draft-reddy-add-enterprise-split-dns-07.txt

ADD                                                             T. Reddy
Internet-Draft                                                    Akamai
Intended status: Standards Track                                 D. Wing
Expires: April 26, 2022                                           Citrix
                                                                K. Smith
                                                                Vodafone
                                                        October 23, 2021


                    Split-Horizon DNS Configuration
                draft-reddy-add-enterprise-split-dns-07

Abstract

   When split-horizon DNS is deployed by a network, certain domains are
   only resolvable by querying the network-designated DNS server rather
   than a public DNS server.  DNS clients which use DNS servers not
   provided by the network need to route those DNS domain queries to the
   network-designated DNS server.  This document informs DNS clients of
   split-horizon DNS, their DNS domains, and is compatible with
   encrypted DNS.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on April 26, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
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   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Split DNS . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  PvD dnsZones  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Authority over the Domains  . . . . . . . . . . . . . . .   5
   5.  An example of Split-Horizon DNS Configuration . . . . . . . .   6
   6.  Split DNS Configuration for IKEv2 . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   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"
   [RFC8499] 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, but the endpoint is
   unable to (properly) resolve split-horizon DNS domains which must
   query the network-designated DNS server.

   This document specifies a mechanism to indicate which DNS zones are
   used for split-horizon DNS.  DNS clients can discover and
   authenticate DNS servers provided by the network, for example using
   the techniques proposed in [I-D.ietf-add-dnr] and [I-D.ietf-add-ddr].

   Provisioning Domains (PvDs) are defined in [RFC7556] as sets of
   network configuration information that clients can use to access
   networks, including rules for DNS resolution and proxy configuration.



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   [RFC8801] 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).  The network lists its claims of
   authority for DNS domains using the "dnsZones" PvD key (defined in
   [RFC8801]).

2.  Terminology

   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.

   This document makes use of the terms defined in [RFC8499].  The terms
   "Private DNS", "Global DNS" and "Split DNS" are defined in [RFC8499].

   'Encrypted DNS' refers to a DNS protocol that provides an encrypted
   channel between a DNS client and server (e.g., DoT, DoH, or DoQ).

3.  Split DNS

   [RFC2826] "does not preclude private networks from operating their
   own private name spaces" but notes that if private networks "wish to
   make use of names uniquely defined for the global Internet, they have
   to fetch that information from the global DNS naming hierarchy".

   There are various DNS deployments outside of the global DNS,
   including "split horizon" deployments and DNS usages on private (or
   virtual private) networks.  In a split horizon, an authoritative
   server gives different responses to queries from the Internet than
   they do to network-designated DNS servers; while some deployments
   differentiate internal queries from public queries by the source IP
   address, the concerns in Section 3.1.1 of [RFC6950] relating to
   trusting source IP addresses apply to such deployments.

   When the internal address space range is private [RFC1918], this
   makes it both easier for the server to discriminate public from
   private and harder for public entities to impersonate nodes in the
   private network.  The use cases that motivate split-horizon DNS
   typically involve restricting access to some network services --
   intranet resources such as internal web sites, development servers,
   or directories, for example -- while preserving the ease of use
   offered by domain names for internal users.





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   A typical use case is an Enterprise network that requires one or more
   DNS domains to be resolved via network-designated DNS servers.  This
   can be a special domain, such as "corp.example.com" for an enterprise
   that is publicly known to use "example.com".  In this case, the
   endpoint needs to be informed what the private domain names are and
   what the IP addresses of the network-designated DNS servers are.  An
   Enterprise can also run a different version of its global domain on
   its internal network.  In that case, the client is instructed to send
   DNS queries for the enterprise public domain (e.g., "example.com") to
   the network-designated DNS servers.  A configuration for this
   deployment scenario is referred to as a Split DNS configuration.
   Another use case for split-horizon DNS is Cellular and Fixed-access
   networks (ISPs) typically offer private domains, including account
   status/controls, and free education initiatives [INS].

   The PvD RA option defined in [RFC8801] SHOULD set the H-flag to
   indicate that Additional Information is available.  This Additional
   Information JSON object SHOULD include the "dnsZones" key to define
   the DNS domains for which the network claims authority.

4.  PvD dnsZones

   As discussed in Section 3, internal resources in a network tend to
   have private DNS names.  A network can also run a different version
   of its global domain on its internal network, and require the use of
   network-designated DNS servers to get resolved.

   The PvD Key dnsZones is defined in [RFC8801].  The PvD Key dnsZones
   adds support for DNS domains for which the network claims authority.
   The private domains specified in the dnsZones key are intended to be
   resolved using network-designated DNS servers.  The private domains
   in dnsZones are only reachable by devices authenticated or attached
   to the network.  The global domains specified in the dnsZones key
   have a different version in the internal network.  DNS resolution for
   other domains remains unchanged.

   The dnsZones PvD Key conveys the specified DNS domains that need to
   be resolved using a network-designated DNS server.  The DNS root zone
   (".") MUST be ignored if it appears in dnsZones.  Other generic or
   global domains, such as Top-Level Domains (TLDs), similarly MUST be
   ignored if they appear in dnsZones.

   For each dnsZones entry, the client can use the network-designated
   DNS servers to resolve the listed domains and its subdomains.  Other
   domain names may be resolved using some other DNS servers that are
   configured independently.  For example, if the dnsZones key specifies
   "example.test", then "example.test", "www.example.test", and
   "mail.eng.example.test" can be resolved using the network-designated



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   DNS resolver(s), but "otherexample.test" and "ple.test" can be
   resolved using the system's public resolver(s).

4.1.  Authority over the Domains

   To comply with [RFC2826] the split-horizon DNS zone must either not
   exist in the global DNS hierarchy or must be authoritatively
   delegated to the split-horizon DNS server to answer.  The client can
   use the mechanism described in [I-D.ietf-add-dnr] to discover the
   network-designated resolvers.  To determine if the network-designated
   encrypted resolvers are authoritative over the domains in DnsZones,
   the client performs the following steps for each domain in DnsZones:

   1.  The client sends an NS query for the domain in DnsZones.  This
       query MUST only be sent over encrypted DNS session to a public
       resolver that is configured independently.  A DNSSEC-validating
       client SHOULD apply the same validation policy to the NS query as
       it does to other queries.  A client that does not validate DNSSEC
       SHOULD apply the same policy (if any) to the NS query as it does
       to other queries.

   2.  The client checks that the NS RRset matches any one of the ADN of
       the discovered network-designated encrypted DNS resolvers.

       A.  If the match fails but if any one of the ADN of the
           discovered network-designated encrypted DNS resolvers is a
           subdomain of NS RRset, the client can then establish a TLS
           connection to that network-designated resolver.  The client
           follows the mechanism discussed in Section 8 of [RFC8310] to
           authenticate the DNS server certificate using the ADN and
           checks if at least one of the values in subjectAltName
           matches NS RRset.  If the server certificate validation and
           match succeeds, the client can subsequently resolve the
           domains in that subtree using the network-designated
           resolver.  If the server certificate does not validate or
           match fails, the client can proceed as discussed in step 2
           (A).

       B.  If the match fails, the client determines the network is not
           authoritative for the indicated domain.  It might log an
           error, reject the network entirely (because the network lied
           about its authority over a domain) or other action.

       C.  If the match succeeds, the client can then establish a TLS
           connection to that network-designated resolver.  The client
           follows the mechanism discussed in Section 8 of [RFC8310] to
           authenticate the DNS server certificate using the ADN.




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           +  If the server certificate does not validate and a secure
              connection cannot be established to the network designated
              resolver, the client can proceed as discussed in step 2
              (A).

           +  If the server certificate validation is successful and a
              secure connection is established, the client can
              subsequently resolve the domains in that subtree using the
              network-designated resolver.

   3.  As an exception to this rule, the client need not perform the
       above validation for domains reserved for special use [RFC6761]
       or [RFC6762] such as ".home.arpa" or ".local".

   4.  Authenticated denial of existence using NSEC3 or NSEC records can
       be used by a client to identify that the domain name does not
       exist in the global DNS.

   For example, if in a network the private domain names are defined
   under "internal.corp1.example.com".  The DnsZones PvD Key would
   indicate that "*.internal.corp1.example.com" are private domain
   names.  The client can trigger a NS query of
   "internal.corp1.example.com" and the NS RRset returns that the
   nameserver is "ns1.corp2.example.com".  The client would then connect
   to the network-designated encrypted resolver whose name is
   "ns1.corp2.example.com", authenticate it using server certificate
   validation in TLS handshake, and use it for resolving the domains in
   the subtree of "*.internal.corp1.example.com".

5.  An example of Split-Horizon DNS Configuration

   In a network the apex domain name is "example.com", which runs a
   different version of its global domain on its internal network.
   Today, on the Internet it publishes two NS records, "ns1.example.com"
   and "ns2.example.com".

   To add support for the mechanism described in this document, the
   network and endpoints first need to support [I-D.ietf-add-dnr] and
   [RFC8801].  Then, for each site the administrator would add DNS
   server names which end in "ns1.example.com" or "ns2.example.com" (the
   names published on the Internet).  Also on its internal network, it
   uses a geographic naming scheme for its internal nameservers with a
   "service dot location" naming scheme.  Assuming its two geographies
   are "us" and "uk".  So the UK site would add "ns1.uk.ns1.example.com"
   and "ns2.uk.ns1.example.com".  Note that these names can be added in
   addition to more traditional names that might already exist for those
   DNS servers (e.g., the common "service dot location" such as




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   "ns1.uk.example.com").  All of those names would be advertised to the
   endpoints as described in [I-D.ietf-add-dnr].

   The endpoints compliant with this specification can then determine
   the network's internal nameservers are owned and managed by the same
   entity that has published the NS records on the Internet, as
   described in the following paragraphs:

   Continuing with the UK site as the example, the endpoint will join
   the network, obtain an IP address, and using [I-D.ietf-add-dnr] will
   discover the resolvers "ns1.uk.ns1.example.com" and
   "ns2.uk.ns1.example.com" and their IP addresses.  Using [RFC8801],
   the endpoint will also discover the PvD FQDN is "pvd.uk.example.com".

   The client establishes an encrypted DNS connection with
   "ns1.uk.ns1.example.com", validates its TLS certificate, and queries
   it for "pvd.uk.example.com" to retrieve the PvD JSON object.  The PvD
   contains:

     {
       "identifier": "pvd.uk.example.com",
       "expires": "2020-05-23T06:00:00Z",
       "prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
       "dnsZones:": ["example.com"]
     }

   The JSON keys "identifier", "expires", and "prefixes" are defined in
   [RFC8801].

   The client then uses an encrypted DNS connection to a public resolver
   (e.g., 1.1.1.1) to issue NS queries for the domains in dnsZones.  The
   NS lookup for "example.com" will return "ns1.example.com" and
   "ns2.example.com".

   As the network-provided nameservers are subdomains of those names
   retrieved from the public resolver and the network-designated
   resolver's certificate includes at least one of the names retrieved
   from the public resolver, the client has finished validation that the
   nameservers signaled in [I-D.ietf-add-dnr] and [RFC8801] are owned
   and managed by the same entity that published the NS records on the
   Internet.  The endpoint will then use that information from
   [I-D.ietf-add-dnr] and [RFC8801] to resolve names within dnsZones.

6.  Split DNS Configuration for IKEv2

   The split-tunnel Virtual Private Network (VPN) configuration allows
   the endpoint to access resources that reside in the VPN [RFC8598] via
   the tunnel; other traffic not destined to the VPN does not traverse



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   the tunnel.  In contrast, a non-split- tunnel VPN configuration
   causes all traffic to traverse the tunnel into the VPN.

   When the VPN tunnel is IPsec, the encrypted DNS resolver hosted by
   the VPN service provider can be securely discovered by the endpoint
   using the ENCDNS_IP*_* IKEv2 Configuration Payload Attribute Types
   defined in [I-D.btw-add-ipsecme-ike].  For split-tunnel VPN
   configurations, the endpoint uses the discovered encrypted DNS server
   to resolve domain names for which the VPN provider claims authority.
   For non-split-tunnel VPN configurations, the endpoint uses the
   discovered encrypted DNS server to resolve both global and private
   domain names.  For split-tunnel VPN configurations, the IKE client
   can use the steps discussed in Section 4.1 to determine if the VPN
   service provider is authoritative over the INTERNAL_DNS_DOMAIN
   domains.

   Other VPN tunnel types have similar configuration capabilities, not
   detailed here.

7.  Security Considerations

   The content of dnsZones may be passed to another (DNS) program for
   processing.  As with any network input, the content SHOULD be
   considered untrusted and handled accordingly.  The client must
   perform the steps discussed in Section 4.1 to determine if the
   network-designated encrypted resolvers are authoritative over the
   domains in DnsZones.  If the network is lying, the client can take
   appropriate action like disconnecting from the network.

8.  IANA Considerations

   This document has no IANA actions..

9.  Acknowledgements

   Thanks to Mohamed Boucadair, Jim Reid, Ben Schwartz, Tommy Pauly,
   Paul Vixie, Paul Wouters and Vinny Parla for the discussion and
   comments.  The authors would like to give special thanks to Ben
   Schwartz for his help.

10.  References

10.1.  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,
              <https://www.rfc-editor.org/info/rfc1918>.



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   [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>.

   [RFC2826]  Internet Architecture Board, "IAB Technical Comment on the
              Unique DNS Root", RFC 2826, DOI 10.17487/RFC2826, May
              2000, <https://www.rfc-editor.org/info/rfc2826>.

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

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,
              <https://www.rfc-editor.org/info/rfc6762>.

   [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>.

   [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>.

   [RFC8801]  Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W.
              Shao, "Discovering Provisioning Domain Names and Data",
              RFC 8801, DOI 10.17487/RFC8801, July 2020,
              <https://www.rfc-editor.org/info/rfc8801>.

10.2.  Informative References

   [I-D.btw-add-ipsecme-ike]
              Boucadair, M., Reddy, T., Wing, D., and V. Smyslov,
              "Internet Key Exchange Protocol Version 2 (IKEv2)
              Configuration for Encrypted DNS", draft-btw-add-ipsecme-
              ike-03 (work in progress), May 2021.

   [I-D.ietf-add-ddr]
              Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
              Jensen, "Discovery of Designated Resolvers", draft-ietf-
              add-ddr-03 (work in progress), October 2021.








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   [I-D.ietf-add-dnr]
              Boucadair, M., Reddy, T., Wing, D., Cook, N., and T.
              Jensen, "DHCP and Router Advertisement Options for the
              Discovery of Network-designated Resolvers (DNR)", draft-
              ietf-add-dnr-02 (work in progress), May 2021.

   [INS]      The Unicode Consortium, "Vodafone Foundation Instant
              Schools for Sub-Saharan Africa",
              <https://www.vodafone.com/about/vodafone-foundation/focus-
              areas/instant-schools>.

   [RFC6950]  Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
              "Architectural Considerations on Application Features in
              the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
              <https://www.rfc-editor.org/info/rfc6950>.

   [RFC7556]  Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
              <https://www.rfc-editor.org/info/rfc7556>.

   [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>.

   [RFC8598]  Pauly, T. and P. Wouters, "Split DNS Configuration for the
              Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 8598, DOI 10.17487/RFC8598, May 2019,
              <https://www.rfc-editor.org/info/rfc8598>.

Authors' Addresses

   Tirumaleswar Reddy
   Akamai
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: kondtir@gmail.com


   Dan Wing
   Citrix Systems, Inc.
   4988 Great America Pkwy
   Santa Clara, CA  95054
   USA

   Email: danwing@gmail.com




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   Kevin Smith
   Vodafone Group
   One Kingdom Street
   London
   UK

   Email: kevin.smith@vodafone.com












































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