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
draft-kolkman-cautious-delegation-02
Abstract
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
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 February 2, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
Kolkman, et al. Expires February 2, 2014 [Page 1]
Internet-Draft Cautious Delegation Aug 2013
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
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. 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
Kolkman, et al. Expires February 2, 2014 [Page 2]
Internet-Draft Cautious Delegation Aug 2013
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,
then:
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 example.org 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 administrative
control of one party. e.g. the .org zone has delegated the
example.org domain to the example.org 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:"
.intranet.
.internal.
.private.
.corp.
.home.
.lan.
In the event such names are delegated for use in the public DNS,
Kolkman, et al. Expires February 2, 2014 [Page 3]
Internet-Draft Cautious Delegation Aug 2013
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 (example.com) to name their employee
workstations, servers, printers and similar. They have an "intranet"
server named intranet.corp.example.com. 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 "corp.example.com, example.com".
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
valuable.
3. Predelegation determination of use of a name
It is possible for the operator of a zone authoritative for some
Kolkman, et al. Expires February 2, 2014 [Page 4]
Internet-Draft Cautious Delegation Aug 2013
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
detail.
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...]
Kolkman, et al. Expires February 2, 2014 [Page 5]
Internet-Draft Cautious Delegation Aug 2013
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
delegation.
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.
Kolkman, et al. Expires February 2, 2014 [Page 6]
Internet-Draft Cautious Delegation Aug 2013
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.
Kolkman, et al. Expires February 2, 2014 [Page 7]
Internet-Draft Cautious Delegation Aug 2013
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, <http://www.icann.org/en/groups/
ssac/documents/sac-045-en.pdf>.
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 $
Kolkman, et al. Expires February 2, 2014 [Page 8]
Internet-Draft Cautious Delegation Aug 2013
A.2. version 01
o Bunch 'o nits.
o Added section on search-path processing.
o
Authors' Addresses
Olaf Kolkman
NLnet Labs
Science Park 400
Amsterdam 1098 XH
The Netherlands
Email: olaf@NLnetLabs.nl
Andrew Sullivan
Dyn, Inc.
150 Dow St
Manchester, NH 03101
U.S.A.
Email: asullivan@dyn.com
Warren Kumari
Google, Inc.
1600 Amphitheatre Pkwy
Mountain View, CA 94043
U.S.A.
Email: warren@kumari.net
Kolkman, et al. Expires February 2, 2014 [Page 9]