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DNSOP Working Group                                              A. Eden
Internet-Draft                                                  DNSimple
Intended status: Standards Track                          March 29, 2017
Expires: September 30, 2017

                             Alias RR Type


   This document describes a new DNS record type, ALIAS, which is used
   by authoritative name servers to resolve a stored host name to its
   corresponding A or AAAA records at request time.

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
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   This Internet-Draft will expire on September 30, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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1.  Introduction

1.1.  Background and Motivation

   DNS [RFC 1035] forbids the use of CNAME records on a node with other
   records.  It is common practice for web sites publish content on
   their second-level domain name, and currently the only standards-
   compliant way to acheive this is to use A and AAAA records on the
   zone apex.

   The challenge with this limitation is that service providers would
   like to have flexibility over their network addressing but are
   required to communicate any address changes to all customers and give
   appropriate time for customers to update their DNS entries to ensure
   a smooth transition to a new address space.  As the number of
   customers increases for a service provider, this approach becomes
   increasingly difficult to manage and results in difficulties for both
   the service provider and their customers.

   The ALIAS record type (also known as ANAME or flattened CNAME)
   provides a way for DNS managers to specify a hostname in their DNS
   records which is then resolved to the correct A or AAAA records at
   request time.

1.2.  Terminology

   "QTYPE" - The query type as defined in [RFC1035] and subsequent DNS

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  The ALIAS Resource Record

   Its RDATA is comprised of a single field, "target", which contains a
   fully qualified domain name that MUST be sent in uncompressed form
   [RFC1035].  The "target" field MUST be present.  The presentation
   format of "target" is that of a domain name [RFC1035].

   The presentation format of the RR is as follows:

       owner ttl class ALIAS target

   An ALIAS record includes a TTL value that represents the maximum
   time-to-live for a cached ALIAS record response in a resolver.

   The ALIAS RDATA wire representation is only used for zone transfers.

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3.  Implementation

3.1.  Resolution Guidelines

   Authoritative name servers with support for ALIAS records MUST
   support both A and AAAA materialization.  When an authoritative name
   server receives a request for a name, and the zone contains an ALIAS
   record at that location, the authoritative name server MUST respond
   as follows:

   The server will respond with one or more A records (for a QTYPE A) or
   one or more AAAA records (for a QTYPE AAAA) obtained by either: *
   executing a recursive query for the ALIAS content or, * returning a
   previously cached response.

   If the recursive query returns an NXDOMAIN response, then the
   authoritative name server MUST return an NXDOMAIN response as well.

   If the recursive query fails, then the server MAY return a cached
   response as long as the cache value is not older than the specified
   TTL value.

3.2.  TTL Calculation

   As described in section [3.1] the ALIAS is stored with its own TTL
   value.  When an ALIAS is resolved to its corresponding A or AAAA
   records, the authoritative name server MUST return the TTL from the
   resolver response.

   When the authoritative name server uses a cached value, it returns
   the lower TTL value.

3.3.  Handling CNAME QTYPE

   Authoritative name servers that receive a CNAME request at a an ALIAS
   node should treat the request as a QTYPE A.

   Authoritative name servers that receive a CNAME request at an ALIAS
   node MUST treat the request as a QTYPE A.

3.4.  Handling ANY QTYPE

   Authoritative name servers that receive an ANY request at an ALIAS
   node SHOULD respond with any A and AAAA records materialized from the
   ALIAS record.

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4.  Security Considerations

   To function properly with DNSSEC-aware resolvers, authoritative name
   servers MUST sign the materialized records produced by the ALIAS

   Implementors MAY either materialize A and AAAA records offline and
   sign the resulting records at that time, or sign the resulting
   materialized records at request time.

5.  Privacy Considerations

   There are no additional privacy concerns introduced by this document.

6.  IANA Considerations

   This document uses a new DNS RR type, ALIAS, whose value must be
   allocated by IANA from the Resource Record (RR) TYPEs subregistry of
   the Domain Name System (DNS) Parameters registry.

7.  Normative References

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

Author's Address

   Anthony Eden

   Email: anthony.eden@dnsimple.com
   URI:   https://dnsimple.com/

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