Network T. Pauly
Internet-Draft Apple Inc.
Intended status: Standards Track P. Wouters
Expires: August 10, 2018 Red Hat
February 6, 2018
Split DNS Configuration for IKEv2
draft-ietf-ipsecme-split-dns-05
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
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This Internet-Draft will expire on August 10, 2018.
Copyright Notice
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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 . . . . . . . . . . . . . . . . . . . . . 9
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
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_DNSSEC_TA attributes as defined in Section 4 as part of the
CFG_REQUEST payload. If an INTERNAL_DNSSEC_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_DNSSEC_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.
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.
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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_DNSSEC_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_DNSSEC_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_DNSSEC_TA(43547,8,1,B6225AB2CC613E0DCA7962BDC2342EA4F1B56083)
INTERNAL_DNSSEC_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. Implementors need to be careful
that this 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 |
+-+-----------------------------+---------------+---------------+
| DNSKEY Key Tag | DNSKEY Alg | Digest Type |
+-------------------------------+---------------+---------------+
| |
~ Digest Data ~
| |
+---------------------------------------------------------------+
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 DNSKEY Key Tag value (2 octets) - Delegation Signer (DS) Key Tag
as specified in [RFC4034] Section 5.1
o DNSKEY Algorithm (1 octet) - DNSKEY algorithm value from the IANA
DNS Security Algorithm Numbers Registry
o Digest Type (1 octet) - DS algorithm value from the IANA
Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms
Registry
o Digest Data (2 or more octets) - The DNSKEY 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).
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
INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can be used without creating
specific DNS exemptions.
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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 payloads MUST immediately follow an
INTERNAL_DNS_DOMAIN payload. 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. As with any network
input, the content should be considered untrusted and handled
accordingly.
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
------ ------------------- ------ ---------- ---------------
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,
<https://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, <https://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,
<https://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,
<https://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, <https://www.rfc-editor.org/info/rfc7296>.
8.2. Informative References
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
DOI 10.17487/RFC2775, February 2000, <https://www.rfc-
editor.org/info/rfc2775>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
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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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