DPRIVE WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track D. Wing
Expires: September 6, 2019
M. Richardson
Sandelman Software Works
M. Boucadair
Orange
March 5, 2019
A Bootstrapping Procedure to Discover and Authenticate DNS-over-(D)TLS
and DNS-over-HTTPS Servers
draft-reddy-dprive-bootstrap-dns-server-00
Abstract
This document specifies mechanisms to automatically bootstrap
endpoints (e.g., hosts, Customer Equipment) to discover and
authenticate DNS-over-(D)TLS and DNS-over-HTTPS servers provided by a
local network.
Status of This Memo
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This Internet-Draft will expire on September 6, 2019.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Bootstrapping IoT Devices and CPE . . . . . . . . . . . . . . 4
4. Bootstrapping Endpoint Devices . . . . . . . . . . . . . . . 5
5. Discovery Procedure . . . . . . . . . . . . . . . . . . . . . 6
5.1. DNS Reference Identifier DHCP Options . . . . . . . . . . 6
5.1.1. DHCPv6 DNS Reference Identifier Option . . . . . . . 7
5.1.2. DHCPv4 DNS Reference Identifier Option . . . . . . . 8
5.2. Resolution . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . . 9
7.2. DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . . 10
7.3. Application Service & Application Protocol Tags . . . . . 10
7.3.1. DNS Application Service Tag Registration . . . . . . 10
7.3.2. dns.tls Application Protocol Tag Registration . . . . 10
7.3.3. dns.dtls Application Protocol Tag Registration . . . 10
7.3.4. dns.https Application Protocol Tag Registration . . . 10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Various network security services are provided by Enterprise, secure
home and wall-gardened networks to protect endpoints (e.g,. hosts,
IoT devices). Some of these security services act on DNS requests
from endpoints. However, if an endpoint is configured to use public
DNS-over-(D)TLS [RFC7858] [RFC8094] or DNS-over-HTTPS [RFC8484]
servers, network security services in the local network cannot act
efficiently on DNS requests from the endpoints. In order to act on
DNS requests from endpoints, network security services can block DNS-
over-(D)TLS traffic by dropping outgoing packets to destination port
853, and by identifying the domains offering DNS-over-HTTPS servers,
DNS-over-HTTPS traffic can be blocked by dropping outgoing packets to
these domains. If the endpoint has enabled strict privacy profile
(Section 5 of [RFC8310]), and the network security service blocks the
traffic to the public DNS server, DNS service is not available to the
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endpoint and ultimately the endpoint cannot access Internet. If the
endpoint has enabled opportunistic privacy profile (Section 5 of
[RFC8310]), and the network security service blocks traffic to the
public DNS server, the endpoint will either fallback to an encrypted
connection without authenticating the DNS-over-(D)TLS and DNS-over-
HTTPS servers provided by the local network or fallback to clear text
DNS, and cannot exchange encrypted DNS messages. This can compromise
the endpoint security and privacy; some of the potential security
threats are listed below:
o Pervasive monitoring of DNS traffic.
o If the endpoint is an IoT device which is configured to use public
DNS-over-(D)TLS or DNS-over-HTTPS servers, and if a policy
enforcement point in the local network is programmed using a
Manufacturer Usage Description (MUD) file [I-D.ietf-opsawg-mud] by
a MUD manager to only allow intented communications to and from
the IoT device, the policy enforcement point cannot enforce the
Network Access Control List rules based on domain names (Section 8
of [I-D.ietf-opsawg-mud]).
o The network security service cannot prevent an endpoint from
accessing malicious domains. Attacks like DNS cache poisoning can
lead the user to visit malicious website to inject malware on the
endpoint. For instance, malwares like DNSChanger can modify the
endpoint's DNS entries to point toward its own rogue name servers
which then injected its own advertising into Web pages.
The DPRIVE and DoH working groups have not defined an automated
mechanism to securely bootstrap the endpoints to discover and
authenticate DNS-over-(D)TLS and DNS-over-HTTPS servers in the local
network. Some clients have pre-configured specific public DNS
servers (such as Mozilla using Cloudflare's DNS-over-HTTPS server).
If endpoints continue to use hard-coded public DNS servers, this has
a risk of relying on few centralized DNS services. Further, Content
Delivery Networks (CDNs) that map traffic based on DNS may lose the
ability to direct end-user traffic to a nearby cluster in cases where
a DNS service is being used that is not affiliated with the local
network and which does not send "EDNS Client Subnet" (ECS)
information to the CDN's DNS authorities [CDN].
The document proposes a mechanism to automatically bootstrap the
endpoints to discover and authenticate the DNS-over-(D)TLS and DNS-
over-HTTPS servers provided by the local network. The overall
procedure can be structured into the following steps:
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o Bootstrapping phase (Section 3 and Section 4) is meant to
automatically to automatically bootstrap endpoints with local
network's CA certificates and DNS server certificate.
o Discovery phase (Section 5) is meant to discover an authentication
domain (defined in [RFC8310]) to authenticate the privacy-enabling
DNS server, the privacy-enabling protocols supported by the DNS
server and usable DNS server IP addresses.
o Connection handshake and service invocation: The DNS client
initiates (D)TLS handshake with the DNS server learned in the
discovery phase. Furthermore, DNS client uses the credentials
discovered during the bootstrapping phase to validate the server
certificate.
This document uses the terms defined in [RFC8499].
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Bootstrapping IoT Devices and CPE
The following steps discuss the mechanism to automatically bootstrap
IoT devices with local network's CA certificates and DNS server
certificate. The below steps can also be used by CPE acting as DNS
forwarders to discover and authenticate DNS-over-(D)TLS and DNS-over-
HTTPS servers provided by the access networks.
o The IoT device can use Bootstrapping Remote Secure Key
Infrastructures (BRSKI) discussed in
[I-D.ietf-anima-bootstrapping-keyinfra] to automatically bootstrap
the IoT device using the IoT manufacturer provisioned X.509
certificate, in combination with a registrar provided by the local
network and IoT device manufacturer's authorizing service (MASA).
1. The IoT device authenticates to the local network using the
IoT manufacturer provisioned X.509 certificate. The IoT
device can request and get a voucher from the MASA service via
the registrar. The voucher is signed by the MASA service and
includes the local network's CA public key.
2. The IoT device validates the signed voucher using the
manufacturer installed trust anchor associated with the MASA,
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stores the CA's public key and validates the provisional TLS
connection to the registrar.
3. The IoT device requests the full Enrollment over Secure
Transport (EST) [RFC7030] distribution of current CA
certificates (Section 5.9.1 in
[I-D.ietf-anima-bootstrapping-keyinfra]) from the registrar
operating as a BRSKI-EST server. The IoT device uses the
Explicit Trust Anchor database to validate the DNS server
certificate.
4. TBD: The IoT device learns the End-Entity certificates
[RFC8295] from the BRSKI-EST server. The certificate
provisioned to the DNS server in the local network will be
treated as a End-Entity certificate. The IoT device needs to
identify the End-Entity certificate is provisioned to the DNS
server, the key usage extension [RFC5280] can be used to
restrict the use of the End-Entity certificate to authenticate
the DNS server, a new bit will be added to the KeyUsage type
to identify the DNS server certificate.
4. Bootstrapping Endpoint Devices
The following steps explain the mechanism to automatically bootstrap
an endpoint with the local network's CA certificates and DNS server
certificate:
1. The endpoint authenticates to the local network and establishes
provisional TLS connection with the registrar operating as the
BRSKI-EST server. The endpoint discovers registrar using DNS-
based Service Discovery [RFC6763].
2. The endpoint uses Salted Challenge Response Authentication
Mechanism (SCRAM) [RFC7804] to perform mutual authentication with
the discovered BRSKI-EST server.
3. If the BRSKI-EST server authentication is successful, the
endpoint requests the full EST distribution of current CA
certificates and validates the provisional TLS connection to the
BRSKI-EST server. If the BRSKI-EST server certificate cannot be
verified using the CA certificates downloaded, the TLS connection
is immediately discarded and the endpoint abandons the attempt to
bootstrap from the BRSKI-EST server and discards the CA
certificates conveyed by the BRSKI-EST server. The endpoint uses
the Explicit Trust Anchor database to validate the DNS server
certificate.
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4. TBD: The endpoint learns the End-Entity certificates [RFC8295]
from the BRSKI-EST server. The certificate provisioned to the
DNS server in the local network will be treated as a End-Entity
certificate. The endpoint needs to identify the End-Entity
certificate is provisioned to the DNS server, the key usage
extension [RFC5280] can be used to restrict the use of the End-
Entity certificate to authenticate the DNS server, a new bit will
be added to the KeyUsage type to identify the DNS server
certificate.
5. Discovery Procedure
A DNS client discovers the DNS server in the local network supporting
DNS-over-TLS, DNS-over-DTLS and DNS-over-HTTPS protocols by using the
following discovery mechanism:
o The DNS client uses DHCP to discover the authentication domain
name for the DNS server, as specified in Section 5.1.
o The DNS client then uses S-NAPTR [RFC3958] lookup to learn the
protocols DNS-over-TLS, DNS-over-DTLS, and DNS-over-HTTPS
supported by the DNS server and the DNS privacy protocol preferred
by the DNS server administrators, as specified in Section 5.2 and
Section 7.3.1. If DNS-over-HTTPS protocol is supported by the DNS
server, the DNS client queries for the URI resource record type
[RFC7553] to use the https URI scheme (Section 3 of [RFC8484]).
o The DNS client initiates (D)TLS handshake with the DNS server, the
server presents its certificate and the client validates the
server certificate using the End-Entity certificate and Explicit
Trust Anchor database downloaded in steps 3 and 4 in Section 3 and
Section 4. The DNS client uses validation techniques as described
in [RFC6125] to compare the authentication domain name to the
certificate provided by the DNS server.
o If the DNS client cannot reach or establish an authenticated and
encrypted connection with the privacy-enabling DNS server provided
by the local network, the DNS client can fallback to the privacy-
enabling public DNS server.
5.1. DNS Reference Identifier DHCP Options
As reported in Section 1.7.2 of [RFC6125]:
"few certification authorities issue server certificates based on
IP addresses, but preliminary evidence indicates that such
certificates are a very small percentage (less than 1%) of issued
certificates".
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In order to allow for certificate authentication between a DNS client
and server while accommodating for the current best practices for
issuing certificates, this document allows for configuring
authentication domain name to clients. This name can be used as a
reference identifier for authentication purposes.
5.1.1. DHCPv6 DNS Reference Identifier Option
5.1.1.1. Option Format
The DHCPv6 DNS Reference Identifier option is used to configure an
authentication domain name. The format of this option is shown in
Figure 1.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_V6_AUTH_DOMAIN | Option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| authentication-domain-name (FQDN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DHCPv6 DNS Reference Identifier option
The fields of the option shown in Figure 1 are as follows:
o Option-code: OPTION_V6_AUTH_DOMAIN (TBA1, see Section 7.1)
o Option-length: Length of the authentication-domain-name field in
octets.
o authentication-domain-name: A fully qualified domain name of the
DNS server. This field is formatted as specified in Section 10 of
[RFC8415].
5.1.1.2. DHCPv6 Client Behavior
DHCP clients MAY request options OPTION_V6_AUTH_DOMAIN as defined in
[RFC8415], Sections 18.2.1, 18.2.2, 18.2.4, 18.2.5, 18.2.6, and 21.7.
As a convenience to the reader, it is mentioned here that the DHCP
client includes the requested option code in the Option Request
Option.
If the DHCP client receives more than one instance of
OPTION_V6_AUTH_DOMAIN option, it MUST use only the first instance of
that option.
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5.1.2. DHCPv4 DNS Reference Identifier Option
5.1.2.1. Option Format
The DHCPv4 DNS Reference Identifier option is used to configure an
authentication domain name. The format of this option is illustrated
in Figure 2.
Code Length authentication domain name
+-----+-----+-----+-----+-----+-----+-----+--
|TBA2 | n | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+--
The values s1, s2, s3, etc. represent the domain name labels in the
domain name encoding.
Figure 2: DHCPv4 DNS Reference Identifier option
The fields of the option shown in Figure 2 are as follows:
o Code: OPTION_V4_AUTH_DOMAIN (TBA2, see Section 7.2);
o Length: Includes the length of the authentication domain name
field in octets; the maximum length is 255 octets.
o Authentication domain name: The domain name of the DNS server.
This field is formatted as specified in Section 10 of [RFC8415].
5.1.2.2. DHCPv4 Client Behavior
To discover a authentication domain name, the DHCPv4 client MUST
include OPTION_V4_AUTH_DOMAIN in a Parameter Request List Option
[RFC2132].
If the DHCP client receives more than one instance of
OPTION_V4_AUTH_DOMAIN option, it MUST use only the first instance of
that option. The content of OPTION_V4_AUTH_DOMAIN is used as
reference identifier for authentication purposes.
5.2. Resolution
Once the DNS client has retrieved the authentication domain name for
the DNS server, an S-NAPTR lookup with 'DPRIVE' application service
and the desired protocol tag is made to obtain information necessary
to securely connect to the DNS server. The S-NAPTR lookup is
performed using an untrusted recursive DNS resolver from an untrusted
source (such as DHCP).
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This specification defines "DPRIVE" as an application service tag
(Section 7.3.1) and "dns.tls" (Section 7.3.2), "dns.dtls"
(Section 7.3.3), and "dns.https" (Section 7.3.4) as application
protocol tags.
If no DNS-specific S-NAPTR records can be retrieved, the discovery
procedure fails for this authentication domain name. However, before
retrying a lookup that has failed, a DNS client MUST wait a time
period that is appropriate for the encountered error (e.g., NXDOMAIN,
timeout, etc.).
6. Security Considerations
The bootstrapping procedure to discover and authenticate DNS-
over-(D)TLS and DNS-over-HTTPS Servers MUST be enabled by the
endpoint in a trusted network (e.g. Enterprise, Secure home
networks) and disabled in a untrusted network (e.g. public WiFi
network), similar to the way VPN connection from the endpoint to a
VPN gateway is disconnected in a trusted network and VPN connection
is established in a untrusted network.
If the endpoint has enabled strict privacy profile, and the network
security service blocks the traffic to the privacy-enabling public
DNS server, a hard failure occurs and the user is notified. The user
has a choice to switch to another network or if the user trusts the
network, the user can enable strict privacy profile with the DNS-
over-(D)TLS or DNS-over-HTTPS server discovered in the network
instead of downgrading to opportunistic privacy profile.
The primary attack against the methods described in Section 5 is one
that would lead to impersonation of a DNS server. An attacker could
attempt to compromise the DHCP discovery and S-NAPTR resolution. The
attack is prevented by validating the certificate presented by the
DNS server. DHCP-related security considerations are discussed in
[RFC2131] and [RFC8415].
Security considerations in [I-D.ietf-anima-bootstrapping-keyinfra]
and [RFC7804] need to be taken into consideration.
7. IANA Considerations
7.1. DHCPv6 Option
IANA is requested to assign the following new DHCPv6 Option Code in
the registry maintained in http://www.iana.org/assignments/
dhcpv6-parameters:
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Option Name Value
--------------------- -----
OPTION_V6_AUTH_DOMAIN TBA1
7.2. DHCPv4 Option
IANA is requested to assign the following new DHCPv4 Option Code in
the registry maintained in http://www.iana.org/assignments/bootp-
dhcp-parameters/:
Option Name Value Data length Meaning
--------------------- ----- -------------------- --------------------
OPTION_V4_AUTH_DOMAIN TBA2 Variable; the Includes the
maximum length is authentication
255 octets. domain name.
7.3. Application Service & Application Protocol Tags
This document requests IANA to make the following allocations from
the registry available at: https://www.iana.org/assignments/s-naptr-
parameters/s-naptr-parameters.xhtml.
7.3.1. DNS Application Service Tag Registration
o Application Protocol Tag: DPRIVE
o Intended Usage: See Section 5.2
o Security Considerations: See Section 6
o Contact Information: <one of the authors>
7.3.2. dns.tls Application Protocol Tag Registration
o Application Protocol Tag: dns.tls
o Intended Usage: See Section 5.2
o Security Considerations: See Section 6
o Contact Information: <one of the authors>
7.3.3. dns.dtls Application Protocol Tag Registration
o Application Protocol Tag: dns.dtls
o Intended Usage: See Section 5.2
o Security Considerations: See Section 6
o Contact Information: <one of the authors>
7.3.4. dns.https Application Protocol Tag Registration
o Application Protocol Tag: dnshttps
o Intended Usage: See Section 5.2
o Security Considerations: See Section 6
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o Contact Information: <one of the authors>
8. Acknowledgments
Thanks to Joe Hildebrand for his comments and suggestions.
9. References
9.1. Normative References
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-18 (work in progress), January 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
<https://www.rfc-editor.org/info/rfc2132>.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958,
January 2005, <https://www.rfc-editor.org/info/rfc3958>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7553] Faltstrom, P. and O. Kolkman, "The Uniform Resource
Identifier (URI) DNS Resource Record", RFC 7553,
DOI 10.17487/RFC7553, June 2015,
<https://www.rfc-editor.org/info/rfc7553>.
[RFC7804] Melnikov, A., "Salted Challenge Response HTTP
Authentication Mechanism", RFC 7804, DOI 10.17487/RFC7804,
March 2016, <https://www.rfc-editor.org/info/rfc7804>.
[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>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8295] Turner, S., "EST (Enrollment over Secure Transport)
Extensions", RFC 8295, DOI 10.17487/RFC8295, January 2018,
<https://www.rfc-editor.org/info/rfc8295>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
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9.2. Informative References
[CDN] "End-User Mapping: Next Generation Request Routing for
Content Delivery", 2015,
<https://conferences.sigcomm.org/sigcomm/2015/pdf/papers/
p167.pdf>.
[I-D.ietf-opsawg-mud]
Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", draft-ietf-opsawg-mud-25 (work
in progress), June 2018.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
Authors' Addresses
Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
Dan Wing
USA
Email: dan@danwing.org
Michael C. Richardson
Sandelman Software Works
USA
Email: mcr+ietf@sandelman.ca
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Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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