Network Working Group P. Pfister
Internet-Draft Cisco Systems
Updates: RFC7788 (if approved) T. Lemon
Intended status: Standards Track Nominum, Inc.
Expires: December 9, 2017 June 7, 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 December 9, 2017.

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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction

Users and devices within a home network require devices and services to be identified by names that are unique within the boundaries of the home network [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, home networks must also function in the absence of such a delegation. A default name with a scope limited to each individual home network needs to be used.

The '' domain corrects an error in [RFC7788], replacing '.home' as the default domain-name for home networks. '.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 5), that an unsigned delegation 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 home network, meaning that identical queries will result in different results from one home network 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 home networks.

2. General Guidance

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

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 home network to which they are connected. Enforcing the fulfillment of this intention is out of scope for this document.

3. 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 connected.
  2. Application software SHOULD NOT process names ending in '' specially. In particular, it would not be correct to assign a higher level of trust to such names: although such names might refer to resources on the application user's home network, there is no basis for validating this assumption at a protocol level, and hence such an assumption would create an attack surface for devices roaming to other networks.
  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 home network. 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. Unless configured to serve subdomains of '', recursive resolvers and DNS proxies MUST behave as described in Locally Served Zones ([RFC6303] Section 3). Recursive resolvers that are part of a home network MAY be configured manually or automatically (e.g., for auto-configuration purposes) to act differently, e.g., by querying another name server configured as authoritative for part or all of the '' domain, or proxying the request through a different mechanism.
  5. Only a DNS server that is authoritative for the '.arpa' zone or is configured to be authoritative for '' or a subdomain of '' will ever answer a query about '' In both of these cases, the server should simply answer as configured: no special handling is required. The delegation returned by servers authoritative for '.arpa' will not match the delegation returned by a local resolver that is actually answering for ''
  6. DNS servers outside a home network should not be configured to be authoritative for
  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.

4. Updates to Home Networking Control Protocol

The final paragraph of Homenet Considerations Protocol [RFC7788], section 8, is updated as follows:



5. 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 home network 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 home network scope an answer belongs. Consequently, users may experience surprising results with such names when roaming to different home networks. To prevent this from happening, it may be useful for the resolver to identify different home networks 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 unsigned delegation.

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 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. Delegation of ''

In order to be fully functional, there must be a delegation of '' in the '.arpa' zone [RFC3172]. This delegation MUST NOT be signed, 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 '' on a homenet name server.

7. IANA Considerations

IANA is requested to record the domain name "" in the Special-Use Domain Names registry [SUDN].

8. 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.

9. References

9.1. Normative References

[RFC3172] Huston, G., "Management Guidelines & Operational Requirements for the Address and Routing Parameter Area Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172, September 2001.
[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.

9.2. 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., 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 Paris, France EMail:
Ted Lemon Nominum, Inc. 800 Bridge Parkway Redwood City, California 94065 United States of America Phone: +1 650 381 6000 EMail: