Network Working Group                                         O. Kolkman
Internet-Draft                                                NLnet Labs
Intended status: Informational                               A. Sullivan
Expires: February 2, 2014                                      Dyn, Inc.
                                                               W. Kumari
                                                            Google, Inc.
                                                             Aug 1, 2013

           A Procedure for Cautious Delegation of a DNS Name


   NOTE: The authors recognize that the statistical models that would
   inform the process are not well understood and that the possibilities
   to game the system might be unmountable.  Unless we reach more
   insights on how to deal with this details this work is abandoned.

   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 dictates that collisions between the private
   uses and the public use be minimized.  We outline a procedure to
   evaluate the harm of delegation.

Status of this Memo

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   This Internet-Draft will expire on February 2, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Background and Introduction . . . . . . . . . . . . . . . . . . 3
     2.1.  Search-path interaction.  . . . . . . . . . . . . . . . . . 4
   3.  Predelegation determination of use of a name  . . . . . . . . . 4
     3.1.  Predelegation testing is needed . . . . . . . . . . . . . . 5
     3.2.  Determining the names of concern  . . . . . . . . . . . . . 5
       3.2.1.  Mode 1: Prior to any delegation . . . . . . . . . . . . 6
       3.2.2.  Mode 2: After delegation  . . . . . . . . . . . . . . . 6
   4.  Parameters for operation of this procedure  . . . . . . . . . . 7
     4.1.  Median or Mean  . . . . . . . . . . . . . . . . . . . . . . 7
     4.2.  Discussion of Alternatives  . . . . . . . . . . . . . . . . 7
   5.  Security considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Informative References  . . . . . . . . . . . . . . . . . . . . 8
   Appendix A.  Document Editing Details . . . . . . . . . . . . . . . 8
     A.1.  version 00  . . . . . . . . . . . . . . . . . . . . . . . . 8
     A.2.  version 01  . . . . . . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Terminology

   NXDOMAIN:  an alternate expression for the "Name Error" RCODE as
         described in [[RFC1035] Section 4.1.1].  The two terms are used
         interchangeably in this document. (definition from [RFC2308])

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

2.  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.  Additionally, 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 internal or
   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,

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   there will be inevitable consequences for such sites.  Some of those
   consequences have implications for security, with the potential for
   leakage of credentials and HTTP cookies ([RFC6265]).  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 (although not uncommon).

2.1.  Search-path interaction.

   In many cases a string appears to be used as an "undelegated TLD"
   (being used as the rightmost label in an name), but this is simply an
   artifact of domain search list processing.

   As an (hypothetical) example, Example Widgets uses a sub-domain
   (.corp) of their primary domain ( to name their employee
   workstations, servers, printers and similar.  They have an "intranet"
   server named  In order to allow their
   employees to simply type "intranet.corp" to access this server, the
   users' workstations are configured (probably using [RFC3379]) with
   the search-list set to ",".

   When a user enters "intranet.corp", their workstation will try and
   resolve the name.  RFC1535 [RFC1535] specifies that "in any event
   where a "." exists in a specified name it should be assumed to be a
   fully qualified domain name (FQDN) and SHOULD be tried as a rooted
   name first." and so the users workstation will first try and resolve
   "intranet.corp.".  As there is (currently) no .corp TLD this will
   result in an NXDOMAIN response.  The workstation will then append
   entries in the search-list until it is able to resolve the (now
   fully-qualified) name.

   If the .corp label were to be delegated as a TLD and the sub-domain
   "intranet" created within .corp, the first lookup ("intranet.corp")
   would no longer generate an NXDOMAIN response.  This would stop the
   search-list processing, and direct the user to the incorrect server.

   It is worth noting that a researcher analyzing DNS queries hitting
   the root servers would see queries before search-list processing
   expands them.  While this may not change whether or not it is safe to
   delegate these names, having an understanding of the cause is

3.  Predelegation determination of use of a name

   It is possible for the operator of a zone authoritative for some

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   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 zone owner 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 for this procedure to 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 descendant name, where some
   intermediate namespace has been delegated.  In that case, it is
   necessary to ensure that the descendant name is not actually
   delegated when evaluating queries against that name.

3.2.  Determining the names of concern

   [ ED NOTE: This methodology needs to tested.  First assessment of
   data indicates that this approach may be far to trivial ]

   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
   useful only as part of a regime of contract enforcement with the
   operator of the (already delegated) sub-domain.  [WK Note: Are we
   sure we even want to address/suggest this second "limited delegation"
   option?  If we are going to discuss it, referring to it as "limited
   delegation" or similar may help clarify.  Personally I think 'tis a
   silly idea, but...  There is talk of doing "test" delegations -
   basically launch a TLD / domain with a low TTL.  If nothing goes
   "boom" then delegate for longer...]

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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
   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.

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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
   popular 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 truly 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.

5.  Security considerations

   Applying this mechanism as the basis for decisions on whether or not
   to delegate domains 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 common use to be delegated (by hiding the actual
   use of names in that domain in the noise).  Careful analysis of data
   (for example, by studying root for queries, and taking into account
   historical trending) could, in case of suspicion of gaming, help to
   supplement decisions.

6.  IANA Considerations

   This document makes no requests of the IANA.

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7.  Informative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC1535]  Gavron, E., "A Security Problem and Proposed Correction
              With Widely Deployed DNS Software", RFC 1535,
              October 1993.

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

   [RFC3379]  Pinkas, D. and R. Housley, "Delegated Path Validation and
              Delegated Path Discovery Protocol Requirements", RFC 3379,
              September 2002.

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

   [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 Committee, "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.

   $Id: draft-kolkman-cautious-delegation.xml 5 2013-06-11 21:49:28Z
   warren $

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A.2.  version 01

   o  Bunch 'o nits.
   o  Added section on search-path processing.

Authors' Addresses

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


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


   Warren Kumari
   Google, Inc.
   1600 Amphitheatre Pkwy
   Mountain View, CA  94043


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