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Internet Engineering Task Force (IETF)                        P. PfisterRequest for Comments: 8375                                 Cisco SystemsUpdates:7788                                                   T. LemonCategory: Standards Track                            Nibbhaya ConsultingISSN: 2070-1721                                                 May 2018Special-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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://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 toBCP 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 Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Pfister & Lemon              Standards Track                    [Page 1]

RFC 8375                       home.arpa.                       May 2018Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Requirements Language . . . . . . . . . . . . . . . . . . . .43.  General Guidance  . . . . . . . . . . . . . . . . . . . . . .44.  Domain Name Reservation Considerations  . . . . . . . . . . .45.  Updates to Home Networking Control Protocol . . . . . . . . .76.  Security Considerations . . . . . . . . . . . . . . . . . . .76.1.  Local Significance  . . . . . . . . . . . . . . . . . . .76.2.  Insecure Delegation . . . . . . . . . . . . . . . . . . .86.3.  Bypassing Manually Configured Resolvers . . . . . . . . .97.  Delegation of 'home.arpa.'  . . . . . . . . . . . . . . . . .98.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .99.  References  . . . . . . . . . . . . . . . . . . . . . . . . .109.1.  Normative References  . . . . . . . . . . . . . . . . . .109.2.  Informative References  . . . . . . . . . . . . . . . . .10   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .12   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .12Pfister & Lemon              Standards Track                    [Page 2]

RFC 8375                       home.arpa.                       May 20181.  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 (seeSection 6), it's   necessary that an insecure delegation (seeSection 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.Pfister & Lemon              Standards Track                    [Page 3]

RFC 8375                       home.arpa.                       May 20182.  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 inBCP 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 inSection 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.Pfister & Lemon              Standards Track                    [Page 4]

RFC 8375                       home.arpa.                       May 2018   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.' (seeSection 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 (seeSection 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 inSection 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.Pfister & Lemon              Standards Track                    [Page 5]

RFC 8375                       home.arpa.                       May 2018           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 inSection 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'.Pfister & Lemon              Standards Track                    [Page 6]

RFC 8375                       home.arpa.                       May 20185.  Updates to Home Networking Control Protocol   The final paragraph inSection 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 Considerations6.1.  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.Pfister & Lemon              Standards Track                    [Page 7]

RFC 8375                       home.arpa.                       May 2018   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 (seeSection 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 (seeSection 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 inSection 7 of [RFC6303].Pfister & Lemon              Standards Track                    [Page 8]

RFC 8375                       home.arpa.                       May 2018   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 ofSection 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 inSection 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" (seeSection 4.8 of [RFC8126]).Pfister & Lemon              Standards Track                    [Page 9]

RFC 8375                       home.arpa.                       May 20189.  References9.1.  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 inRFC2119 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>.Pfister & Lemon              Standards Track                   [Page 10]

RFC 8375                       home.arpa.                       May 2018   [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/>.Pfister & Lemon              Standards Track                   [Page 11]

RFC 8375                       home.arpa.                       May 2018Acknowledgments   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.comPfister & Lemon              Standards Track                   [Page 12]