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Special Use Domain ''

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8375.
Authors Pierre Pfister , Ted Lemon
Last updated 2017-08-31 (Latest revision 2017-08-29)
Replaces draft-pfister-homenet-dot
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Ray Bellis
Shepherd write-up Show Last changed 2017-07-25
IESG IESG state Became RFC 8375 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Needs a YES. Needs 9 more YES or NO OBJECTION positions to pass.
Responsible AD Terry Manderson
Send notices to Ray Bellis <>
IANA IANA review state IANA OK - Actions Needed
Network Working Group                                         P. Pfister
Internet-Draft                                             Cisco Systems
Updates: RFC7788 (if approved)                                  T. Lemon
Intended status: Standards Track                           Nominum, Inc.
Expires: March 2, 2018                                   August 29, 2017

                    Special Use Domain ''


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

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

   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 March 2, 2018.

Copyright Notice

   Copyright (c) 2017 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
   ( 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 Simplified BSD License text as described in Section 4.e of

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

1.  Introduction

   Users and devices within a home network (hereafter "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.  A default name with a
   scope limited to each individual homenet needs to be used.

   This document corrects an error in [RFC7788], replacing '.home' with
   '' as the default domain-name for homenets. '.home' had
   been 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, it's necessary, for compatibility with DNSSEC
   (Section 6), that an insecure delegation ([RFC4035] section 4.3) 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, the use of
   '.home' is deprecated.

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   This document registers the domain '' 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 ''.  Queries for
   names ending with '' 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 '' is not globally unique.

   Although this document makes specific reference to RFC7788, it is not
   intended that the use of '' be restricted solely to
   networks where HNCP is deployed; it is rather the case that
   '' is 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",
   "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 '' is to be used for naming within
   residential homenets.  Names ending with '' reference a
   locally-served zone, 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 '' 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, it is still expected that in some cases, users will need to
   see, remember, and even type, names ending with ''.  The
   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

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4.  Domain Name Reservation Considerations

   This section defines the behavior of systems involved in domain name
   resolution when resolving queries for names ending with ''
   (as per [RFC6761]).

   1.  Users can use names ending with '' just as they would
       use any other domain name.  The '' 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

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

   3.  Name resolution APIs and libraries MUST NOT recognize names that
       end in '' 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 names in '',
       such as a homenet, the recursive resolvers provided by that
       domain will be able to answer queries for subdomains of; other resolvers will not, or 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, names in sub domains of
       ''.  In order to avoid this, it is permissible that
       hosts use the locally-provided resolvers for resolving
       '' even when they are configured to use other


       A.  Recursive resolvers at sites using ''  MUST
           transparently support DNSSEC queries: queries for DNSSEC
           records and queries with the DO bit set ([RFC4035] section
           3.2.1).  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.

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       B.  Unless configured otherwise, recursive resolvers and DNS
           proxies MUST behave as described in Locally Served Zones
           ([RFC6303] Section 3).  That is, queries for domains that are
           subdomains of ''  MUST NOT be forwarded, with one
           important exception: a query for a DS record when 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 ''
           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
           whatever queries are necessary being forwarded; 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
           with a delegation to an authoritative server for that
           particular homenet's instance of the domain ''.

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

   5.  No special processing of '' is required for
       authoritative DNS server implementations.  It is possible that an
       authoritative DNS server might attempt to check the authoritative
       servers for '' 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 '' 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
       '' domain, or it ignores the results of the check.

   6.  DNS server operators MAY configure an authoritative server for
       '' for use in homenets and other home networks.  The
       operator for the DNS servers authoritative for '' in

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       the global DNS will configure any such servers as described in
       Section 7.

   7.  '' 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 of Home Networking Control Protocol [RFC7788],
   section 8, is updated as follows:


      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.


      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. '' 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.

      The '' special-use name does not require a special
      resolution protocol.  Names for which the rightmost two labels are
      '' 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 an FQDN in
   the domain '' 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 response

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   MUST NOT be considered more trustworthy than would be a similar
   response for any other DNS query.

   Because '' 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 may be useful for the resolver to identify different
   homenets on which it has resolved names, but this is out of scope for
   this document.

   Locally Served Zones ([RFC6303] section 7) recommends installing
   trust anchors for locally served zones.  However, in order for this
   to be effective, there must be 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 in principle it might be useful to install a trust
   anchor for a particular instance of '', 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
   ''.  Such a host would be unable to access services on any
   instance of '' other than the one for which a trust anchor
   was configured.

   It is in principle possible to attach an identifier to an instance of
   '' 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
   ([RFC4034] Section 5).  Since the zone is not globally unique, no one
   key would work.

   An alternative would be to provide a authenticated denial of
   existence ([RFC4033] Section 3.2).  This would be done simply by not
   having a delegation from the 'arpa.' zone.  However, this requires
   the validating resolver to treat '' specially.  If a
   validating resolver that doesn't treat '' specially
   attempts to validate a name in '', an authenticated denial

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   of existence of 'home' as a subdomain of 'arpa.' would cause the
   validation to fail.  Therefore, the only delegation that will allow
   names under '' to be resolved by all validating resolvers
   is an insecure delegation as in [RFC6303] section 7.

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

6.3.  Bypassing Manually Configured Resolvers

   In Section 4, item 3, an exception is made to the behavior of stub
   resolvers allowing them to query local resolvers for subdomains of
   '' 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 ''.  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 ''

   In order to be fully functional, there must be a delegation of
   '' 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 '' and 'blackhole-'.  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 '' on a homenet name server.

8.  IANA Considerations

   IANA is requested to record the domain name '' in the
   Special-Use Domain Names registry [SUDN].  IANA is requested, with
   the approval of IAB, to implement the delegation requested in
   Section 7.

9.  Acknowledgments

   The authors would like to thank Stuart Cheshire for his prior work on
   '.home', as well as the homenet chairs: Mark Townsley and Ray Bellis.
   We would also like to thank Paul Hoffman for providing review and

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   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 to Daniel Migault
   for a thorough SecDir review.

10.  References

10.1.  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-

   [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, <>.

   [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,

   [RFC6303]  Andrews, M., "Locally Served DNS Zones", BCP 163,
              RFC 6303, DOI 10.17487/RFC6303, July 2011,

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

10.2.  Informative References

   [ICANN1]   "New gTLD Collision Risk Mitigation", October 2013,

   [ICANN2]   "New gTLD Collision Occurence Management", October 2013,

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   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [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,

   [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,

   [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,

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <>.

   [SUDN]     "Special-Use Domain Names Registry", July 2012,

Authors' Addresses

   Pierre Pfister
   Cisco Systems


   Ted Lemon
   Nominum, Inc.
   800 Bridge Parkway
   Redwood City, California  94065
   United States of America

   Phone: +1 650 381 6000

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