Network T. Pauly
Internet-Draft Apple Inc.
Intended status: Standards Track P. Wouters
Expires: November 28, 2016 Red Hat
May 27, 2016
Split-DNS Configuration for IKEv2
draft-pauly-ipsecme-split-dns-01
Abstract
This document defines two Configuration Payload Attribute Types for
the IKEv2 protocol that define sets of private DNS domains which
should be resolved by DNS servers reachable through an IPsec
connection, while leaving all other DNS resolution unchanged. The
options define the set of DNS domains, DNS nameserver IP addresses
and DNSSEC trust anchors to use for these DNS domains. This approach
of resolving a subset of domains using an IPSec connection is
referred to as "split-DNS". The information obtained via these
attribute types can be used to reconfigure the local DNS resolution
to use DNS forwarding for specific private domains.
Status of This Memo
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This Internet-Draft will expire on November 28, 2016.
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Copyright (c) 2016 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
Provisions Relating to IETF Documents
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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 . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
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. 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".
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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, 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, an initiator sending a CFG_REQUEST
payload MAY include one or more INTERNAL_DNS_DOMAIN attributes as
defined in Section 4. 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 length of the INTERNAL_DNS_DOMAIN attribute is zero, then the
initiator is requesting that the attribute be assigned without
restricting the subdomains that it will accept.
If the length of the INTERNAL_DNS_DOMAIN is greater than zero, the
value is a single DNS domain. The initiator is indicating that it
will only allow this domain and any sub-domains within this domain to
be resolved using the internal DNS servers. The list of
INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST defines the full
set of domains the intiator is willing to resolve using the internal
DNS servers.
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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.
3.2. Configuration Reply
Responders MAY send one or more INTERNAL_DNS_DOMAIN attributes in
their CFG_REPLY payload if the CFG_REQUEST contained at least one
INTERNAL_DNS_DOMAIN attribute. If the CFG_REQUEST did not contain an
INTERNAL_DNS_DOMAIN attribute, the responder MUST NOT include an
INTERNAL_DNS_DOMAIN attribute in the CFG_REPLY. If an
INTERNAL_DNS_DOMAIN attribute is included in the CFG_REPLY, the
responder SHOULD also include one or both of the INTERNAL_IP4_DNS and
INTERNAL_IP6_DNS attributes in its CFG_REPLY. 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 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 attribute, an
INTERNAL_DNSSEC_TA 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 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 its CFG_REQUEST, but does not
specify any value for either. This indicates that it supports split-
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DNS, but has no preference for which DNS requests should be routed
through the tunnel.
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.
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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)
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
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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
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 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 attributes to contain these IP addresses.
If a CFG_REPLY contains one or more INTERNAL_DNS_DOMAIN 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
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names MUST 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 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" MUST be resolved using 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 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
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 attributes.
Indirect reference RRtypes include CNAME, DNAME, MX and SRV RR's.
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.
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 be
terminated.
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If the IP address value of the received INTERNAL_IP4_DNS or
INTERNAL_IP6_DNS attribute is not covered by the proposed IPsec
connection, then the local DNS should not be reconfigured until a
CREATE_CHILD Exchange is received 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 configured to use
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.
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>.
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[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
[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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