Network                                                         T. Pauly
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                              P. Wouters
Expires: March 27, 2016                                          Red Hat
                                                      September 24, 2015


                   Split-DNS Configuration for IKEv2
                    draft-pauly-ipsecme-split-dns-00

Abstract

   This document defines two new Configuration Payload Attribute Types
   for the IKEv2 protocol that together define a set of private DNS
   domains which should be resolved by DNS servers reachable through an
   IPsec connection, while leaving all other DNS resolution unchanged.
   This allows for split-DNS views for multiple domains and includes
   support for private DNSSEC trust anchors.  The information obtained
   via the new attribute types can be used to reconfigure a locally
   running DNS server with DNS forwarding for specific private domains.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 27, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
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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 . . . . . . . . . . . . . . . . . .   3
     3.2.  Configuration Reply . . . . . . . . . . . . . . . . . . .   4
     3.3.  Mapping DNS Servers to Domains  . . . . . . . . . . . . .   4
     3.4.  Example Exchanges . . . . . . . . . . . . . . . . . . . .   4
       3.4.1.  Simple Case . . . . . . . . . . . . . . . . . . . . .   4
       3.4.2.  Requesting Limited Domains  . . . . . . . . . . . . .   5
   4.  Payload Formats . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  INTERNAL_DNS_DOMAIN Configuration Attribute Type  . . . .   6
     4.2.  INTERNAL_DNSSEC_TA Configuration Attribute  . . . . . . .   6
   5.  Split-DNS Usage Guidelines  . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Internet Key Exchange protocol version 2 [RFC7296] negotiates
   configuration parameters using Configuration Payload Attribute Types.
   This document adds two new Configuration Payload Attribute Types to
   support trusted split-DNS domains.  The INTERNAL_DNS_DOMAIN attribute
   type is used to convey one or more local DNS domains.  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, this Configuration Payload
   option 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 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 can use



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   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

3.1.  Configuration Request

   To indicate support for split-DNS, initiators sending a CFG_REQUEST
   payload MAY include one or more of the INTERNAL_DNS_DOMAIN
   configuration attribute in their configuration payloads.  See
   Section 4 for details on the payload format.  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 attribute length is zero, then the initiator is only
   requesting that the attribute be assigned, without restricting the
   subdomains that it will accept.

   If the attribute length is non-zero, it contains a single DNS domain
   . The initiator is indicating that it will allow this domain and its
   sub-domains to be resolved over the IPsec connection.  The list of
   INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST defines the full
   set of domains the intiator is willing to resolve over the tunnel.







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3.2.  Configuration Reply

   Responders MAY send one or more INTERNAL_DNS_DOMAIN configuration
   attributes in their CFG_REPLY payload if the CFG_REQUEST contained at
   least one INTERNAL_DNS_DOMAIN configuration attribute.  If the
   CFG_REQUEST did not contain an INTERNAL_DNS_DOMAIN configuration
   attribute, the responder MUST NOT include an INTERNAL_DNS_DOMAIN
   configuration attribute in the CFG_REPLY.  If an INTERNAL_DNS_DOMAIN
   configuration attribute is included in the CFG_REPLY, the responder
   SHOULD also include one or both of the INTERNAL_IP4_DNS and
   INTERNAL_IP6_DNS configuration attributes in its CFG_REPLY.  If the
   CFG_REQUEST included an INTERNAL_DNS_DOMAIN configuration attribute,
   but the CFG_REPLY does 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 configuration
   attribute, an INTERNAL_DNSSEC_TA configuration attribute may be
   included by the responder.  This attribute lists the corresponding
   DSSNEC trust anchor in the presentation format of a DS record as
   specified in [RFC4034].

3.3.  Mapping DNS Servers to Domains

   All DNS servers provided in the CFG_REPLY MUST support all domains.
   The INTERNAL_DNS_DOMAIN attributes in a CFG_REPLY payload form a
   single list of split-DNS domains, that apply 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.




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   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.

   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)




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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
      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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                     DNSSEC TRUST ANCHOR                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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  DNSSEC Trust anchor (multiple octets) - The presentation format of
      one DS record as specified in [RFC4034].  The TTL value MAY be
      omited and when present MUST be ignored.  The domain name is



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      specified as a Fully Qualified Domain Name (FQDN) - irrespective
      of the presence of a trailing dot, and consits of a string of
      ASCII characters with labels separated by dots and uses IDNA
      [RFC5890] for non-ASCII DNS domains.  The value is NOT null-
      terminated.

5.  Split-DNS Usage Guidelines

   If a CFG_REPLY payload contains no INTERNAL_DNS_DOMAIN configuration
   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.

   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 configuration attributes to contain these IP
   addresses.

   If a CFG_REPLY contains one or more INTERNAL_DNS_DOMAIN configuration
   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 SHOULD 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 configuration attribute specifies
   "example.com", then "example.com", "www.example.com" and
   "mail.eng.example.com" SHOULD be resolved using the internal DNS
   resolver(s), but "anotherexample.com" and "ample.com" SHOULD be
   resolved using the system's external DNS resolver(s).

   An initiator MAY ignore INTERNAL_DNS_DOMAIN configuration 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, for
   example "onion" [I-D.ietf-dnsop-onion-tld].

   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



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   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 configuration
   attributes.  Indirect reference resource record types include CNAME,
   DNAME, MX and SRV resource records.

   INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA configuration 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 excemptions.

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 configuration attribute, the IKE connection
   should be terminated.

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

   INTERNAL_DNSSEC_TA directives MUST have an accompanying
   INTERNAL_DNS_DOMAIN directive.  This prevents the insertion of rogue
   DNSSEC trust anchors for domains that have not been yielded to the
   IPsec connection.

7.  IANA Considerations

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




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                                    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

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

   [I-D.ietf-dnsop-onion-tld]
              Appelbaum, J. and A. Muffett, "The .onion Special-Use
              Domain Name", draft-ietf-dnsop-onion-tld-01 (work in
              progress), September 2015.

   [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>.




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   [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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