



DNSSD                                                           T. Lemon
Internet-Draft                                                 Apple Inc
Intended status: Standards Track                              M. Kardous
Expires: 30 July 2026                                       Silicon Labs
                                                         26 January 2026


               Providing DNSSD Service on Infrastructure
                       draft-tlmk-infra-dnssd-01

Abstract

   DNS Service Discovery provides several mechanisms whereby hosts can
   discover and advertise services on an IP network.  Such discovery can
   be done using Multicast DNS (mDNS) or DNS, and advertising can be
   done with DNSSD Service Registration Protocol (SRP) or mDNS.  This
   document describes a way to provide a unified DNSSD proxy service
   that allows hosts to advertise services using SRP and discover
   services using unicast DNS via a Discovery Proxy rather than using of
   mDNS, in scenarios where mDNS is currently the only option.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-tlmk-infra-dnssd/.

   Discussion of this document takes place on the DNSSD Working Group
   mailing list (mailto:dnssd@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/dnssd/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/dnssd/.

   Source for this draft and an issue tracker can be found at
   https://github.com/https://github.com/Abhayakara/draft-tlmk-infra-
   dnssd.

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/.





Lemon & Kardous           Expires 30 July 2026                  [Page 1]

Internet-Draft           DNSSD on Infrastructure            January 2026


   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 30 July 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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Previous work . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Modes of deployment . . . . . . . . . . . . . . . . . . . . .   4
   4.  Content of Service Advertisement  . . . . . . . . . . . . . .   4
     4.1.  Service Advertisement on Infrastructure . . . . . . . . .   5
     4.2.  Ad-Hoc Service Advertisement  . . . . . . . . . . . . . .   5
     4.3.  Content of SRV record . . . . . . . . . . . . . . . . . .   6
     4.4.  Content of the TXT record . . . . . . . . . . . . . . . .   6
       4.4.1.  Interface-specific domains  . . . . . . . . . . . . .   7
       4.4.2.  Service Priority  . . . . . . . . . . . . . . . . . .   7
   5.  Discovering the DNSSD service . . . . . . . . . . . . . . . .   8
     5.1.  Advertising using RAs . . . . . . . . . . . . . . . . . .   8
   6.  Dual-homed infrastructure DNSSD service . . . . . . . . . . .   8
     6.1.  Unmanaged networks  . . . . . . . . . . . . . . . . . . .   9
   7.  Service Availability Monitoring . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11





Lemon & Kardous           Expires 30 July 2026                  [Page 2]

Internet-Draft           DNSSD on Infrastructure            January 2026


1.  Introduction

   DNS Service Discovery (DNS-SD) [RFC6763] is a general mechanism for
   advertising and discovering services on IP networks. mDNS is a
   commonly used transport for DNS-SD.  However, it has several
   shortcomings: it relies entirely on multicast, which works somewhat
   poorly on WiFi networks.  Devices publishing services have to always
   be available to answer mDNS queries, which can have significant
   battery impact.  When doing service discovery, such devices may do
   WiFi beacon skipping to save power, and in so doing, miss a large
   percentage of multicast traffic, making mDNS unreliable.

   To address this, this document describes a way of combining several
   existing technologies to reduce reliance on multicast.  This can be
   done in, for example, a CE router [RFC7084], or a SNAC Router
   [I-D.draft-ietf-snac-simple].  It can actually be done in any device
   that is expected to be continuously operational on a network link and
   has sufficient resources to provide the service.

   There are four logical parts to the service: - The DNS [RFC1035] zone
   in which DNSSD information will be stored - The SRP [RFC9665]
   service, which is used to add and update services in the DNS zone -
   The Advertising Proxy [I-D.draft-ietf-dnssd-advertising-proxy]
   service, which advertises the contents of the zone using mDNS on the
   infrastructure link - The Discovery Proxy [RFC8766], which enables
   discovery of local services that are advertised using mDNS using the
   unicast DNS protocol.

   In addition, the service must be advertised so that devices that
   would like to make use of it can discover it.

1.1.  Previous work

   This specification relies on existing technology and makes reference
   to that technology assuming that the reader is already familiar with
   it.  Readers should familiarize themselves with at least the
   following documents.

   *  The DNS specification [RFC1035] which discusses DNS zones

   *  The SRP specification [RFC9665] which explains how to register
      services in the DNS without a pre-shared key

   *  The Advertising Proxy specification
      [I-D.draft-ietf-dnssd-advertising-proxy] which explains how to
      advertise the contents of a DNS zone using mDNS





Lemon & Kardous           Expires 30 July 2026                  [Page 3]

Internet-Draft           DNSSD on Infrastructure            January 2026


   *  The Discovery Proxy specification [RFC8766] which describes how to
      discover mDNS services on a link using DNS queries

   *  The DNS Push Specification [RFC8765] which describes how to
      efficiently do long-lived DNS queries

   *  The DNS-SD specification [RFC6763] which describes how to discover
      services using the DNS and mDNS protocols

2.  Conventions and Definitions

   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.

3.  Modes of deployment

   This service can be deployed either as a centralized service provided
   by infrastructure, or as an ad-hoc service that takes advantage of
   infrastructure but is not part of infrastructure.  An example of the
   first would be a Customer Edge router (CE Router) [RFC7084].  CE
   routers are typically autonomously operating devices--although they
   can be configured by the end user, this is not typical.  However,
   since they are the basis for the network infrastructure of a home
   network, we think of DNSSD service provided by a CE router as network
   infrastructure.

   An example of a device that provides full DNSSD service on an ad-hoc
   basis would be a SNAC router.  SNAC routers connect infrastructure
   networks to stub networks on an ad-hoc basis and provide all four of
   the services required for DNSSD service to the SNAC network, but only
   provide Advertising Proxy service to the infrastructure network.
   This means that devices on infrastructure can discover devices on the
   stub network, but not to register with SRP service nor use the SNAC
   advertising proxy.  A SNAC router that implements the behavior
   described in this document no longer has this limitation.

4.  Content of Service Advertisement

   The goal of advertising the service is to provide sufficient
   information that, having resolved the service advertisement, a user
   of the service has all the information needed to use the service.
   This includes at least:

   *  Name of the domain to use for service discovery




Lemon & Kardous           Expires 30 July 2026                  [Page 4]

Internet-Draft           DNSSD on Infrastructure            January 2026


   *  Name of the domain to use for service registration

   *  Name of the host providing the DNSSD service

   *  Ports to use for the UDP DNS protocol when communicating with the
      service

4.1.  Service Advertisement on Infrastructure

   Service advertisement on infrastructure is provided using the
   'dnssd.service.arpa.' domain.  This is a locally-served domain
   [RFC6303].  The local DNS resolver on infrastructure MUST answer
   authoratively for queries in the dnssd.service.arpa zone.  Because
   this is an infrastructure-provided service, infrastructure advertises
   only one service instance, with the service instance name
   "infrastructure."  Therefore, an infrastructure-provided DNSSD
   service advertises the infrastructure service instance in
   dnssd.service.arpa as follows:

   infrastructure.'service-name'.dnssd.service.arpa IN SRV 'data'
   infrastructure.'service-name'.dnssd.service.arpa IN TXT 'data'

   The infrastructure DNSSD service MUST support [I-D.draft-ietf-dnssd-
   multi-qtypes].  Therefore, this query can be done as a single multi-
   qtype query.  Typical DNS servers will, when answering an SRV query,
   include additional data containing address [RFC2782] pp 4-5.  In such
   situations, if the DNSSD service is provided by infrastructure, all
   of the information required to discover it will be returned in
   response to a single query.

4.2.  Ad-Hoc Service Advertisement

   What we mean by "ad hoc" is something that is not integrated into
   infrastructure.  Ad hoc servers do not have control of the local DNS
   resolver, and therefore cannot be discovered using DNS, and must
   instead be discovered using mDNS.  Because there is no coordination,
   it is possible (and in some cases likely) that there will be more
   than one such server, so the service instance name should be handled
   normally [RFC6763] section 4.1.1.

   Therefore, when advertising with mDNS, the service instance will be
   advertised as follows:

   'instance-name'.'service-name'.local IN SRV 'data'
   'instance-name'.'service-name'.local IN TXT 'data'






Lemon & Kardous           Expires 30 July 2026                  [Page 5]

Internet-Draft           DNSSD on Infrastructure            January 2026


4.3.  Content of SRV record

   mDNS APIs typically do not provide a way of setting the priority and
   weight of the SRV record, and the infrastructure service always has
   the highest priority.  Therefore, these fields SHOULD be set to zero,
   and MUST be ignored.  The reason they MUST be ignored is that since
   they SHOULD be zero, and most devices will not be able to set them to
   any other value, treating them as described in [RFC2782] presents an
   opportunity for an attack by advertising a service with a weight of
   65535.

   The port field should be set to the UDP port on which SRP service is
   provided.

   The target is the hostname of the host providing the service.

4.4.  Content of the TXT record

   TXT records are made up of a series of name=value pairs.  The
   following names are defined:

   srp-tcp='port': the port number to use for SRP registrations using
   the DNS Protocol over TCP.  If not present, this service is assumed
   to be available on the port provided in the SRV record.

   dns-udp='port': the port number to use for DNSSD queries using the
   DNS protocol over UDP.  If not present, this service is assumed to be
   available on the port provided in the SRV record.

   dns-tcp='port': the port number to use for DNSSD queries using the
   DNS protocol over TCP.  If not present, this service is assumed to be
   available on the port provided in the SRV record.

   srp-tls='port': the port number to use for SRP registrations using
   TLS.  If not present, port 853 is assumed.

   dns-tls='port': the port number to use for DNSSD queries using the
   DNS protocol over TLS.  If not present, port 853 is assumed.

   reg-dn='domain': the domain name to use in SRP registrations.  If not
   present, default.service.arpa is assumed.

   domains='domain-list': a comma-separated list of domains in which
   service discovery is available.  If not present, dnssd.service.arpa
   and local are assumed to be the only domains.






Lemon & Kardous           Expires 30 July 2026                  [Page 6]

Internet-Draft           DNSSD on Infrastructure            January 2026


   'domain'='ip-subnet-list': a link-specific domain that can be used to
   query services on that specific IP link.  The link is identified by a
   comma-separated list of IPv4 and/or IPv6 prefixes that are present on
   that link.  See Section 4.4.1.

   priority='priority': a priority for this service.  See Section 4.4.2

4.4.1.  Interface-specific domains

   A DNSSD service may support link-specific discovery proxy service.
   In such cases, each IP link must have its own unique domain, which is
   specific to the individual DNSSD service.  Each such domain must have
   an name=value entry in the TXT record.  This entry has as its name a
   domain name.  Its value is a comma-separated list of IP prefixes that
   are on-link for the IP link identified by the domain.

   IP subnets are in the form 'IP address'/'prefix-length'.  IP
   addresses are represented according to the IP address family.  IPv4
   addresses are in the dotted-decimal format as defined in [RFC952] in
   the section titled GRAMMATICAL HOST TABLE SPECIFICATION, in
   subsection A under 'address'.  IPv6 addresses are represented as
   described in [RFC5952].

   As a special (common) case, if the service only provides discovery
   proxy for a single link, and that is the link on which the DNSSD
   service is advertised, discovery of services on that link can use the
   "local" domain.  In this case, no domains will be listed in the TXT
   record; if "local" discovery is to be supported alongside other
   domains, then the "local" domain must be included in the TXT record.
   If a service DNSSD service is advertised on more than one link, the
   local domain is specific to the link for which the destination
   address for the query is on-link.  If the destination address is not
   on-link for any link, queries in .local are not valid and MUST be
   responded to with the REFUSED response code.

4.4.2.  Service Priority

   Infrastructure service is always the highest priority, and there can
   be only one such service.  When infrastructure service is discovered,
   this is done using infrastructure.  Consequently there is no need to
   try to discover an ad hoc service, and no need to choose amongst
   services.  The infrastructure service therefore MUST NOT include a
   priority.  Ad-hoc servers SHOULD include a priority.  If a priority
   is not included, the priority of the Ad-Hoc service is assumed to be
   65535.

   Services should choose a priority based on their capabilities.  The
   following priorities are defined:



Lemon & Kardous           Expires 30 July 2026                  [Page 7]

Internet-Draft           DNSSD on Infrastructure            January 2026


   0: Server is not constrained and is connected to a high-speed wired
   network link (that is, not WiFi, probably Ethernet or a fiber optic
   network).

   100: Server is not constrained and is connected to a WiFi link

   200: Server is constrained, but otherwise well able to provide
   service.

   65535: Server can provide service if needed, but should not be
   preferred.

5.  Discovering the DNSSD service

   A host that wishes to use the DNSSD service must first discover it.
   Discovery follows a series of steps:

   1.  Attempt to discover an infrastructure-provided DNSSD service

   2.  Failing that, browse for a list of Ad-Hoc services.

   3.  If one or more Ad-Hoc services are returned by the browse, choose
       one using the priority specified in the TXT record.

   4.  If no server is discovered, or if no discovered server appears to
       work, fall back to mDNS-based DNSSD service

5.1.  Advertising using RAs

   DNSSD servers that send RAs MUST include a DNSSD-Service RA option in
   RAs that they send when the DNSSD service is active.  DNSSD clients
   can distinguish infrastructure DNSSD service from ad-hoc service
   because infrastructure routers have nonzero lifetimes.

   It can be the case that there is more than one infrastructure router.
   In some cases these routers will be part of a managed infrastructure,
   in which case DNSSD service provided by these routers MUST be a
   common service.

6.  Dual-homed infrastructure DNSSD service

   In a dual-homed network, there is more than one default router and
   potentially more than one DNSSD service.  In the case of managed
   networks, the network operator MUST ensure that there is a single
   DNSSD service, even if it is advertised by more than one default
   router.





Lemon & Kardous           Expires 30 July 2026                  [Page 8]

Internet-Draft           DNSSD on Infrastructure            January 2026


6.1.  Unmanaged networks

   In an unmanaged network, there is no way for the operator to decide
   which default router will provide the DNSSD service when more than
   one default router is able to do so.  So we have the following
   options:

   1.  One router defers to the other

   2.  The routers share a common DNS zone either using SRP replication
       or DNS zone transfers with secondary failover

   3.  SRP clients are required to register with both services

   Practically speaking option 3 is the only easy option, although it
   places a greater burden on the client.  With option 1, the SRP client
   may take some time to notice that an SRP service has gone away and
   then reregister, and this is not ideal.  Option 2 requires mechanisms
   that are not yet described in a standard.  Consequently, when more
   than one infrastructure DNSSD service is present, consumers of the
   DNSSD service that will register their service using SRP MUST
   register with all infrastructure DNSSD servers.

7.  Service Availability Monitoring

   Once the consumer has registered with the DNSSD service, it is
   important to monitor the availability of the service.

   If the service being used is provided by a router, whether it be a CE
   router [RFC7084] or a SNAC router [I-D.draft-ietf-snac-simple], the
   consumer MUST monitor periodic RAs to ensure the service is still
   available.

   If the service being used is provided by a non-router device that
   relies on mDNS, the consumer must monitor the service provider to
   ensure it is still available.  This can be done by sending periodic
   queries to the service provider, listening for Time-To-Live updates,
   etc.

   If the consumer detects that the service is no longer available, it
   must restart the service discovery process defined in this
   specification.

8.  Security Considerations

   TODO Security





Lemon & Kardous           Expires 30 July 2026                  [Page 9]

Internet-Draft           DNSSD on Infrastructure            January 2026


9.  IANA Considerations

   Allocate 'service-name', "_dnssd-server" is preferred

10.  References

10.1.  Normative References

   [I-D.draft-ietf-dnssd-advertising-proxy]
              Cheshire, S. and T. Lemon, "Advertising Proxy for DNS-SD
              Service Registration Protocol", Work in Progress,
              Internet-Draft, draft-ietf-dnssd-advertising-proxy-04, 4
              March 2024, <https://datatracker.ietf.org/doc/html/draft-
              ietf-dnssd-advertising-proxy-04>.

   [I-D.draft-ietf-snac-simple]
              Lemon, T. and J. Hui, "Automatically Connecting Stub
              Networks to Unmanaged Infrastructure", Work in Progress,
              Internet-Draft, draft-ietf-snac-simple-08, 10 October
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              snac-simple-08>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/rfc/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              DOI 10.17487/RFC2782, February 2000,
              <https://www.rfc-editor.org/rfc/rfc2782>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/rfc/rfc5952>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
              <https://www.rfc-editor.org/rfc/rfc6763>.







Lemon & Kardous           Expires 30 July 2026                 [Page 10]

Internet-Draft           DNSSD on Infrastructure            January 2026


   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/rfc/rfc7084>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8765]  Pusateri, T. and S. Cheshire, "DNS Push Notifications",
              RFC 8765, DOI 10.17487/RFC8765, June 2020,
              <https://www.rfc-editor.org/rfc/rfc8765>.

   [RFC8766]  Cheshire, S., "Discovery Proxy for Multicast DNS-Based
              Service Discovery", RFC 8766, DOI 10.17487/RFC8766, June
              2020, <https://www.rfc-editor.org/rfc/rfc8766>.

   [RFC952]   Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
              host table specification", RFC 952, DOI 10.17487/RFC0952,
              October 1985, <https://www.rfc-editor.org/rfc/rfc952>.

   [RFC9665]  Lemon, T. and S. Cheshire, "Service Registration Protocol
              for DNS-Based Service Discovery", RFC 9665,
              DOI 10.17487/RFC9665, June 2025,
              <https://www.rfc-editor.org/rfc/rfc9665>.

10.2.  Informative References

   [RFC6303]  Andrews, M., "Locally Served DNS Zones", BCP 163,
              RFC 6303, DOI 10.17487/RFC6303, July 2011,
              <https://www.rfc-editor.org/rfc/rfc6303>.

Acknowledgments

   TODO acknowledge.

Authors' Addresses

   Ted Lemon
   Apple Inc
   Email: mellon@fugue.com


   Mathieu Kardous
   Silicon Labs
   Email: somebody@example.com





Lemon & Kardous           Expires 30 July 2026                 [Page 11]
