draft-reddy-add-enterprise-policy-01.xml

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<rfc category="std" docName="draft-reddy-add-enterprise-policy-01"
     ipr="trust200902">
  <front>
    <title abbrev="Network policy to use Resolvers">Network policy to use
    Network-designated DNS Resolvers</title>

    <author fullname="Tirumaleswar Reddy" initials="T." surname="Reddy">
      <organization>Akamai</organization>

      <address>
        <postal>
          <street>Embassy Golf Link Business Park</street>

          <city>Bangalore</city>

          <region>Karnataka</region>

          <code>560071</code>

          <country>India</country>
        </postal>

        <email>kondtir@gmail.com</email>
      </address>
    </author>

    <author fullname="Dan Wing" initials="D." surname="Wing">
      <organization abbrev="Citrix">Citrix Systems, Inc.</organization>

      <address>
        <postal>
          <street>4988 Great America Pkwy</street>

          <city>Santa Clara</city>

          <region>CA</region>

          <code>95054</code>

          <country>USA</country>
        </postal>

        <email>danwing@gmail.com</email>
      </address>
    </author>

    <author fullname="Kevin Smith" initials="K." surname="Smith">
      <organization abbrev="Vodafone">Vodafone Group</organization>

      <address>
        <postal>
          <street>One Kingdom Street</street>

          <city>London</city>

          <country>UK</country>
        </postal>

        <email>kevin.smith@vodafone.com</email>
      </address>
    </author>

    <date />

    <workgroup>ADD</workgroup>

    <abstract>
      <t>This document specifies a mechanism to inform endpoints about any
      network policy mandating the use of network-designated DNS
      resolvers.</t>
    </abstract>
  </front>

  <middle>
    <section anchor="intro" title="Introduction">
      <t>Historically, an endpoint would utilize network-designated DNS
      servers upon joining a network (e.g., DHCP OFFER, IPv6 Router
      Advertisement). While it has long been possible to configure endpoints
      to ignore the network's suggestions and use a (public) DNS server on the
      Internet, this was seldom used because some networks block UDP/53 (in
      order to enforce their own DNS policies). Also, there has been an
      increase in the availability of "public resolvers" <xref
      target="RFC8499"></xref> which DNS clients may be pre-configured to use
      instead of the default network resolver for a variety of reasons (e.g.,
      offer a good reachability, support an encrypted transport, provide a
      claimed privacy policy, (lack of) filtering). With the advent of DoT and
      DoH, such network blocking is more difficult. The network is unable to
      express its policy to use network-designated resolvers to the endpoints
      and the endpoint is unable to identify the reason why the public DNS
      server is not reachable.</t>

      <t>If DNS resolvers not signaled by the network (e.g., DNS-over-TLS
      (DoT) <xref target="RFC7858"></xref> or DNS-over-HTTPS (DoH) <xref
      target="RFC8484"></xref>) are used instead of using network-designated
      DNS servers, it can adversely impact Enterprise network-based security
      features. Indeed, various network security services are provided by
      Enterprise networks to protect endpoints (e.g., laptops, printers, IoT
      devices) and to enforce enterprise-specific policies. These policies may
      be necessary to protect employees, customers, or enterprise network. It
      is out of the scope of this memo to characterize such policies nor
      assess that they achieve the claimed intent. Nevertheless,
      network-designated DNS servers in place for these purposes act on DNS
      messages involving endpoints connected to the Enterprise network to
      enforce these policies. Therefore, if an endpoint uses a DNS resolver
      not signaled by the network, the desired enterprise protection level and
      enforcement will be bypassed and thus nullified.</t>

      <t>In order to act on DNS messages involving endpoints connected to an
      Enterprise network, network security services can be configured to block
      DoT traffic by dropping outgoing packets to destination port number 853.
      Identifying DoH traffic is far more challenging than identifying DoT
      traffic. Network security services may try to identify the well-known
      DoH resolvers by their domain name and DoH traffic can be blocked by
      dropping outgoing packets to these domains. However, DoH traffic can not
      be fully identified without acting as a TLS proxy.</t>

      <t>With the advent of DoT and DoH, the network is unable to express any
      such policy to the endpoints, and if the network is blocking alternative
      resolvers, endpoints are unable to identify the reason why their choice
      of public DNS resolver is not reachable. This results in
      incompatibilities with the privacy profiles discussed in <xref
      target="RFC8310"></xref>:</t>

      <t><list style="symbols">
          <t>If an endpoint has enabled strict privacy profile (Section 5 of
          <xref target="RFC8310"></xref>), the endpoint cannot resolve DNS
          names.</t>

          <t>If an endpoint has enabled opportunistic privacy profile (Section
          5 of <xref target="RFC8310"></xref>), the endpoint will either
          fallback to an encrypted connection without authenticating the DNS
          server signaled by the local network or fallback to clear text DNS,
          and cannot exchange encrypted DNS messages. <vspace
          blankLines="1" />The fallback adversely impacts security and privacy
          as internal attacks are possible within Enterprise networks. For
          example, an internal attacker can modify the DNS responses to
          re-direct a client to malicious servers or pervasively monitor the
          DNS traffic.</t>
        </list></t>

      <t>This document describes a mechanism for informing endpoints of
      network policy related to network-designated DNS servers, such as those
      DNS servers signaled using <xref target="I-D.ietf-add-dnr"></xref> and
      <xref target="I-D.ietf-add-ddr"></xref>.</t>
    </section>

    <section anchor="notation" title="Terminology">
      <t>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
      <xref target="RFC2119"></xref><xref target="RFC8174"></xref> when, and
      only when, they appear in all capitals, as shown here.</t>

      <t>This document makes use of the terms defined in <xref
      target="RFC8499"></xref>. The terms "Private DNS", "Global DNS" and
      "Split DNS" are defined in <xref target="RFC8499"></xref>.</t>

      <t>'Encrypted DNS' refers to a DNS protocol that provides an encrypted
      channel between a DNS client and server (e.g., DoT, DoH, or DoQ).</t>

      <t>The term "enterprise network" in this document extends to a wide
      variety of deployment scenarios. For example, an "enterprise" can be a
      Small Office, Home Office or Corporation. The clients that connect to a
      enterprise network can securely authenticate that network and the client
      is sure that it has connected to the network it was expecting.</t>
    </section>

    <section anchor="SplitDNSAllowed"
             title="PvD NetworkDNSOnly and ErrorNetworkDNSOnly Keys">
      <t>Provisioning Domains (PvDs) are defined in <xref
      target="RFC7556"></xref> as sets of network configuration information
      that clients can use to access networks, including rules for DNS
      resolution and proxy configuration. <xref target="RFC8801"></xref>
      defines a mechanism for discovering multiple Explicit PvDs on a single
      network and their Additional Information by means of an HTTP-over-TLS
      query using a URI derived from the PvD ID. This set of additional
      configuration information is referred to as a Web Provisioning Domain
      (Web PvD).</t>

      <t>This document defines two PvD Key:<list style="hanging">
          <t hangText="The NetworkDNSOnly PvD Key:">which determines if
          network will block, or attempt to block, DNS queries sent to DNS
          servers that were not signaled by the network. This key has the
          value True or False (case insensitive).</t>

          <t hangText="The ErrorNetworkDNSOnly PvD Key:">which contains a
          extended DNS error code defined in <xref target="RFC8914"></xref>
          for the NetworkDNSOnly block. This key is only present if
          NetworkDNSOnly is True. Note that the extended error code "Blocked"
          defined in Section 4.16 of <xref target="RFC8914"></xref> identifies
          access to domains is blocked due to an policy by the operator of the
          DNS server, extended error code "Censored" defined in Section 4.17
          of <xref target="RFC8914"></xref> identifies access to domains is
          blocked based on a requirement from an external entity and the
          extended error code "Filtered" defined in Section 4.18 of <xref
          target="RFC8914"></xref> identifies access to domains is blocked
          based on the request from the client to blacklist domains.</t>
        </list></t>

      <t>Some enterprise networks require clients to query the
      network-designated DNS servers, it sets the PvD NetworkDNSOnly key to
      True, otherwise sets NetworkDNSOnly to False. If NetworkDNSOnly is set
      to True, it implies the network will block, or attempt to block, DNS
      queries sent to DNS servers that were not signaled by the network. If
      NetworkDNSOnly is True, the ErrorNetworkDNSOnly key MUST contain the
      extended DNS error code defined in <xref target="RFC8914"></xref> for
      this block. The ErrorNetworkDNSOnly key is useful when the client does
      not use DNS resolution by the network-designated DNS server to reach the
      DNS servers not signaled by the network. For example, the client can be
      pre-configured with both the domain name and IP addresses of the DNS
      server not signaled by the network (Section 7.1 in <xref
      target="RFC8310"></xref>) or the client can be pre-configured with the
      IP address of the resolver, and it uses IP address in the certificate as
      identifier (see <xref target="RFC8738"></xref>). In this case, the
      extended error code "Blocked" defined in <xref target="RFC8914"></xref>
      cannot be returned to the client to provide additional information about
      the cause for the block. Further, the ErrorNetworkDNSOnly key is useful
      when the network security service fails to block access to the DNS
      server not signaled by the network but successfully filters traffic from
      the endpoint to IP addresses not conveyed to the endpoint as part of DNS
      resolution by the network-designated DNS server.</t>

      <t>The NetworkDNSOnly set to True is an internal security policy
      expression by the operator of the network but is not a policy
      prescription to the endpoints to disable its use of its other configured
      DNS servers; that is, the endpoint can ignore NetworkDNSOnly set to
      True. If joining an un-trusted network (e.g., coffeeshop, hotel, airport
      network), a True value of NetworkDNSOnly MUST be ignored. The mechanism
      the client uses to determine 'trusted network' to assist the user MUST
      involve authenticated identity of the network (not merely matching SSID
      in the case of WiFi), such as 802.1X or confirming the
      network-designated encrypted resolver name is pre-configured in the
      Operating System and TLS handshake with it succeeds. For example, the
      client can determine "Open" (unencrypted) wireless networks are
      untrusted networks, notify the user that using a shared and public
      Pre-Shared Key (PSK) for wireless authentication is a untrusted network.
      If the pre-shared-key is the same for all clients that connect to the
      same WLAN, the shared key will be available to all nodes, including
      attackers, so it is possible to mount an active on-path attack (e.g.,
      <xref target="Evil-Twin"></xref>, <xref target="Krack"></xref>, <xref
      target="Dragonblood"></xref>). For example, coffee shops and air ports
      use PSK and are unwilling to perform complex configuration on their
      networks. In addition, customers are generally unwilling to do
      complicated provisioning on their devices just to obtain free Wi-Fi.
      This type of networks can be tagged as "untrusted networks" with minimal
      human intervention. In such cases the endpoint MAY choose to use an
      alternate network (e.g., cellular) to resolve the global domain
      names.</t>
    </section>

    <section anchor="Scope" title="Scope of NetworkDNSOnly Key">
      <t>If a device is managed by an enterprise's IT department, the device
      can be configured to use a specific encrypted DNS server. This
      configuration may be manual or rely upon whatever deployed device
      management tool in an enterprise network. For example, customizing
      Firefox using Group Policy to use the Enterprise DoH server is discussed
      in <xref target="Firefox-Policy"></xref> for Windows and MacOS, and
      setting Chrome policies is discussed in <xref
      target="Chrome-Policy"></xref> and <xref
      target="Chrome-DoH"></xref>.</t>

      <t>If mobile device management (MDM) (e.g., <xref
      target="MDM-Apple"></xref>) secures a device, MDM can configure
      OS/browser with a specific encrypted DNS server. If an endpoint is
      on-boarded, for example, using Over-The-Air (OTA) enrollment <xref
      target="OTA"></xref> to provision the device with a certificate and
      configuration profile, the configuration profile can include the
      authentication domain name (ADN) of the encrypted DNS server. The
      OS/Browser can use the configuration profile to use a specific encrypted
      DNS server. In this case, MDM is not installed on the device.</t>

      <t>Provisioning IT-managed devices, BYOD devices with MDM or
      configuration profile with network-designated DNS server is outside the
      scope of this document.</t>

      <t>Typically, Enterprise networks do not assume that all devices in
      their network are managed by the IT team or MDM, especially in the quite
      common BYOD scenario. The endpoint can use the discovered
      network-designated DNS server to only access DNS names for which the
      Enterprise network claims authority and use another public DNS server
      for global domains or use the discovered network-designated DNS server
      to access both private domains and global domains.</t>

      <t>The scope of NetworkDNSOnly key is restricted to unmanaged BYOD
      devices without a configuration profile on explicitly trusted networks.
      In this use case, the user has authorized the client to override local
      DNS settings for a specific network. It is similar to the way users
      explicitly disable VPN connection in specific networks and VPN
      connection is enabled by default in other networks for privacy. The
      unmanaged BYOD devices use mutual authentication of the client and the
      enterprise network. The client is typically authenticated with their
      user credentials (e.g., username and password). The network is typically
      authenticated with a certificate (e.g., PEAP-MSCHAPv2 <xref
      target="PEAP"></xref>) or a mutually-authenticated key exchange which is
      well-defended from offline attacks (e.g., EAP-pwd <xref
      target="RFC8146"></xref>, EAP-PSK <xref target="RFC4764"></xref>).
      Importantly, WPA-PSK and WPA2-PSK are not well-defended from offline
      attacks and MUST NOT be used in conjunction with NetworkDNSOnly set to
      True.</t>

      <t><list style="hanging">
          <t hangText="Note: ">Many users have privacy and personal data
          sovereignty concerns with employers installing MDM on their personal
          devices; they are concerned that admin can glean personal
          information and could control how they use their devices. When users
          do not install MDM on their devices, IT admins do not get visibility
          into the security posture of those devices. To overcome this
          problem, a host agent can cryptographically attest the security
          status associated with device, such as minimum pass code length,
          biometric login enabled, OS version etc. This approach is fast
          gaining traction especially with the advent of closed OS like <xref
          target="win10s">Windows 10 in S mode</xref> or <xref
          target="Chromebook">Chromebook</xref>, where applications are
          sandboxed (e.g., ransomware attack is not possible) and applications
          can only be installed via the OS store.</t>
        </list></t>
    </section>

    <section title="An Example">
      <t>The following example shows how the JSON keys defined in this
      document can be used:</t>

      <t><figure>
          <artwork><![CDATA[   {
     "identifier": "cafe.example.com.",
     "expires": "2020-05-23T06:00:00Z",
     "prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
     "NetworkDNSOnly": True, 
     "ErrorNetworkDNSOnly": 15
   }]]></artwork>
        </figure></t>

      <t>The JSON keys "identifier", "expires", and "prefixes" are defined in
      <xref target="RFC8801"></xref>. </t>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>The content of NetworkDNSOnly and ErrorSplitDNSBlocked may be passed
      to another (DNS) program for processing. As with any network input, the
      content SHOULD be considered untrusted and handled accordingly. The
      security considerations discussed in <xref
      target="SplitDNSAllowed"></xref> and <xref target="Scope"></xref> need
      to be considered to restrict the scope of NetworkDNSOnly and
      ErrorSplitDNSBlocked PvD Keys to explicitly trusted networks. The
      NetworkDNSOnly and ErrorSplitDNSBlocked PvD Keys assigned by an
      anonymous or unknown network (e.g., coffee shops) MUST be ignored by the
      client.</t>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>IANA is requested to add NetworkDNSOnly and ErrorSplitDNSBlocked PvD
      Keys to the Additional Information PvD Keys registry
      (https://www.iana.org/assignments/pvds/pvds.xhtml).</t>
    </section>

    <section title="Acknowledgements">
      <t>Thanks to Mohamed Boucadair, Jim Reid, Ben Schwartz, Tommy Pauly,
      Paul Vixie, Ben Schwartz, and Vinny Parla for the discussion and
      comments.</t>
    </section>
  </middle>

  <!--  *****BACK MATTER ***** -->

  <back>
    <references title="Normative References">
      <?rfc include='reference.RFC.2119'?>

      <?rfc include='reference.RFC.8174'?>

      <?rfc include='reference.RFC.8801'?>

      <?rfc include='reference.RFC.7858'
?>

      <?rfc include='reference.RFC.8484'?>
    </references>

    <references title="Informative References">
      <?rfc include='reference.RFC.8499'?>

      <?rfc include='reference.RFC.8146' ?>

      <?rfc include='reference.RFC.4764' ?>

      <?rfc include='reference.RFC.7626' ?>

      <?rfc include='reference.RFC.7556' ?>

      <?rfc include='reference.RFC.8310'?>

      <?rfc include='reference.RFC.8914'?>

      <?rfc include='reference.RFC.8738'?>

      <?rfc include='reference.I-D.ietf-add-dnr'?>

      <?rfc include='reference.I-D.ietf-add-ddr'?>

      <!-- not yet in XML library           <?rfc include='reference.I-D.ietf-add-ddr'?> 
           <?rfc include='reference.I-D.ietf-add-dnr'?> -->

      <reference anchor="Firefox-Policy"
                 target="https://github.com/mozilla/policy-templates/blob/master/README.md#dnsoverhttps">
        <front>
          <title>Policy templates for Firefox</title>

          <author></author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="Chrome-Policy"
                 target="https://support.google.com/chrome/a/answer/2657289?hl=en">
        <front>
          <title>Chrome policies for users or browsers</title>

          <author>
            <organization>The Unicode Consortium</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="Chrome-DoH"
                 target="https://www.chromium.org/developers/dns-over-https">
        <front>
          <title>Chrome DNS over HTTPS (aka DoH)</title>

          <author>
            <organization>The Unicode Consortium</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="win10s"
                 target="https://www.microsoft.com/en-us/windows/s-mode">
        <front>
          <title>Windows 10 in S mode</title>

          <author>
            <organization>Microsoft</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="Chromebook"
                 target="https://support.google.com/chromebook/answer/3438631?hl=en">
        <front>
          <title>Chromebook security</title>

          <author>
            <organization>Microsoft</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="MDM-Apple"
                 target="https://developer.apple.com/documentation/devicemanagement">
        <front>
          <title>Mobile Device Management</title>

          <author>
            <organization>Apple</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="OTA"
                 target="https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/iPhoneOTAConfiguration/OTASecurity/OTASecurity.html">
        <front>
          <title>Over-the-Air Profile Delivery Concepts</title>

          <author>
            <organization>Apple</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="PEAP"
                 target="https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-peap/5308642b-90c9-4cc4-beec-fb367325c0f9">
        <front>
          <title>[MS-PEAP]: Protected Extensible Authentication Protocol
          (PEAP)</title>

          <author>
            <organization>Microsoft</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="Evil-Twin"
                 target="https://en.wikipedia.org/wiki/Evil_twin_(wireless_networks)">
        <front>
          <title>Evil twin (wireless networks)</title>

          <author>
            <organization>The Unicode Consortium</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <reference anchor="Krack" target="https://www.krackattacks.com/">
        <front>
          <title>Key Reinstallation Attacks</title>

          <author>
            <organization>The Unicode Consortium</organization>
          </author>

          <date day="" month="" year="2017" />
        </front>
      </reference>

      <reference anchor="Dragonblood"
                 target="https://papers.mathyvanhoef.com/dragonblood.pdf">
        <front>
          <title>Dragonblood: Analyzing the Dragonfly Handshake of WPA3 and
          EAP-pwd</title>

          <author>
            <organization>The Unicode Consortium</organization>
          </author>

          <date day="" month="" year="" />
        </front>
      </reference>

      <!---->
    </references>
  </back>
</rfc>