, are: 1. *IdentityLog witness. This defence does not hold as specified.* ilr= carries a bare tree root and no proof of anything, so a resolver can confirm that the named root was witnessed but CANNOT confirm that the envelope in front of it is a leaf under that root, and no field of Section 7.2 would let it. A zone attacker therefore mints an envelope, copies any witnessed root out of the public log, signs, and publishes. The result satisfies every check the recognition procedure of Section 12.3 specifies. As specified, ilr= establishes only that the publisher could read a public value. Implementers MUST NOT rely on ilr= to detect substitution. 2. *Ed25519 signature.* The detached signature binds the envelope to a specific Ed25519 key. An attacker who does not hold the private key cannot forge a valid sig. An attacker who does hold the private key has already compromised the handle; the revocation path (Section 10) is the residual mitigation. 3. *DNSSEC.* Section 8 prevents tampering with the TXT RRset in transit, which prevents third-party substitution. It does not prevent a malicious zone operator from publishing a malicious envelope. Defence (1) does not hold against that attack, and defence (2) holds only where the operator does not hold the private key. 14.4. Revocation Opacity Revocation is effected by revealing the pre-image to the IdentityLog, not by removing the TXT record. Absence of a record is indistinguishable from misconfiguration; resolvers MUST NOT treat absence as revocation. A zone briefly unreachable (DNS outage, registrar incident, tooling error) must not accidentally become a revocation event. Section 13.1.1 applies the same position to a pinned _mcp key binding, and says why it differs from [DOMAIN-SET]. The cost is that a compromised zone may continue to serve a valid (but intended-to-be-revoked) envelope until the rightful handle- holder reveals the pre-image. This document does not specify where a reveal is published, and Section 10 says why no such surface can be assumed, so revocation is not presently actionable by a resolver working from this document alone. Handle-holders SHOULD establish a pre-committed revocation reveal procedure at mint time. Morrison Expires 12 April 2027 [Page 47] Internet-Draft MCP DNS Discovery October 2026 14.5. Clock Skew and ts= The ts= inception timestamp is advisory: resolvers MAY use it to detect implausibly future envelopes (e.g. minted more than a few hundred seconds after current wall time) but MUST NOT rely on local clock for security-critical decisions. This document specifies no authoritative ordering anchor. ts= is self-asserted by the publisher and is advisory only. 14.6. Cross-Record Key Consistency Where all three records (_mcp, _org-alter, _alter) are published under one zone and each carries a pk field, the values MUST be evaluated for consistency. Two different rules apply. The _mcp.pk and _org-alter.pk fields are the service key and the organisational key. Step 5 of Section 12.2, restated from [DNSDISC-02], requires them to MATCH where both are published, and requires a bootstrapping wizard to refuse and to surface the discrepancy where they do not. That rule is unchanged. A mismatch across that pair indicates a configuration error or a key compromise. The _alter.pk field is the envelope key. It is a structurally distinct key with a distinct purpose, it is NOT subject to the bootstrap match rule, and it MAY differ from both of the others. A resolver MUST NOT treat a difference between _alter.pk and either of the other two as evidence of anything. Where a zone operator has bound all three to one Ed25519 key, as a single-operator deployment may do, a later mismatch indicates either a rotation in progress or a compromise, and resolvers SHOULD surface it. A resolver cannot distinguish that deployment from one that intended three distinct keys, because this document publishes no signal of the operator's intent, so the surfacing is advisory and MUST NOT be fatal. 14.7. Passive-Stream Coupling A publisher SHOULD NOT ride an inferred trait, a passive-stream derivative, or a provenance-tagged attribute on the _alter. record. This is a recommendation, and nothing in the grammar enforces it. The ABNF of Section 7.2 admits unknown-field = token "=" *qtext, which admits arbitrary attributes, and Section 7.5 requires resolvers to IGNORE unknown fields rather than reject the record. The qtext rule bounds only the field DELIMITER, so that an unknown field cannot swallow the semicolon and consume the fields after it. It bounds Morrison Expires 12 April 2027 [Page 48] Internet-Draft MCP DNS Discovery October 2026 nothing about the field's meaning. Nothing in this document structurally prevents a publisher from riding additional attributes on this owner name, and a resolver MUST NOT infer from a record's conformance that it carries nothing else. Two consequences follow. An unknown-field is NOT covered by the signing input of Section 7.4, which spans the six required fields other than sig, plus the derived signature_alg and an empty caveats array, and nothing else. Any attribute riding the record is therefore UNSIGNED, and a resolver MUST NOT attribute it to the handle-holder. And because a resolver ignores what it does not recognise, the record is a viable carrier for data the envelope was never meant to convey. The privacy implications of passive inference are out of scope for this document. 14.8. Change of Control Every record this document defines names its subject by a domain, and a domain can change hands. When a registration lapses and the name is registered again, the new registrant controls the zone and can publish any of the three records. Nothing in the records changes shape when that happens, and no single resolution can tell the new operator from the old one. For the _mcp record, Section 13.1 is the defence. A client that pinned the prior operator's key refuses an undeclared key change and an epoch that goes down, keeps its pin when the record disappears, and, where it can read registration data, discards the pin on a changed creation date rather than carrying it to the new operator. A client that has never connected before has no pin, and for that client a re-registered domain is indistinguishable from any other first use. For the _alter record, the limit stated in Section 14.3 applies without change. The envelope carries no epoch, and this document specifies no pin for it. A new registrant can mint an envelope for a handle under a key of its own and satisfy every FATAL step of Section 12.3. A resolver that has previously verified an envelope for the same handle, and now finds a different pk, SHOULD surface the change. It learns nothing further from this document about which of the two keys the handle-holder controls. 15. Privacy Considerations The privacy considerations of [DNSDISC-01] Section 8 apply to the _mcp record, and those of [DNSDISC-02] Section 11 apply to the _org- alter record. The subsections below cover the _alter envelope record. Morrison Expires 12 April 2027 [Page 49] Internet-Draft MCP DNS Discovery October 2026 15.1. Public Handle Disclosure Publishing _alter. exposes the bound ~handle, its Ed25519 public key, its IdentityLog root, its inception timestamp, and its revocation-hash commitment to any DNS observer. Public verifiability does not require public enumeration, and Section 7.1.1 sets out why DNS publication brings both. A handle-holder who requires concealment MUST NOT publish an _alter. record. Means of recognition that do not publish in DNS are outside the scope of this document. 15.2. DNS Query Metadata A resolver querying _alter.example.com reveals to its recursive resolver that it intends to verify the envelope hosted under that zone. Query metadata privacy is addressed at the transport layer: clients SHOULD prefer DoH ([RFC8484]) or DoT ([RFC7858]) over UDP/53 where operationally feasible. This consideration is the same as in revisions 01 and 02, and matters more here because the envelope names an individual. 15.3. Revocation Unlinkability The rev= field is the SHA-256 of a secret pre-image; publishing it does not disclose the pre-image. An observer cannot predict the pre- image or link it back to any identifier. Reveal at revocation time links the pre-image to the envelope, but only at the moment of revocation, not during the envelope's active lifetime. 16. IANA Considerations 16.1. Underscored DNS Node Name Registration This document requests IANA to update the entries in the "Underscored and Globally Scoped DNS Node Names" registry established by [RFC8552] as follows. Each label is defined by this document, in the section named, and no longer by an earlier revision of it. Morrison Expires 12 April 2027 [Page 50] Internet-Draft MCP DNS Discovery October 2026 +=========+============+============================+ | RR Type | _NODE NAME | Reference | +=========+============+============================+ | TXT | _mcp | Section 5 of this document | +---------+------------+----------------------------+ | TXT | _org-alter | Section 6 of this document | +---------+------------+----------------------------+ | TXT | _alter | Section 7 of this document | +---------+------------+----------------------------+ Table 1 The _alter label is used to publish envelope records as defined in Section 7 of this document. 16.2. alter: URI Scheme Registration This document cross-references the provisional registration of alter: per [RFC7595] Section 4, which IANA made on 5 October 2026. The registration template is carried in [ALTER-URI]. This document notes that recognition verifiers invoked via alter: URIs MUST follow Section 12.3 of this document for envelope verification. 16.3. Envelope Version Registry This document defines the version tag v=alter1 for the _alter. record, independent of the identically-named tag on the _org-alter. record. Future versions (v=alter2 and beyond) SHOULD be coordinated with implementers and documented in successor revisions of this draft. Until a working group takes up identity-envelope DNS publication, the author maintains the version namespace. A new envelope version is the only way a new envelope field is introduced (Section 7.3.8). 16.4. Org-Alter Version Registry (unchanged from revision 02) The version tag v=alter1 for the _org-alter. record is preserved from revision 02. No changes are requested in this revision. 16.5. Registry Namespace Registry (unchanged from revision 02) The initial set of entity field registry namespaces (abn, acn, ein, ch, cro, lei) defined in revision 02 is preserved unchanged. Morrison Expires 12 April 2027 [Page 51] Internet-Draft MCP DNS Discovery October 2026 16.6. Framework Token Registry (unchanged from revision 02) The initial set of regulated framework tokens (disp, itar, ear, hipaa, gdpr, soc2, iso27001, iso42001, essential8, aprs) defined in revision 02 is preserved unchanged. 16.7. Signature Algorithm Registry This document defines the initial pk= and sig= algorithm namespace ed25519 for the _alter. record. Future algorithms (e.g. ed448, ml-dsa-65) MAY be registered by successor documents. Resolvers MUST reject records whose algorithm prefix is not registered at the resolver's protocol version. 17. Examples This section provides non-normative examples of Envelope Records for common deployment scenarios. 17.1. Minimal Envelope for a Single Handle (NOT RECOMMENDED) A zone hosting a single Sovereign-tier handle publishes its envelope at _alter..: _alter.example.com. 3600 IN TXT ( "v=alter1; h=~alice; " "pk=ed25519:; " "ilr=; " "ts=1729123456; " "rev=; " "sig=" ) All base64url values in this example are illustrative. Production values are the Ed25519 public key, SHA-256 digests, and 64-byte detached signature encoded per [RFC4648] Section 5 without padding. 17.2. Zone Hosting Multiple Handles (a publisher MUST NOT do this) This example is retained so that a resolver can read the records a revision 04 publisher may already have published. It is NOT a pattern to follow. The shape below IS the enumeration exposure described in the Applicability statement. One query at the owner name returns every handle the zone hosts, and none of the individuals listed can consent on behalf of the others. A publisher MUST NOT create it (Section 7.1). Resolvers disambiguate by the h= field: Morrison Expires 12 April 2027 [Page 52] Internet-Draft MCP DNS Discovery October 2026 _alter.example.org. 3600 IN TXT "v=alter1; h=~alice; pk=..." _alter.example.org. 3600 IN TXT "v=alter1; h=~bob; pk=..." _alter.example.org. 3600 IN TXT "v=alter1; h=~carol.bot; pk=..." A resolver asked to verify ~bob at example.org selects the second RR. 17.3. Full Zone (All Three Records; the _alter record is NOT RECOMMENDED) A zone operator running an org-alter instance for their own principal handle publishes all three records: _mcp.example.com. IN TXT "v=mcp1; url=https://mcp.example.com/" _org-alter.example.com. IN TXT "v=alter1; org=Example Org; ..." _alter.example.com. IN TXT "v=alter1; h=~alice; " "pk=ed25519:...; ilr=...; " "ts=...; rev=...; sig=..." _443._tcp.mcp.example.com. IN TLSA 3 1 1 Together these expose: the MCP service endpoint and its capabilities (_mcp); the legal entity, regulatory posture, and jurisdictional regions (_org-alter); the Sovereign-tier envelope for ~alice (_alter); and the DANE TLSA pin on the MCP endpoint. A resolver may consume any subset according to its recognition requirement. 18. Interoperability with Earlier Record Generations A domain that publishes only an _mcp. record published under revision 01 continues to work with all revision 01, 02, and 03 clients. Where that record carries a transport value in proto, a client conforming to this revision reads it under steps A and B of Section 5.3.5 and reaches the same endpoint over the same transport. No republication is required for the record to keep working, and none is required for a record carrying a proto value that no revision recognised, because such a record was skipped by revision 01 clients and is skipped by these. A domain that publishes _mcp. and _org-alter. (revision 02) continues to work with revision 02 clients and with clients conforming to this document, unchanged. A client conforming to this document may additionally query _alter. and MUST handle its absence gracefully, which is the common case and the recommended one: publication of that record is NOT RECOMMENDED (Section 7.1.1), so a conforming client should expect to find it absent and MUST NOT treat its absence as an error. Morrison Expires 12 April 2027 [Page 53] Internet-Draft MCP DNS Discovery October 2026 A domain that publishes only _alter. (envelope-only, no MCP server, no organisational record) is permitted by the grammar. The configuration is NOT RECOMMENDED per Section 7.1.1. The three records are orthogonal along their semantic axes but share the zone's DNSSEC trust root. A resolver conforming to this document that resolves any subset of the three records treats each resolution as independent and does not fail the resolution of one record because another is absent or malformed. 19. Implementation Status This section records the status of known implementations at the time of publication, per [RFC7942]. Deployed and resolvable in the truealter.com zone: * _mcp.truealter.com, carrying v=mcp1 with url, proto, pk, epoch, and cap. This is the only record in the zone that a resolver can verify against this document today. * _alter.truealter.com, carrying v=alter1. It does not carry the envelope field set (h, ilr, ts, rev, sig) and is therefore NOT an instance of the Envelope Record of Section 7. No conformant Envelope Record is published in this zone. * _org-alter.truealter.com, carrying v=alter1 with org, entity, entity-type, founded, regions, mcp-policy, epoch, pk, and attest. It omits regulated and bootstrap. Its pk is the same key the _mcp record carries, as step 5 of Section 12.2.2 requires. The zone is DNSSEC-signed, so the requirement of Section 8 is met by the operator. truealter.com publishes a key-signing key and a zone- signing key, both algorithm 13, and the parent zone holds a corresponding DS record. Implemented in code, and NOT exercised against any conformant envelope, because none is published: * A resolver and verification library implementing the JCS signing- input construction of Section 7.4 and the Ed25519 signature check. It conforms to this revision on the signing input and the signature check. It does NOT conform on two steps of the recognition procedure of Section 12.3: it still treats the IdentityLog cross-reference as fatal, where step 9 now says a resolver MUST NOT abort, and it still fetches caveats over HTTPS, which step 11 now places out of scope. Those two steps follow revision 04. It also does not yet perform the revocation check of Morrison Expires 12 April 2027 [Page 54] Internet-Draft MCP DNS Discovery October 2026 step 12, so it does not refuse a claim signed under a revoked key, and it does not check the h field against the grammar of Section 7.3.2. NOT deployed: * _443._tcp.mcp.truealter.com does not resolve, so no DANE TLSA pin is published and the DANE binding of Section 9 is untested in deployment. * There is no signed-tree-head federation and no witness-mirror network. * No inclusion proof is generated or checked anywhere. The ilr field of Section 7.2 is published as a bare root with no proof attached. Section 14.3 sets out what that permits. The Envelope Record of Section 7 therefore has NO conformant deployment at the time of writing, in this zone or any other known to the author. It is specified, implemented in a verifier, and unpublished. The deployed _alter.truealter.com record carries none of the envelope fields that Section 7 defines, so it is not an instance of the Envelope Record and a resolver MUST NOT treat it as one. The key continuity rule of Section 13.1 is new in revision 06. No implementation of it is claimed. 20. Normative References [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, . Morrison Expires 12 April 2027 [Page 55] Internet-Draft MCP DNS Discovery October 2026 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005, . [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, . [RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case Insensitivity Clarification", RFC 4343, DOI 10.17487/RFC4343, January 2006, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August 2012, . [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1", RFC 7208, DOI 10.17487/RFC7208, April 2014, . [RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines and Registration Procedures for URI Schemes", BCP 35, RFC 7595, DOI 10.17487/RFC7595, June 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8461] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A., and J. Jones, "SMTP MTA Strict Transport Security (MTA- STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018, . Morrison Expires 12 April 2027 [Page 56] Internet-Draft MCP DNS Discovery October 2026 [RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource Records through "Underscored" Naming of Attribute Leaves", BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019, . [RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON Canonicalization Scheme (JCS)", RFC 8785, DOI 10.17487/RFC8785, June 2020, . [RFC9421] Backman, A., Ed., Richer, J., Ed., and M. Sporny, "HTTP Message Signatures", RFC 9421, DOI 10.17487/RFC9421, February 2024, . [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding and Parameter Specification via the DNS (SVCB and HTTPS Resource Records)", RFC 9460, DOI 10.17487/RFC9460, November 2023, . [MCP] Agentic AI Foundation, "Model Context Protocol Specification", 2026, . 21. Informative References [RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK) Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September 2015, . [AGENT-AID] Nemethi, B., "Agent Identity and Discovery (AID)", 2026, . [DNS-AID] Mozley, J., Williams, N., Sarikaya, B., Schott, R., and J. Damick, "DNS for AI Discovery", 2026, . [MDNS-AGENT] Jakab, L. and F. Brockners, "Zero-Configuration Agent Discovery", 2026, . [MDNS-ARCHITECT] Yao, J., Geng, G., Chen, M., and H. Li, "Agent Discovery Architecture", 2026, . Morrison Expires 12 April 2027 [Page 57] Internet-Draft MCP DNS Discovery October 2026 [SAIP] Jovancevic, S., "SAIP: Signed Agent Identity Protocol", 2026, . [ALTER-URI] Morrison, B., "The 'alter' URI Scheme for Dispatchable ~handle References", Work in Progress, Internet-Draft, draft-morrison-alter-uri-scheme, 2026, . [DNSDISC-01] Morrison, B., "Discovery of Model Context Protocol Servers via DNS TXT Records", Work in Progress, Internet-Draft, draft-morrison-mcp-dns-discovery-01, April 2026, . [DNSDISC-02] Morrison, B., "Discovery of Model Context Protocol Servers via DNS TXT Records", Work in Progress, Internet-Draft, draft-morrison-mcp-dns-discovery-02, April 2026, . [DOMAIN-SET] Barrett, T., Schaub, C., Barrett, A., and P. Kowalik, "The Domain Set Discovery Protocol (domain-set)", Work in Progress, Internet-Draft, draft-barrett-dnsop-domain-set- 00, August 2026, . [RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS Names", BCP 32, RFC 2606, DOI 10.17487/RFC2606, June 1999, . [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, September 2011, . [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC Operational Practices, Version 2", RFC 6781, DOI 10.17487/RFC6781, December 2012, . Morrison Expires 12 April 2027 [Page 58] Internet-Draft MCP DNS Discovery October 2026 [RFC9989] Herr, T., Ed. and J. Levine, Ed., "Domain-Based Message Authentication, Reporting, and Conformance (DMARC)", RFC 9989, DOI 10.17487/RFC9989, May 2026, . [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 2016, . [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, . [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [RFC9083] Hollenbeck, S. and A. Newton, "JSON Responses for the Registration Data Access Protocol (RDAP)", STD 95, RFC 9083, DOI 10.17487/RFC9083, June 2021, . [SEP-1649] "MCP Server Cards", n.d., . [SEP-1960] ".well-known/mcp Discovery Endpoint", n.d., . [MORRISON-IFT] Morrison, B., "Identity Field Theory: Toward a Physics of Being Known", 2026, . Appendix A. Recognition Pseudocode The following pseudocode illustrates the combined recognition procedure defined in Section 12.3. It is non-normative; the normative procedure is the twelve-step algorithm in the body of this document. Morrison Expires 12 April 2027 [Page 59] Internet-Draft MCP DNS Discovery October 2026 function recognise_envelope(handle, zone): # Step 1-2: Query + DNSSEC response = dns_query("_alter." + zone, type=TXT, prefer=DoH) if not response.ad_bit and not local_rrsig_validate(response): raise UnauthenticatedResponse # Step 3-5: Chunk reassembly + handle disambiguation + fields records = [parse_alter_record(rr) for rr in response.rrset] record = find(records, lambda r: r.h == handle) if record is None or record.v != "alter1": raise RecordNotFound for f in ["h", "pk", "ilr", "ts", "rev", "sig"]: if not hasattr(record, f): raise MalformedRecord # Step 6-7: Envelope reconstruction + JCS. Keys are the TXT # field names; every value stays a string, ts included. alg = signature_alg_for_prefix(record.pk) # Signature Algorithm # Registry envelope = { "v": record.v, "h": record.h, "pk": record.pk, "ilr": record.ilr, "ts": record.ts, "rev": record.rev, "caveats": [], "signature_alg": alg, } signing_input = jcs_canonicalise(envelope) # Step 8: signature verify under the derived algorithm if not signature_verify(alg, record.pk, record.sig, signing_input): raise SignatureInvalid # Step 9: IdentityLog cross-ref. ADVISORY. Confirms the ROOT # was published; cannot confirm THIS envelope is under that # root, so a failure annotates and never aborts. See 12.3. ilr_root_seen = identitylog_root_published(record.ilr) # Step 10: DANE TLSA (if establishing MCP session) if establishing_mcp_session(zone): tlsa = dns_query("_443._tcp.mcp." + zone, type=TLSA) if not tlsa_matches_endpoint(tlsa, "mcp." + zone): raise TLSAFailure # Step 11: Caveats are OUT OF SCOPE for this document (Sec 12.3). Morrison Expires 12 April 2027 [Page 60] Internet-Draft MCP DNS Discovery October 2026 # No transport and no vocabulary are specified, so the verified # envelope carries none and the signature is checked over []. caveats = [] # Step 12: Revocation if identitylog_revocation_revealed(record.rev): raise EnvelopeRevoked return VerifiedEnvelope(record, caveats, ilr_root_seen) Appendix B. Document History draft-morrison-mcp-dns-discovery-08 (October 2026): One change to a record format: the handle in the h field now follows the handle-name grammar of [ALTER-URI]. It begins with a letter, admits "." so that an organisation's handle such as ~example.com can be carried, and no longer admits "_". No change to any procedure. Two new requirements: a publisher SHOULD NOT publish an envelope for an Instrument-tier handle (Section 7.3.2), and a verifier MUST NOT honour a claim signed under the key of a revoked envelope (Section 7.3.6). * Records in the Abstract, Section 2 and Section 16.2 that IANA provisionally registered the alter: scheme on 5 October 2026, and says in Section 19 that the verifier does not yet perform the step 12 revocation check or check the h grammar. * States in Section 7.3.6, the Erasure paragraph of Section 7.1.1 and step 12 of Section 12.3 that revocation takes effect when the pre-image is revealed, with no grace period, and that every claim signed under the revoked envelope's key is invalid from that moment, whenever it was signed. The epoch rotation of the _mcp record keeps its per-claim expiry grace. * Says in Section 7.3.8, Section 7.5 and Section 16.3 that a new envelope field is introduced only together with a new envelope version, and that resolvers ignore fields they do not know. Earlier text pointed new fields at a registry that does not exist. * Replaces the notes at the head of Section 14 and Section 15, which said the revision 01 and 02 considerations were retained, with sentences citing [DNSDISC-01] Sections 7 and 8 and [DNSDISC-02] Sections 10 and 11. No consideration is added or removed. Morrison Expires 12 April 2027 [Page 61] Internet-Draft MCP DNS Discovery October 2026 * Strikes the sentence saying this document is what the [AGENT-AID] mcp protocol token defers to, at the request of the [AGENT-AID] author, whose registry points that token at the MCP specification. Section 3 now says only that a client that learns p=mcp may also look up _mcp. * Cites [ALTER-URI] for the alter: scheme, corrects the [RFC7595] section for provisional registration to Section 4, and says in Section 12.3 that an alter: URI supplies the handle and that the zone is never derived from the handle's spelling. Removes editing-history notes from the Introduction and Terminology, and trims wording in Section 3 and Section 4. * Rewrites Section 3 to describe each neighbouring draft by what it specifies, without characterising its intent or scope. * Moves accounts of earlier revisions out of the body and into this appendix, and removes commentary on the document's own candour. * Removes the identity field framing from the Introduction, and cites [MORRISON-IFT] from the ~handle definition instead. Removes two terminology notes that were editorial guidance rather than definitions. * Makes entity and regulated proper subsections of Section 6.3. States the forward-compatibility rule for unknown regulated tokens by reference to step 4 of Section 12.2. * Corrects item 3 of Section 14.3, which said a malicious zone operator is caught by defence (1), which does not hold. Corrects a section reference in Appendix A. Removes the provisional-use sentence from Section 16.1. * Corrects the Instrument-tier description in Section 2 to match Section 8.5 of [MORRISON-IFT], says at the h field of Section 7.3.2 that an Instrument-tier handle has no envelope of its own, and removes the Instrument-tier envelope example, which contradicted it. * Corrects statements in Section 3, Section 4 and Section 5.3.3 about what neighbouring drafts specify. * Removes a schema URL that does not resolve, and a fallback in Section 11 that no procedure defines. * Corrects revision references in Section 1, Section 5, Section 12.1 and Section 13, and replaces references to earlier record generations with section numbers. Morrison Expires 12 April 2027 [Page 62] Internet-Draft MCP DNS Discovery October 2026 * Removes product terms and an undefined term from Section 2, Section 9, Section 12.2.2 and Section 15.1, and replaces a third- party name in an example. * Replaces the authoring organisation's own name and ABN in the examples of Section 6.3.3 and the section before it with example values. draft-morrison-mcp-dns-discovery-07 (September 2026): Tracks the current [AGENT-AID] revision and corrects the status of the alter: URI scheme. No change to any record defined here. * Stops describing the alter: URI scheme as provisionally registered with IANA (Section 2, Section 11, Section 16.2). Revision 06 said it was, and it was not. Provisional registration is now requested. * Moves the revision summary out of the Abstract. This appendix carries it in full. * Names the revision that made each change in four sentences that said "this revision" about revisions 05 and 06. * Describes the [AGENT-AID] record in its aid2 format, where revision 06 still described aid1. The endpoint-proof key is now an unpadded base64url JWK x value with its JWK thumbprint [RFC7638] as the signature keyid, and the i rotation identifier is gone. aid1 stays valid through [AGENT-AID]'s compatibility window. * Points the [AGENT-AID] reference at draft-nemethi-dawn-aid, the name the document now carries. draft-morrison-mcp-dns-discovery-06 (September 2026): Adds a key continuity rule for the _mcp record, the first normative change since revision 05, and corrects two statements in the revision 05 Implementation Status section. No record format changes and no field is added. Morrison Expires 12 April 2027 [Page 63] Internet-Draft MCP DNS Discovery October 2026 * Adds Section 13.1. Every earlier revision described the _mcp key binding as trust on first use with periodic re-verification, and none said what a client does when the re-verification disagrees. A client following revision 05 that had pinned a key would accept a different one on the next connection, which is the case of a lapsed domain registered again by someone else. The new section covers a changed key under the same epoch, an epoch that goes down, a declared rotation, and a record that drops its pk. * States that an epoch decrease is never a conformant publisher state (Section 5.3.7). The earlier rules covered a claim whose epoch is below or above the record's, and nothing covered the record's own epoch going down, which is what a new registrant publishing epoch=0 over a pinned epoch=2 looks like. * Extends step 7b of Section 12.1.2 to apply the rule, and to verify against a pinned key where the record no longer carries one. The procedure's opening sentence no longer claims the algorithm of [DNSDISC-01] unchanged. * Adopts the graded change-of-control signals of [DOMAIN-SET] Section 6.3 for the pinned binding (Section 13.1.2), and adds [DOMAIN-SET] and [RFC9083] as informative references. [DOMAIN-SET] already specified a consumer-side rule for a lapsed and re-registered domain, and this document had none. * Keeps absence of a record distinct from revocation, and says the difference from [DOMAIN-SET] Section 6.4 is deliberate (Section 13.1.1). That document treats removal of a record as revocation. This one does not, for the envelope record since revision 03 and now for the pinned key binding, because clearing a pin on absence would let one suppressed resolution reset a client to first use. * Adds Section 14.8, which states the change-of-control exposure for all three records, and states for the _alter record that this document specifies no pin and that a new registrant passes every FATAL step of Section 12.3. * Records in Section 19 that no implementation of the new rule is claimed. The two Implementation Status corrections, both of which understated the deployment: * Corrects the DNSSEC statement. Revision 05 said truealter.com was not DNSSEC-signed and that the parent zone held no DS. The zone was signed nine days before revision 05 was filed and is signed Morrison Expires 12 April 2027 [Page 64] Internet-Draft MCP DNS Discovery October 2026 today, with a key-signing key and a zone-signing key at algorithm 13 and a DS in the parent. The consequence revision 05 drew from the erroneous statement, that no Envelope Record could be relied upon in this zone, is withdrawn with it. * Records _org-alter.truealter.com as deployed. Revision 05 recorded it as NXDOMAIN, which was accurate when filed. It has since been provisioned and carries the field set named in the Implementation Status section. * The remaining statements of that section were re-checked against the zone and against the code and are carried forward unchanged. The absent DANE TLSA pin, the absence of any conformant Envelope Record, the two recognition steps on which the verifier still follows revision 04, the absent federation and witness network, and the absence of inclusion proofs all still hold. draft-morrison-mcp-dns-discovery-05 (July 2026): Corrections to -04, and the record formats and procedures restated in full. No new mechanism. * Restores the citation of [AGENT-AID], which revision 01 carried and revisions 02 through 04 dropped, and distinguishes it from [DNS-AID], a different draft with the same acronym. Revision 05 also said that this document is what the [AGENT-AID] mcp protocol token defers to. Revision 08 strikes that sentence at the request of the [AGENT-AID] author. * Gives all three record formats (Section 5, Section 6, Section 7), all three procedures (Section 12.1, Section 12.2, Section 12.3) and the caching rules (Section 13) in full. Revisions 03 and 04 incorporated the first two records and their procedures by reference to revisions 01 and 02. * Separates the agent protocol family from the transport binding in the _mcp record. Revision 01 used proto for the transport. proto now names the protocol family and transport names the binding, which is the term the Model Context Protocol specification uses. * States how to read an _mcp record published under revision 01 (Section 5.3.5). A proto value that names neither the protocol family nor a known transport causes the record to be SKIPPED, as revision 01 required. * Reconciles the _mcp grammar with its prose. The grammar admits any token in proto and transport; proto has exactly one defined value and transport exactly three, and the two sets are disjoint. Morrison Expires 12 April 2027 [Page 65] Internet-Draft MCP DNS Discovery October 2026 * Replaces 1*VCHAR for org, entity and entity-type with a text-value rule that admits SP and excludes only the field separator (Section 6.2). * Stops every value rule in all three grammars from running past the end of its own field. unknown-field and https-uri were defined over *VCHAR, which includes the semicolon. qtext admits SP and excludes the semicolon; uri-char excludes both. * States that unknown-field matches only a field name this document does not define, so a defined field whose value is malformed makes the record malformed (Section 5.2). The split-on-semicolon parse in Section 12.1 already behaved this way. * Requires a publisher emitting transport to emit proto=mcp with it (Section 5.3.5). * Adds Section 3 and Section 4. * Cites each label in the IANA table (Section 16.1) to the section of this document that defines it. * Rewrites Section 19 against the deployed zone and code. The -04 section claimed an _org-alter record, a DANE TLSA pin, a conformant envelope record and a signed-tree-head witness federation, none of which existed. * Withdraws the claim in Section 14.3 defence (1) that ilr= defeats envelope substitution. * Fixes the signing input of Section 7.4. The keys are the TXT field names, v is inside the signed object, and ts is a JSON string. An envelope signed under -04 does not verify under -05. No envelope signed under -04 exists. * Derives signature_alg from the pk= algorithm prefix via the registry of Section 16.7. * Allows a split within a key-value pair in Section 7.6, so a field longer than 255 octets can be carried. * Marks publication of a per-individual envelope in DNS as NOT RECOMMENDED, and forbids more than one handle at one owner name (Section 7.1, Section 7.1.1). Morrison Expires 12 April 2027 [Page 66] Internet-Draft MCP DNS Discovery October 2026 * Withdraws the IdentityLog witness federation everywhere -04 asserted it, and makes the cross-reference at step 9 of Section 12.3 advisory. The ilr= field is kept so the wire format does not change. * States that a reader implementing from this document alone cannot check revocation. * Repairs every internal cross-reference. * Corrects all four references into [DNSDISC-01] and [DNSDISC-02]. The _mcp record format is Section 5 of [DNSDISC-01], not Section 3, and its discovery procedure is Section 6, not Section 4. The _org-alter record format is Section 6 of [DNSDISC-02], not Section 4, and its bootstrap procedure is Section 7, not Section 6. * Gives the _alter record two ABNF grammars (Section 7.2), one for publisher emission and one for resolver acceptance, with the field-cardinality rule stated beside them. * Reconciles Section 14.6 with step 5 of Section 12.2. The _mcp and _org-alter keys must match; only the envelope key of Section 7 MAY differ. * Removes two hand-written reference sections that duplicated the generated ones. * Corrects the field count to seven REQUIRED fields. draft-morrison-mcp-dns-discovery-03 (April 2026): Editorial corrections (retiring -02): * Removes the third-party-domain worked example used in -02 and replaces all instances with [RFC2606] reserved example-domain forms; no third-party operational domain appears in any illustrative DNS record in this revision. * Strips city and locality fields from the author front-matter block, retaining only name, organisation, and email per editorial policy. Substantive additions: * Adds the _alter. Envelope Record (Section 7). * Defines v, h, pk, ilr, ts, rev, sig fields for the new record. Morrison Expires 12 April 2027 [Page 67] Internet-Draft MCP DNS Discovery October 2026 * Introduces a mandatory DNSSEC validation requirement for _alter. responses (Section 8). * Introduces a mandatory DANE TLSA [RFC6698] pin on the MCP endpoint (Section 9) for envelope-triggered MCP sessions. * Adds the IdentityLog cross-reference requirement (Section 10). Revision 05 withdraws it; see the -05 entry above. * Adds a provisional alter: URI scheme cross-reference per [RFC7595] (Section 11). * Adds the envelope recognition procedure (Section 12.3), a twelve- step algorithm. * Adds IANA registration for _alter underscore-prefixed label (Section 16.1) and the independent v=alter1 envelope version namespace. * Adds a Signature Algorithm Registry (Section 16.7) with initial value ed25519. * Adds Security Considerations for DNSSEC downgrade, TLSA pin rotation, envelope substitution, revocation opacity, clock skew, cross-record key consistency, and passive-stream coupling. * Adds Privacy Considerations for public handle disclosure, DNS query metadata, and revocation unlinkability. * Adds Examples for minimal envelope, multi-handle zone, full ~alter zone with all three records, and Instrument-tier handle. * Adds Implementation Status entry for the envelope reference implementation. * Incorporated the v01 _mcp. and v02 _org-alter. record specifications by reference, leaving them unchanged. Revision 05 restates both in full; see the -05 entry above. draft-morrison-mcp-dns-discovery-02 (April 2026): * Adds the _org-alter. Org-Identity Record. * Defines org, entity, entity-type, founded, regions, regulated, bootstrap, mcp-policy, epoch, pk, attest, ext fields for the organisational record. * Adds the Identity Bootstrap procedure. Morrison Expires 12 April 2027 [Page 68] Internet-Draft MCP DNS Discovery October 2026 * Adds IANA registration for _org-alter underscore-prefixed label. * Adds version tag v=alter1 (org-alter namespace) and registry namespace and framework token registries. * Adds Examples for minimal, full, regulated (DISP), and multi- regulator deployments. * Adds Implementation Status entry for the orgalter_discover reference library. * v01 _mcp. record specification is incorporated by reference and remains unchanged. draft-morrison-mcp-dns-discovery-01 (April 2026): * Adds Identity Field Theory grounding for epoch and scope. * Refines security considerations for identity assurance decay. * Refines privacy considerations for scope as a privacy boundary. * Adds Coexistence section with SEP-1959, AID, A2A. * Adds Implementation Status section. draft-morrison-mcp-dns-discovery-00 (April 2026): * Initial submission. * Defines _mcp. TXT record format with ABNF grammar. * Defines discovery procedure with HTTPS fallback. * Defines pk, epoch, attest, scope, cap, priority, ttl, and ext fields. * Registers _mcp in the underscored DNS node name registry. Contributors Christopher Whiteside Email: cwhiteside.engineering@gmail.com Author's Address Morrison Expires 12 April 2027 [Page 69] Internet-Draft MCP DNS Discovery October 2026 Blake Morrison Alter Meridian Pty Ltd Email: blake@truealter.com Morrison Expires 12 April 2027 [Page 70]