Internet DRAFT - draft-trammell-inip-pins
draft-trammell-inip-pins
Network Working Group B. Trammell
Internet-Draft ETH Zurich
Intended status: Informational September 20, 2017
Expires: March 24, 2018
Properties of an Ideal Naming Service
draft-trammell-inip-pins-04
Abstract
This document specifies a set of necessary functions and desirable
properties of an ideal system for resolving names to addresses and
associated information for establishing communication associations in
the Internet. For each property, it briefly explains the rationale
behind it, and how the property is or could be met with the present
Domain Name System. It is intended to start a discussion within the
IAB's Names and Identifiers program about gaps between the present
reality of DNS and the naming service the Internet needs by returning
to first principles.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on March 24, 2018.
Copyright Notice
Copyright (c) 2017 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
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publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Query Interface . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Name to Address . . . . . . . . . . . . . . . . . . . . . 4
3.2. Address to Name . . . . . . . . . . . . . . . . . . . . . 4
3.3. Name to Name . . . . . . . . . . . . . . . . . . . . . . 4
3.4. Name to Auxiliary Information . . . . . . . . . . . . . . 5
3.5. Name/Address to Auxiliary Information . . . . . . . . . . 5
4. Authority Interface . . . . . . . . . . . . . . . . . . . . . 5
5. Properties . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1.1. Meaningfulness . . . . . . . . . . . . . . . . . . . 5
5.1.2. Distinguishability . . . . . . . . . . . . . . . . . 6
5.1.3. Minimal Structure . . . . . . . . . . . . . . . . . . 6
5.2. Authority . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2.1. Federation of Authority . . . . . . . . . . . . . . . 6
5.2.2. Uniqueness of Authority . . . . . . . . . . . . . . . 6
5.2.3. Transparency of Authority . . . . . . . . . . . . . . 7
5.2.4. Revocability of Authority . . . . . . . . . . . . . . 7
5.2.5. Consensus on Root of Authority . . . . . . . . . . . 7
5.3. Authenticity . . . . . . . . . . . . . . . . . . . . . . 7
5.3.1. Authenticity of Delegation . . . . . . . . . . . . . 7
5.3.2. Authenticity of Response . . . . . . . . . . . . . . 8
5.3.3. Authenticity of Negative Response . . . . . . . . . . 8
5.4. Consistency . . . . . . . . . . . . . . . . . . . . . . . 8
5.4.1. Dynamic Consistency . . . . . . . . . . . . . . . . . 8
5.4.2. Explicit Inconsistency . . . . . . . . . . . . . . . 8
5.4.3. Global Invariance . . . . . . . . . . . . . . . . . . 9
5.5. Performance Properties . . . . . . . . . . . . . . . . . 9
5.5.1. Availability . . . . . . . . . . . . . . . . . . . . 9
5.5.2. Lookup Latency . . . . . . . . . . . . . . . . . . . 10
5.5.3. Bandwidth Efficiency . . . . . . . . . . . . . . . . 10
5.5.4. Query Linkability . . . . . . . . . . . . . . . . . . 10
5.5.5. Explicit Tradeoff . . . . . . . . . . . . . . . . . . 10
5.6. Trust in Infrastructure . . . . . . . . . . . . . . . . . 11
6. Observations . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Delegation and redirection are separate operations . . . 11
6.2. Queries and assertion contexts are presently implicit . . 11
6.3. Unicode alone may not be sufficient for distinguishable
names . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Implicit inconsistency makes global invariance
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challenging to verify . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
10. Informative References . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
The Internet's Domain Name System (DNS) [RFC1035] is an excellent
illustration of the advantages of the decentralized architecture that
have made the Internet able to scale to its present size. However,
the choices made in the evolution of the DNS since its initial design
are only one path through the design space of Internet-scale naming
services. Many other naming services have been proposed, though none
has been remotely as successful for general- purpose use in the
Internet.
This document returns to first principles, to determine the
dimensions of the design space of desirable properties of an
Internet-scale naming service. It is a work in progress, intended to
start a discussion within the IAB's Names and Identifiers program
about gaps between the present reality of DNS and the naming service
the Internet needs.
Section 3 and Section 4 define the set of operations a naming service
should provide for queriers and authorities, Section 5 defines a set
of desirable properties of the provision of this service, and
Section 6 examines implications of these properties.
2. Terminology
The following capitalized terms are defined and used in this
document:
o Subject: A name, address, or name-address pair about which the
naming service can answer queries
o Association: A mapping between a Subject and information about
that Subject
o Authority: An entity that has the right to determine which
Associations exist within its namespace
o Delegation: An Association that indicates that an Authority has
given the right to make assertions about the Associations within
the part of a namespace identified by a Subject to a subordinate
Authority.
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3. Query Interface
At its core, a naming service must provide a few basic functions for
queriers, associating a Subject of a query with information about
that subject. The information available from a naming service is
that which is necessary for a querier to establish a connection with
some other entity in the Internet, given a name identifying it.
3.1. Name to Address
Given a Subject name, the naming service returns a set of addresses
associated with that name, if such an association exists, where the
association is determined by the authority for that name. Names may
be associated with addresses in one or more address families (e.g.
IP version 4, IP version 6). A querier may specify which address
families it is interested in receiving addresses for, and the naming
system treats all address families equally.
This mapping is implemented in the DNS protocol via the A and AAAA
RRTYPES.
3.2. Address to Name
Given an Subject address, the naming service returns a set of names
associated with that address, if such an association exists, where
the association is determined by the authority for that address.
This mapping is implemented in the DNS protocol via the PTR RRTYPE.
IPv4 mappings exist within the in-addr.arpa. zone, and IPv6 mappings
in the ip6.arpa. zone. This mechanism has the disadvantage that
delegations in IPv4 only happen on octet (8-bit) boundaries, and in
IPv6 only happen on hex digit (4-bit) boundaries, which make
delegations on other prefixes operationally difficult.
3.3. Name to Name
Given a Subject name, the naming service returns a set of object
names associated with that name, if such an association exists, where
the association is determined by the authority for the subject name.
This mapping is implemented in the DNS protocol via the CNAME RRTYPE.
CNAME does not allow the association of multiple object names with a
single subject, and CNAME may not combine with other RRTYPEs (e.g.
NS, MX) arbitrarily.
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3.4. Name to Auxiliary Information
Given a Subject name, the naming service returns other auxiliary
information associated with that name that is useful for establishing
communication over the Internet with the entities associated with
that name.
Most of the other RRTYPES in the DNS protocol implement these sort of
mappings.
3.5. Name/Address to Auxiliary Information
As a name might be associated with more than one address, auxiliary
information as above may be associated with a name/address pair, as
opposed to just with a name.
This mapping is not presently supported by the DNS protocol.
4. Authority Interface
The query interface is not the only interface to the naming service:
the interface a naming service presents to an Authority allows
updates to the set of Associations and Delegations in that
Authority's namespace. Updates consist of additions of, changes to,
and deletions of Associations and Delegations. In the present DNS,
this interface consists of the publication of a new zone file with an
incremented version number, but other authority interfaces are
possible.
5. Properties
The following properties are desirable in a naming service providing
the functions in Section 3 and Section 4.
5.1. Semantics
Since the point of a naming service is to replace network-layer
identifiers with more useful identifiers for humans (whether end
users, software developers, or network administrators), the Subject
names the naming service can provide must meet two semantic criteria:
5.1.1. Meaningfulness
A naming service must provide the ability to name objects that its
human users find more meaningful than the objects themselves.
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5.1.2. Distinguishability
A naming service must make it possible to guarantee that two
different names are easily distinguishable from each other by its
human users.
5.1.3. Minimal Structure
A naming service should impose as little structure on the names it
supports as practical in order to be universally applicable. Naming
services that impose a given organizational structure on the names
expressible using the service will not translate well to societies
where that organizational structure is not prevalent.
5.2. Authority
Every Association among names, addresses, and auxiliary data is
subject to some Authority: an entity which has the right to determine
which Associations and Subjects exist in its namespace. The
following are properties of Authorities in our ideal naming service:
5.2.1. Federation of Authority
An Authority can delegate some part of its namespace to some other
subordinate Authority. This property allows the naming service to
scale to the size of the Internet, and leads to a tree-structured
namespace, where each Delegation is itself identified with a Subject
at a given level in the namespace.
In the DNS protocol, this federation of authority is implemented
through delegation using the NS RRTYPE, redirecting queries to
subordinate authorities recursively to the final authority. When
DNSSEC is used, the DS RRTYPE is used to verify this delegation.
5.2.2. Uniqueness of Authority
For a given Subject, there is a single Authority that has the right
to determine the Associations and/or Delegations for that subject.
The unitary authority for the root of the namespace tree may be
special, though; see Section 5.2.5.
In the DNS protocol as deployed, unitary authority is approximated by
the entity identified by the SOA RRTYPE. The existence of
registrars, which use the Extensible Provisioning Protocol (EPP)
[RFC5730] to modify entries in the zones under the authority of a
top-level domain registry, complicates this somewhat.
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5.2.3. Transparency of Authority
A querier can determine the identity of the Authority for a given
Association. An Authority cannot delegate its rights or
responsibilities with respect to a subject without that Delegation
being exposed to the querier.
In DNS, the authoritative name server(s) to which a query is
delegated via the NS RRTYPE are known. However, we note that in the
case of authorities which delegate the ability to write to the zone
to other entities (i.e., the registry-registrar relationship), the
current DNS provides no facility for a querier to understand on whose
behalf an authoritative assertion is being made; this information is
instead available via WHOIS. To our knowledge, no present DNS name
servers use WHOIS information retrieved out of band to make policy
decisions.
5.2.4. Revocability of Authority
An ideal naming service allows the revocation and replacement of an
authority at any level in the namespace, and supports the revocation
and replacement of authorities with minimal operational disruption.
The current DNS allows the replacement of any level of delegation
except the root through changes to the appropriate NS and DS records.
Authority revocation in this case is as consistent as any other
change to the DNS.
5.2.5. Consensus on Root of Authority
Authority at the top level of the namespace tree is delegated
according to a process such that there is universal agreement
throughout the Internet as to the subordinates of those Delegations.
5.3. Authenticity
A querier must be able to verify that the answers that it gets from
the naming service are authentic.
5.3.1. Authenticity of Delegation
Given a Delegation from a superordinate to a subordinate Authority, a
querier can verify that the superordinate Authority authorized the
Delegation.
Authenticity of delegation in DNS is provided by DNSSEC [RFC4033].
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5.3.2. Authenticity of Response
The authenticity of every answer is verifiable by the querier. The
querier can confirm that the Association returned in the answer is
correct according to the Authority for the Subject of the query.
Authenticity of response in DNS is provided by DNSSEC.
5.3.3. Authenticity of Negative Response
Some queries will yield no answer, because no such Association
exists. In this case, the querier can confirm that the Authority for
the Subject of the query asserts this lack of Association.
Authenticity of negative response in DNS is provided by DNSSEC.
5.4. Consistency
Consistency in a naming service is important. The naming service
should provide the most globally consistent view possible of the set
of associations that exist at a given point in time, within the
limits of latency and bandwidth tradeoffs.
5.4.1. Dynamic Consistency
When an Authority makes changes to an Association, every query for a
given Subject returns either the new valid result or a previously
valid result, with known and/or predictable bounds on "how
previously". Given that additions of, changes to, and deletions of
associations may have different operational causes, different bounds
may apply to different operations.
The time-to-live (TTL) on a resource record in DNS provides a
mechanism for expiring old resource records. We note that this
mechanism makes additions to the system propagate faster than changes
and deletions, which may not be a desirable property. However, as no
context information is explicitly available in DNS, the DNS cannot be
said to be dynamically consistent, as different implicitly
inconsistent views of an association may be persistent.
5.4.2. Explicit Inconsistency
Some techniques require giving different answers to different
queries, even in the absence of changes: the stable state of the
namespace is not globally consistent. This inconsistency should be
explicit: a querier can know that an answer might be dependent on its
identity, network location, or other factors.
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One example of such desirable inconsistency is the common practice of
"split horizon" DNS, where an organization makes internal names
available on its own network, but only the names of externally-
visible subjects available to the Internet at large.
Another is the common practice of DNS-based content distribution, in
which an authoritative name server gives different answers for the
same query depending on the network location from which the query was
received, or depending on the subnet in which the end client
originating a query is located (via the EDNS Client Subnet extension
{RFC7871}}). Such inconsistency based on client identity or network
address may increase query linkability (see Section 5.5.4).
These forms of inconsistency are implicit, not explicit, in the
current DNS. We note that while DNS can be deployed to allow
essentially unlimited kinds of inconsistency in its responses, there
is no protocol support for a query to express the kind of consistency
it desires, or for a response to explicitly note that it is
inconsistent. [RFC7871] does allow a querier to note that it would
specifically like the view of the state of the namespace offered to a
certain part of the network, and as such can be seen as inchoate
support for this property.
5.4.3. Global Invariance
An Association which is not intended to be explicitly inconsistent by
the Authority issuing it must return the same result for every Query
for it, regardless of the identity or location of the querier.
This property is not provided by DNS, as it depends on the robust
support on the Explicit Inconsistency property above. Examples of
global invariance failures include geofencing and DNS-based
censorship ordered by a local jurisdiction.
5.5. Performance Properties
A naming service must provide appropriate performance guarantees to
its clients. As these properties deal with the operational
parameters of the naming service, interesting tradeoffs are available
among them, both at design time as well as at run time (on which see
Section 5.5.5).
5.5.1. Availability
The naming service as a whole is resilient to failures of individual
nodes providing the naming service, as well as to failures of links
among them. Intentional prevention of successful, authenticated
query by an adversary should be as hard as practical.
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The DNS protocol was designed to be highly available through the use
of secondary nameservers. Operational practices (e.g. anycast
deployment) also increase the availability of DNS as currently
deployed.
5.5.2. Lookup Latency
The time for the entire process of looking up a name and other
necessary associated data from the point of view of the querier,
amortized over all queries for all connections, should not
significantly impact connection setup or resumption latency.
5.5.3. Bandwidth Efficiency
The bandwidth cost for looking up a name and other associated data
necessary for establishing communication with a given Subject, from
the point of view of the querier, amortized over all queries for all
connections, should not significantly impact total bandwidth demand
for an application.
5.5.4. Query Linkability
It should be costly for an adversary to monitor the infrastructure in
order to link specific queries to specific queriers.
DNS over TLS [RFC7858] and DNS over DTLS [RFC8094] provide this
property between a querier and a recursive resolver; mixing by the
recursive helps with mitigating upstream linkability.
5.5.5. Explicit Tradeoff
A querier should be able to indicate the desire for a benefit with
respect to one performance property by accepting a tradeoff in
another, including:
o Reduced latency for reduced dynamic consistency
o Increased dynamic consistency for increased latency
o Reduced request linkability for increased latency and/or reduced
dynamic consistency
o Reduced aggregate bandwidth use for increased latency and/or
reduced dynamic consistency
There is no support for explicit tradeoffs in performance properties
available to clients in the present DNS.
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5.6. Trust in Infrastructure
A querier should not need to trust any entity other than the
authority as to the correctness of association information provided
by the naming service. Specifically, the querier should not need to
trust any intermediary of infrastructure between itself and the
authority, other than that under its own control.
DNS provides this property with DNSSEC. However, the lack of
mandatory DNSSEC, and the lack of a viable transition strategy to
mandatory DNSSEC, means that trust in infrastructure will remain
necessary for DNS even with large scale DNSSEC deployment.
6. Observations
On a cursory examination, many of the properties of our ideal name
service can be met, or could be met, by the present DNS protocol or
extensions thereto. We note that there are further possibilities for
the future evolution of naming services meeting these properties.
This section contains random observations that might inform future
work.
6.1. Delegation and redirection are separate operations
Any system which can provide the authenticity properties in
Section 5.3 is freed from one of the design characteristics of the
present domain name system: the requirement to bind a zone of
authority to a specific set of authoritative servers. Since the
authenticity of delegation must be a protected by a chain of
signatures back to the root of authority, the location within the
infrastructure where an authoritative mapping "lives" is no longer
bound to a specific name server. While the present design of DNS
does have its own scalability advantages, this implication allows a
much larger design space to be explored for future name service work,
as a Delegation need not always be implemented via redirection to
another name server.
6.2. Queries and assertion contexts are presently implicit
Much of the difficulty with explicit inconsistency (Section 5.4.2)
derives from the fact that assertions and queries about subjects
exist within a context: .local names on the local network (whether
link or site local), split-DNS names within the context of the
"inside" side of the recursive resolver, DNS geographic load
balancing within the geographic context of the client. Because DNS
provides no protocol-level support for expressing these contexts,
they remain implicit.
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We note that protocol-level support for this context explicit could
point toward solutions for a variety of problems in currently
deployed naming services, from generalized solutions with privacy/
efficiency tradeoffs ({RFC7871}} aside), to explicit redirection to
alternate naming resolution for "special" names [RFC6761].
6.3. Unicode alone may not be sufficient for distinguishable names
Allowing names to be encoded in Unicode goes a long way toward
meeting the meaningfulness property (see Section 5.1.1) for the
majority of speakers of human languages. However, as noted by the
Internet Architecture Board (see [IAB-UNICODE7]) and discussed at the
Locale-free Unicode Identifiers (LUCID) BoF at IETF 92 in Dallas in
March 2015 (see [LUCID]), it is not in the general case sufficient
for distinguishability (see Section 5.1.2). An ideal naming service
may therefore have to supplement Unicode by providing runtime support
for disambiguation of queries and assertions where the results may be
indistinguishable.
6.4. Implicit inconsistency makes global invariance challenging to
verify
DNS does not provide a generalized form of explicit inconsistency, so
efforts to verify global invariance, or rather, to discover
Associations for which global invariance does not hold, are
necessarily effort-intensive and dynamic. For example, the Open
Observatory of Network Interference performs DNS consistency checking
from multiple volunteer vantage points for a set of targeted (i.e.,
likely to be globally variant) domain names; see
https://ooni.torproject.org/nettest/dns-consistency/
7. IANA Considerations
This document has no actions for IANA.
8. Security Considerations
Protocols implementing name resolution systems that meet these ideal
properties will have to consider tradeoffs, especially with respect
to privacy (Section 5.5.4) versus performance, as in Section 5.5.5.
Many properties are security and privacy relevant. All the
properties in Section 5.3 must hold for a client to be able to trust
that assertions about a name are as intended by the authority for
that name. Section 5.1.2 specifies a property which, when it does
not hold, may be exploitable for phishing attacks, and Section 5.2.3
specifies a property which may ease operational defense against
malware abuse of the naming system.
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9. Acknowledgments
This document is, in part, an output of design work on naming
services at the Network Security Group at ETH Zurich. Thanks to the
group, including Daniele Asoni, Steve Matsumoto, and Stephen Shirley,
for discussions leading to this document. Thanks as well to Ted
Hardie, Wendy Selzter, Andrew Sullivan, and Suzanne Woolf for input
and feedback.
10. Informative References
[I-D.ietf-dprive-dns-over-tls]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over TLS", draft-
ietf-dprive-dns-over-tls-09 (work in progress), March
2016.
[I-D.ietf-dprive-dnsodtls]
Reddy, T., Wing, D., and P. Patil, "Specification for DNS
over Datagram Transport Layer Security (DTLS)", draft-
ietf-dprive-dnsodtls-15 (work in progress), December 2016.
[IAB-UNICODE7]
IAB, ., "IAB Statement on Identifiers and Unicode 7.0.0",
n.d., <https://www.iab.org/documents/
correspondence-reports-documents/2015-2/
iab-statement-on-identifiers-and-unicode-7-0-0/>.
[LUCID] Freytag, A. and A. Sullivan, "LUCID problem (slides, IETF
92 LUCID BoF)", n.d.,
<https://www.ietf.org/proceedings/92/slides/
slides-92-lucid-0.pdf>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
<https://www.rfc-editor.org/info/rfc5730>.
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[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871,
DOI 10.17487/RFC7871, May 2016,
<https://www.rfc-editor.org/info/rfc7871>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/info/rfc8094>.
Author's Address
Brian Trammell
ETH Zurich
Universitaetstrasse 6
Zurich 8092
Switzerland
Email: ietf@trammell.ch
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