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Versions: 00 01

Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Informational                                  T. Adams
Expires: December 13, 2019                                    Proofpoint
                                                           June 11, 2019


                         DNS Perimeter Overlay
                    draft-dcrocker-dns-perimeter-01

Abstract

   The Domain Name System (DNS) naming syntax provides no meta-data for
   indicating administrative transitions through the hierarchy.  For
   example, it does not distinguish the higher-level portions that
   operate as public registries, versus those that operate as private
   organizations.  This specification creates a basic overlay mechanism
   for defining a logical Perimeter between administrative entities
   through the naming hierarchy.  The mechanism can then be applied for
   a variety of independent administrative indications.

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 https://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 December 13, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (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



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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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  History . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Perimeter Overlay Overview  . . . . . . . . . . . . . . . . .   5
   4.  DNS Perimeter Overlay Syntax  . . . . . . . . . . . . . . . .   6
     4.1.  Perimeter Branch Indication . . . . . . . . . . . . . . .   6
     4.2.  Perimeter TXT RR  . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Syntax ExampleS . . . . . . . . . . . . . . . . . . . . .   8
   5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  End/Begin Interaction . . . . . . . . . . . . . . . . . .   9
     5.2.  Schema/Schema Interaction . . . . . . . . . . . . . . . .   9
   6.  Sample Overlay Templates  . . . . . . . . . . . . . . . . . .   9
     6.1.  Default/Override 'Convenience' Overlay  . . . . . . . . .  10
     6.2.  Master/Addition 'Control' Overlay . . . . . . . . . . . .  10
     6.3.  Vendor/Customer Overlay . . . . . . . . . . . . . . . . .  11
     6.4.  Organizational Alias  . . . . . . . . . . . . . . . . . .  11
   7.  Propogating 'Begin' Location for Search Efficiency  . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  _perim Registration in DNS Underscore Global Scoped
           Entry Registry  . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  DNS Perimeter Overlay Registry  . . . . . . . . . . . . .  13
     8.3.  Suffix Entry in DNS Perimeter Overlay Registry  . . . . .  14
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  References - Normative . . . . . . . . . . . . . . . . .  15
     10.2.  References - Informative . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  17
   Appendix B.  DNS Suffix Perimeter . . . . . . . . . . . . . . . .  17
     B.1.  IANA DNS Suffix Registration  . . . . . . . . . . . . . .  18
     B.2.  Suffix Perimeter TXT Syntax . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   Although some administrative structure can be inferred for the Domain
   Name System (DNS), there is no formalized syntax that distinguishes
   between the sequence of names in its referenced hierarchy.  It does
   not mark any differentiating characteristics, such as transitions
   across administrative perimeters, as the sequence is followed.  For
   example, it does not mark a change in administrative authority for
   subordinate names.  A common example of needing such differentiation




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   is to indicate what part of a name belongs to a 'public' registry and
   what part belongs to a private registrant within that registry.

   This specification defines a mechanism for marking perimeters in
   domain names, thereby permitting creation of logical overlays to the
   DNS.  Various types of administrative distinctions could be useful.
   To facilitate creation of multiple, logical overlays, this
   specification only defines a basic, extensible mechanism for marking
   the presence of a Perimeter between administrations, and indicating
   where the semantics of the Perimeter are defined.

   As a detailed example and to satisfy a real-world need, an overlay
   that emulates the established Public Suffix List ([PubSuff],
   [PubSuff-SSAC]) is provided in Appendix B.

   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 in
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  History

   A number of Internet functions seek to discern a 'base' portion in a
   domain name, such as the basic organizational name like example.com,
   from a longer name, like marketing.west.example.com.  An approach to
   accomplishing this is to distinguish the part that belongs to
   "public" registries, and consider the next node name below that as
   the base name.

   The Public Suffix List has been used to satisfy this requirement.  It
   has two kinds of domain names.  One is for these 'public' names that
   operate through ICANN coordination.  The other is 'private' which
   serves as a naming base in some cases [PubSuff], [PubSuff-SSAC].  The
   list is maintained as an independent effort producing a standalone
   document, with all of the challenges involved in such an operation.
   Entries are manually registered, which requires vetting of the source
   and on-going validation.  Entries can be for a single name or can use
   a wildcard notation, to cover all names below the one that is
   registered.  It is also possible to enter a name declared to be an
   exception to the wildcard cover.  In keeping with the move towards
   support of non-ASCII names, entries are in UTF-8.

   For 2015-2016, IETF's DBOUND working group explored possible DNS
   enhancements that would permit embedded information to support uses
   such as the Public Suffix List.  The effort ultimately was
   unsuccessful.  Several drafts were used as input to the working group
   discussions [DBOUNDwg].



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      NOTE:   _The following summaries are intentionally terse and
              simplified.  Suggestions for superior language that
              remains terse are eagerly sought. /dcrocker_

   Two were considerations of underlying issues:

   DABprob:  _"DBOUND: DNS Administrative Boundaries Problem Statement"_
           offers a "Problem Statement" and offered an extensive list of
           possible uses [DABprob].

   DNRcon: _"Concepts for Domain Name Relationships"_ explores the
           general topic of "relationships" between different domain
           names.  It considers structural choices, such as within the
           same naming hierarchy, versus across separate branches.  It
           also considers types of relationships, such as public vs.
           private.  Some use cases are considered, as are some solution
           considerations [DNRcon].

   The proffered specifications were:

   ODuse:  _"Organizational Domains and Use Policies for Domain Names"_
           proposes "an extensible system in which domain name policies
           can be discovered at various levels in the DNS tree."  A
           policy record is stored under an underscored node name in a
           TXT record.  The record can indicate that the current node is
           an organization name or that the name one level down is.
           Wildcards are permitted, to cover sub-domains, indicating a
           limit to the number of levels down.  Usage policies are
           marked as allowed or not allowed.  Initial types of policies
           were httpcookie and all (to indicate a default.)  There is a
           mechanism for using URIs to retrieve parameters.[ODuse]

   OBD:    _"Publishing Organization Boundaries in the DNS"_ offers a
           specification "to publish in the DNS the boundaries between
           organizations that can be adapted to various policy models".
           Policies are expressed within a 16-bit bit-masked field.  A
           demarcation point is indicated by a published record above
           the point, using a new DBOUND RR.  The record can indicate
           that there are no boundaries lower than this name.  The
           search algorithm is fully specified for all uses.  It also
           indicates that "[d]ifferent sets of boundary rules can be
           published for different applications."  The applicable
           application of a boundary is indicated by a numeric value in
           the record [OBD].

   ODUP:   _"Resource Record for DNS Administrative Boundaries"_
           specifies a method for "judging domain name administrative
           boundaries" and considers the records within a boundary to be



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           related and those across a boundary to be unrelated.  The
           specification defines a different DBOUND RR, from that of
           [OBD].  If supports assorted flags plus an "Anchor Name/Name
           Collection" field.  The Anchor Name usage "build a connection
           between the owner name and the anchor name which is a FQDN",
           where"owner name" is defined as "some names' anchor name" in
           a different DBOUND RR.  The Name Collection usage lists
           "names which are supposed to share the same DNS boundaries
           under the same anchor name" [ODUP].

   SOPA:   _"Asserting DNS Administrative Boundaries Within DNS Zones"_
           defines "...a way to assert that two domains lie in the same
           policy realm..." or that they do not [SOPA].

   In general terms, it's important for any effort in this space to
   carefully consider the guidance in both [RFC5507] and [RFC6950].  Of
   particular concern to the current draft are the caveats highlighted
   in Section 3.3.1 of [RFC6950], about synchronization, authorization
   and delegation.

3.  Perimeter Overlay Overview

   A Domain Name Perimeter (DNS Perimeter) distinguishes a logical
   separation, occurring between two adjacent nodes in the DNS
   hierarchy.  The name that is lower in the hierarchy marks the
   beginning of its portion (identified by "BEGIN"), and the name higher
   marks the end of its portion (identified by the term "END").  As
   such, a Perimeter is the interface between segments along a domain
   name branch, for which there can be different administrative
   authorities and to which different policies can be applied.

   Because the DNS does not permit associating information with the
   graph connector 'between' names, information about a Perimeter needs
   to be associated with one or both of the nodes adjacent to the
   Perimeter.  One possible advantage of this requirement is permitting
   flexibility in the operational management of marking a Perimeter.
   The organization 'above' the Perimeter might have more or less
   incentive to mark the Perimeter than the organization 'below' it.  In
   this way, the Perimeter can be marked by the organization with the
   greater incentive (or by both organizations, depending on the use
   case.)

   Definition of a DNS Perimeter:

      A logical demarcation between two, adjacent DNS nodes, where one
      node is the parent of the other, and the child is part of a branch
      spanning one or more subdomains.




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   The metadata that is associated with such a node name needs to
   indicate:

   Position: Whether this node name is at the 'end' of am administrative
             sub-hierarchy, before a Perimeter transition -- and
             therefore the final node name 'above' the Perimeter;
             whether it 'begin's a portion of administrative sub-
             hierarchy, immediately after a Perimeter transition; or
             whether it is a node name that is an internal 'part' of a
             sub-hierarchy.

             The 'part' construct might be useful for defining a place
             to hold parametric detail specific to that node within the
             hierarchy.  It might also be useful to hold a pointer to
             the 'begin' node name.

   Schema:   The registered name of the perimeter definition.  The
             Schema name identifies the semantic discipline for the
             record containing the reference.  This permits multiple
             Schemas to share the same perimeter.

   Parameters:  Any schema-specific information required by the schema
             definition.

   Note:  DNS Perimeter Overlay uses a TXT RRset to an _underscored node
        name (_perim).  This constrains queries for TXT records to only
        Perimeter records.  Still, a query to a Perimeter Overlay node
        will return all of the TXT records stored there, and there might
        be multiple 'users' (schemas) using the same DNS node name.  So,
        the client will need to do a simple search of the returned TXT
        RRs, for the one that is desired.  It is expected that there
        will never be a large number of such records; so the burden of
        distinguishing among multiple records is expected to be small.

4.  DNS Perimeter Overlay Syntax

   A node that is immediately above or below a DNS Perimeter indicates
   itself with TXT DNS RR, in an _underscore-labeled sub-branch under
   that node [RFC8552].

4.1.  Perimeter Branch Indication

   The scoped use of the Perimeter TXT RR is indicated with a
   subordinate, leaf node name of:

      "_perim."





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   The IANA registration information for the _perim DNS scoped attribute
   name is in Section 8.1.

4.2.  Perimeter TXT RR

   A TXT RR that is used to indicate a Perimeter is composed of an
   initial identifier, followed by three fields, as described in
   Section 3.

   The ABNF [RFC5234] for the Perimeter TXT RR is:

Perim TXT:  "perim" sp Pos sp Schema [sp Params]
            ; ISSUE: the 'perim' string is arguably redundant, given that the
            ; _underscored node naming approach already defines this as a
            ; perimeter record.
            ; I encourage keeping it, so interpretation of the record can stand
            ; on its own. /dcrocker

Pos:        "begin" / "end" / "part"
            ; begin = first in the perimeter hierarchy sub-sequence
            ; part = within the hierarchy sub-sequence
            ; end = last in the hierarchy sub-sequence

Schema:     { Entry from DNS Perimeter Registry }

Params:     Param *("," Param)

Param:      attr [eq val]

attr:       1*alpha
            ; what is a better choice than <alpha>? /dcrocker

eq:         "="

val:        1*alpha
            ; what is a better choice than <alpha>? /dcrocker

                           Perimeter TXT RR ABNF

   Schema is the registered name for a specific use of the DNS Perimeter
   Overlay mechanism.  The IANA registration information for the _perim
   DNS scoped attribute name is in Section 8.2.

   That is, a TXT record under _perim has a series of space-separated
   fields:

   1.  Identifies this as a _perim TXT record.




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   2.  Indicates whether the record 'begins' an administrative area, by
       appearing as the first node after a Perimeter, or whether it
       'ends' an administrative area, by appearing as the last node
       before a Perimeter.

   3.  Indicates the controlling Schema.

   4.  Optional to the syntactic mechanism, this is a series of one or
       more comma-separated (with no white space) parameters, as defined
       by the particular Schema specification, where a parameter can be
       a simple string or an attribute/value pair.

4.3.  Syntax ExampleS

   Therefore, an organization might indicate the top of its naming
   hierarchy with:

                    _perim.company.pubregistry.example
                       /
                      TXT  "perim begin suffix private"

                           Suffix BEGIN Example

   while the parent registry for this organization's name might also
   indicate the name above it is the bottom of the delegating
   organization's naming branch:

                     _perim.pubregistry.example
                        /
                       TXT  "perim end suffix public"

                         Public Suffix END Example

   and a node within a private organization's branch might point to its
   'organizational domain' that begins this private suffix:

     _perim.dept.company.pubregistry.example
        /
       TXT  "perim part suffix private od=company.pubregistry.example"

                            Suffix PART Example

5.  Discussion








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5.1.  End/Begin Interaction

   The occurrence of either a 'begin' or an 'end' _perim TXT resource
   record defines the Perimeter, in terms of basic Perimeter existence.
   The presence of both _perim TXT records both above and below the
   Perimeter is redundant.

   For this core mechanism, a 'begin' _perim TXT record MAY occur in a
   top-level domain, immediately under the DNS root.  It would, of
   course, have no corresponding 'end' parameter "above" the Perimeter.
   Beyond specification of the technical details, actual usage of a
   Perimeter record for a name administered through a "public" registry
   is a matter of registry policy and is, therefore, outside the scope
   of this specification.

   A particular Schema might define specific requirements or constraints
   on the occurrence of its Perimeter records.  The Schema might mandate
   only one type of record.  Or it might permit policy parameters that
   could conflict.  Such issues are entirely within the purview of the
   Schema specification and are invisible to this core DNS Perimeters
   Overlay mechanism.

5.2.  Schema/Schema Interaction

   For simplicity and commonality, the core DNS Perimeter Overlay
   mechanism defers policy and usage detail up to the Schema
   specifications that rely on that detail.

      The semantics and extended syntax of a Perimeter are defined by a
      specific, registered Schema that is referenced in a _perim TXT RR.
      In terms of the core Perimeter Overlay mechanism, a Perimeter that
      is defined by one Schema is invisible to other Schemas by default,
      even if they share the same node.

      However a Schema specification MAY define its own rules regarding
      the occurrence of different Perimeter Schemas and/or the
      relationship of this Schema to another.  For example, one Schema's
      Perimeter Overlay might create dependencies and interactions with
      another Schema Perimeter Overlay.

6.  Sample Overlay Templates

   Here are some notional use cases, for abstract usage models using DNS
   Perimeter Overlays.  They are provided as basic discussions, rather
   than detailed specifications, to serve both as simple examples and as
   guidance for possible adaption to specific needs.  Other models are
   certainly plausible.




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   NOTE:  This section might be appropriate to move into an independent
      document, as a larger repertoire of examples is developed and
      specified.  As this document develops, suggestions for additional
      samples is encouraged.  /dcrocker

   A Schema specification needs to make clear what operational and
   policy models it is using, to distinguish it from other Schemas that
   might seem similar.

   CAVEAT:    There is a basic (but easily-forgotten) reality that the
      registry for a parent domain has ultimate control over the
      descendant domains.  All sorts of anomalies are possible (and
      likely) when a descendant is a different organization, but
      ultimately, that's the type of issue that isn't directly
      discernible via DNS.  Concern for such issues is internal to the
      administration of that DNS node hierarchy.  responsible

6.1.  Default/Override 'Convenience' Overlay

   An organization might want to have a Perimeter early in the DNS
   hierarchy that defines a basic set of parameters and policies, as
   defaults for names within the Perimeter.  It might then permit nodes
   under this to override any of these defaults.  The default record,
   therefore, serves as a convenience, to reduce the amount of detail
   that needs to be provided at lower levels in the DNS hierarchy.

   Specifying the details that can be provided as defaults is
   straightforward.

   The basic operational model is for the client to start with the full
   DNS name, down to the lower level and then look up to the higher-
   level 'base' name.  There needs to be a simple, efficient means for
   the client to determine what that 'base' name is, so that it can
   deterministically query it for the default information.

6.2.  Master/Addition 'Control' Overlay

   An organization might want to have a Perimeter early in the DNS
   hierarchy that defines a rigorous set of mandatory parameters and
   policies.  Within its administrative purview, these would be global
   details, enforced for all subordinate names.

   As for the Convenience model, the overlay specification here needs to
   make clear what operational model applies.  The remaining technical
   details are the same as for the Convenience model.  What differs is
   the semantics of using the superior/subordinate overlay records.





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   Note that most of the operational details of the 'Control" model are
   the same as the 'Convenience' model, although their semantics have a
   basic difference.

6.3.  Vendor/Customer Overlay

   A vendor that services customers via subdomains under their corporate
   domain might opt to publish DNS Perimeter declarations as clear
   demarcations between their "enterprise" and "customer" nodes.  The
   Schema might define semantics that enable third parties to support
   the customers, potentially applying different rules per customer
   node.  In this case, each "begin" _perim TXT RR associated with a
   node will define the policies that apply to that customer, while the
   "end" _perim DNS TXT will act as the demarcation line between the
   customer(s) and the vendor.

6.4.  Organizational Alias

   There are various relationships that might exist between two domain
   names in different DNS branches.  One example is complete
   equivalence.  That is, the two names are aliases for the same
   organizational unit.  A DNS Perimeter Overlay Schema could support
   this construct by having a Schema parameter that specifies a the
   domain name of organizational alias.  Each name could point to the
   other.  (The 'part' example in Section 4.3 demonstrates the simpler
   case of merely pointing to a name earlier in the branch, but a Scheme
   could define a similar construct that instead points to names in
   other branches.)  Concerns for authorization and accuracy would be
   internal to the Schema.

7.  Propogating 'Begin' Location for Search Efficiency

   NOTE:  This section is currently offered as a discussion, to consider
        the plausibility of an approach at efficiently finding a 'begin'
        record, given a name farther down its branch. /dcrocker

   One concern for the pragmatics of DNS operation is being able to
   easily populate records into a large number of sub-domains.  Another
   is producing a useful response for names that are not registered,
   such as for communicating policies related to an organization's sub-
   domains.  In both cases, the information can be stored in a higher-
   level name.

   However it is one thing to list data in the DNS -- somewhere up the
   branch of the hierarchy -- and quite another to find it, when its
   location is not already known.





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      _Given a longer domain name, what is the process of finding the
      shorter portion containing a _perim TXT 'begin' declaration?_

   In the worst case, a tree-walk is required, querying each, next-
   higher portion of the DNS, or starting at the root and querying each
   node down.  For a name with many components, this can be expensive
   and slow, while essentially creating a vector for a denial of service
   attack.

   A feature embedded in the basic DNS specification is the wildcard, as
   defined in Section 4.3.3 of [RFC1034].  This permits server-side
   configuration into a higher-level domain name and delivers the
   information for queries to subordinate names.  Unfortunately, this
   feature cannot be used for records that are stored under a
   specialized naming branch such as those using underscored scoping,
   since they are in an adjacent branch under the name and cannot
   propagate.

      _So how can a user process that has a fully qualified domain name,
      find Perimeter information from some upper level in the hierarchy,
      such as the base "organizational domain", when the classic DNS
      wildcard feature cannot be used?_

   In some cases, the queried name will exist and might have a 'part'
   record to provide the information, or it might exist and not have the
   information, or it might not exist.  The latter two cases requires
   some additional means for obtaining information about the containing
   Perimeter.

   Absent additional mechanism, finding a DNS Perimeter requires some
   sort of tree walk, which has the problems cited above.  Use of a
   purpose-built RR -- rather than underscore-scoped naming -- would
   permit employing wildcards, but new RRs continue to suffer deployment
   and use barriers.

   Having a tree-walk done offline and publishing a list is a
   possibility.  That is, publish a table that shows the entries which
   were found by a background searching process.  When there are
   relatively few entries and the search space is relatively small and
   the rate of change is relatively slow, this approach can be useful.
   However it requires consulting an external table and requires an
   effort to maintain it.

   Another approach is use of the DNS Additional section in the server
   response:

      Query for a Perimeter node; the server will return would include
      the associated Perimeter BEGIN record from earlier in the



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      hierarchy, if the queried node is within that hierarchy -- that
      is, is above the actual or virtual END record.  (As for any
      information supplied through the Additional section, the
      responding server will need to be modified to provide this
      enhanced information for specific kinds of queries.)

   It might be reasonable to constrain this behavior only to a Perimeter
   record that requests it, by adding a wildcard construct to the basic
   Perimeter BEGIN syntax.

   A Perimeter-aware client -- or recursive server -- could cache these
   results, building an incremental portion of the overall table for
   this type of Perimeter.

8.  IANA Considerations

8.1.  _perim Registration in DNS Underscore Global Scoped Entry Registry

   The following entry is to be added to the DNS Underscore Global
   Scoped Entry Registry:

          +---------+-------------+----------------------------+
          | RR Type | _NODE NAME  | REFERENCE                  |
          +---------+-------------+----------------------------+
          | TXT     | _perim      | {this document}, Section 4 |
          +---------+-------------+----------------------------+

       Table 1: _perim Registration in Global Scoped Entry Registry

8.2.  DNS Perimeter Overlay Registry

   The DNS Perimeter Overlay Registry lists specific uses of the DNS
   Perimeter Overlay mechanism.

   The registration table for the DNS Perimeter Overlay Registry will
   contain two columns:

                          +--------+-----------+
                          | SCHEMA | REFERENCE |
                          +--------+-----------+
                          +--------+-----------+

               Table 2: DNS Perimeter Overlay Registry Table

   o  This registry is to operate under the IANA rules for "Expert
      Review" registration; see Section 8.2.1.





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   o  The detail to be provided by a DNS Perimeter Overlay entry's
      referenced Schema specification is defined in Section 4.2.

   o  The specification referenced in a DNS Perimeter Overlay
      registration MUST contain values for all of the fields specified
      in Section 4.2.

   o  Within the registry, each Schema name must be unique.

   o  The table is to be maintained with entries sorted by the Schema
      name.

   o  The required Reference for an entry MUST have a stable resolution
      to the organization controlling that registry entry.

8.2.1.  Guidance for Expert Review

   This section provides guidance for expert review of registration
   requests in the DNS Perimeter Overlay Registry.

      This review is solely to determine adequacy of a requested entry
      in this Registry, and does not include review of other aspects of
      the document specifying that entry.  For example such a document
      might also contain a definition of the resource record type that
      is referenced by the requested entry.  Any required review of that
      definition is separate from the expert review required here.

   The review is for the purposes of ensuring that:

   o  The details for creating the registry entry are sufficiently
      clear, precise and complete

   o  The Schema name is unique in the table

   For the purposes of this Expert Review, other matters of the
   specification's technical quality, adequacy or the like are outside
   of scope.

8.3.  Suffix Entry in DNS Perimeter Overlay Registry

   NOTE:   As a formality, this section is in the IANA section for this
      document.  However it is expected that the Public Suffix use of
      DNS Perimeter Overlay will be moved to a separate specification
      document, before this document is published. /dcrocker







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                 +--------+-----------------------------+
                 | SCHEMA | REFERENCE                   |
                 +--------+-----------------------------+
                 | suffix | {this document}, Appendix B |
                 +--------+-----------------------------+

               Table 3: DNS Perimeter Overlay Registry Table

9.  Security Considerations

   This memo defines a mechanism for signaling information about
   administrative perimeters.  The mechanism itself introduces no
   security issues.  However specific uses of the mechanism might define
   transitions in authority that offer new attack surfaces.

   o  A basic opportunity for concern is authorization to make a
      particular assertion, using a DNS Perimeter Overlay.  The basic
      mechanism defined here offers no means for validating an
      assertion.  So any detailed specification for a particular use
      needs to consider the potential of unauthorized assertions.

   o  Conflicting Perimeter entries for adjacent 'begin' and 'end'
      assertions could be problematic.  That is, information in the
      _perim TXT RR for the parent name might conflict with information
      in the _perim TXT RR for the child.  Consideration of such a
      conflict is left to the individual Schema specifications that use
      the DNS Perimeter Overlay mechanism.

10.  References

10.1.  References - Normative

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

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

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 5234, January 2008.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", RFC 8162, May 2017.

   [RFC8552]  Crocker, D., "Scoped Interpretation of DNS Resource
              Records through "Underscored" Naming of Attribute Leaves",
              RFC 8552, ISSN 2070-1721, March 2019.




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10.2.  References - Informative

   [DABprob]  Sullivan, A., Hodges, J., and J. Levine, "DBOUND: DNS
              Administrative Boundaries Problem Statement", I-D draft-
              sullivan-dbound-problem-statement-02, August 2016.

   [DBOUNDwg]
              IETF, "Domain Boundaries (dbound)", 2016.

   [DNRcon]   Deccio, C. and J. Levine, "Concepts for Domain Name
              Relationships", I-D draft-deccio-dbound-name-
              relationships-00, July 2015.

   [OBD]      Levine, J., "Publishing Organization Boundaries in the
              DNS", I-D draft-levine-dbound-dns-01, September 2016.

   [ODUP]     Yao, J., Kong, N., and X. Li, "Resource Record for DNS
              Administrative Boundaries", I-D C. Deccio, January 2016.

   [ODuse]    Deccio, C., "Organizational Domains and Use Policies for
              Domain Names", I-D draft-deccio-dbound-organizational-
              domain-policy-03, July 2016.

   [PubSuff]  Foundation, M., "Public Suffix List",
              URL https://publicsuffix.org.

   [PubSuff-SSAC]
              Committee, I. S. A. S. A., "SAC070: SSAC Advisory on the
              Use of Static TLD / Suffix Lists", URL
              https://www.icann.org/en/system/files/files/sac-
              070-en.pdf, May 2015.

   [PubSuffSyn]
              Foundation, M., "Public Suffix List Format",
              URL https://publicsuffix.org/list/.

   [RFC5507]  IAB, Faltstrom, P., Austein, R., and P. Koch, "Design
              Choices When Expanding the DNS", RFC 5507, April 2009.

   [RFC6950]  Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
              "Architectural Considerations on Application Features in
              the DNS", RFC 6950, October 2013.

   [SOPA]     Sullivan, A. and J. Hodges, "Asserting DNS Administrative
              Boundaries Within DNS Zones", I-D draft-sullivan-domain-
              policy-authority-02, February 2016.





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   [SubTLD]   Pettersen, Y., "The Public Suffix Structure file format
              and its use for Cookie domain validation", I-D draft-
              pettersen-subtld-structure-10, February 2014.

Appendix A.  Acknowledgements

Appendix B.  DNS Suffix Perimeter

   ISSUE:  _Specification of Perimeter use to replicate Public Suffix
           List functionality.  This section needs careful review and
           revision by the PSL community. _ /dcrocker

           _It appears that there are a number of adjunct uses of Domain
           Names that get merged with the PSL.  These probably are
           candidates for other Perimeter Overlay encodings. /d_

   ISSUE:  _The basic usage mode for PSL information is for an
           application that has a fully qualified domain name to 'find'
           the portion that is public, as distinct from the remaining
           portion that is assigned by a private registry.  The
           'finding' process is not facilitated by the DNS, which only
           queries for an exact name, rather than doing "searching".
           Worse, this impedes building a table by brute-force testing
           of the tree._

           _So an open issue is the method for either real-time or
           background use of PSL information through DNS Perimeter
           Overlay.  /dcrocker_

   The Public Suffix List describes itself as [PubSuff]:

      "A "public suffix" is one under which Internet users can (or
      historically could) directly register names."

   An advisory report by the ICANN Security and Stability Advisory
   Committee uses a definition of PSL from [SubTLD]:

      "A domain under which multiple parties that are unaffiliated with
      the owner of the Public Suffix domain may register subdomains."

   The basic semantics of the list are quite simple, only marking the
   Perimeter between the portion of a domain name -- it's suffix --
   administered by a public registry and the remaining portion of the
   name administered by a registrant.  Some uses of the list have more
   elaborate semantics, but these really are value-added features beyond
   the basic mechanism -- even though some are encoded in the published
   list.  The details of the Public Suffix list are not amenable to
   algorithmic derivation, because the criteria for determining whether



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   a suffix is 'public' varies significantly from one DNS naming branch
   to another.

   The goal in defining a Public Suffix Perimeter within the DNS itself
   is to permit the owner of a name at a Public Suffix Perimeter to mark
   its presence directly, rather than having to go through an
   independent registration service.  Anyone can then discern the
   Perimeter directly, without needing access to a separate list.
   Further much, or all of, the compiled list can be developed by a
   rigorous DNS tree walk, rather than by relying on additions and
   deletions each being submitted to the Public Suffix registration
   service.

   A particular efficiency and convenience in this direct publication
   method is that the public registry can have a single entry for the
   'end' name in the public suffix and implicitly thereby mark all of
   the children names as the 'begin' of the private part of the name.



      NOTE:   The details provided here are a bare minimum to define
              Public Suffix Perimeters.  As this specification is
              reviewed by subject matter experts, it is expected that
              the details will be enhanced.  /dcrocker

B.1.  IANA DNS Suffix Registration

   The IANA registration information for the Suffix Perimeter entry is
   at Section 8.3.

B.2.  Suffix Perimeter TXT Syntax

   This specification for DNS Suffix information, stored in a _perim TXT
   record, is meant to approximate what is specified in [PubSuffSyn].
   Each DNS Perimeter Overlay Suffix Schema TXT RR serves as a 'rule' in
   the Public Suffix table.  Some accommodations have been made, to the
   constraints of fitting this within a TXT value segment.

   Given the variety of uses of information called "Public Suffix List",
   there could reasonably be different specifications offered.  Two
   possibilities are listed here:

B.2.1.  Core PSL

   This provides a simple capability for marking a Perimeter, without
   labeling their 'type'.





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           Perim Params: extra SP  comment

           extra:        ["!"] *("*.")
                         ; ! = exception
                         ; * = wildcard for node name field(s),
                         ;     creating prefix to current name.

           comment:      "//" *CHAR

                       'Core' DNS Suffix Params ABNF

   A simple entry will have no parameters; the existence of the TXT
   record defines the DNS node containing it as an entry in the Public
   Suffix List.  If wildcard fields are specified, they are added as a
   prefix to the current node's name.  An 'exception' indicator marks
   this name as overriding a higher-level rule.

B.2.2.  PubPrivPSL

   This permits distinguishing between portions of the namespace that
   are public and those, below this, that are private.  In order to
   prevent a private entry from claiming that it is public, a private
   registry can declare that it is the lowest-level (final) public
   registry

Perim Params: pubpriv extra SP  comment

pubpriv:      "pub" [", fin"] / "priv"
              ; distinguish between public vs. private registry
              ; public registry can indicate it is the final (lowest) one

extra:        ["!"] *("*.")
              ; ! = exception
              ; * = wildcard for node name field(s),
              ;     creating prefix to current name.

comment:      "//" *CHAR

                  'Public/Private' DNS Suffix Params ABNF

   There can be layers of public registries and layers of private
   registries, for a single, fully qualified domain name.  This version
   of the specification permits multiple boundaries; an explicit
   indication of the type of registry is required.  A simple entry will
   have no <extra> parameters; the existence of the TXT record defines
   the DNS node containing it as an entry in the Public Suffix List.  If
   wildcard fields are specified, they are added as a prefix to the




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   current node's name.  An 'exception' indicator marks this name as
   overriding a higher-level rule.

Authors' Addresses

   D. Crocker
   Brandenburg InternetWorking
   675 Spruce Dr.
   Sunnyvale, CA  94086
   USA

   Phone: +1.408.246.8253
   Email: dcrocker@bbiw.net
   URI:   http://bbiw.net/


   T. Adams
   Proofpoint

   Email: tadams@proofpoint.com































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