Network                                                         T. Pauly
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                              P. Wouters
Expires: March 25, 2017                                          Red Hat
                                                      September 21, 2016


                   Split DNS Configuration for IKEv2
                    draft-pauly-ipsecme-split-dns-02

Abstract

   This document defines two Configuration Payload Attribute Types for
   the IKEv2 protocol that add support for private DNS domains.  These
   domains should be resolved using DNS servers reachable through an
   IPsec connection, while leaving all other DNS resolution unchanged.
   This approach of resolving a subset of domains using non-public DNS
   servers is referred to as "Split DNS".

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 25, 2017.

Copyright Notice

   Copyright (c) 2016 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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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Exchange . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Configuration Request . . . . . . . . . . . . . . . . . .   4
     3.2.  Configuration Reply . . . . . . . . . . . . . . . . . . .   4
     3.3.  Mapping DNS Servers to Domains  . . . . . . . . . . . . .   5
     3.4.  Example Exchanges . . . . . . . . . . . . . . . . . . . .   5
       3.4.1.  Simple Case . . . . . . . . . . . . . . . . . . . . .   5
       3.4.2.  Requesting Limited Domains  . . . . . . . . . . . . .   6
       3.4.3.  Requesting Domains and DNSSEC trust anchors . . . . .   6
   4.  Payload Formats . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  INTERNAL_DNS_DOMAIN Configuration Attribute Type  . . . .   7
     4.2.  INTERNAL_DNSSEC_TA Configuration Attribute  . . . . . . .   8
   5.  Split DNS Usage Guidelines  . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Split DNS is a common configuration for secure tunnels, such as
   Virtual Private Networks in which host machines private to an
   organization can only be resolved using internal DNS resolvers
   [RFC2775].  In such configurations, it is often desirable to only
   resolve hosts within a set of private domains using the tunnel, while
   letting resolutions for public hosts be handled by a device's default
   DNS configuration.

   The Internet Key Exchange protocol version 2 [RFC7296] negotiates
   configuration parameters using Configuration Payload Attribute Types.
   This document defines two Configuration Payload Attribute Types that
   add support for trusted Split DNS domains.

   The INTERNAL_DNS_DOMAIN attribute type is used to convey one or more
   DNS domains that should be resolved only using the provided DNS
   nameserver IP addresses, causing these requests to use the IPsec
   connection.





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   The INTERNAL_DNSSEC_TA attribute type is used to convey DNSSEC trust
   anchors for those domains.

   When only a subset of traffic is routed into a private network using
   an IPsec SA, these Configuration Payload options can be used to
   define which private domains should be resolved through the IPsec
   connection without affecting the client's global DNS resolution.

   For the purposes of this document, DNS resolution servers accessible
   through an IPsec connection will be referred to as "internal DNS
   servers", and other DNS servers will be referred to as "external DNS
   servers".

   A client using these configuration payloads will be able to request
   and receive Split DNS configurations using the INTERNAL_DNS_DOMAIN
   and INTERNAL_DNSSEC_TA configuration attributes.  The client device
   can use the internal DNS server(s) for any DNS queries within the
   assigned domains, while routing other DNS queries to its regular
   external DNS server.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Background

   Split DNS is a common configuration for enterprise VPN deployments,
   in which only one or a few private DNS domains are accessible and
   resolvable via an IPsec based VPN connection.

   Other tunnel-establishment protocols already support the assignment
   of Split DNS domains.  For example, there are proprietary extensions
   to IKEv1 that allow a server to assign Split DNS domains to a client.
   However, the IKEv2 standard does not include a method to configure
   this option.  This document defines a standard way to negotiate this
   option for IKEv2.

3.  Protocol Exchange

   In order to negotiate which domains are considered internal to an
   IKEv2 tunnel, initiators indicate support for Split DNS in their
   CFG_REQUEST payloads, and responders assign internal domains (and
   DNSSEC trust anchors) in their CFG_REPLY payloads.  When Split DNS
   has been negotiated, the existing DNS server configuration attributes
   will be interpreted as internal DNS servers that can resolve
   hostnames within the internal domains.



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3.1.  Configuration Request

   To indicate support for Split DNS, an initiator sending a CFG_REQUEST
   payload MAY include one or more INTERNAL_DNS_DOMAIN attributes as
   defined in Section 4.  If an INTERNAL_DNS_DOMAIN attribute is
   included in the CFG_REQUEST, the initiator SHOULD also include one or
   both of the INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in its
   CFG_REQUEST.

   If the length of the INTERNAL_DNS_DOMAIN attribute is zero, then the
   initiator is requesting that the attribute be assigned without
   restricting the subdomains that it will accept.

   If the length of the INTERNAL_DNS_DOMAIN is greater than zero, the
   value is a single DNS domain.  The initiator is indicating that it
   will only allow this domain and any sub-domains within this domain to
   be resolved using the internal DNS servers.  The list of
   INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST defines the full
   set of domains the intiator is willing to resolve using the internal
   DNS servers.

   The absence of INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST
   payload indicates that the initiator does not support or is unwilling
   to accept Split DNS configuration.

   To indicate support for DNSSEC, an initiator sending a CFG_REQUEST
   payload MAY include one or more INTERNAL_DNS_TA attributes as defined
   in Section 4.  These payloads MUST immediately follow a
   INTERNAL_DNS_DOMAIN attribute, which binds the DNSSEC trust anchor
   request to the domain.

   An initiator MAY convey its current DNSSEC trust anchors for the
   domain specified in the INTERNAL_DNS_DOMAIN attribute.  If it does
   not wish to convey this information, it MUST use a length of 0.

   The absence of INTERNAL_DNS_TA attributes in the CFG_REQUEST payload
   indicates that the initiator does not support or is unwilling to
   accept DNSSEC trust anchor configuration.

3.2.  Configuration Reply

   Responders MAY send one or more INTERNAL_DNS_DOMAIN attributes in
   their CFG_REPLY payload if the CFG_REQUEST contained at least one
   INTERNAL_DNS_DOMAIN attribute.  If the CFG_REQUEST did not contain an
   INTERNAL_DNS_DOMAIN attribute, the responder MUST NOT include an
   INTERNAL_DNS_DOMAIN attribute in the CFG_REPLY.  If an
   INTERNAL_DNS_DOMAIN attribute is included in the CFG_REPLY, the
   responder SHOULD also include one or both of the INTERNAL_IP4_DNS and



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   INTERNAL_IP6_DNS attributes in its CFG_REPLY.  These DNS server
   configurations are necessary to define which servers should receive
   queries for hostnames in internal domains.  If the CFG_REQUEST
   included an INTERNAL_DNS_DOMAIN attribute, but the CFG_REPLY does not
   include an INTERNAL_DNS_DOMAIN attribute, the initiator should behave
   as if Split DNS configurations are not supported by the server.

   Each INTERNAL_DNS_DOMAIN represents a domain that the DNS servers
   address listed in INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can resolve.

   If the CFG_REQUEST included INTERNAL_DNS_DOMAIN attributes with non-
   zero lengths, the CFG_REPLY MUST NOT assign any domains in its
   INTERNAL_DNS_DOMAIN attributes that are not contained within the
   requested domains.  The initiator SHOULD ignore any domains beyond
   its requested list.

   For each DNS domain specified in an INTERNAL_DNS_DOMAIN attribute,
   one or more INTERNAL_DNSSEC_TA attributes MAY be included by the
   responder.  This attribute lists the corresponding DSSNEC trust
   anchor in the DNS wire format of a DS record as specified in
   [RFC4034].  The INTERNAL_DNSSEC_TA attribute MUST immediately follow
   the INTERNAL_DNS_DOMAIN attribute that it applies to.

3.3.  Mapping DNS Servers to Domains

   All DNS servers provided in the CFG_REPLY MUST support resolving
   hostnames within all INTERNAL_DNS_DOMAIN domains.  In other words,
   the INTERNAL_DNS_DOMAIN attributes in a CFG_REPLY payload form a
   single list of Split DNS domains that applies to the entire list of
   INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes.

3.4.  Example Exchanges

3.4.1.  Simple Case

   In this example exchange, the initiator requests INTERNAL_IP4_DNS and
   INTERNAL_DNS_DOMAIN attributes in its CFG_REQUEST, but does not
   specify any value for either.  This indicates that it supports Split
   DNS, but has no preference for which DNS requests should be routed
   through the tunnel.

   The responder replies with two DNS server addresses, and one internal
   domain, "example.com".

   Any subsequent DNS queries from the initiator for domains such as
   "www.example.com" should use 198.51.100.2 or 198.51.100.4 to resolve.





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   CP(CFG_REQUEST) =
     INTERNAL_IP4_ADDRESS()
     INTERNAL_IP4_DNS()
     INTERNAL_DNS_DOMAIN()

   CP(CFG_REPLY) =
     INTERNAL_IP4_ADDRESS(198.51.100.234)
     INTERNAL_IP4_DNS(198.51.100.2)
     INTERNAL_IP4_DNS(198.51.100.4)
     INTERNAL_DNS_DOMAIN(example.com)

3.4.2.  Requesting Limited Domains

   In this example exchange, the initiator requests INTERNAL_IP4_DNS and
   INTERNAL_DNS_DOMAIN attributes in its CFG_REQUEST, specifically
   requesting only "example.com" and "other.com".  The responder replies
   with two DNS server addresses, 198.51.100.2 and 198.51.100.4, and two
   domains, "example.com" and "city.other.com".  Note that one of the
   domains in the CFG_REPLY, "city.other.com", is a subset of the
   requested domain, "other.com".  This indicates that hosts within
   "other.com" that are not within "city.other.com" should be resolved
   using an external DNS server.  The CFG_REPLY would not be allowed to
   respond with "com" or "example.net", however, since these were
   contained within the limited set of requested domains.

   Any subsequent DNS queries from the initiator for domains such as
   "www.example.com" or "city.other.com" should use 198.51.100.2 or
   198.51.100.4 to resolve.

   CP(CFG_REQUEST) =
     INTERNAL_IP4_ADDRESS()
     INTERNAL_IP4_DNS()
     INTERNAL_DNS_DOMAIN(example.com)
     INTERNAL_DNS_DOMAIN(other.com)

   CP(CFG_REPLY) =
     INTERNAL_IP4_ADDRESS(198.51.100.234)
     INTERNAL_IP4_DNS(198.51.100.2)
     INTERNAL_IP4_DNS(198.51.100.4)
     INTERNAL_DNS_DOMAIN(example.com)
     INTERNAL_DNS_DOMAIN(city.other.com)

3.4.3.  Requesting Domains and DNSSEC trust anchors

   In this example exchange, the initiator requests INTERNAL_IP4_DNS,
   INTERNAL_DNS_DOMAIN and INTERNAL_DNS_TA attributess in its
   CFG_REQUEST




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   Any subsequent DNS queries from the initiator for domains such as
   "www.example.com" or "city.other.com" would be DNSSEC validated using
   the DNSSEC trust anchor received in the CFG_REPLY

   In this example, the initiator has no existing DNSSEC trust anchors
   would the requested domain. the "example.com" dommain has DNSSEC
   trust anchors that are returned, while the "other.com" domain has no
   DNSSEC trust anchors

   CP(CFG_REQUEST) =
     INTERNAL_IP4_ADDRESS()
     INTERNAL_IP4_DNS()
     INTERNAL_DNS_DOMAIN(example.com)
     INTERNAL_DNS_TA()
     INTERNAL_DNS_DOMAIN(other.com)
     INTERNAL_DNS_TA()

   CP(CFG_REPLY) =
     INTERNAL_IP4_ADDRESS(198.51.100.234)
     INTERNAL_IP4_DNS(198.51.100.2)
     INTERNAL_IP4_DNS(198.51.100.4)
     INTERNAL_DNS_DOMAIN(example.com)
     INTERNAL_DNS_TA(43547,8,1,B6225AB2CC613E0DCA7962BDC2342EA4F1B56083)
     INTERNAL_DNS_TA(31406,8,2,F78CF3344F72137235098ECBBD08947C2C90....)
     INTERNAL_DNS_DOMAIN(city.other.com)

4.  Payload Formats

4.1.  INTERNAL_DNS_DOMAIN Configuration Attribute Type

                       1                   2                   3
   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
   +-+-----------------------------+-------------------------------+
   |R|         Attribute Type      |            Length             |
   +-+-----------------------------+-------------------------------+
   |                                                               |
   ~                          Domain Name                          ~
   |                                                               |
   +---------------------------------------------------------------+

   o  Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296].

   o  Attribute Type (15 bits) [TBD IANA] - INTERNAL_DNS_DOMAIN.

   o  Length (2 octets, unsigned integer) - Length of domain name.

   o  Domain Name (0 or more octets) - A domain or subdomain used for
      Split DNS rules, such as example.com.  This is a string of ASCII



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      characters with labels separated by dots, with no trailing dot,
      using IDNA [RFC5890] for non-ASCII DNS domains.  The value is NOT
      null-terminated.

4.2.  INTERNAL_DNSSEC_TA Configuration Attribute

                       1                   2                   3
   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
   +-+-----------------------------+-------------------------------+
   |R|         Attribute Type      |            Length             |
   +-+-----------------------------+---------------+---------------+
   |           Key Tag             |  Algorithm    |  Digest Type  |
   +-------------------------------+---------------+---------------+
   |                                                               |
   ~                            Digest                             ~
   |                                                               |
   +---------------------------------------------------------------+

   o  Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296].

   o  Attribute Type (15 bits) [TBD IANA] - INTERNAL_DNSSEC_TA.

   o  Length (2 octets, unsigned integer) - Length of DNSSEC Trust
      Anchor data.

   o  Key Tag value (0 or 2 octets, unsigned integer) - Key Tag as
      specified in [RFC4034] Section 5.1

   o  DNSKEY algorithm (0 or 1 octet) - Value from the IANA DNS Security
      Algorithm Numbers Registry

   o  DS algorithm (0 or 1 octet) - Value from the IANA Delegation
      Signer (DS) Resource Record (RR) Type Digest Algorithms Registry

   o  Digest (0 or more octets) - The raw digest as specified in
      [RFC4034] Section 5.1

5.  Split DNS Usage Guidelines

   If a CFG_REPLY payload contains no INTERNAL_DNS_DOMAIN attributes,
   the client MAY use the provided INTERNAL_IP4_DNS or INTERNAL_IP6_DNS
   servers as the default DNS server(s) for all queries.

   For each INTERNAL_DNS_DOMAIN entry in a CFG_REPLY payload, the client
   SHOULD use the provided INTERNAL_IP4_DNS or INTERNAL_IP6_DNS DNS
   servers as the only resolvers for the listed domains and its sub-
   domains and it SHOULD NOT attempt to resolve the provided DNS domains
   using its external DNS servers.



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   If the initiator host is configured to block DNS answers containing
   IP addresses from special IP address ranges such as those of
   [RFC1918], the initiator SHOULD allow the DNS domains listed in the
   INTERNAL_DNS_DOMAIN attributes to contain these IP addresses.

   If a CFG_REPLY contains one or more INTERNAL_DNS_DOMAIN attributes,
   the client SHOULD configure its DNS resolver to resolve those domains
   and all their subdomains using only the DNS resolver(s) listed in
   that CFG_REPLY message.  If those resolvers fail, those names SHOULD
   NOT be resolved using any other DNS resolvers.  All other domain
   names MUST be resolved using some other external DNS resolver(s),
   configured independently, and SHOULD NOT be sent to the internal DNS
   resolver(s) listed in that CFG_REPLY message.  For example, if the
   INTERNAL_DNS_DOMAIN attribute specifies "example.com", then
   "example.com", "www.example.com" and "mail.eng.example.com" MUST be
   resolved using the internal DNS resolver(s), but "anotherexample.com"
   and "ample.com" MUST be resolved using the system's external DNS
   resolver(s).

   An initiator SHOULD ignore INTERNAL_DNS_DOMAIN attributes containing
   domains that are designated Special Use Domain Names in [RFC6761],
   such as "local", "localhost", "invalid", etc.  Although it may
   explicitly wish to support some Special Use Domain Names.

   When an IPsec connection is terminated, the DNS forwarding must be
   unconfigured.  The DNS forwarding itself MUST be be deleted.  All
   cached data of the INTERNAL_DNS_DOMAIN provided DNS domainis MUST be
   flushed.  This includes negative cache entries.  Obtained DNSSEC
   trust anchors MUST be removed from the list of trust anchors.  The
   outstanding DNS request queue MAY be cleared.

   A domain that is served via INTERNAL_DNS_DOMAIN MUST NOT have
   indirect references to DNS records that point to other Split DNS
   domains that are not served via INTERNAL_DNS_DOMAIN attributes.
   Indirect reference RRtypes include CNAME, DNAME, MX and SRV RR's.

   INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA attributes SHOULD only be
   used on split tunnel configurations where only a subset of traffic is
   routed into a private remote network using the IPsec connection.  If
   all traffic is routed over the IPsec connection, the existing global
   INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can be used without creating
   specific DNS exemptions.

6.  Security Considerations

   The use of Split DNS configurations assigned by an IKEv2 responder is
   predicated on the trust established during IKE SA authentication.
   However, if IKEv2 is being negotiated with an anonymous or unknown



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   endpoint (such as for Opportunistic Security [RFC7435]), the
   initiator MUST ignore Split DNS configurations assigned by the
   responder.

   If a host connected to an authenticated IKE peer is connecting to
   another IKE peer that attempts to claim the same domain via the
   INTERNAL_DNS_DOMAIN attribute, the IKE connection should be
   terminated.

   If the IP address value of the received INTERNAL_IP4_DNS or
   INTERNAL_IP6_DNS attribute is not covered by the proposed IPsec
   connection, then the local DNS should not be reconfigured until a
   CREATE_CHILD Exchange is received that covers these IP addresses.

   INTERNAL_DNSSEC_TA directives MUST immediately follow an
   INTERNAL_DNS_DOMAIN directive.  As the INTERNAL_DNSSEC_TA format
   itself does not contain the domain name, it relies on the preceding
   INTERNAL_DNS_DOMAIN to provide the domain for which it specifies the
   trust anchor.

   If the initiator is using DNSSEC validation for a domain in its
   public DNS view, and it requests and receives an INTERNAL_DNS_DOMAIN
   attribute without an INTERNAL_DNSSEC_TA, it will need to reconfigure
   its DNS resolver to allow for an insecure delegation.  It SHOULD NOT
   accept insecure delegations for domains that are DNSSEC signed in the
   public DNS view, for which it has not explicitely requested such
   deletation by specifying the domain specifically using a
   INTERNAL_DNS_DOMAIN(domain) request.

7.  IANA Considerations

   This document defines two new IKEv2 Configuration Payload Attribute
   Types, which are allocated from the "IKEv2 Configuration Payload
   Attribute Types" namespace.

                                    Multi-
   Value    Attribute Type       Valued  Length      Reference
   ------   -------------------  ------  ----------  ---------------
   [TBD]    INTERNAL_DNS_DOMAIN   YES     0 or more  [this document]
   [TBD]    INTERNAL_DNSSEC_TA    YES     0 or more  [this document]

                                 Figure 1

8.  References







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8.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <http://www.rfc-editor.org/info/rfc4034>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <http://www.rfc-editor.org/info/rfc5890>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <http://www.rfc-editor.org/info/rfc7296>.

8.2.  Informative References

   [RFC2775]  Carpenter, B., "Internet Transparency", RFC 2775,
              DOI 10.17487/RFC2775, February 2000,
              <http://www.rfc-editor.org/info/rfc2775>.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <http://www.rfc-editor.org/info/rfc6761>.

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <http://www.rfc-editor.org/info/rfc7435>.

Authors' Addresses









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   Tommy Pauly
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   US

   Email: tpauly@apple.com


   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com






































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