Network Working Group R. Pioli Internet-Draft Independent Intended status: Informational February 2026 Expires: 7 August 2026 Agent Registration and Discovery Protocol (ARDP) draft-pioli-agent-discovery-00 Abstract This document specifies the Agent Registration and Discovery Protocol (ARDP), a lightweight protocol for registering, discovering, and reaching autonomous software agents in distributed and federated environments. ARDP provides stable agent identities, dynamic endpoint resolution, capability advertisement (including protocol selection among MCP, A2A, HTTP, and gRPC), minimal presence signaling, and a security-first discovery control plane. ARDP is transport-agnostic and complementary to existing agent interaction protocols. 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." This Internet-Draft will expire on 5 August 2026. 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. Code Components Pioli Expires 7 August 2026 [Page 1] Internet-Draft Agent Registration and Discovery Protoco February 2026 extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Architecture Overview . . . . . . . . . . . . . . . . . . . . 3 5. Agent Identity . . . . . . . . . . . . . . . . . . . . . . . 3 5.1. AID Syntax . . . . . . . . . . . . . . . . . . . . . . . 4 5.2. Canonical Form . . . . . . . . . . . . . . . . . . . . . 4 6. Registration Model . . . . . . . . . . . . . . . . . . . . . 4 6.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . . . 4 6.2. DEREGISTER . . . . . . . . . . . . . . . . . . . . . . . 4 6.3. Registration Semantics . . . . . . . . . . . . . . . . . 4 6.4. TTL and Refresh . . . . . . . . . . . . . . . . . . . . . 5 6.5. Meta Resource (Minimal) . . . . . . . . . . . . . . . . . 5 7. Discovery and Resolution . . . . . . . . . . . . . . . . . . 5 7.1. RESOLVE . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.2. QUERY . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.3. Privacy Defaults and Redaction . . . . . . . . . . . . . 5 8. Capabilities . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Capability Bindings . . . . . . . . . . . . . . . . . . . 6 9. Presence and Health . . . . . . . . . . . . . . . . . . . . . 6 10. Security Considerations . . . . . . . . . . . . . . . . . . . 6 10.1. Proof of Control (Mandatory Profile) . . . . . . . . . . 6 10.2. Authorization Scopes . . . . . . . . . . . . . . . . . . 6 11. Federation . . . . . . . . . . . . . . . . . . . . . . . . . 7 11.1. Federation Profile (Minimum) . . . . . . . . . . . . . . 7 12. Relationship to Existing Protocols . . . . . . . . . . . . . 7 13. Wire Format Sketch (Non-Normative) . . . . . . . . . . . . . 7 13.1. Error Model . . . . . . . . . . . . . . . . . . . . . . 7 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 14.1. Well-Known URI . . . . . . . . . . . . . . . . . . . . . 7 14.2. Agent Identifier Namespace . . . . . . . . . . . . . . . 8 15. Capability Schema v0 . . . . . . . . . . . . . . . . . . . . 8 16. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 8 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Autonomous and semi-autonomous software agents introduce challenges in discoverability, reachability, and interoperability. Agents may be ephemeral, mobile across execution environments, and implemented by heterogeneous vendors. Pioli Expires 7 August 2026 [Page 2] Internet-Draft Agent Registration and Discovery Protoco February 2026 ARDP addresses stable addressing of agents whose runtime location changes, authorized discovery by identity and declared capabilities, capability-driven selection among interaction protocols (e.g., MCP, A2A, HTTP, gRPC), and minimal, privacy-aware presence signaling. 2. Design Goals Stable Identity; Dynamic Reachability; Minimalism (control plane only); Security by Default; Federation-Friendly; Extensibility. 3. Terminology The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL are to be interpreted as described in RFC 2119 and RFC 8174. * Agent: Autonomous software entity capable of initiating and receiving interactions. * Agent Identifier (AID): Stable, namespaced identifier of the form agent:@. * Registrar: Service that accepts agent registrations and maintains bindings. * Resolver: Service that resolves an AID to active endpoints. * Endpoint: Network location and protocol tuple through which an agent can be reached. * Capability: Declarative description of supported protocols and interaction modes. 4. Architecture Overview ARDP defines a logical control plane composed of registrars and resolvers. Agents register their presence and capabilities with a registrar. Authorized clients query resolvers to obtain endpoint and capability information. 5. Agent Identity Each agent SHALL have a unique AID. The authority component denotes the administrative authority responsible for the identity. Agents MUST prove control of an AID during registration using cryptographic credentials bound to that identity. Pioli Expires 7 August 2026 [Page 3] Internet-Draft Agent Registration and Discovery Protoco February 2026 5.1. AID Syntax An ARDP Agent Identifier (AID) MUST follow this grammar (ABNF per RFC 5234): aid = "agent:" local-id "@" authority local-id = 1*( ALPHA / DIGIT / "_" / "-" / "." / "/" ) authority = dns-name / internal-name / opaque-authority dns-name = 1*( ALPHA / DIGIT / "-" / "." ) ; see IDNA2008 notes internal-name = 1*( ALPHA / DIGIT / "-" / "." ) opaque-authority = "tenant-" 1*( ALPHA / DIGIT / "-" ) Note: When internationalized domain names are used, implementers should follow the IDNA2008 RFC series. 5.2. Canonical Form The canonical AID string is: 1. The literal prefix agent: in lowercase. 2. The authority normalized to lowercase (including IDNA2008 normalization where applicable); internal-name is lowercased as- is. 3. local-id is case-sensitive and MUST be preserved as sent. 4. AIDs MUST be compared using the canonical form. 6. Registration Model 6.1. REGISTER A REGISTER request includes: AID; one or more endpoints; capability document (versioned); TTL; and cryptographic proof. Registrations are soft-state and MUST be refreshed before expiration. 6.2. DEREGISTER An agent MAY explicitly remove its registration. 6.3. Registration Semantics Registration is idempotent on (aid, binding_id). If a client sends the same (aid, binding_id), the server MUST treat it as a refresh. Pioli Expires 7 August 2026 [Page 4] Internet-Draft Agent Registration and Discovery Protoco February 2026 If a client sends the same aid with a different binding_id, the server MUST return a conflict error unless the client has registry:override scope. 6.4. TTL and Refresh The server MUST be authoritative for expires_at and SHOULD return it in responses. Clients SHOULD refresh at <= 0.5 * ttl with random jitter. The server MUST define and enforce TTL bounds and advertise them in a metadata resource (recommended: /.well-known/ardp/meta). 6.5. Meta Resource (Minimal) This section defines a minimal metadata resource for deployments using HTTPS bindings. Path: /.well-known/ardp/meta The response includes TTL bounds and supported auth profiles: { "ttl_min": 30, "ttl_max": 3600, "auth_profiles": ["jws-proof-of-control"], "supported_protocols": ["MCP","A2A","HTTP","gRPC"] } 7. Discovery and Resolution 7.1. RESOLVE RESOLVE maps an AID to active endpoints and capabilities. Access MUST be authorized. 7.2. QUERY QUERY allows authorized discovery by capability or namespace. Results SHOULD be minimized to prevent metadata leakage. 7.3. Privacy Defaults and Redaction By default, QUERY returns only aid and status. Clients MAY request full details via a detail=full parameter. Pioli Expires 7 August 2026 [Page 5] Internet-Draft Agent Registration and Discovery Protoco February 2026 If redaction applies, the server MUST omit restricted fields and include "redacted": true in the response. 8. Capabilities Capability documents MAY include supported protocols (MCP, A2A, HTTP, gRPC), transport bindings, authentication mechanisms, modalities, rate or cost hints, and protocol-specific metadata. Capabilities are declarative and do not imply authorization. 8.1. Capability Bindings Capabilities MUST include protocol-specific bindings when a protocol is declared. 9. Presence and Health Presence is limited to: online, offline, degraded. 10. Security Considerations Threats include identity spoofing, registration poisoning, unauthorized discovery, replay and downgrade attacks, and registrar compromise. Mitigations include cryptographic identity proof, signed registrations, strict authorization, rate limiting, and audit logging. 10.1. Proof of Control (Mandatory Profile) Clients MUST present a JWS-signed proof for register and refresh. The signed payload is the canonical JSON of the registration body plus a server-provided nonce and an issued_at timestamp (RFC 3339). Servers MUST verify the JWS using a JWKS key set (RFC 7517). Replay windows MUST be enforced. 10.2. Authorization Scopes Operations require scopes such as: registry:register, registry:refresh, registry:resolve, registry:query, and registry:deregister. Pioli Expires 7 August 2026 [Page 6] Internet-Draft Agent Registration and Discovery Protoco February 2026 11. Federation Registrars MAY federate across domains via explicit trust relationships and policy agreements. 11.1. Federation Profile (Minimum) Federation is allowed only between explicit trust anchors. Responses from remote registrars MUST include provenance fields: origin_authority, origin_registrar_id, origin_signature. Caches MUST honor remote TTL and mark records as federated. 12. Relationship to Existing Protocols ARDP complements, and does not replace, agent interaction protocols such as MCP and A2A. 13. Wire Format Sketch (Non-Normative) JSON over HTTPS is shown as an example binding. Alternative encodings (e.g., CBOR, gRPC) are possible. 13.1. Error Model Servers MUST return errors with: code (stable error code), message (human-readable), and correlation_id (for tracing). Required codes: invalid_aid, unauthorized, forbidden, conflict, not_found, expired. 14. IANA Considerations 14.1. Well-Known URI IANA is requested to register the following URI suffix per RFC 8615 in the "Well-Known URIs" registry: URI suffix: ardp Change controller: IETF Specification document(s): This document Pioli Expires 7 August 2026 [Page 7] Internet-Draft Agent Registration and Discovery Protoco February 2026 14.2. Agent Identifier Namespace The agent: prefix is used as an internal identifier namespace and is not registered as a URI scheme in this version. 15. Capability Schema v0 A minimal JSON schema for capability documents is provided as a companion artifact in the GitHub mirror. 16. Open Issues Capability schema evolution; Privacy-preserving discovery; Federation bootstrapping. 17. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", 1997. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", 2017. [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", 2002. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", 2008. [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", 2010. [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", 2015. [RFC7517] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Key (JWK)", 2015. [RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers (URIs)", 2019. Author's Address Roberto Pioli Independent Email: roberto.pioli@gmail.com Pioli Expires 7 August 2026 [Page 8]