Skip to main content

A Procedure for Cautious Delegation of a DNS Name

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Olaf Kolkman , Andrew Sullivan
Last updated 2013-05-02
RFC stream (None)
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date (None)
Responsible AD (None)
Send notices to (None)
Network Working Group                                         O. Kolkman
Internet-Draft                                                NLnet Labs
Intended status: Informational                               A. Sullivan
Expires: November 3, 2013                                      Dyn, Inc.
                                                             May 2, 2013

           A Procedure for Cautious Delegation of a DNS Name


   Sometimes, a DNS name is known to be in use in the wild even though
   it was never properly delegated.  This situation appears
   particularly, but not only, true in certain domains near the root of
   the tree: people have independently used those non-existent top-level
   domains as private namespaces.  If those names are to be delegated in
   the public DNS, prudence demands that collisions between the private
   uses and the public use be minimized.  At the same time, the public
   use should not be prohibited on the grounds of what is, after all,
   "hijacking" of a name space.  We outline a procedure to minimize harm
   while permitting delegation to proceed.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 3, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of

Kolkman & Sullivan      Expires November 3, 2013                [Page 1]
Internet-Draft             Cautious Delegation                  May 2013

   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Background and Introduction . . . . . . . . . . . . . . . . . . 3
   2.  terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Predelegation determination of use of a name  . . . . . . . . . 4
     3.1.  Predelegation testing is needed . . . . . . . . . . . . . . 4
     3.2.  Determining the names of concern  . . . . . . . . . . . . . 4
       3.2.1.  Mode 1: prior to any delegation . . . . . . . . . . . . 5
       3.2.2.  Mode 2: After delegation  . . . . . . . . . . . . . . . 5
   4.  Parameters for operation of this procedure  . . . . . . . . . . 6
     4.1.  Median or Mean  . . . . . . . . . . . . . . . . . . . . . . 6
     4.2.  Discussion of Alternatives  . . . . . . . . . . . . . . . . 6
     4.3.  Security considerations . . . . . . . . . . . . . . . . . . 6
   5.  Informative References  . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Document Editing Details . . . . . . . . . . . . . . . 7
     A.1.  version 00  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

Kolkman & Sullivan      Expires November 3, 2013                [Page 2]
Internet-Draft             Cautious Delegation                  May 2013

1.  Background and Introduction

   DNS names have always co-existed with other namespaces that are
   virtually indistinguishable from the DNS.  The DNS was itself
   deployed alongside the host ### table.  NetBIOS ### names, though
   only one label long, could always interact with the DNS search path
   mechanism to generate DNS names.  Additinally, mDNS [RFC6762] names
   look just like DNS names.  Because different naming systems are
   usually linked together in the user interface, from an end user's
   point of view these name spaces are all one -- even though they
   function differently on the Internet.

   While [RFC6761] reserved certain special names for private use, there
   is evidence [SAC45] that various sites connected to the Internet have
   used other names for internal purposes.  In fact, [RFC6762] advises
   not to use .local for private use and observes: "the following top-
   level domains have been used on private internal networks without the
   problems caused by trying to reuse ".local." for this purpose:"
   In the event such names are delegated for use in the public DNS,
   there will be inevitable consequences for such sites.  Some of those
   consequences have implications for security, with the potential for
   leakage of username and password combinations.  Responsible
   administration of the public namespace therefore requires great care
   in permitting public delegation of any name where there is good
   reason to suppose it is in widespread use as a private namespace,
   even though such private namespaces are (from the point of view of
   the DNS) irregular.

2.  terminology

   In this document we will be using the terms zone, domain and sub-
   domain.  When envisioning the domain namespace as a tree, with nodes
   at the places where the dots seperate the labels in a domain name,

   a 'domain'  is an entire branch. e.g.  The .org domain is the branch
         of the domain name tree for which all names end in .org.

Kolkman & Sullivan      Expires November 3, 2013                [Page 3]
Internet-Draft             Cautious Delegation                  May 2013

   a 'sub-domain'  is a subordinate namespace of a given domain. e.g.
         all names ending in are in the domain example org
         which is a sub-domain of .org.
   a 'zone'  is a piece of the domain space that is under
         andministrative control of one party. e.g. the .org zone has
         delegated the domain to the

3.  Predelegation determination of use of a name

   It is possible for the operator of a zone authoritative for some
   domain name to tell whether a particular subordinate name has a
   widespread use outside the DNS.  In order to do this, the operator of
   the zone monitors queries against the zone to learn the names for
   which there are queries, ignoring those names that actually exist
   i.e. those names the zoneowner delegated or created resource records
   for (in the remainder of this document we will not make the
   distinction between entering data with a name or making a delegation,
   within the context of this document the same considerations apply).
   The operator then establishes a baseline "noise" level of queries for
   non-existent subordinate names.  Any name that is queried with
   significantly greater frequency is to be treated as in widespread
   private use, and it should not be released for delegation.  The rest
   of this section describes the mechanisms for such determination in

3.1.  Predelegation testing is needed

   In order that this procedure be useful, it should be undertaken
   before any subordinate names are delegated.  Otherwise, it will be
   difficult to tell whether a subordinate name is being queried because
   it is already delegated, or because it is in private use.

   At the same time, it is possible that the operator of a zone may wish
   to consider the private use of a descendent name, where some
   intermediate namespace has been delegated.  In that case, it is
   necessary to ensure that the descendent name is not actually
   delegated when evaluating queries against that name.

3.2.  Determining the names of concern

   There are two modes of operation for determining names of concern.
   The most usual is to examine names for which there is no intermediate
   delegation.  This is useful in case the operator of the zone is
   deciding whether to permit delegation or addition of a particular
   name.  The second, more unusual mode, is to examine subordinate names
   inside a sub-domain that has already been delegated.  This mode is

Kolkman & Sullivan      Expires November 3, 2013                [Page 4]
Internet-Draft             Cautious Delegation                  May 2013

   useful only as part of a regime of contract enforcement with the
   operator of the (already delegated) sub-domain.

3.2.1.  Mode 1: prior to any delegation

   The procedure starts with the name of a zone, which is called the
   "starting domain".  In order to determine what subordinate names may
   be problematic, the starting domain zone operator captures all the
   names it receives in queries.  The operator discards as irrelevant
   any sub-domain it has already delegated in its namespace.  Every
   other queried name will result in a response of Name Error, RCODE=3
   ###STD13 ("NXDOMAIN" ###Negative cache).  We call the resulting list
   the "NX names".  (See Section 4 for guidance on the sample size.)

   The operator then takes the list of NX names, and builds a frequency
   of queries for each potential delegation point (in practice all
   immediately subordinate names).  The operator proceeds in the fully-
   qualified domain name ("FQDN") label by label until the next label
   past the operator's namespace (in practice these are the names at
   which delegation will potentially take place).  We call these the
   "target names".  The operator counts the number of queries for each
   target name.

   The operator determines the mean and median number of queries over
   the set of target names.  Any name that receives more queries than
   ###SIGMA -- needs xref to params### greater than the mean, or
   ###SIGMA2### greater than the median, should be regarded as in
   widespread private use on the Internet and therefore not a candidate
   for delegation.

   It is possible that only a portion of a namespace subordinate to a
   target name is actually in private use.  It is possible to measure
   this situation simply by treating the beginning of the namespace in
   question as the starting domain, and then repeating the procedure
   above.  This could be useful in order to establish baseline
   restrictions on the operator of a subordinate namespace prior to

3.2.2.  Mode 2: After delegation

   This mode is more likely to be useful if the evaluation at the end of
   the previous section has already been performed.  In this case, some
   sub-domain to the operator's zone is to be evaluated for possible
   private use, where that sub domain has already been delegated.  The
   zone operator operates the "parent starting zone", and is evaluating
   use inside a starting domain already operated by someone else.  The
   very same mechanisms as are outlined in Section 3.2.1 are used, but
   the evaluation must take into consideration the effects of negative

Kolkman & Sullivan      Expires November 3, 2013                [Page 5]
Internet-Draft             Cautious Delegation                  May 2013

   TTLs ### for the starting domain.  Because of the combining effects
   of multiple negative TTLs, it is inadvisable to attempt to perform
   this evaluation beyond the boundary of a single delegation.

4.  Parameters for operation of this procedure

   This section ought to have some words about sane parameters to use
   for the procedure.

4.1.  Median or Mean

   In this section we would like to describe some likely distributions.
   Our assumption is that incoming queries will usually follow some
   dictionary pattern.  The 'everybody wants to be mr.  Black'
   [ResevoirDogs] effect is that queries are much more likely for
   pupular names than for labels filled with random content.  Therefore
   distributions for non-existent names will have relatively little
   power in the long tail.  However, the long tail is significant in the
   sense that the names in the long tail are most likely not to exist.

   The exact type of distribution and the statistical parameters that
   signify it is subject for a future version of the draft.

4.2.  Discussion of Alternatives

   The above method is based on looking at names that the querying
   population perceives to exist.  Alternatively one could count queries
   for a set of random name like "ao42hft3tofj4irsavc4owajhro.example".
   That type of measurement will set the baseline of _real_ non-existing
   names and set the noise level (likely zero queries within a
   reasonable timescale).  However, using trully random names introduced
   the problem that any signal (e.g. a handful of queries used for
   probing of availability) will make the domain name unavailable.

4.3.  Security considerations

   Applying this mechansism as the basis for decisions to delegate
   domains, or not, introduces a motivation for gaming the system.  The
   reception of a lot of queries for a particular domain may cause it to
   not be delegated while the reception of many random queries (changing
   the properties of the query distribution) may cause a domain that is
   in comon use to be delegated.  Careful analysis of data i.e. by
   studying root for queries could, in case of suspicion of gaming, help
   to supplement decisions.

Kolkman & Sullivan      Expires November 3, 2013                [Page 6]
Internet-Draft             Cautious Delegation                  May 2013

5.  Informative References

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, February 2013.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.

   [SAC45]    ICANN Security and Stability Advisory Commitee, "Invalid
              Top Level Domain Queries at the Root Level of the Domain
              Name System", 11 2010, <

Appendix A.  Document Editing Details

   [To Be Removed before publication]

   $Id: draft-kolkman-cautious-delegation.xml 3 2013-05-02 14:27:06Z
   olaf $

A.1.  version 00

   Documenting the first rough outline based on hallway discussions with
   the specific purpose to document the idea in the public domain.

Authors' Addresses

   Olaf Kolkman
   NLnet Labs
   Science Park 400
   Amsterdam  1098 XH
   The Netherlands


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


Kolkman & Sullivan      Expires November 3, 2013                [Page 7]