draft-ietf-dprive-dnsodtls-06.txt   draft-ietf-dprive-dnsodtls-07.txt 
DPRIVE T. Reddy DPRIVE T. Reddy
Internet-Draft D. Wing Internet-Draft D. Wing
Intended status: Standards Track P. Patil Intended status: Standards Track P. Patil
Expires: October 6, 2016 Cisco Expires: January 7, 2017 Cisco
April 4, 2016 July 6, 2016
DNS over DTLS (DNSoD) DNS over DTLS (DNSoD)
draft-ietf-dprive-dnsodtls-06 draft-ietf-dprive-dnsodtls-07
Abstract Abstract
DNS queries and responses are visible to network elements on the path DNS queries and responses are visible to network elements on the path
between the DNS client and its server. These queries and responses between the DNS client and its server. These queries and responses
can contain privacy-sensitive information which is valuable to can contain privacy-sensitive information which is valuable to
protect. An active attacker can send bogus responses causing protect. An active attacker can send bogus responses causing
misdirection of the subsequent connection. misdirection of the subsequent connection.
To counter passive listening and active attacks, this document To counter passive listening and active attacks, this document
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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 October 6, 2016. This Internet-Draft will expire on January 7, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 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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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Relationship to TCP Queries and to DNSSEC . . . . . . . . 3 1.1. Relationship to TCP Queries and to DNSSEC . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DTLS session initiation, Polling and Discovery . . . . . . . 3 3. Establishing and Managing DNS-over-DTLS Sessions . . . . . . 3
4. Performance Considerations . . . . . . . . . . . . . . . . . 4 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 3
5. Established sessions . . . . . . . . . . . . . . . . . . . . 4 3.2. DTLS Handshake and Authentication . . . . . . . . . . . . 4
6. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Established Sessions . . . . . . . . . . . . . . . . . . 4
7. Downgrade attacks . . . . . . . . . . . . . . . . . . . . . . 6 4. Performance Considerations . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Authenticating a DNS Privacy Server . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
The Domain Name System is specified in [RFC1034] and [RFC1035]. DNS The Domain Name System is specified in [RFC1034] and [RFC1035] . DNS
queries and responses are normally exchanged unencrypted and are thus queries and responses are normally exchanged unencrypted and are thus
vulnerable to eavesdropping. Such eavesdropping can result in an vulnerable to eavesdropping. Such eavesdropping can result in an
undesired entity learning domains that a host wishes to access, thus undesired entity learning domains that a host wishes to access, thus
resulting in privacy leakage. DNS privacy problem is further resulting in privacy leakage. DNS privacy problem is further
discussed in [RFC7626]. discussed in [RFC7626] .
Active attackers have long been successful at injecting bogus Active attackers have long been successful at injecting bogus
responses, causing cache poisoning and causing misdirection of the responses, causing cache poisoning and causing misdirection of the
subsequent connection (if attacking A or AAAA records). A popular subsequent connection (if attacking A or AAAA records). A popular
mitigation against that attack is to use ephemeral and random source mitigation against that attack is to use ephemeral and random source
ports for DNS queries [RFC5452]. ports for DNS queries [RFC5452] .
This document defines DNS over DTLS (DNSoD, pronounced "dee-enn-sod") This document defines DNS over DTLS (DNSoD, pronounced "dee-enn-sod")
which provides confidential DNS communication between stub resolvers which provides confidential DNS communication between stub resolvers
and recursive resolvers, stub resolvers and forwarders, forwarders and recursive resolvers, stub resolvers and forwarders, forwarders
and recursive resolvers. and recursive resolvers.
The motivations for proposing DNSoD are that The motivations for proposing DNSoD are that
o TCP suffers from network head-of-line blocking, where the loss of o TCP suffers from network head-of-line blocking, where the loss of
a packet causes all other TCP segments to not be delivered to the a packet causes all other TCP segments to not be delivered to the
application until the lost packet is re-transmitted. DNSoD, application until the lost packet is re-transmitted. DNSoD,
because it uses UDP, does not suffer from network head-of-line because it uses UDP, does not suffer from network head-of-line
blocking. blocking.
o DTLS session resumption consumes 1 round trip whereas TLS session o DTLS session resumption consumes 1 round trip whereas TLS session
resumption can start only after TCP handshake is complete. resumption can start only after TCP handshake is complete.
Although TCP Fast Open [RFC7413] can reduce that handshake, TCP Although TCP Fast Open [RFC7413] can reduce that handshake, TCP
Fast Open is not yet available in commercially-popular operating Fast Open is only available on a few OSs, it is not yet
systems. ubiquitous.
1.1. Relationship to TCP Queries and to DNSSEC 1.1. Relationship to TCP Queries and to DNSSEC
DNS queries can be sent over UDP or TCP. The scope of this document, DNS queries can be sent over UDP or TCP. The scope of this document,
however, is only UDP. DNS over TCP could be protected with TLS, as however, is only UDP. DNS over TCP could be protected with TLS, as
described in [I-D.ietf-dprive-dns-over-tls]. described in [RFC7858].
DNS Security Extensions (DNSSEC [RFC4033]) provides object integrity DNS Security Extensions ( DNSSEC [RFC4033] ) provides object
of DNS resource records, allowing end-users (or their resolver) to integrity of DNS resource records, allowing end-users (or their
verify legitimacy of responses. However, DNSSEC does not protect resolver) to verify legitimacy of responses. However, DNSSEC does
privacy of DNS requests or responses. DNSoD works in conjunction not protect privacy of DNS requests or responses. DNSoD works in
with DNSSEC, but DNSoD does not replace the need or value of DNSSEC. conjunction with DNSSEC, but DNSoD does not replace the need or value
of DNSSEC.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119] .
3. DTLS session initiation, Polling and Discovery 3. Establishing and Managing DNS-over-DTLS Sessions
DNSoD MUST run over standard UDP port 853 as defined in Section 8. A 3.1. Session Initiation
DNS server that supports DNSoD MUST listen for and accept DTLS
packets on a designated port 853. DNSoD MUST run over standard UDP port 853 as defined in Section 7.
The host should determine if the DNS server supports DNSoD by sending The host should determine if the DNS server supports DNSoD by sending
a DTLS ClientHello message. A DNS server that does not support DNSoD a DTLS ClientHello message. A DNS server that does not support DNSoD
will not respond to ClientHello messages sent by the client. The will not respond to ClientHello messages sent by the client. If no
client MUST use timer values defined in Section 4.2.4.1 of [RFC6347] response is received from that server, and the client has no better
for retransmission of ClientHello message and if no response is round-trip estimate, the client MUST retransmit the DTLS ClientHello
received from the DNS server. After 15 seconds, it MUST cease according to Section 4.2.4.1 of [RFC6347]. After 15 seconds, it MUST
attempts to re-transmit its ClientHello. The client MAY repeat that cease attempts to re-transmit its ClientHello. The client MAY repeat
procedure in the event the DNS server has been upgraded to support that procedure in the event the DNS server upgrades to support DNSoD,
DNSoD, but such probing SHOULD NOT be done more frequently than every but such probing SHOULD NOT be done more frequently than every 24
24 hours and MUST NOT be done more frequently than every 15 minutes. hours and MUST NOT be done more frequently than every 15 minutes.
This mechanism requires no additional signaling between the client This mechanism requires no additional signaling between the client
and server. and server. Behavior for an unsuccessful DTLS connection is
discussed in Section 6.
4. Performance Considerations
To reduce number of octets of the DTLS handshake, especially the size
of the certificate in the ServerHello (which can be several
kilobytes), DNS client and server can use raw public keys [RFC7250]
or Cached Information Extension [I-D.ietf-tls-cached-info]. Cached
Information Extension avoids transmitting the server's certificate
and certificate chain if the client has cached that information from
a previous TLS handshake.
Since pipelined responses can arrive out of order, clients MUST match 3.2. DTLS Handshake and Authentication
responses to outstanding queries on the same DTLS connection using
the Message ID. If the response contains a question section, the
client MUST match the QNAME, QCLASS, and QTYPE fields. Failure by
clients to properly match responses to outstanding queries can have
serious consequences for interoperability ([RFC7766], Section 7).
It is highly advantageous to avoid server-side DTLS state and reduce Once the DNS client succeeds in receiving HelloVerifyRequest from the
the number of new DTLS sessions on the server which can be done with server via UDP on the well-known port for DNS over DTLS, it proceeds
[RFC5077]. This also eliminates a round-trip for subsequent DNSoD with DTLS handshake as described in [RFC6347], following the best
queries, because with [RFC5077] the DTLS session does not need to be practices specified in [RFC7525].
re-established.
Compared to normal DNS, DTLS adds at least 13 octets of header, plus DNS privacy requires encrypting the query (and response) from passive
cipher and authentication overhead to every query and every response. attacks. Such encryption typically provides integrity protection as
This reduces the size of the DNS payload that can be carried. DNS a side-effect, which means on-path attackers cannot simply inject
client and server MUST support the EDNS0 option defined in [RFC6891] bogus DNS responses. However, to provide stronger protection from
so that the DNS client can indicate to the DNS server the maximum DNS active attackers pretending to be the server, the server itself needs
response size it can handle without IP fragmentation. If the DNS to be authenticated. To authenticate the server providing DNS
server's response exceeds the EDNS0 value, the DNS server sets the TC privacy, DNS client can use the authenication mechanisms discussed in
(truncated) bit. On receiving a response with the TC bit set, the [I-D.ietf-dprive-dtls-and-tls-profiles]. This document does not
client establishes a DNS-over-TLS connection to the same server, and propose new ideas for authentication.
sends a new DNS request for the same resource record
DNSoD puts an additional computational load on servers. The largest After DTLS negotiation completes, the connection will be encrypted
gain for privacy is to protect the communication between the DNS and is now protected from eavesdropping.
client (the end user's machine) and its caching resolver.
5. Established sessions 3.3. Established Sessions
In DTLS, all data is protected using the same record encoding and In DTLS, all data is protected using the same record encoding and
mechanisms. When the mechanism described in this document is in mechanisms. When the mechanism described in this document is in
effect, DNS messages are encrypted using the standard DTLS record effect, DNS messages are encrypted using the standard DTLS record
encoding. When a user of DTLS wishes to send an DNS message, it encoding. When a user of DTLS wishes to send an DNS message, it
delivers it to the DTLS implementation as an ordinary application delivers it to the DTLS implementation as an ordinary application
data write (e.g., SSL_write()). To reduce client and server data write (e.g., SSL_write()). To reduce client and server
workload, clients SHOULD re-use the DTLS session. A single DTLS workload, clients SHOULD re-use the DTLS session. A single DTLS
session can be used to send multiple DNS requests and receive session can be used to send multiple DNS requests and receive
multiple DNS responses. multiple DNS responses.
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ServerHello ServerHello
(empty SessionTicket extension) (empty SessionTicket extension)
Certificate* Certificate*
ServerKeyExchange* ServerKeyExchange*
CertificateRequest* CertificateRequest*
<-------- ServerHelloDone <-------- ServerHelloDone
Certificate* Certificate*
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] (ChangeCipherSpec)
Finished --------> Finished -------->
NewSessionTicket NewSessionTicket
[ChangeCipherSpec] (ChangeCipherSpec)
<-------- Finished <-------- Finished
DNS Request ---------> DNS Request --------->
<--------- DNS Response <--------- DNS Response
Message Flow for Full Handshake Issuing New Session Ticket Message Flow for Full Handshake Issuing New Session Ticket
6. Anycast 4. Performance Considerations
To reduce number of octets of the DTLS handshake, especially the size
of the certificate in the ServerHello (which can be several
kilobytes), DNS client and server can use raw public keys [RFC7250]
or Cached Information Extension [I-D.ietf-tls-cached-info] . Cached
Information Extension avoids transmitting the server's certificate
and certificate chain if the client has cached that information from
a previous TLS handshake.
Since pipelined responses can arrive out of order, clients MUST match
responses to outstanding queries on the same DTLS connection using
the Message ID. If the response contains a question section, the
client MUST match the QNAME, QCLASS, and QTYPE fields. Failure by
clients to properly match responses to outstanding queries can have
serious consequences for interoperability ( [RFC7766] , Section 7).
It is highly advantageous to avoid server-side DTLS state and reduce
the number of new DTLS sessions on the server which can be done with
[RFC5077] . This also eliminates a round-trip for subsequent DNSoD
queries, because with [RFC5077] the DTLS session does not need to be
re-established.
Compared to normal DNS, DTLS adds at least 13 octets of header, plus
cipher and authentication overhead to every query and every response.
This reduces the size of the DNS payload that can be carried. DNS
client and server MUST support the EDNS0 option defined in [RFC6891]
so that the DNS client can indicate to the DNS server the maximum DNS
response size it can reassemble and deliver in the DNS client's
network stack. The client sets its EDNS0 value as if DTLS is not
being used. The DNS server must ensure that the DNS response size
does not exceed the Path MTU. The DNS server must consider the
amount of record expansion expected by the DTLS processing when
calculating the size of DNS response that fits within the path MTU.
Path MTU MUST be greater than equal to [DNS response size + DTLS
overhead of 13 octets + padding size ([RFC7830]) + authentication
overhead of the negotiated DTLS cipher suite + block padding
(Section 4.1.1.1 of [RFC6347]]. If the DNS server's response were to
exceed that calculated value, the server sends a response that does
fit within that value and sets the TC (truncated) bit. The client,
upon receiving a response with the TC bit set and wanting to receive
the entire response, establishes a DNS-over-TLS [RFC7858] connection
to the same server, and sends a new DNS request for the same resource
record.
DNSoD puts an additional computational load on servers. The largest
gain for privacy is to protect the communication between the DNS
client (the end user's machine) and its caching resolver.
5. Anycast
DNS servers are often configured with anycast addresses. While the DNS servers are often configured with anycast addresses. While the
network is stable, packets transmitted from a particular source to an network is stable, packets transmitted from a particular source to an
anycast address will reach the same server that has the cryptographic anycast address will reach the same server that has the cryptographic
context from the DNS over DTLS handshake. But when the network context from the DNS over DTLS handshake. But when the network
configuration changes, a DNS over DTLS packet can be received by a configuration changes, a DNS over DTLS packet can be received by a
server that does not have the necessary cryptographic context. To server that does not have the necessary cryptographic context. To
encourage the client to initiate a new DTLS handshake, DNS servers encourage the client to initiate a new DTLS handshake, DNS servers
SHOULD generate a DTLS Alert message in response to receiving a DTLS SHOULD generate a DTLS Alert message in response to receiving a DTLS
packet for which the server does not have any cryptographic context. packet for which the server does not have any cryptographic context.
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DNS servers are often configured with anycast addresses. While the DNS servers are often configured with anycast addresses. While the
network is stable, packets transmitted from a particular source to an network is stable, packets transmitted from a particular source to an
anycast address will reach the same server that has the cryptographic anycast address will reach the same server that has the cryptographic
context from the DNS over DTLS handshake. But when the network context from the DNS over DTLS handshake. But when the network
configuration changes, a DNS over DTLS packet can be received by a configuration changes, a DNS over DTLS packet can be received by a
server that does not have the necessary cryptographic context. To server that does not have the necessary cryptographic context. To
encourage the client to initiate a new DTLS handshake, DNS servers encourage the client to initiate a new DTLS handshake, DNS servers
SHOULD generate a DTLS Alert message in response to receiving a DTLS SHOULD generate a DTLS Alert message in response to receiving a DTLS
packet for which the server does not have any cryptographic context. packet for which the server does not have any cryptographic context.
Upon receipt of an un-authenicated DTLS alert, the DTLS client Upon receipt of an un-authenicated DTLS alert, the DTLS client
validates the Alert is within the replay window (Section 4.1.2.6 of validates the Alert is within the replay window (Section 4.1.2.6 of
[RFC6347]). It is difficult for the DTLS client to validate the DTLS [RFC6347] ). It is difficult for the DTLS client to validate that
alert was generated by the DTLS server in response to a request or the DTLS alert was generated by the DTLS server in response to a
was generated by an on- or off-path attacker. Thus, upon receipt of request or was generated by an on- or off-path attacker. Thus, upon
an in-window DTLS Alert, the client SHOULD continue re-transmitting receipt of an in-window DTLS Alert, the client SHOULD continue re-
the DTLS packet (in the event the Alert was spoofed), and at the same transmitting the DTLS packet (in the event the Alert was spoofed),
time it SHOULD initiate DTLS session resumption. and at the same time it SHOULD initiate DTLS session resumption.
When the DTLS client receives authenticated DNS response from one of
those DTLS sessions, the other DTLS session should be terminated.
7. Downgrade attacks 6. Usage
Using DNS privacy with an authenticated server is most preferred, DNS Using DNS privacy with an authenticated server is most preferred, DNS
privacy with an unauthenticated server is next preferred, and plain privacy with an unauthenticated server is next preferred, and plain
DNS is least preferred. This section gives a non-normative DNS is least preferred. This section gives a non-normative
discussion on common behaviors and choices. discussion on common behaviors and choices.
An implementation MAY attempt to obtain DNS privacy by contacting DNS An implementation MAY attempt to obtain DNS privacy by contacting DNS
servers on the local network (provided by DHCP) and on the Internet, servers on the local network (provided by DHCP) and on the Internet,
and make those attempts in parallel to reduce user impact. If DNS and make those attempts in parallel to reduce user impact. If DNS
privacy cannot be successfully negotiated for whatever reason, the privacy cannot be successfully negotiated for whatever reason, the
client can do three things: client can do three things, in order from best to worst for privacy:
1. refuse to send DNS queries on this network, which means the 1. refuse to send DNS queries on this network, which means the
client cannot make effective use of this network, as modern client cannot make effective use of this network, as modern
networks require DNS; or, networks require DNS; or,
2. use opportunistic security, as described in [RFC7435]. or, 2. use opportunistic security, as described in [RFC7435] or,
3. send plain DNS queries on this network, which means no DNS 3. send plain DNS queries on this network, which means no DNS
privacy is provided. privacy is provided.
Heuristics can improve this situation, but only to a degree (e.g., Heuristics can improve this situation, but only to a degree (e.g.,
previous success of DNS privacy on this network may be reason to previous success of DNS privacy on this network may be reason to
alert the user about failure to establish DNS privacy on this network alert the user about failure to establish DNS privacy on this network
now). Still, the client (in cooperation with the end user) has to now). Still, the client (in cooperation with the end user) has to
decide to use the network without the protection of DNS privacy. decide to use the network without the protection of DNS privacy.
8. IANA Considerations 7. IANA Considerations
IANA is requested to add the following value to the "Service Name and
Transport Protocol Port Number Registry" registry in the System
Range. The registry for that range requires IETF Review or IESG
Approval [RFC6335] and such a review has been requested using the
Early Allocation process [RFC7120] for the well-known UDP port in
this document.
Service Name domain-s This specification uses port 853 already allocated in the IANA port
Transport Protocol(s) UDP/TCP number registry as defined in Section 6 of [RFC7858].
Port 853
Assignee IESG
Contact dwing@cisco.com
Description DNS query-response protocol runs over
DTLS and TLS
Reference This document
9. Security Considerations 8. Security Considerations
The interaction between a DNS client and DNS server requires Datagram The interaction between a DNS client and DNS server requires Datagram
Transport Layer Security (DTLS) with a ciphersuite offering Transport Layer Security (DTLS) with a ciphersuite offering
confidentiality protection and guidance given in [RFC7525] must be confidentiality protection and guidance given in [RFC7525] must be
followed to avoid attacks on DTLS. DNS clients keeping track of followed to avoid attacks on DTLS. DNS clients keeping track of
servers known to support DTLS enables clients to detect downgrade servers known to support DTLS enables clients to detect downgrade
attacks. To interfere with DNS over DTLS, an on- or off-path attacks. To interfere with DNS over DTLS, an on- or off-path
attacker might send an ICMP message towards the DTLS client or DTLS attacker might send an ICMP message towards the DTLS client or DTLS
server. As these ICMP messages cannot be authenticated, all ICMP server. As these ICMP messages cannot be authenticated, all ICMP
errors should be treated as soft errors [RFC1122]. For servers with errors should be treated as soft errors [RFC1122] . For servers with
no connection history and no apparent support for DTLS, depending on no connection history and no apparent support for DTLS, depending on
their Privacy Profile and privacy requirements, clients may choose to their Privacy Profile and privacy requirements, clients may choose to
(a) try another server when available, (b) continue without DTLS, or (a) try another server when available, (b) continue without DTLS, or
(c) refuse to forward the query. Once a DNSoD client has established (c) refuse to forward the query. Once a DNSoD client has established
a security association with a particular DNS server, and outstanding a security association with a particular DNS server, and outstanding
normal DNS queries with that server (if any) have been received, the normal DNS queries with that server (if any) have been received, the
DNSoD client MUST ignore any subsequent normal DNS responses from DNSoD client MUST ignore any subsequent normal DNS responses from
that server, as all subsequent responses should be encrypted. This that server, as all subsequent responses should be encrypted. This
behavior mitigates all possible attacks described in Measures for behavior mitigates all possible attacks described in Measures for
Making DNS More Resilient against Forged Answers [RFC5452]. Making DNS More Resilient against Forged Answers [RFC5452] .
A malicious client might attempt to perform a high number of DTLS A malicious client might attempt to perform a high number of DTLS
handshakes with a server. As the clients are not uniquely identified handshakes with a server. As the clients are not uniquely identified
by the protocol and can be obfuscated with IPv4 address sharing and by the protocol and can be obfuscated with IPv4 address sharing and
with IPv6 temporary addresses, a server needs to mitigate the impact with IPv6 temporary addresses, a server needs to mitigate the impact
of such an attack. Such mitigation might involve rate limiting of such an attack. Such mitigation might involve rate limiting
handshakes from a certain subnet or more advanced DoS/DDoS techniques handshakes from a certain subnet or more advanced DoS/DDoS techniques
beyond the scope of this paper. beyond the scope of this paper.
9.1. Authenticating a DNS Privacy Server 9. Acknowledgements
DNS privacy requires encrypting the query (and response) from passive
attacks. Such encryption typically provides integrity protection as
a side-effect, which means on-path attackers cannot simply inject
bogus DNS responses. However, to provide stronger protection from
active attackers pretending to be the server, the server itself needs
to be authenticated. To authenticate the server providing DNS
privacy, DNS client can use the authenication mechanisms discussed in
[I-D.dgr-dprive-dtls-and-tls-profiles].
10. Acknowledgements
Thanks to Phil Hedrick for his review comments on TCP and to Josh Thanks to Phil Hedrick for his review comments on TCP and to Josh
Littlefield for pointing out DNSoD load on busy servers (most notably Littlefield for pointing out DNSoD load on busy servers (most notably
root servers). The authors would like to thank Simon Josefsson, root servers). The authors would like to thank Simon Josefsson,
Daniel Kahn Gillmor, Bob Harold, Ilari Liusvaara, Sara Dickinson, Daniel Kahn Gillmor, Bob Harold, Ilari Liusvaara, Sara Dickinson,
Christian Huitema and Stephane Bortzmeyer for discussions and Christian Huitema, Stephane Bortzmeyer and Geoff Huston for
comments on the design of DNSoD. discussions and comments on the design of DNSoD.
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>. <http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 9, line 10 skipping to change at page 9, line 29
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without "Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077, Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <http://www.rfc-editor.org/info/rfc5077>. January 2008, <http://www.rfc-editor.org/info/rfc5077>.
[RFC5452] Hubert, A. and R. van Mook, "Measures for Making DNS More [RFC5452] Hubert, A. and R. van Mook, "Measures for Making DNS More
Resilient against Forged Answers", RFC 5452, Resilient against Forged Answers", RFC 5452,
DOI 10.17487/RFC5452, January 2009, DOI 10.17487/RFC5452, January 2009,
<http://www.rfc-editor.org/info/rfc5452>. <http://www.rfc-editor.org/info/rfc5452>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>. January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport [RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security (TLS) and Datagram Transport Layer Security Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension", RFC 6520, (DTLS) Heartbeat Extension", RFC 6520,
DOI 10.17487/RFC6520, February 2012, DOI 10.17487/RFC6520, February 2012,
<http://www.rfc-editor.org/info/rfc6520>. <http://www.rfc-editor.org/info/rfc6520>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, DOI 10.17487/RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>. <http://www.rfc-editor.org/info/rfc6891>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <http://www.rfc-editor.org/info/rfc7120>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>. 2015, <http://www.rfc-editor.org/info/rfc7525>.
11.2. Informative References [RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
DOI 10.17487/RFC7830, May 2016,
<http://www.rfc-editor.org/info/rfc7830>.
[I-D.dgr-dprive-dtls-and-tls-profiles] 10.2. Informative References
Dickinson, S., Gillmor, D., and T. Reddy, "Authentication
and (D)TLS Profile for DNS-over-TLS and DNS-over-DTLS",
draft-dgr-dprive-dtls-and-tls-profiles-00 (work in
progress), December 2015.
[I-D.ietf-dprive-dns-over-tls] [I-D.ietf-dprive-dtls-and-tls-profiles]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., Dickinson, S., Gillmor, D., and T. Reddy, "Authentication
and P. Hoffman, "Specification for DNS over TLS", draft- and (D)TLS Profile for DNS-over-(D)TLS", draft-ietf-
ietf-dprive-dns-over-tls-09 (work in progress), March dprive-dtls-and-tls-profiles-02 (work in progress), June
2016. 2016.
[I-D.ietf-tls-cached-info] [I-D.ietf-tls-cached-info]
Santesson, S. and H. Tschofenig, "Transport Layer Security Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", draft-ietf-tls- (TLS) Cached Information Extension", draft-ietf-tls-
cached-info-22 (work in progress), January 2016. cached-info-23 (work in progress), May 2016.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989, DOI 10.17487/RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>. <http://www.rfc-editor.org/info/rfc1122>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
skipping to change at page 10, line 44 skipping to change at page 10, line 46
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626, [RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015, DOI 10.17487/RFC7626, August 2015,
<http://www.rfc-editor.org/info/rfc7626>. <http://www.rfc-editor.org/info/rfc7626>.
[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation D. Wessels, "DNS Transport over TCP - Implementation
Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
<http://www.rfc-editor.org/info/rfc7766>. <http://www.rfc-editor.org/info/rfc7766>.
[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, <http://www.rfc-editor.org/info/rfc7858>.
Authors' Addresses Authors' Addresses
Tirumaleswar Reddy Tirumaleswar Reddy
Cisco Systems, Inc. Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103 Bangalore, Karnataka 560103
India India
Email: tireddy@cisco.com Email: tireddy@cisco.com
Dan Wing Dan Wing
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