Network Working Group                                         P. Pfister
Internet-Draft                                             Cisco Systems
Updates: RFC7788 (if approved)                                  T. Lemon
Intended status: Standards Track                           Nominum, Inc.
Expires: February 9, 11, 2018                               August 8, 10, 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

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   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  General Guidance  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Domain Name Reservation Considerations  . . . . . . . . . . .   3
   5.  Updates to Home Networking Control Protocol . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5   6
   7.  Delegation of ''  . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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.

   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 ''.  It is
   therefore desirable that users identify the domain and understand
   that using it expresses the intention to connect to a service that is
   specific to the homenet to which they are connected.  Enforcing the
   fulfillment of this intention is out of scope for this document.

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
       differently.  Name resolution APIs MUST send queries for such
       names to a recursive DNS server that is configured to be
       authoritative for the '' zone appropriate to the
       homenet.  One or more IP addresses for recursive DNS servers will
       usually be supplied to the client through router advertisements
       or DHCP.  If a host is configured to use a resolver other than
       one that is authoritative for the appropriate '' zone,
       the client may be unable to resolve, or may receive incorrect
       results for, names in sub domains of ''.

   4.  Caching resolvers conforming to this specification MUST support
       DNSSEC queries.  While validation is not required, it is strongly
       encouraged; a caching resolver that does not validate answers
       that can be validated may cache invalid data; this will prevent
       validating stub resolvers from successfully validating answers.

       Unless configured otherwise, recursive resolvers and DNS proxies
       MUST behave as described in Locally Served Zones ([RFC6303]
       Section 3).  Recursive  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 ([RFC4035]
       section 3.2.1) 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.

       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
       '', and, when so configured, MUST NOT attempt ''.

       It is permissible to look
       up a delegation for '' in combine the public DNS.  Of course,
       from an implementation standpoint it may be that a hybrid name
       server acts as a caching recursive resolver or DNS proxy function for non-local
       domains and as
       general DNS lookups with an authoritative server resolver for '' and other
       locally served zones, responding directly to
       ''; in this case, rather than forwarding queries for
       subdomains of '' rather than using a delegation. 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
       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

   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
   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.

   It is not possible to install a trust anchor 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 install a authenticated denial of
   existence ([RFC4033] Section 3.2).  However, this assumes that
   validation is being done on a caching resolver that is aware of the
   special local meaning of ''.  If a host stub resolver
   attempts to validate a name in '', 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 '' to be resolved 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 of names within the ''
   zone is not possible.

   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

   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.

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
   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.

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,

   [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,

   [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