Special-Use Domain 'home.arpa.'

Internet Engineering Task Force (IETF)                        P. Pfister
Request for Comments: 8375                                 Cisco Systems
Updates: 7788                                                   T. Lemon
Category: Standards Track                            Nibbhaya Consulting
ISSN: 2070-1721                                                 May 2018


                    Special-Use Domain 'home.arpa.'

Abstract

   This document specifies the behavior that is expected from the Domain
   Name System with regard to DNS queries for names ending with
   '.home.arpa.' and designates this domain as a special-use domain
   name. 'home.arpa.' is designated for non-unique use in residential
   home networks.  The Home Networking Control Protocol (HNCP) is
   updated to use the 'home.arpa.' domain instead of '.home'.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8375.

Copyright Notice

   Copyright (c) 2018 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
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  General Guidance  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Domain Name Reservation Considerations  . . . . . . . . . . .   4
   5.  Updates to Home Networking Control Protocol . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     6.1.  Local Significance  . . . . . . . . . . . . . . . . . . .   7
     6.2.  Insecure Delegation . . . . . . . . . . . . . . . . . . .   8
     6.3.  Bypassing Manually Configured Resolvers . . . . . . . . .   9
   7.  Delegation of 'home.arpa.'  . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Users and devices within a home network (hereafter referred to as
   "homenet") require devices and services to be identified by names
   that are unique within the boundaries of the homenet [RFC7368].  The
   naming mechanism needs to function without configuration from the
   user.  While it may be possible for a name to be delegated by an ISP,
   homenets must also function in the absence of such a delegation.
   This document reserves the name 'home.arpa.' to serve as the default
   name for this purpose, with a scope limited to each individual
   homenet.

   This document corrects an error in [RFC7788] by replacing '.home'
   with 'home.arpa.' as the default domain name for homenets. '.home'
   was selected as the most user-friendly option; however, there are
   existing uses of '.home' that may be in conflict with this use.
   Evidence indicates that '.home' queries frequently leak out and reach
   the root name servers [ICANN1] [ICANN2].

   In addition, for compatibility with DNSSEC (see Section 6), it's
   necessary that an insecure delegation (see Section 4.3 of [RFC4035])
   be present for the name.  There is an existing process for allocating
   names under '.arpa.'  [RFC3172].  No such process is available for
   requesting a similar delegation in the root at the request of the
   IETF, which does not administer that zone.  As a result, all
   unregistered uses of '.home' (that is, all current uses at the time
   of this document's publication), particularly as specified in
   [RFC7788], are deprecated.

   This document registers the domain 'home.arpa.' as a special-use
   domain name [RFC6761] and specifies the behavior that is expected
   from the Domain Name System with regard to DNS queries for names
   whose rightmost non-terminal labels are 'home.arpa.'.  Queries for
   names ending with '.home.arpa.' are of local significance within the
   scope of a homenet, meaning that identical queries will result in
   different results from one homenet to another.  In other words, a
   name ending in '.home.arpa.' is not globally unique.

   Although this document makes specific reference to [RFC7788], it is
   not intended that the use of 'home.arpa.' be restricted solely to
   networks where HNCP is deployed.  Rather, 'home.arpa.' is intended to
   be the correct domain for uses like the one described for '.home' in
   [RFC7788]: local name service in residential homenets.

2.  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.

3.  General Guidance

   The domain name 'home.arpa.' is to be used for naming within
   residential homenets.  Names ending with '.home.arpa.' reference a
   zone that is served locally, the contents of which are unique only to
   a particular homenet and are not globally unique.  Such names refer
   to nodes and/or services that are located within a homenet (e.g., a
   printer or a toaster).

   DNS queries for names ending with '.home.arpa.' are resolved using
   local resolvers on the homenet.  Such queries MUST NOT be recursively
   forwarded to servers outside the logical boundaries of the homenet.

   Some service discovery user interfaces that are expected to be used
   on homenets conceal information such as domain names from end users.
   However, in some cases, it is still expected that users will need to
   see, remember, and even type names ending with '.home.arpa.'.  The
   Homenet Working Group hopes that this name will in some way indicate
   to as many readers as possible that such domain names are referring
   to devices in the home, but we recognize that it is an imperfect
   solution.

4.  Domain Name Reservation Considerations

   This section specifies considerations for systems involved in domain
   name resolution when resolving queries for names ending with
   '.home.arpa.'.  Each item in this section addresses some aspect of
   the DNS or the process of resolving domain names that would be
   affected by this special-use allocation.  Detailed explanations of
   these items can be found in Section 5 of [RFC6761].  Although the
   term 'homenet' in [RFC7788] refers to home networks that implement a
   particular set of features, in this document the term is used to mean
   any home network, regardless of the set of features it implements.

   1.  Users can use names ending with '.home.arpa.' just as they would
       use any other domain name.  The 'home.arpa.' name is chosen to be
       readily recognized by users as signifying that the name is
       addressing a service on the homenet to which the user's device is
       connected.

   2.  Application software SHOULD NOT treat names ending in
       '.home.arpa.' differently than other names.  In particular, there
       is no basis for trusting names that are subdomains of
       'home.arpa.' (see Section 6).

   3.  Name resolution APIs and libraries MUST NOT recognize names that
       end in '.home.arpa.' as special and MUST NOT treat them as having
       special significance, except that it may be necessary that such
       APIs not bypass the locally configured recursive resolvers.

       One or more IP addresses for recursive DNS servers will usually
       be supplied to the client through router advertisements or DHCP.
       For an administrative domain that uses subdomains of
       'home.arpa.', such as a homenet, the recursive resolvers provided
       by that domain will be able to answer queries for subdomains of
       'home.arpa.'; other resolvers will not, or they will provide
       answers that are not correct within that administrative domain.

       A host that is configured to use a resolver other than one that
       has been provided by the local network may be unable to resolve,
       or may receive incorrect results for, subdomains of 'home.arpa.'.
       In order to avoid this, it is permissible that hosts use the
       resolvers that are locally provided for resolving 'home.arpa.',
       even when they are configured to use other resolvers.

   4.  There are three considerations for recursive resolvers that
       follow this specification:

       A.  Recursive resolvers at sites using 'home.arpa.'  MUST
           transparently support DNSSEC queries: queries for DNSSEC
           records and queries with the DNSSEC OK (DO) bit set (see
           Section 3.2.1 of [RFC4035]).  While validation is not
           required, it is strongly encouraged: a caching recursive
           resolver that does not validate answers that can be validated
           may cache invalid data.  This, in turn, will prevent
           validating stub resolvers from successfully validating
           answers.

       B.  Unless configured otherwise, recursive resolvers and DNS
           proxies MUST behave as described in Section 3 of the Locally
           Served Zones document [RFC6303].  That is, queries for
           'home.arpa.' and subdomains of 'home.arpa.'  MUST NOT be
           forwarded, with one important exception: a query for a DS
           record with the DO bit set MUST return the correct answer for
           that question, including correct information in the authority
           section that proves that the record is nonexistent.

           So, for example, a query for the NS record for 'home.arpa.'
           MUST NOT result in that query being forwarded to an upstream
           cache nor to the authoritative DNS server for '.arpa.'.
           However, as necessary to provide accurate authority
           information, a query for the DS record MUST result in
           forwarding whatever queries are necessary; typically, this
           will just be a query for the DS record, since the necessary
           authority information will be included in the authority
           section of the response if the DO bit is set.

       C.  In addition to the behavior specified above, recursive
           resolvers that can be used in a homenet MUST be configurable
           to forward queries for 'home.arpa.' and subdomains of
           'home.arpa.' to an authoritative server for 'home.arpa.'.
           This server will provide authoritative data for 'home.arpa.'
           within a particular homenet.  The special handling for DS
           records for the 'home.arpa.' delegation is still required.

           It is permissible to combine the recursive resolver function
           for general DNS lookups with an authoritative resolver for
           'home.arpa.'; in this case, rather than forwarding queries
           for subdomains of 'home.arpa.' to an authoritative server,
           the resolver answers them authoritatively.  The behavior with
           respect to forwarding queries specifically for 'home.arpa.'
           remains the same.

   5.  No special processing of 'home.arpa.' is required for
       authoritative DNS server implementations.  It is possible that an
       authoritative DNS server might attempt to check the authoritative
       servers for 'home.arpa.' for a delegation beneath that name
       before answering authoritatively for such a delegated name.  In
       such a case, because the name always has only local significance,
       there will be no such delegation in the 'home.arpa.' zone, and so
       the server would refuse to answer authoritatively for such a
       zone.  A server that implements this sort of check MUST be
       configurable so that either it does not do this check for the
       'home.arpa.' domain or it ignores the results of the check.

   6.  DNS server operators MAY configure an authoritative server for
       'home.arpa.' for use in homenets and other home networks.  The
       operator for the DNS servers authoritative for 'home.arpa.' in
       the global DNS will configure any such servers as described in
       Section 7.

   7.  'home.arpa.' is a subdomain of the 'arpa' top-level domain, which
       is operated by IANA under the authority of the Internet
       Architecture Board according to the rules established in
       [RFC3172].  There are no other registrars for '.arpa'.

5.  Updates to Home Networking Control Protocol

   The final paragraph in Section 8 of [RFC7788], the Home Networking
   Control Protocol, is updated as follows:

   OLD:
      Names and unqualified zones are used in an HNCP network to provide
      naming and service discovery with local significance.  A network-
      wide zone is appended to all single labels or unqualified zones in
      order to qualify them. ".home" is the default; however, an
      administrator MAY configure the announcement of a Domain-Name TLV
      (Section 10.6) for the network to use a different one.  In case
      multiple are announced, the domain of the node with the greatest
      node identifier takes precedence.

   NEW:
      Names and unqualified zones are used in an HNCP network to provide
      naming and service discovery with local significance.  A network-
      wide zone is appended to all single labels or unqualified zones in
      order to qualify them. 'home.arpa.' is the default; however, an
      administrator MAY configure the announcement of a Domain-Name TLV
      (Section 10.6) for the network to use a different one.  In case
      multiple TLVs are announced, the domain of the node with the
      greatest node identifier takes precedence.

      The 'home.arpa.' special-use name does not require a special
      resolution protocol.  Names for which the rightmost two labels are
      'home.arpa.' are resolved using the DNS protocol [RFC1035].

6.  Security Considerations

6.1.  Local Significance

   A DNS record that is returned as a response to a query for a Fully
   Qualified Domain Name (FQDN) that is a subdomain of 'home.arpa.' is
   expected to have local significance.  It is expected to be returned
   by a server involved in name resolution for the homenet the device is
   connected in.  However, such a response MUST NOT be considered more
   trustworthy than a similar response for any other DNS query.

   Because 'home.arpa.' is not globally scoped and cannot be secured
   using DNSSEC based on the root domain's trust anchor, there is no way
   to tell, using a standard DNS query, in which homenet scope an answer
   belongs.  Consequently, users may experience surprising results with
   such names when roaming to different homenets.

   To prevent this from happening, it could be useful for the resolver
   on the host to securely differentiate between different homenets and
   between identical names on different homenets.  However, a mechanism
   for doing this has not yet been standardized and doing so is out of
   scope for this document.  It is expected that this will be explored
   in future work.

   The advice in [RFC6303], Section 7, to install local trust anchors
   for locally served zones can only work if there is some way of
   configuring the trust anchor in the host.  Homenet currently
   specifies no mechanism for configuring such trust anchors.  As a
   result, while this advice sounds good, it is not practicable.

   Also, although it might be useful to install a trust anchor for a
   particular instance of 'home.arpa.', it's reasonable to expect that a
   host with such a trust anchor might, from time to time, connect to
   more than one network with its own instance of 'home.arpa.'.  Such a
   host would be unable to access services on any instance of
   'home.arpa.' other than the one for which a trust anchor was
   configured.

   It is, in principle, possible to attach an identifier to an instance
   of 'home.arpa.' that could be used to identify which trust anchor to
   rely on for validating names in that particular instance.  However,
   the security implications of this are complicated, and such a
   mechanism, as well as a discussion of those implications, is out of
   scope for this document.

6.2.  Insecure Delegation

   It is not possible to install a trust anchor (a DS RR) for this zone
   in the '.arpa' zone.  The reason for this is that in order to do so,
   it would be necessary to have the key-signing key for the zone (see
   Section 5 of [RFC4034]).  Since the zone is not globally unique, no
   one key would work.

   An alternative would be to provide an authenticated denial of
   existence (see Section 3.2 of [RFC4033]).  This would be done simply
   by not having a delegation from the 'arpa.' zone.  However, this
   requires the validating resolver to treat 'home.arpa.' specially.  If
   a validating resolver that doesn't treat 'home.arpa.' specially
   attempts to validate a name in 'home.arpa.', an authenticated denial
   of existence of 'home' as a subdomain of 'arpa.' would cause the
   validation to fail.  Therefore, the only delegation that will allow
   names under 'home.arpa.' to be resolved by all validating resolvers
   is an insecure delegation, as in Section 7 of [RFC6303].

   Consequently, unless a trust anchor for the particular instance of
   the 'home.arpa.' zone being validated is manually configured on the
   validating resolver, DNSSEC signing and validation of names within
   the 'home.arpa.' zone is not possible.

6.3.  Bypassing Manually Configured Resolvers

   In item 3 of Section 4, an exception is made to the behavior of stub
   resolvers that allows them to query local resolvers for subdomains of
   'home.arpa.' even when they have been manually configured to use
   other resolvers.  This behavior obviously has security and privacy
   implications and may not be desirable depending on the context.  It
   may be better to simply ignore this exception and, when one or more
   recursive resolvers are configured manually, simply fail to provide
   correct answers for subdomains of 'home.arpa.'.  At this time, we do
   not have operational experience that would guide us in making this
   decision; implementors are encouraged to consider the context in
   which their software will be deployed when deciding how to resolve
   this question.

7.  Delegation of 'home.arpa.'

   In order to be fully functional, there must be a delegation of
   'home.arpa.' in the '.arpa.' zone [RFC3172].  This delegation MUST
   NOT include a DS record and MUST point to one or more black hole
   servers, for example, 'blackhole-1.iana.org.' and 'blackhole-
   2.iana.org.'.  The reason that this delegation must not be signed is
   that not signing the delegation breaks the DNSSEC chain of trust,
   which prevents a validating stub resolver from rejecting names
   published under 'home.arpa.' on a homenet name server.

8.  IANA Considerations

   IANA has recorded the domain name 'home.arpa.' in the "Special-Use
   Domain Names" registry [SUDN].  IANA, with the approval of the IAB,
   has implemented the delegation requested in Section 7.

   IANA has created a new subregistry within the "Locally-Served DNS
   Zones" registry [LSDZ], titled "Transport-Independent Locally-Served
   DNS Zone Registry", with the same format as the other subregistries.
   IANA has added an entry in this new registry for 'home.arpa.' with
   the description "Homenet Special-Use Domain", listing this document
   as the reference.  The registration procedure for this subregistry
   should be the same as for the others, currently "IETF Review" (see
   Section 4.8 of [RFC8126]).

9.  References

9.1.  Normative References

   [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/info/rfc2119>.

   [RFC3172]  Huston, G., Ed., "Management Guidelines & Operational
              Requirements for the Address and Routing Parameter Area
              Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
              September 2001, <https://www.rfc-editor.org/info/rfc3172>.

   [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,
              <https://www.rfc-editor.org/info/rfc4035>.

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

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <https://www.rfc-editor.org/info/rfc6761>.

   [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/info/rfc8174>.

9.2.  Informative References

   [ICANN1]   "New gTLD Collision Risk Mitigation", August 2013,
              <https://www.icann.org/en/system/files/files/
              new-gtld-collision-mitigation-05aug13-en.pdf>.

   [ICANN2]   "New gTLD Collision Occurence Management", October 2013,
              <https://www.icann.org/en/system/files/files/
              resolutions-new-gtld-annex-1-07oct13-en.pdf>.

   [LSDZ]     "Locally-Served DNS Zones", July 2011,
              <https://www.iana.org/assignments/
              locally-served-dns-zones/>.

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

   [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,
              <https://www.rfc-editor.org/info/rfc4033>.

   [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,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC7368]  Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
              Weil, "IPv6 Home Networking Architecture Principles",
              RFC 7368, DOI 10.17487/RFC7368, October 2014,
              <https://www.rfc-editor.org/info/rfc7368>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <https://www.rfc-editor.org/info/rfc7788>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [SUDN]     "Special-Use Domain Names", July 2012,
              <https://www.iana.org/assignments/
              special-use-domain-names/>.

Acknowledgments

   The authors would like to thank Stuart Cheshire, as well as the
   homenet chairs, Mark Townsley and Ray Bellis, for their prior work on
   '.home'.  We would also like to thank Paul Hoffman for providing
   review and comments on the IANA Considerations section, Andrew
   Sullivan for his review and proposed text, and Suzanne Woolf and Ray
   Bellis for their very detailed review comments and process insights.
   Thanks to Mark Andrews for providing an exhaustive reference list on
   the topic of insecure delegations.  Thanks to Dale Worley for
   catching a rather egregious mistake and for the Gen-Art review, and
   thanks to Daniel Migault for a thorough SecDir review.  Thanks to
   Warren Kumari for catching some additional issues and to Adam Roach
   for some helpful clarifications.

Authors' Addresses

   Pierre Pfister
   Cisco Systems
   Paris
   France

   Email: pierre.pfister@darou.fr


   Ted Lemon
   Nibbhaya Consulting
   P.O. Box 958
   Brattleboro, Vermont  05301-0958
   United States of America

   Email: mellon@fugue.com