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Versions: (draft-pauly-ipsecme-split-dns) 00 01 02

Network                                                         T. Pauly
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                              P. Wouters
Expires: January 30, 2018                                        Red Hat
                                                           July 29, 2017


                   Split DNS Configuration for IKEv2
                    draft-ietf-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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 January 30, 2018.

Copyright Notice

   Copyright (c) 2017 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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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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 Domains and DNSSEC trust anchors . . . . .   6
   4.  Payload Formats . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  INTERNAL_DNS_DOMAIN Configuration Attribute Type  . . . .   6
     4.2.  INTERNAL_DNSSEC_TA Configuration Attribute  . . . . . . .   7
   5.  Split DNS Usage Guidelines  . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   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.

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



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   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.  DNS queries for other domains should be send to
   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 includes one more
   more INTERNAL_DNS_DOMAIN attributes as defined in Section 4 as part
   of the CFG_REQUEST payload.  If an INTERNAL_DNS_DOMAIN attribute is
   included in the CFG_REQUEST, the initiator SHOULD also include one or
   more INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the
   CFG_REQUEST.

   The INTERNAL_DNS_DOMAIN attribute sent by the initiator is usually
   empty but MAY contain a suggested domain name.

   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 includes one or more
   INTERNAL_DNS_TA attributes as defined in Section 4 as part of the
   CFG_REQUEST payload.  If an INTERNAL_DNS_TA attriute is included in
   the CFG_REQUEST, the initiator SHOULD also include one or more
   INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST.

   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 an INTERNAL_DNS_DOMAIN attribute is
   included in the CFG_REPLY, the responder MUST also include one or
   both of the INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the
   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.






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   If the CFG_REQUEST included INTERNAL_DNS_DOMAIN attributes with non-
   zero lengths, the content MAY be ignored or be interpreted as a
   suggestion by the responder.

   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 internal DNSSEC
   trust anchor in the DNS presentation 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 the 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 two internal
   domains, "example.com" and "city.other.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.

   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)
     INTERNAL_DNS_DOMAIN(city.other.com)




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3.4.2.  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 the
   CFG_REQUEST

   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()
     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 in DNS presentation format            ~
   |                                                               |
   +---------------------------------------------------------------+

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

   o  Attribute Type (15 bits) 25 - INTERNAL_DNS_DOMAIN.




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

   o  Domain Name (0 or more octets) - A Fully Qualified Domain Name
      used for Split DNS rules, such as example.com, in DNS presentation
      format and optionally using IDNA [RFC5890] for Internationalized
      Domain Names.  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 digest as specified in [RFC4034]
      Section 5.1 in presentation format.

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.






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   If a client is configured by local policy to only accept a limited
   number of INTERNAL_DNS_DOMAIN values, the client MUST ignore any
   other INTERNAL_DNS_DOMAIN values.

   For each INTERNAL_DNS_DOMAIN entry in a CFG_REPLY payload that is not
   prohibited by local policy, the client MUST 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 MUST NOT
   attempt to resolve the provided DNS domains using its external DNS
   servers.

   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 those Special IP addresses.

   If a CFG_REPLY contains one or more INTERNAL_DNS_DOMAIN attributes
   and its local policy does not forbid these values, the client MUST
   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 MUST NOT be resolved
   using any other DNS resolvers.  Other domain names SHOULD be resolved
   using some other external DNS resolver(s), configured independently
   from IKE.  Queries for these other domains MAY be sent to the
   internal DNS resolver(s) listed in that CFG_REPLY message, but have
   no guarantee of being answered.  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" SHOULD NOT be resolved using the internal resolver
   and SHOULD use 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 IKE SA 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 MUST be cleared.

   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



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   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
   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 only process
   the DNS information if the two connections are part of the same
   logical entity.  Otherwise, the client should refuse the DNS
   information and potentially warn the enduser.

   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.

   A domain that is served via INTERNAL_DNS_DOMAIN should pay close
   attention to their use of indirect reference RRtypes such as CNAME,
   DNAME, MX or SRV records so that resolving works as intended when
   all, some or none of the IPsec connections are established.

   The content of INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA may be
   passed to another (DNS) program for processing.  The content MUST be
   verified and sanitized before passing it to other software.  For
   example, domain names are limited to alphanumeric characters and the
   minus ("-") and underscore ("_") symbol and if other other characters
   are present, the entire payload could be ignored and not passed to
   DNS software, or the malicious characters could be filtered out
   before passing the payload to DNS software.




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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
   ------   -------------------  ------  ----------  ---------------
   25       INTERNAL_DNS_DOMAIN   YES     0 or more  [this document]
   [TBD]    INTERNAL_DNSSEC_TA    YES     0 or more  [this document]

                                 Figure 1

8.  References

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>.



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   [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

   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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