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
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This Internet-Draft will expire on March 27, 2016.
Copyright Notice
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document authors. All rights reserved.
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publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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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 . . . . . . . . . . . . . . . . . . . . . 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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