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Versions: (draft-sullivan-domain-origin-assert) 00 01 02

IETF                                                         A. Sullivan
Internet-Draft                                                 Dyn, Inc.
Intended status: Standards Track                               J. Hodges
Expires: August 21, 2016                                          PayPal
                                                       February 18, 2016

        Asserting DNS Administrative Boundaries Within DNS Zones


   Some entities on the Internet make inferences about the
   administrative relationships among Internet services based on the
   domain names at which those services are offered.  At present, it is
   not possible to ascertain organizational administrative boundaries in
   the DNS; therefore such inferences can be erroneous.  Mitigation
   strategies deployed so far will not scale.  This memo provides a
   means to make explicit assertions regarding certain kinds of
   administrative relationships between domain names.

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 http://datatracker.ietf.org/drafts/current/.

   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 August 21, 2016.

Copyright Notice

   Copyright (c) 2016 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
   (http://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

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   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 and Motivation . . . . . . . . . . . . . . . . .   3
     1.1.  Organization of This Memo . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Start Of Policy Authority (SOPA)  . . . . . . . .   4
     3.1.  Identifying a Target Name for Policy
           Authority . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Where SOPA Works Well . . . . . . . . . . . . . . . . . .   7
     4.2.  Where SOPA Works Less Well  . . . . . . . . . . . . . . .   8
   5.  The SOPA Resource Record  . . . . . . . . . . . . . . . . . .   8
     5.1.  The Relation Field  . . . . . . . . . . . . . . . . . . .   9
     5.2.  The Target Field  . . . . . . . . . . . . . . . . . . . .   9
   6.  Expressing Different Policies with the SOPA RRTYPE  . . . . .  10
     6.1.  The Exclusion Relation  . . . . . . . . . . . . . . . . .  11
     6.2.  The Inclusion Relation  . . . . . . . . . . . . . . . . .  11
     6.3.  Interpreting DNS Responses  . . . . . . . . . . . . . . .  12
     6.4.  Wildcards in Targets  . . . . . . . . . . . . . . . . . .  12
     6.5.  TTLs and SOPA RRs . . . . . . . . . . . . . . . . . . . .  14
   7.  What Can be Done With a SOPA RR . . . . . . . . . . . . . . .  14
     7.1.  Exclusion has Priority  . . . . . . . . . . . . . . . . .  14
   8.  An Example Case . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Examples of Using the SOPA Record for Determining
           Boundaries  . . . . . . . . . . . . . . . . . . . . . . .  16
       8.1.1.  Declaring a Public Suffix . . . . . . . . . . . . . .  16
       8.1.2.  One Delegation, Eight Administrative
               Realms, Wildcard Exclusions . . . . . . . . . . . . .  16
       8.1.3.  One Delegation, Eight Administrative
               Realms, Exclusion Wildcards . . . . . . . . . . . . .  17
   9.  Limitations of the approach and other considerations  . . . .  17
     9.1.  Handling truncation . . . . . . . . . . . . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   11. Internationalization Considerations . . . . . . . . . . . . .  19
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     14.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Discussion Venue . . . . . . . . . . . . . . . . . .  22
   Appendix B.  Change History . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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1.  Introduction and Motivation

   Many Internet resources and services, especially at the application
   layer, are identified primarily by domain names [RFC1034].  As a
   result, domain names have become fundamental elements in building
   security policies and also in affecting user agent behaviour.
   Discussion of several of these uses, and some of the associated
   issues can be found in [I-D.sullivan-dbound-problem-statement].

   Historically, attempts to build the security policies have relied on
   the public suffix list (see discussion in
   [I-D.sullivan-dbound-problem-statement]).  We proceed from the view
   that some uses of the public-suffix list never were going to achieve
   their goal, and that the public/private distinction may be a poor
   proxy for the kinds of relationships that are actually needed.  At
   the same time, it will be necessary to continue to use something like
   a public suffix list for some important classes of behaviour (both to
   achieve acceptable performance characteristics and to deal with
   deployed software).  Therefore, the proposal below does not attempt
   to address all the issues in [I-D.sullivan-dbound-problem-statement],
   but offers a way to solve one important class of problems -- the
   "orphan type" policies.

1.1.  Organization of This Memo

   [[CREF1: I find this section awkward here.  Ditch it?

   Necessary terminology is established in Section 2.  Section 3
   provides an overview of what the mechanism is supposed to do.  Then,
   Section 4 discusses the conditions where the technique outlined here
   may be useful, and notes some cases that the technique is not
   intended solve.  A definition of a new RRTYPE to support the
   technique is in Section 5.  There is some discussion of the use of
   the RRTYPE in Section 6.  Section 7 attempts to show how the
   mechanism is generally useful.  Then, Section 8 offers an example
   portion of a DNS tree in an effort to illustrate how the mechanism
   can be useful in certain example scenarios.  Section 9 notes some
   limitations of the mechanism.  Section 10 outlines how the mechanism
   might be used securely, and Section 11 addresses the
   internationalization consequences of the SOPA record.  Finally,
   Section 12 includes the requests to IANA for registration.

2.  Terminology

   The reader is assumed to be familiar with the DNS ([RFC1034]
   [RFC1035]) and the Domain Name System Security Extensions (DNSSEC)

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   ([RFC4033] [RFC4034] [RFC4035] [RFC5155]).  A number of DNS terms can
   be found in [RFC7719].

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

   The terms "policy realm" and "policy authority" are defined in
   [I-D.sullivan-dbound-problem-statement].  For the purposes of
   discussion here, it is important to remember that it is a matter of
   fact as to whether two domains lie in the same policy realm.  The
   point of the mechanism here is not to create such facts, but merely
   to expose them.  The terms "inheritance type" and "orphan type" are
   also defined in [I-D.sullivan-dbound-problem-statement].  The text
   below attempts to apply the categories when they seem useful.

3.  Overview of Start Of Policy Authority (SOPA)

   When an application is attempting to make security decisions based on
   domain names, it needs to answer questions about the relation between
   those names.  Suppose that the question to be answered is, "Given any
   two domain names, do they lie in the same policy realm appropriate
   for a given application?"  In order to answer this, there are two
   pieces of information needed: first, does the application need an
   inheritance or orphan type of policy?  Second do the two names lie in
   the same policy realm?  For orphan types of policy, the best way to
   determine whether two names lie in the same policy realm is to look
   for assertions about the two domain names.  A good place to look for
   assertions about domain names is in the DNS.

   This memo presents a way to assert that two domains lie in the same
   policy realm by placing a resource record (RR) at the affected domain
   names in the DNS.  The mechanism requires a new resource record type
   (RRTYPE).  It is called SOPA, for "Start Of Policy Authority" and
   echoing the Start Of Authority or SOA record.  While there are
   reported difficulties in deploying new RRTYPEs, the only RRTYPE that
   could be used to express all the necessary variables is the TXT
   record, and it is unsuitable because it can also be used for other
   purposes (so it needs to be covered itself).  The use of this
   mechanism does not require "underscore labels" to scope the
   interpretation of the RR, in order to make it possible to use the
   mechanism where the underscore label convention is already in use.
   The SOPA RRTYPE is class-independent.

   The use of SOPA records can do one of two things: it can confirm that
   two names are in the same policy realm, or it can refute a claim that
   they are.  In order to learn whether a.long.example.com and
   b.example.com are in the same policy realm, perform a DNS query for

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   the SOPA record for a.long.example.com.  If the answer's RDATA
   contains b.example.com, that is an assertion from the nameservers for
   a.long.example.com that it is in the same policy realm as
   b.example.com.  Next, make a DNS query for the SOPA record for
   b.example.com.  If the answer's RDATA contains a.long.example.com,
   then the two names are in the same policy realm.  A positive policy
   realm relationship ought to be symmetric: if example.com is in the
   same policy realm as example.net, then example.net should be (it
   would seem) in the same policy realm as example.com.  In principle,
   then, if a SOPA RR at a.long.example.com provides a target at
   b.example.com, there should be a complementary SOPA RR at
   b.example.com with a target of a.long.example.com.  Because of the
   distributed nature of the DNS, and because other DNS administrative
   divisions need not be congruent to policy realms, the only way to
   know whether two domain names are in the same policy realm is to
   query at each domain name, and to correlate the responses.  If any of
   the forgoing conditions fails, then the two names are not in the same
   policy realm.

   [[CREF2: Something that could be useful here is a transitivity bit in
   the SOPA record.  That would allow SOPAs between a.example.com and
   example.com, and b.example.com and example.com, to mean that
   a.example.com and b.example.com are also in the same realm (but you
   could shut it off by clearing the bit).  I'm leery of this because of
   the potential for abuse and also because I doubt it saves very much.
   Might be useful for administrative saving, but it won't save lookups.

   It is also possible for a SOPA record to contain the explicit
   statement that other names do not lie in the same policy authority as
   it.  This negative assertion permits processing to stop.  If the
   assertion is about all other names, then the capability is
   functionally equivalent to declaring a name to be a public suffix.

   In operation where latency is an important consideration (such as in
   a web browser), it is anticipated that the above correlations could
   happen in advance of the user connection (that is, roughly the way
   the existing public suffix list is compiled), and then additional
   queries could be undertaken opportunistically.  This would allow the
   detection of changes in operational policy and make maintenance of
   the installed list somewhat easier, but not require additional DNS
   lookups while a user is waiting for interaction.

   While many policies of the sort discussed in
   [I-D.sullivan-dbound-problem-statement] appear to be based on domain
   names, they are actually often only partly based on them.  Often,
   there are implicit rules that stem from associated components of
   composite names such as URIs [RFC3986], e.g., the destination port

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   [RFC6335] or URI scheme [RFC4395] (or both).  It is possible to make
   those assumptions explicit, but at the cost of expressing in the
   resulting resource record a tighter relationship between the DNS and
   the services offered at domain names.  SRV [RFC2782] records offer a
   mechanism for expressing such relationships, and a SOPA record in
   conjunction with an SRV record appears to provide the necessary
   mechanism to express such relationships.  (SRV records use underscore
   labels, and this is an example of why underscore labels themselves
   need to be coverable by SOPA records.)

3.1.  Identifying a Target Name for Policy Authority

   The RDATA of a SOPA RR contains a "target name" that either lies in
   the same policy realm as the owner name of the RR, or that lies
   outside of that policy realm.  The SOPA record is therefore an
   assertion, on the part of the authoritative DNS server for the given
   owner name, that there is some policy relationship between the owner
   name and the target name.  If a given owner name lies in the same
   policy realm as several other target names, an additional RR is
   necessary for each such relationship, with one exception.  It is not
   uncommon for a name to have policy relationships with all the
   children beneath it.  Using the SOPA RR, it is possible to specify
   that the policy target is all the names beneath a given owner name,
   by using a wildcard target.

4.  Use Cases

   In the most general sense, this memo presents a mechanism that can be
   used either as a replacement of the public suffix list
   <publicsuffix.org>, or else as a way to build and maintain such a
   list.  Performance characteristics may make the mechanism impractical
   as a full replacement, in which case a list will likely need to be
   built and maintained.  In the latter case, this mechanism is still
   preferable because it aligns the policy assertions with the operation
   of the domains themselves, and allows maintenance to be distributed
   in much the way the operation of the DNS is (instead of being

   It is worth noting that the mechanism outlined here could be used for
   names that are not along the same branch of the DNS tree (i.e. it
   could permit the statement that the policy authority of
   some.example.com and some.other.example.net is the same).  Such uses
   are unlikely to work in practice and probably should not be used for
   general purposes.  Most deployed code implicitly uses ancestor-
   descendent relations as part of understanding the policy, and such
   code will undoubtedly ignore cross-tree dependencies.  [[CREF3: This
   relaxes a restriction that was in previous versions, which officially
   specified the use only for ancestor-descendent uses.  It seems better

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   to make that a deployment consideration so that the restriction could
   be relaxed in some circumstances where it would be appropriate.

   By and large, the mechanism is best suited to "orphan" types of
   policy.  Where inheritance types of policy can use this, it is mostly
   by treating the mechanism as a generator for public suffix

4.1.  Where SOPA Works Well

   HTTP state management cookies  The mechanism can be used to determine
      the scope for data sharing of HTTP state management cookies
      [RFC6265].  Using this mechanism, it is possible to determine
      whether a service at one name may be permitted to set a cookie for
      a service at a different name.  (Other protocols use cookies, too,
      and those approaches could benefit similarly.)  Because handling
      of state management cookies often happens during user interaction,
      this use case probably requires a cached copy of the relevant
      list.  In that case, the mechanism can be used to maintain the

   User interface indicators  User interfaces sometimes attempt to
      indicate the "real" domain name in a given domain name.  A common
      use is to highlight the portion of the domain name believed to be
      the "real" name -- usually the rightmost three or four labels in a
      domain name string.  This has similar performance needs as HTTP
      state management cookies.

   Setting the document.domain property  The DOM same-origin policy
      might be helped by being able to identify a common policy realm.
      This case again has a need for speedy determination of the
      appropriate policy and would benefit from a cached list.  It is
      likely that the SOPA record on its own is inadequate for this
      case, but the combination of SOPA and SRV records might be

   SSL and TLS certificates  Certificate authorities need to be able to
      discover delegation-centric domains in order to avoid issuance of
      certificates at or above those domains.  More generally, a CA
      needs to decide whether, given a request, it should sign a
      particular domain.  This can be especially tricky in the case of

   HSTS and Public Key Pinning with               includeSubDomains flag
      Clients that are using HSTS and public key pinning using
      includeSubDomains need to be able to determine whether a subdomain

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      is properly within the policy realm of the parent.  An application
      performing this operation must answer the question, "Should I
      accept the rules for using X as valid for Y.X?"  This use case
      sounds like an inheritance type, but it is in fact an orphan type.

   Linking domains together for reporting               purposes  It can
      be useful when preparing reports to be able to count different
      domains as "the same thing".  This is an example where special use
      of SOPA even across the DNS tree could be helpful.

4.2.  Where SOPA Works Less Well

   Email authentication mechanisms  Mail authentication mechanisms such
      as DMARC [RFC7489] need to be able to find policy documents for a
      domain name given a subdomain.  This use case is an inheritance
      type.  Because the point of mechanisms like DMARC is to prevent
      abuse, it is not possible to rely on the candidate owner name to
      report accurately its policy relationships.  But some ancestor is
      possibly willing to make assertions about the policy under which
      that ancestor permits names in the name space.  This sort of case
      can only use SOPA indirectly, via a static list that is composed
      over time by SOPA queries.  Other mechanisms will likely better
      satisfy this need.

5.  The SOPA Resource Record

   The SOPA resource record, type number [TBD1], contains two fields in
   its RDATA:

   Relation:   A one-octet field used to indicate the relationship
               between the owner name and the target.

   Target:     A field used to contain a fully-qualified domain name
               that is in some relationship with the owner name.  This
               field is a maximum of 255 octets long, to match the
               possible length of a fully-qualified domain name.

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |   Relation    |                                               /
      +-+-+-+-+-+-+-+-+                                               /
      /                            Target                             /
      /                                                               /
      /                                                               /

                                 Figure 1

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5.1.  The Relation Field

   The relation field is REQUIRED and contains an indicator of the
   relationship between the owner name and the target name.  This memo
   specifies two possible values:

   | Value | Setting  | Meaning                                        |
   | 0     | Excluded | The target is not in the same policy realm as  |
   |       |          | the owner name                                 |
   | 1     | Included | The target is in the same policy realm as the  |
   |       |          | owner name                                     |

                                  Table 1

   Additional values may be defined in future, according to the rules
   set out in Section 12.

5.2.  The Target Field

   The target field contains a fully-qualified domain name, and is
   REQUIRED to be populated.  The name MUST be a domain name according
   to the rules in [RFC1034] and [RFC1035], except that the any label of
   the target MAY be the wildcard character ("*"; further discussion of
   wildcards is in Section 6.4).  The target MUST be sent in
   uncompressed form [RFC1035], [RFC3597].  The target MUST NOT be an
   alias [RFC2181], such as the owner name of a CNAME RR [RFC1034],
   DNAME RR [RFC6672], or other similar such resource records.  Note
   that this is a fully-qualified domain name, so the trailing null
   label is required.  [[CREF4: This is a change from previous versions;
   previously, the target was a root-relative domain name.  So it's now
   example.com. and used to be example.com (no trailing dot) when in
   presentation format.  The new form makes this a domain name, whereas
   before it could really have been a text field.  Not sure which is
   better.  --ajs@anvilwalrusden.com]]

   The target name SHOULD be either an ancestor, a descendent, or a
   sibling of the owner name in the record.  This requirement is
   intended to limit the applicability of the SOPA RR to names in the
   same DNS hierarchy, thereby avoiding possible negative side effects
   of unbounded linkages across disparate DNS subtrees, including those
   subtrees rooted close to, or immediately below, the DNS root.  In
   special uses, however, it may be desirable to link across the DNS
   tree.  General-purpose clients MAY ignore target names that are
   neither an ancestor, nor a descendent, nor a sibling of the owner

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   name in the record (and abort processing) in order to avoid the
   aforementioned negative side-effects.

   Targets MAY contain any series of octets, in order to accommodate
   labels other than LDH labels [RFC6365].  No processing of labels
   prior to matching targets is to be expected, however, and therefore
   internationalized domain name targets use whatever form they appear
   in the DNS.  In particular, IDNA labels [RFC5890], [RFC5891],
   [RFC5892], [RFC5893], [RFC5894] SHOULD appear in A-label form.  A
   SOPA-using client that receives a target containing octets outside
   LDH MUST NOT treat the affected labels as U-labels, because there is
   no way to discover whether the affected label is encoded as UTF-8 or
   something else.

6.  Expressing Different Policies with the SOPA RRTYPE

   A SOPA RR has one of three different functions.  The first is to
   claim that two domain names are not in the same policy realm
   ("exclusion").  The second is to claim that two domain names are in
   the same policy realm ("inclusion").  In both of these cases, it is
   possible to make the assertion over groups of DNS names.

   The third function describes a portion of the tree that would be
   covered by targets containing a wildcard, but where the policy is the
   opposite of that expressed with the wildcard.  This is expressed
   simply by including the relevant specific exception.  For example,
   all the subdomains under example.com could be indicated in a target
   "*.example.com".  To express a different policy for
   exception.example.com than for the rest of the names under
   example.com requires two SOPA RRs, one with the target
   "*.example.com" and the other with the target
   "exception.example.com".  The most-specific match to a target always

   Is is important to note that the default setting is "exclusion".  A
   domain name does not lie in any other name's policy realm unless
   there is an explicit statement by appropriate SOPA resource record(s)
   to the contrary.  If a candidate name does not appear in the target
   of any SOPA record for some owner name, then that candidate target
   does not lie in the same policy realm as that owner name.

   It is acceptable for there to be more than one SOPA resource record
   per owner name in a response.  Each RR in the returned RRset is
   treated as a separate policy statement about the original queried
   name (QNAME).  Note, however, that the QNAME might not be the owner
   name of the SOPA RR: if the QNAME is an alias, then the actual SOPA
   owner name in the DNS database will be different than the QNAME.  In
   other words, even though a SOPA target field is not allowed to be an

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   an alias, when resolving the SOPA RR aliases are followed; and SOPA
   records are accepted transitively from the canonical name back to the

6.1.  The Exclusion Relation

   A SOPA record where the relation field has value 0 states that the
   owner name and the target name are not in the same policy realm.
   While this might seem useless (given the default of exclude), a SOPA
   record with a relation field value of 0 can be useful in combination
   with a long TTL field, in order to ensure long term caching of the

   In addition, an important function of SOPA is to enable the explicit
   assertion that no other name lies in the same policy realm as the
   owner name (or, what is equivalent, that the owner name should be
   treated as a public suffix).  In order to achieve this, the operator
   of the zone may use a wildcard target together with a relation field
   value of 0.  See Section 6.4.

   In addition, an more-specific target can be used to override a more
   general target (i.e. with a wildcard in the target) at the same owner
   name.  For example,

         example.tld   86400 IN    SOPA  0  *.example.tld

         example.tld   86400 IN    SOPA  1  www.example.tld

   A SOPA-using client that receives a SOPA resource record with a
   relation value of 0 MUST treat the owner name and the target name as
   lying in different policy realms.

6.2.  The Inclusion Relation

   A SOPA record with a relation field set to 1 is an indicator that the
   target name lies in the same policy realm as the owner name.  In
   order to limit the scope of security implications, the target name
   and the owner name SHOULD stand in some ancestor-descendant or
   sibling relationship to one another.  A SOPA-using client that is not
   prepared for inclusion relationships outside the same branch of the
   DNS MAY ignore such relationships and treat them as though they did
   not exist.

   The left-most label of a target may be a wildcard record, in order to
   indicate that all descendant or sibling names lie in the same policy
   realm as the owner name.  See Section 6.4.

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   A SOPA-using client that receives a SOPA resource record where
   relation is set to 1 SHOULD treat the owner name and the target name
   as lying in the same policy realm.  If a client does not, it is
   likely to experience unexpected failures because the client's policy
   expectations are not aligned with those of the service operator.

6.3.  Interpreting DNS Responses

   There are three possible responses to a query for the SOPA RRTYPE at
   an owner name that are relevant to determining the policy realm.  The
   first is Name Error (RCODE=3, also known as NXDOMAIN).  In this case,
   the owner name itself does not exist, and no further processing is

   The second is a No Data response [RFC2308] of any type.  The No Data
   response means that the owner name in the QNAME does not recognize
   any other name as part of a common policy realm.  That is, a No Data
   response is to be interpreted as though there were a SOPA resource
   record with relation value 0 and a wildcard target.  The TTL on the
   policy in this case is the negative TTL from the SOA record, in case
   it is available.

   The final is a response with one or more SOPA resource records in the
   Answer section.  Each SOPA resource record asserts a relationship
   between the owner name and the target name, according to the
   functions of the SOPA RRTYPE outlined above.

   Any other response is no different from any other sort of response
   from the DNS, and is not in itself meaningful for determining the
   policy realm of a name (though it might be meaningful for finding the
   SOPA record).

6.4.  Wildcards in Targets

   The special character "*" in the target field is used to match any
   label, but not according to the wildcard label rules in section 4.3.3
   of [RFC1034].  Note that, because of the way wildcards work in the
   DNS, is it not possible to place a restriction to the left of a
   wildcard; so, for instance, example.*.example.com. does not work.  In
   a SOPA target, it is possible to place such a restriction.  In such
   use, a wildcard label matches exactly one label:
   example.*.example.com. matches the target example.foo.example.com.
   and example.bar.example.com., but not example.foo.bar.example.com.
   To match the latter, it would be necessary also to include
   example.*.*.example.com, which is also permitted in a target.  This
   use of the wildcard is consistent with the use in

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   If a SOPA target's first label is a wildcard label, the wildcard then
   matches any number of labels.  Therefore, a target of *.example.com.
   matches both onelabel.example.com. and two.labels.example.com.; the
   second match would not be a match in the DNS.  This use of the
   wildcard label does not match the public suffix list, but is included
   for brevity of RRsets for certain presumed-common cases.  This rule
   is subject to more-specific matching (as discussed in Section 6.1 and
   Section 6.2).  To simplify implementation, more-specific matches
   cannot have internal wildcards as described above.

   The reason for these differences in wildcard-character handling is
   because of the purpose of the wildcard character.  In DNS matching,
   processing happens label by label proceeding down the tree, and the
   goal is to find a match.  But in the case of SOPA, the candidate
   match is presumed available, because the application would not
   perform a SOPA look up if there were not a different target domain at
   hand.  Therefore, strict conformance with the DNS semantics of the
   wildcard is not necessary.  It is useful to be able to express
   potential matches as briefly as possible, to keep DNS response sizes

   Multiple leading wildcard labels (e.g. *.*.example.com.) is an error.
   An authoritative name server SHOULD NOT serve a SOPA RR with
   erroneous wildcards when it is possible to suppress them, and clients
   receiving such a SOPA RR MUST discard the RR.  If the discarded RR is
   the last RR in the answer section of the response, then the response
   is treated as a No Data response.

   It is possible for the wildcard label to be the only label in the
   target name.  In this case, the target is "every name".  This makes
   it trivial for an owner name to assert that there are no other names
   in its policy realm.

   Because it would be absurd for there to be more than one SOPA RR with
   the same target (including wildcard target) in a SOPA RRset, a server
   encountering more than one such target SHOULD only serve the RR for
   the exclusion relation, discarding others when possible.  Discarding
   other RRs in the RRset is not possible when serving a signed RRset.
   A client receiving multiple wildcard targets in the RRset MUST use
   only the RR with relation set to 0.

   As already noted, when a SOPA RR with a wildcard target appears in
   the same RRset as a SOPA RR with a target that would be covered by
   the wildcard, the specific (non-wildcard) RR expresses the policy for
   that specific owner name/target pair.  This way, exceptions to a
   generic policy can be expressed.

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6.5.  TTLs and SOPA RRs

   The TTL field in the DNS is used to indicate the period (in seconds)
   during which an RRset may be cached after first encountering it (see
   [RFC1034]).  As is noted in Section 4, however, SOPA RRs could be
   used to build something like the public suffix list, and that list
   would later be used by clients that might not themselves have access
   to SOPA DNS RRsets.  In order to support that use as reliably as
   possible, a SOPA RR MAY continue to be used even after the TTL on the
   RRset has passed, until the next time that a SOPA RRset from the DNS
   for the owner name (or a No Data response) is available.  It is
   preferable to fetch the more-current data in the DNS, and therefore
   if such DNS responses are available, a SOPA-aware client SHOULD use
   them.  Note that the extension of the TTL when DNS records are not
   available does not extend to the use of the negative TTL field from
   No Data responses.

7.  What Can be Done With a SOPA RR

   Use of a SOPA RR enables a site administrator to assert or deny
   relationships between names.  By the same token, it permits a a
   consuming client to detect these assertions and denials.

   The use of SOPA RRs could either replace the public suffix list or
   (often more likely due to some limitations -- see Section 9) simplify
   and automate the management of the public suffix list.  A client
   could use the responses to SOPA queries to refine its determinations
   about http cookie Domain attributes.  In the absence of SOPA RRs at
   both owner names, a client might treat a Domain attribute as though
   it were omitted.  More generally, SOPA RRs would permit additional
   steps similar to steps 4 and 5 in [RFC6265].

   SOPA RRs might be valuable for certificate authorities when issuing
   certificates, because it would allow them to check whether two names
   are related in the way the party requesting the certificate claims
   they are.

7.1.  Exclusion has Priority

   In order to minimize the chance of policy associations where none
   exist, this memo always assumes exclusion unless there is an explicit
   policy for inclusion.  Therefore, a client processing SOPA records
   can stop as soon as it encounters an exclusion record: if a parent
   record excludes a child record, it makes no difference whether the
   child includes the parent in the policy realm, and conversely.  By
   the same token, an inclusion SOPA record that specifies a target,
   where the target does not publish a corresponding inclusion SOPA
   record, is not effective.

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8.  An Example Case

   For the purposes of discussion, it will be useful to imagine a
   portion of the DNS, using the domain example.tld.  A diagram of the
   tree of this portion is in Figure 2.  In the example, the domain
   example.tld includes several other names: www.example.tld,
   account.example.tld, cust1.example.tld, cust2.example.tld,
   test.example.tld, cust1.test.example.tld, and cust2.test.example.tld.

                     ------example -----
                    /     /   |  \      \
                   /     /    |   \      \
                  /   www  account \      cust2
              test                  \
             /   \                   cust1
         cust1   cust2

                                 Figure 2

   In the example, the domain tld delegates the domain example.tld.
   There are other possible cut points in the example, and depending on
   whether the cuts exist there may be implications for the use of the
   examples.  See Section 8.1, below.

   The (admittedly artificial) example permits us to distinguish a
   number of different roles.  To begin with, there are three parties
   involved in the operation of services:

   o  OperatorV, the operator of example.tld;

   o  Operator1, the operator of cust1.example.tld;

   o  Operator2, the operator of cust2.example.tld.

   Since there are three parties, there are likely three administrative
   boundaries as well; but the example contains some others.  For
   instance, the names www.example.tld and example.tld are in this case
   in the same policy realm.  By way of contrast, account.example.tld
   might be treated as completely separate, because OperatorV might wish
   to ensure that the accounts system is never permitted to share
   anything with any other name.  By the same token, the names
   underneath test.example.tld are actually the test-instance sites for
   customers.  So cust1.test.example.tld might be in the same policy
   realm as cust1.example.tld, but test.example.tld is certainly not in
   the same administrative realm as www.example.tld.

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   Finally, supposing that Operator1 and Operator2 merge their
   operations, it seems that it would be useful for cust1.example.tld
   and cust2.example.tld to lie in the same policy realm, without
   including everything else in example.tld.

8.1.  Examples of Using the SOPA Record for Determining Boundaries

   This section provides some examples of different configurations of
   the example tree in Section 8, above.  The examples are not
   exhaustive, but may provide an indication of what might be done with
   the mechanism.

8.1.1.  Declaring a Public Suffix

   Perhaps the most important function of the SOPA RR is to identify
   public suffixes.  In this example, the operator of TLD publishes a
   single SOPA record:

      tld.  86400 IN SOPA 0 *.

8.1.2.  One Delegation, Eight Administrative Realms, Wildcard Exclusions

   In this scenario, the example portion of the domain name space
   contains all and only the following SOPA records:

      example.tld.  86400 IN SOPA 1 www.example.tld.

      www.example.tld.  86400 IN SOPA 1 example.tld.

   Tld is the top-level domain, and has delegated example.tld.  The
   operator of example.tld makes no delegations.  There are four
   operators involved: the operator of tld; OperatorV; Operator1, the
   operator of the services at cust1.example.tld and
   cust1.test.example.tld; and Operator2, the operator of the services
   at cust2.example.tld and cust2.test.example.tld.

   In this arrangement, example.tld and www.example.tld positively claim
   to be within the same policy realm.  Every other name stands alone.
   A query for an SOPA record at any of those other names will result in
   a No Data response, which means that none of them include any other
   name in the same policy realm.  As a result, there are eight separate
   policy realms in this case: tld, {example.tld and www.example.tld},
   test.example.tld, cust1.test.example.tld, cust2.test.example.tld,
   account.example.tld, cust1.example.tld, and cust2.example.tld.

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8.1.3.  One Delegation, Eight Administrative Realms, Exclusion Wildcards

   This example mostly works the same way as the one in
   Section Section 8.1.2, but there is a slight difference.  In this
   case, in addition to the records listed in Section 8.1.2, both tld
   and test.example.tld publish exclusion of all names in their SOPA

      tld.  86400 IN SOPA 0 *.

      test.example.tld.  86400 IN SOPA 0 *.

   The practical effect of this is largely the same as the previous
   example, except that these expressions of policy last (at least)
   86,400 seconds instead of the length of time on the negative TTL in
   the relevant SOA for the zone.  Many zones have short negative TTLs
   because of expectations that newly-added records will show up
   quickly.  This mechanism permits such names to express their
   administrative isolation for predictable minimum periods of time.  In
   addition, because clients are permitted to retain these records
   during periods when DNS service is not available, a client could go
   offline for several weeks, and return to service with the presumption
   that test.example.tld is still not in any policy realm with any other

9.  Limitations of the approach and other considerations

   There are four significant problems with this proposal, all of which
   are related to using DNS to deliver the data.

   The first is that new DNS RRTYPEs are difficult to deploy.  While
   adding a new RRTYPE is straightforward, many provisioning systems do
   not have the necessary support and some firewalls and other edge
   systems continue to filter RRTYPEs they do not know.  This is yet
   another reason why this mechanism is likely to be initially more
   useful for constructing and maintaining the public suffix list than
   for real-time queries.

   The second is that it is difficult for an application to obtain data
   from the DNS.  The TTL on an RRset, in particular, is usually not
   available to an application, even if the application uses the
   facilities of the operating system to deliver other parts of an
   unknown RRTYPE.

   The third, which is mostly a consequence of the above two, is that
   there is a significant barrier to adoption: until browsers have

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   mostly all implemented this, operations need to proceed as though
   nobody has.  But browsers will need to support two mechanisms for
   some period of time if they are to implement this mechanism at all,
   and they are unlikely to want to do that.  This may mean that there
   is no reason to implement, which also means no reason to deploy.
   This is made worse because, to be safe, the mechanism really needs
   DNSSEC, and performing DNSSEC validation at end points is still an
   unusual thing to do.  This limitation may not be as severe for use-
   cases that are directed higher in the network (such as using this
   mechanism as an automatic feed to keep the public suffix list
   updated, or for the use of CAs when issuing certificates).  This
   limitation could be reduced by using SOPA records to maintain
   something like the current public suffix list in an automatic

   Fourth, in many environments the system hosting the application has
   only proxied access to the Internet, and cannot query the DNS
   directly.  It is not clear how such clients could ever possibly
   retrieve the SOPA record for a name.

9.1.  Handling truncation

   It is possible to put enough SOPA records into a zone such that the
   resulting response will exceed DNS or UDP protocol limits.  In such
   cases, a UDP DNS response will arrive with the TC (truncation) bit
   set.  A SOPA response with the TC bit must be queried again in order
   to retrieve a complete response, generally using TCP.  This increases
   the cost of the query, increases the time to being able to use the
   answer, and may not work at all in networks where administrators
   mistakenly block port 53 using TCP.

10.  Security Considerations

   This mechanism enables publication of assertions about administrative
   relationships of different DNS-named systems on the Internet.  If
   such assertions are accepted without checking that both sides agree
   to the assertion, it would be possible for one site to become an
   illegitimate source for data to be consumed in some other site.  In
   general, assertions about another name should never be accepted
   without querying the other name for agreement.

   Undertaking any of the inferences suggested in this draft without the
   use of the DNS Security Extensions exposes the user to the
   possibility of forged DNS responses.

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11.  Internationalization Considerations

   There is some discussion of how to treat targets that appear to have
   internationalized data in Section 5.2.  Otherwise, this memo raises
   no internationalization considerations.

12.  IANA Considerations

   IANA will be requested to register the SOPA RRTYPE if this proceeds.

   IANA will be requested to create a SOPA relation registry if this
   proceeds.  The initial values are to be found in the table in
   Section 5.1.  Registration rules should require a high bar, because
   it's a one-octet field.  Maybe RFC required?

13.  Acknowledgements

   The authors thank Adam Barth, Dave Crocker, Brian Dickson, Phillip
   Hallam-Baker, John Klensin, Murray Kucherawy, John Levine, Gervase
   Markham, Patrick McManus, Henrik Nordstrom, Yngve N.  Pettersen, Eric
   Rescorla, Thomas Roessler, Peter Saint-Andre, and Maciej Stachowiak
   for helpful comments.

14.  References

14.1.  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,

14.2.  Informative References

              Sullivan, A., Hodges, J., and J. Levine, "DBOUND: DNS
              Administrative Boundaries Problem Statement", draft-
              sullivan-dbound-problem-statement-01 (work in progress),
              July 2015.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [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>.

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   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              DOI 10.17487/RFC2782, February 2000,

   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
              (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
              2003, <http://www.rfc-editor.org/info/rfc3597>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,

   [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,

   [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,

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", RFC 4395,
              DOI 10.17487/RFC4395, February 2006,

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,

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   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,

   [RFC5891]  Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891,
              DOI 10.17487/RFC5891, August 2010,

   [RFC5892]  Faltstrom, P., Ed., "The Unicode Code Points and
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5892, DOI 10.17487/RFC5892, August 2010,

   [RFC5893]  Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts
              for Internationalized Domain Names for Applications
              (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,

   [RFC5894]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Background, Explanation, and
              Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,

   [RFC6365]  Hoffman, P. and J. Klensin, "Terminology Used in
              Internationalization in the IETF", BCP 166, RFC 6365,
              DOI 10.17487/RFC6365, September 2011,

   [RFC6672]  Rose, S. and W. Wijngaards, "DNAME Redirection in the
              DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,

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   [RFC7489]  Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
              Message Authentication, Reporting, and Conformance
              (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <http://www.rfc-editor.org/info/rfc7719>.

Appendix A.  Discussion Venue

   This Internet-Draft is discussed in the dbound working group:

Appendix B.  Change History

   00 to 01:

      *  Changed the mnemonic from BOUND to AREALM

      *  Added ports and scheme to the RRTYPE

      *  Added some motivating text and suggestions about what can be
         done with the new RRTYPE

      *  Removed use of "origin" term, because it was confusing.  The
         document filename preserves "origin" in the name in order that
         the tracker doesn't lose the change history, but that's just a

      *  Removed references to cross-document information sharing and
         ECMAScript.  I don't understand the issues there, but Maciej
         Stachowiak convinced me that they're different enough that this
         mechanism probably won't work.

      *  Attempted to respond to all comments received.  Thanks to the
         commenters; omissions and errors are mine.

   01 to 02:

      *  Changed mnemonic again, from AREALM to SOPA.  This in response
         to observation by John Klensin that anything using
         "administrative" risks confusion with the standard
         administrative boundary language of zone cuts.

      *  Add discussion of two strategies: name-only or scheme-and-port.

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      *  Increase prominence of utility to CAs.  This use emerged in
         last IETF meeting.

   02 to 03:

      *  Removed discussion of scheme-and-port, which was confusing.

      *  Add inclusion/exclusion/exception approach in response to
         comment by Phill H-B.

      *  Change mechanism for indicating "no others" to a wildcard

      *  Added better discussion of use cases

   03 to 00:

      *  Renamed file to get rid of "origin", which caused confusion.

      *  Added Jeff as co-author

      *  Remove exception relation; instead, more than one RR is

      *  Added discussion of SRV records

   00 to 01:

      *  Failed to include change control entry

      *  Modest rearrangement of text, little improvement

   01 to 02:

      *  Significant rearrangement of sections

      *  Large removal of text (moved to problem statement document)

      *  Considerably more detail in specification, including more
         rigorous description of RRTYPE

      *  Altered handling of wildcard targets

      *  Attempt to improve overview to make it plainer what the system

      *  Clarify what use cases really work

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      *  Reversion to permit cross-tree use, with deployment warnings
         that it won't be useful

Authors' Addresses

   Andrew Sullivan
   Dyn, Inc.
   150 Dow St
   Manchester, NH  03101

   Email: asullivan@dyn.com

   Jeff Hodges
   2211 North First Street
   San Jose, California  95131

   Email: Jeff.Hodges@PayPal.com

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