draft-ietf-dprive-dns-over-tls-00.txt   draft-ietf-dprive-dns-over-tls-01.txt 
Network Working Group Z. Hu Network Working Group Z. Hu
Internet-Draft L. Zhu Internet-Draft L. Zhu
Intended status: Standards Track J. Heidemann Intended status: Standards Track J. Heidemann
Expires: March 21, 2016 USC/Information Sciences Expires: April 13, 2016 USC/Information Sciences
Institute Institute
A. Mankin A. Mankin
D. Wessels D. Wessels
Verisign Labs Verisign Labs
P. Hoffman P. Hoffman
ICANN ICANN
September 18, 2015 October 11, 2015
DNS over TLS: Initiation and Performance Considerations DNS over TLS: Initiation and Performance Considerations
draft-ietf-dprive-dns-over-tls-00 draft-ietf-dprive-dns-over-tls-01
Abstract Abstract
This document describes the use of TLS to provide privacy for DNS. This document describes the use of TLS to provide privacy for DNS.
Encryption provided by TLS eliminates opportunities for eavesdropping Encryption provided by TLS eliminates opportunities for eavesdropping
on DNS queries in the network, such as discussed in RFC 7258. In and on-path tampering with DNS queries in the network, such as
addition, this document specifies two usage profiles for DNS-over-TLS discussed in RFC 7258. In addition, this document specifies two
and provides advice on performance considerations to minimize usage profiles for DNS-over-TLS and provides advice on performance
overhead from using TCP and TLS with DNS. considerations to minimize overhead from using TCP and TLS with DNS.
Note: this document was formerly named Note: this document was formerly named
draft-ietf-dprive-start-tls-for-dns. Its name has been changed to draft-ietf-dprive-start-tls-for-dns. Its name has been changed to
better describe the mechanism now used. Please refer to working better describe the mechanism now used. Please refer to working
group archives under the former name for history and previous group archives under the former name for history and previous
discussion. [RFC Editor: please remove this paragraph prior to discussion. [RFC Editor: please remove this paragraph prior to
publication] publication]
Status of this Memo Status of this Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 21, 2016. This Internet-Draft will expire on April 13, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.3. Transmitting and Receiving Messages . . . . . . . . . . . 5 3.3. Transmitting and Receiving Messages . . . . . . . . . . . 5
3.4. Connection Reuse, Close and Reestablishment . . . . . . . 5 3.4. Connection Reuse, Close and Reestablishment . . . . . . . 5
4. Usage Profiles . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Usage Profiles . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Opportunistic Privacy Profile . . . . . . . . . . . . . . 7 4.1. Opportunistic Privacy Profile . . . . . . . . . . . . . . 7
4.2. Pre-Deployed Profile . . . . . . . . . . . . . . . . . . . 7 4.2. Pre-Deployed Profile . . . . . . . . . . . . . . . . . . . 7
5. Performance Considerations . . . . . . . . . . . . . . . . . . 8 5. Performance Considerations . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Design Evolution . . . . . . . . . . . . . . . . . . . . . . . 9 7. Design Evolution . . . . . . . . . . . . . . . . . . . . . . . 9
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 10 8. Implementation Status . . . . . . . . . . . . . . . . . . . . 10
8.1. Unbound . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Unbound . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. ldns . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.2. ldns . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.3. digit . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.3. digit . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.4. getdns . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.4. getdns . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 12 10. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . . 12 12.1. Normative References . . . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . . 13 12.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
Today, nearly all DNS queries [RFC1034], [RFC1035] are sent Today, nearly all DNS queries [RFC1034], [RFC1035] are sent
unencrypted, which makes them vulnerable to eavesdropping by an unencrypted, which makes them vulnerable to eavesdropping by an
attacker that has access to the network channel, reducing the privacy attacker that has access to the network channel, reducing the privacy
of the querier. Recent news reports have elevated these concerns, of the querier. Recent news reports have elevated these concerns,
and recent IETF work has specified privacy considerations for DNS and recent IETF work has specified privacy considerations for DNS
[RFC7626]. [RFC7626].
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Establishing and Managing DNS-over-TLS Sessions 3. Establishing and Managing DNS-over-TLS Sessions
3.1. Session Initiation 3.1. Session Initiation
A DNS server that supports DNS-over-TLS SHOULD listen for and accept A DNS server that supports DNS-over-TLS SHOULD listen for and accept
TCP connections on a designated port TBD identified in Section 6. TCP connections on port 853.
DNS clients desiring privacy from DNS-over-TLS from a particular DNS clients desiring privacy from DNS-over-TLS from a particular
server SHOULD establish a TCP connection to port TBD on the server. server SHOULD establish a TCP connection to port 853 on the server.
Upon successful establishment of the TCP connection, client and Upon successful establishment of the TCP connection, client and
server SHOULD immediately initiate a TLS handshake using the server SHOULD immediately initiate a TLS handshake using the
procedure described in [RFC5246]. procedure described in [RFC5246].
DNS clients SHOULD remember server IP addresses that don't support DNS clients SHOULD remember server IP addresses that don't support
DNS-over-TLS, including timeouts, connection refusals, and TLS DNS-over-TLS, including timeouts, connection refusals, and TLS
handshake failures, and not request DNS-over-TLS from them for a handshake failures, and not request DNS-over-TLS from them for a
reasonable period (such as one hour per server). DNS clients reasonable period (such as one hour per server). DNS clients
following a pre-deployed privacy profile MAY be more aggressive about following a pre-deployed privacy profile MAY be more aggressive about
retrying DNS-over-TLS connection failures. retrying DNS-over-TLS connection failures.
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After TLS negotiation completes, the connection will be encrypted and After TLS negotiation completes, the connection will be encrypted and
is now protected from eavesdropping. At this point, normal DNS is now protected from eavesdropping. At this point, normal DNS
queries SHOULD take place. queries SHOULD take place.
3.3. Transmitting and Receiving Messages 3.3. Transmitting and Receiving Messages
All messages (requests and responses) in the established TLS session All messages (requests and responses) in the established TLS session
MUST use the two-octet length field described in Section 4.2.2 of MUST use the two-octet length field described in Section 4.2.2 of
[RFC1035]. For reasons of efficiency, DNS clients and servers SHOULD [RFC1035]. For reasons of efficiency, DNS clients and servers SHOULD
transmit the two-octet length field, and the message described by transmit the two-octet length field, and the message described by
that length field, in a single TCP segment ([I-D.ietf-dnsop-5966bis], that length field, to the TCP layer at the same time (e.g., in a
Section 8). single "write" system call) to make it more likely that all the data
will be transmitted in a single TCP segment
([I-D.ietf-dnsop-5966bis], Section 8).
In order to minimize latency, clients SHOULD pipeline multiple In order to minimize latency, clients SHOULD pipeline multiple
queries over a TLS session. When a DNS client sends multiple queries queries over a TLS session. When a DNS client sends multiple queries
to a server, it should not wait for an outstanding reply before to a server, it should not wait for an outstanding reply before
sending the next query ([I-D.ietf-dnsop-5966bis], Section 6.2.1.1). sending the next query ([I-D.ietf-dnsop-5966bis], Section 6.2.1.1).
Since pipelined responses can arrive out-of-order, clients MUST match Since pipelined responses can arrive out-of-order, clients MUST match
responses to outstanding queries using the ID field and port number. responses to outstanding queries using the ID field, query name,
Failure by clients to properly match responses to outstanding queries type, and class. Failure by clients to properly match responses to
can have serious consequences for interoperability outstanding queries can have serious consequences for
([I-D.ietf-dnsop-5966bis], Section 7). interoperability ([I-D.ietf-dnsop-5966bis], Section 7).
3.4. Connection Reuse, Close and Reestablishment 3.4. Connection Reuse, Close and Reestablishment
For DNS clients that use library functions such as "gethostbyname()", For DNS clients that use library functions such as "getaddrinfo()"
current implementations are known to open and close TCP connections and "gethostbyname()", current implementations are known to open and
each DNS call. To avoid excess TCP connections, each with a single close TCP connections each DNS call. To avoid excess TCP
query, clients SHOULD reuse a single TCP connection to the recursive connections, each with a single query, clients SHOULD reuse a single
resolver. Alternatively they may prefer to use UDP to a DNS-over-TLS TCP connection to the recursive resolver. Alternatively they may
enabled caching resolver on the same machine that then uses a system- prefer to use UDP to a DNS-over-TLS enabled caching resolver on the
wide TCP connection to the recursive resolver. same machine that then uses a system-wide TCP connection to the
recursive resolver.
In order to amortize TCP and TLS connection setup costs, clients and In order to amortize TCP and TLS connection setup costs, clients and
servers SHOULD NOT immediately close a connection after each servers SHOULD NOT immediately close a connection after each
response. Instead, clients and servers SHOULD reuse existing response. Instead, clients and servers SHOULD reuse existing
connections for subsequent queries as long as they have sufficient connections for subsequent queries as long as they have sufficient
resources. In some cases, this means that clients and servers may resources. In some cases, this means that clients and servers may
need to keep idle connections open for some amount of time. need to keep idle connections open for some amount of time.
Proper management of established and idle connections is important to Proper management of established and idle connections is important to
the healthy operation of a DNS server. An implementor of DNS-over- the healthy operation of a DNS server. An implementor of DNS-over-
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configuring a network. For example, for clients on networks that configuring a network. For example, for clients on networks that
require authentication through web-based login, such authentication require authentication through web-based login, such authentication
may rely on DNS interception and spoofing. Techniques such as those may rely on DNS interception and spoofing. Techniques such as those
used by DNSSEC-trigger [dnssec-trigger] MAY be used during network used by DNSSEC-trigger [dnssec-trigger] MAY be used during network
configuration, with the intent to transition to the designated DNS configuration, with the intent to transition to the designated DNS
provider after authentication. The user MUST be alerted that the DNS provider after authentication. The user MUST be alerted that the DNS
is not private during such bootstrap. is not private during such bootstrap.
Methods for pre-deployment of the designated DNS provider are outside Methods for pre-deployment of the designated DNS provider are outside
the scope of this document. In corporate settings, such information the scope of this document. In corporate settings, such information
may be provided at system installation, for instance within the may be provided at system installation.
authenticated DHCP exchange [RFC3118].
5. Performance Considerations 5. Performance Considerations
DNS-over-TLS incurs additional latency at session startup. It also DNS-over-TLS incurs additional latency at session startup. It also
requires additional state (memory) and increased processing (CPU). requires additional state (memory) and increased processing (CPU).
1. Latency: Compared to UDP, DNS-over-TCP requires an additional 1. Latency: Compared to UDP, DNS-over-TCP requires an additional
round-trip-time (RTT) of latency to establish a TCP connection. round-trip-time (RTT) of latency to establish a TCP connection.
TCP Fast Open [RFC7413] can eliminate that RTT when information TCP Fast Open [RFC7413] can eliminate that RTT when information
exists from prior connections. The TLS handshake adds another exists from prior connections. The TLS handshake adds another
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A full performance evaluation is outside the scope of this A full performance evaluation is outside the scope of this
specification. A more detailed analysis of the performance specification. A more detailed analysis of the performance
implications of DNS-over-TLS (and DNS-over-TCP) is discussed in implications of DNS-over-TLS (and DNS-over-TCP) is discussed in
[tdns] and [I-D.ietf-dnsop-5966bis]. [tdns] and [I-D.ietf-dnsop-5966bis].
6. IANA Considerations 6. IANA Considerations
IANA is requested to add the following value to the "Service Name and IANA is requested to add the following value to the "Service Name and
Transport Protocol Port Number Registry" registry in the System Transport Protocol Port Number Registry" registry in the System
Range. The registry for that range requires IETF Review or IESG Range. The registry for that range requires IETF Review or IESG
Approval [RFC6335] and such a review has been requested using the Approval [RFC6335] and such a review was requested using the Early
Early Allocation process [RFC7120] for the well-known TCP port in Allocation process [RFC7120] for the well-known TCP port in this
this document. document.
We further recommend that IANA reserve the same port number over UDP We further recommend that IANA reserve the same port number over UDP
for the proposed DNS-over-DTLS protocol [draft-ietf-dprive-dnsodtls]. for the proposed DNS-over-DTLS protocol [draft-ietf-dprive-dnsodtls].
Service Name domain-s IANA responded to the early allocation request with the following
Transport Protocol(s) TCP/UDP TEMPORARY assignment:
Assignee IESG
Contact TBD Service Name domain-s
Description DNS query-response protocol run over TLS Port Number 853
Reference This document Transport Protocol(s) TCP/UDP
Assignee IETF DPRIVE Chairs
Contact Paul Hoffman
Description DNS query-response protocol run over TLS/DTLS
Reference This document
The TEMPORARY assignment expires 2016-10-08. IANA is requested to
make the assigmnent permanent upon publication of this document as an
RFC.
7. Design Evolution 7. Design Evolution
[Note to RFC Editor: please do not remove this section prior to [Note to RFC Editor: please do not remove this section prior to
publication as it may be useful to future Foo-over-TLS efforts] publication as it may be useful to future Foo-over-TLS efforts]
Earlier versions of this document proposed an upgrade-based approach Earlier versions of this document proposed an upgrade-based approach
to establishing a TLS session. The client would signal its interest to establishing a TLS session. The client would signal its interest
in TLS by setting a "TLS OK" bit in the EDNS0 flags field. A server in TLS by setting a "TLS OK" bit in the EDNS0 flags field. A server
would signal its acceptance by responding with the TLS OK bit set. would signal its acceptance by responding with the TLS OK bit set.
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arise out of the ability to eavesdrop on DNS messages. It does not arise out of the ability to eavesdrop on DNS messages. It does not
address other security issues in DNS, and there are a number of address other security issues in DNS, and there are a number of
residual risks that may affect its success at protecting privacy: residual risks that may affect its success at protecting privacy:
1. There are known attacks on TLS, such as person-in-the-middle and 1. There are known attacks on TLS, such as person-in-the-middle and
protocol downgrade. These are general attacks on TLS and not protocol downgrade. These are general attacks on TLS and not
specific to DNS-over-TLS; please refer to the TLS RFCs for specific to DNS-over-TLS; please refer to the TLS RFCs for
discussion of these security issues. Clients and servers MUST discussion of these security issues. Clients and servers MUST
adhere to the TLS implementation recommendations and security adhere to the TLS implementation recommendations and security
considerations of [RFC7525]. DNS clients keeping track of considerations of [RFC7525]. DNS clients keeping track of
servers known to support TLS (i.e., "pinning") enables clients to servers known to support TLS enables clients to detect downgrade
detect downgrade attacks. For servers with no connection history attacks. For servers with no connection history and no apparent
and no apparent support for TLS, clients depending on their support for TLS, clients depending on their Privacy Profile and
Privacy Profile and privacy requirements may choose to (a) try privacy requirements may choose to (a) try another server when
another server when available, (b) continue without TLS, or (c) available, (b) continue without TLS, or (c) refuse to forward the
refuse to forward the query. query.
2. Middleboxes [RFC3234] are be present in some networks and have 2. Middleboxes [RFC3234] are present in some networks and have been
been known to interfere with normal DNS resolution. Use of a known to interfere with normal DNS resolution. Use of a
designated port for DNS-over-TLS should avoid such interference. designated port for DNS-over-TLS should avoid such interference.
In general, clients that attempt TLS and fail can either fall In general, clients that attempt TLS and fail can either fall
back on unencrypted DNS, or wait and retry later, depending on back on unencrypted DNS, or wait and retry later, depending on
their Privacy Profile and privacy requirements. their Privacy Profile and privacy requirements.
3. Any protocol interactions prior to the TLS handshake are 3. Any DNS protocol interactions prior to the TLS handshake that are
performed in the clear and can be modified by a person-in-the- performed in the clear can be modified by a person-in-the-middle
middle attacker. For this reason, clients MAY discard cached attacker. For example, unencrypted queries and responses might
information about server capabilities advertised prior to the take place over port 53 between a client and server prior to TLS.
start of the TLS handshake. For this reason, clients MAY discard cached information about
server capabilities advertised prior to the start of the TLS
handshake.
4. This document does not itself specify ideas to resist known 4. This document does not itself specify ideas to resist known
traffic analysis or side channel leaks. Even with encrypted traffic analysis or side channel leaks. Even with encrypted
messages, a well-positioned party may be able to glean certain messages, a well-positioned party may be able to glean certain
details from an analysis of message timings and sizes. Clients details from an analysis of message timings and sizes. Clients
and servers may consider the use of a padding method to address and servers may consider the use of a padding method to address
privacy leakage due to message sizes [I-D.edns0-padding] privacy leakage due to message sizes [I-D.edns0-padding]
10. Contributing Authors 10. Contributing Authors
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Mohaisen, "Opportunistic Encryption with DANE Semantics Mohaisen, "Opportunistic Encryption with DANE Semantics
and IPsec: IPSECA", draft-osterweil-dane-ipsec-03 (work in and IPsec: IPSECA", draft-osterweil-dane-ipsec-03 (work in
progress), July 2015, progress), July 2015,
<http://tools.ietf.org/html/ <http://tools.ietf.org/html/
draft-osterweil-dane-ipsec-03>. draft-osterweil-dane-ipsec-03>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/ [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/
RFC2818, May 2000, RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>. <http://www.rfc-editor.org/info/rfc2818>.
[RFC3118] Droms, R. and W. Arbaugh., Ed., "Authentication for DHCP
Messages", RFC 3118, DOI 10.17487/RFC3118, June 2001,
<http://www.rfc-editor.org/info/rfc3118>.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002, Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<http://www.rfc-editor.org/info/rfc3234>. <http://www.rfc-editor.org/info/rfc3234>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005, RFC 4033, DOI 10.17487/RFC4033, March 2005,
<http://www.rfc-editor.org/info/rfc4033>. <http://www.rfc-editor.org/info/rfc4033>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
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