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draft-reddy-add-enterprise-split-dns-05.txt
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ADD T. Reddy
Internet-Draft Akamai
Intended status: Standards Track D. Wing
Expires: February 25, 2022 Citrix
K. Smith
Vodafone
August 24, 2021
Split-Horizon DNS Configuration
draft-reddy-add-enterprise-split-dns-05
Abstract
When split-horizon DNS is deployed by a network, certain domains are
only resolvable by querying the network-designated DNS server. DNS
clients which use DNS servers not provided by the network need to
route those DNS domain queries to the network-designated DNS server.
This document informs DNS clients of split-horizon DNS, their DNS
domains, and is compatible with encrypted 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://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 February 25, 2022.
Copyright Notice
Copyright (c) 2021 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Reddy, et al. Expires February 25, 2022 [Page 1]
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Split DNS . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. PvD dnsZones . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Authority over the Domains . . . . . . . . . . . . . . . 5
5. An Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Split DNS Configuration for IKEv2 . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Historically, an endpoint would utilize network-designated DNS
servers upon joining a network (e.g., DHCP OFFER, IPv6 Router
Advertisement). While it has long been possible to configure
endpoints to ignore the network's suggestions and use a (public) DNS
server on the Internet, this was seldom used because some networks
block UDP/53 (in order to enforce their own DNS policies). Also,
there has been an increase in the availability of "public resolvers"
[RFC8499] which DNS clients may be pre-configured to use instead of
the default network resolver for a variety of reasons (e.g., offer a
good reachability, support an encrypted transport, provide a claimed
privacy policy, (lack of) filtering). With the advent of DoT and
DoH, such network blocking is more difficult, but the endpoint is
unable to (properly) resolve split-horizon DNS domains which must
query the network-designated DNS server.
This document specifies a mechanism to indicate which DNS zones are
used for split-horizon DNS. DNS clients can discover and
authenticate DNS servers provided by the network, for example using
the techniques proposed in [I-D.ietf-add-dnr] and [I-D.ietf-add-ddr].
Provisioning Domains (PvDs) are defined in [RFC7556] as sets of
network configuration information that clients can use to access
networks, including rules for DNS resolution and proxy configuration.
[RFC8801] defines a mechanism for discovering multiple Explicit PvDs
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on a single network and their Additional Information by means of an
HTTP-over-TLS query using a URI derived from the PvD ID. This set of
additional configuration information is referred to as a Web
Provisioning Domain (Web PvD). The network lists its claims of
authority for DNS domains using the "dnsZones" PvD key (defined in
[RFC8801]).
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document makes use of the terms defined in [RFC8499]. The terms
"Private DNS", "Global DNS" and "Split DNS" are defined in [RFC8499].
'Encrypted DNS' refers to a DNS protocol that provides an encrypted
channel between a DNS client and server (e.g., DoT, DoH, or DoQ).
The term "enterprise network" in this document extends to a wide
variety of deployment scenarios. For example, an "enterprise" can be
a Small Office, Home Office or Corporation.
3. Split DNS
[RFC2826] "does not preclude private networks from operating their
own private name spaces" but notes that if private networks "wish to
make use of names uniquely defined for the global Internet, they have
to fetch that information from the global DNS naming hierarchy".
There are various DNS deployments outside of the global DNS,
including "split horizon" deployments and DNS usages on private (or
virtual private) networks. In a split horizon, an authoritative
server gives different responses to queries from the Internet than
they do to network-designated DNS servers; while some deployments
differentiate internal queries from public queries by the source IP
address, the concerns in Section 3.1.1 of [RFC6950] relating to
trusting source IP addresses apply to such deployments.
When the internal address space range is private [RFC1918], this
makes it both easier for the server to discriminate public from
private and harder for public entities to impersonate nodes in the
private network. The use cases that motivate split-horizon DNS
typically involve restricting access to some network services --
intranet resources such as internal web sites, development servers,
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or directories, for example -- while preserving the ease of use
offered by domain names for internal users.
A typical use case is an Enterprise network can require one or more
DNS domains to be resolved via network-designated DNS servers. This
can be a special domain, such as "corp.example.com" for an enterprise
that is publicly known to use "example.com". In this case, the
endpoint needs to be informed what the private domain names are and
what the IP addresses of the network-designated DNS servers are. An
Enterprise can also run a different version of its global domain on
its internal network. In that case, the client is instructed to send
DNS queries for the enterprise public domain (e.g., "example.com") to
the network-designated DNS servers. A configuration for this
deployment scenario is referred to as a Split DNS configuration.
Another use case for split-horizon DNS is Cellular and Fixed-access
networks (ISPs) typically offer private domains, including account
status/controls, and free education initiatives [INS].
The PvD RA option defined in [RFC8801] SHOULD set the H-flag to
indicate that Additional Information is available. This Additional
Information JSON object SHOULD include the "dnsZones" key to define
the DNS domains for which the network claims authority.
4. PvD dnsZones
As discussed in Section 3, internal resources in a network tend to
have private DNS names. A network can also run a different version
of its global domain on its internal network, and require the use of
network-designated DNS servers to get resolved.
The PvD Key dnsZones is defined in [RFC8801]. The PvD Key dnsZones
adds support for DNS domains for which the network claims authority.
The private domains specified in the dnsZones key are intended to be
resolved using network-designated DNS servers. The private domains
in dnsZones are only reachable by devices authenticated or attached
to the network. The global domains specified in the dnsZones key
have a different version in the internal network. DNS resolution for
other domains remains unchanged.
The dnsZones PvD Key conveys the specified DNS domains that need to
be resolved using a network-designated DNS server. The DNS root zone
(".") MUST be ignored if it appears in dnsZones. Other generic or
global domains, such as Top-Level Domains (TLDs), similarly MUST be
ignored if they appear in dnsZones.
For each dnsZones entry, the client can use the network-designated
DNS servers to resolve the listed domains and its subdomains. Other
domain names may be resolved using some other DNS servers that are
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configured independently. For example, if the dnsZones key specifies
"example.test", then "example.test", "www.example.test", and
"mail.eng.example.test" can be resolved using the network-designated
DNS resolver(s), but "otherexample.test" and "ple.test" can be
resolved using the system's public resolver(s).
4.1. Authority over the Domains
To comply with [RFC2826] the split-horizon DNS zone must either not
exist in the global DNS hierarchy or must be authoritatively
delegated to the split-horizon DNS server to answer. The client can
use the mechanism described in [I-D.ietf-add-dnr] to discover the
network-designated resolvers. To determine if the network-designated
encrypted resolvers are authoritative over the domains in DnsZones,
the client performs the following steps for each domain in DnsZones:
1. The client sends an NS query for the domain in DnsZones. This
query MUST only be sent over encrypted DNS session to a public
resolver that is configured independently or to a network-
designated resolver whose response will be validated using DNSSEC
as described in [RFC6698].
2. The client checks that the NS RRset matches, or is a subdomain
of, any one of the ADN of the discovered network-designated
encrypted DNS resolvers.
A. If the match fails, the client determines the network is not
authoritative for the indicated domain. It might log an
error, reject the network entirely (because the network lied
about its authority over a domain) or other action.
B. If the match succeeds, the client can then establish a secure
connection to that network-designated resolver and validate
its certificate.
+ If the server certificate does not validate and a secure
connection cannot be established to the network designated
resolver, the client can action as discussed in step 3
(A).
+ If the server certificate validation is successful and a
secure connection is established, the client can
subsequently resolve the domains in that subtree using the
network-designated resolver.
3. As an exception to this rule, the client need not perform the
above validation for domains reserved for special use [RFC6761]
or [RFC6762] such as ".home.arpa" or ".local".
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4. If the client uses a public resolver, authenticated denial of
existence using NSEC3 or NSEC records can be used by a client to
identify that the domain name does not exist in the global DNS.
[RFC7149] recommends validation of responses using NSEC3.
For example, if in a network the private domain names are defined
under "internal.corp1.example.com". The DnsZones PvD Key would
indicate that "*.internal.corp1.example.com" are private domain
names. The client can trigger a NS query of
"internal.corp1.example.com" and the NS RRset returns that the
nameserver is "ns1.corp2.example.com". The client would then connect
to the network-designated encrypted resolver whose name is
"ns1.corp2.example.com", authenticate it using server certificate
validation in TLS handshake, and use it for resolving the domains in
the subtree of "*.internal.corp1.example.com".
5. An Example
The following example shows how the JSON keys defined in this
document can be used:
{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
"dnsZones:": ["city.other.test", "example.com"]
}
The JSON keys "identifier", "expires", and "prefixes" are defined in
[RFC8801].
6. Split DNS Configuration for IKEv2
The split-tunnel Virtual Private Network (VPN) configuration allows
the endpoint to access resources that reside in the VPN [RFC8598] via
the tunnel; other traffic not destined to the VPN does not traverse
the tunnel. In contrast, a non-split- tunnel VPN configuration
causes all traffic to traverse the tunnel into the VPN.
When the VPN tunnel is IPsec, the encrypted DNS resolver hosted by
the VPN service provider can be securely discovered by the endpoint
using the ENCDNS_IP*_* IKEv2 Configuration Payload Attribute Types
defined in [I-D.btw-add-ipsecme-ike]. For split-tunnel VPN
configurations, the endpoint uses the discovered encrypted DNS server
to resolve domain names for which the VPN provider claims authority.
For non-split-tunnel VPN configurations, the endpoint uses the
discovered encrypted DNS server to resolve both global and private
domain names. For split-tunnel VPN configurations, the IKE client
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can use the steps discussed in Section 4.1 to determine if the VPN
service provider is authoritative over the INTERNAL_DNS_DOMAIN
domains.
Other VPN tunnel types have similar configuration capabilities, not
detailed here.
7. Security Considerations
The content of dnsZones may be passed to another (DNS) program for
processing. As with any network input, the content SHOULD be
considered untrusted and handled accordingly. The client must
perform the steps discussed in Section 4.1 to determine if the
network-designated encrypted resolvers are authoritative over the
domains in DnsZones. If the network is lying, the client can take
appropriate action like disconnecting from the network.
As an additional precaution, clients may want to preconfigure global
domains for TLDs and Second-Level Domains (SLDs) to prevent malicious
DNS redirections for well-known domains. This prevents users from
unknowingly giving DNS queries to third parties. This is even more
important if those well-known domains are not deploying DNSSEC, as
the attached network could then even modify the DNS answers without
detection. It is similar to the mechanism discussed in Section 8 of
[RFC8598].
8. IANA Considerations
This document has no IANA actions..
9. Acknowledgements
Thanks to Mohamed Boucadair, Jim Reid, Ben Schwartz, Tommy Pauly,
Paul Vixie and Vinny Parla for the discussion and comments. The
authors would like to give special thanks to Ben Schwartz for his
help.
10. References
10.1. 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>.
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[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>.
[RFC2826] Internet Architecture Board, "IAB Technical Comment on the
Unique DNS Root", RFC 2826, DOI 10.17487/RFC2826, May
2000, <https://www.rfc-editor.org/info/rfc2826>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8801] Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W.
Shao, "Discovering Provisioning Domain Names and Data",
RFC 8801, DOI 10.17487/RFC8801, July 2020,
<https://www.rfc-editor.org/info/rfc8801>.
10.2. Informative References
[I-D.btw-add-ipsecme-ike]
Boucadair, M., Reddy, T., Wing, D., and V. Smyslov,
"Internet Key Exchange Protocol Version 2 (IKEv2)
Configuration for Encrypted DNS", draft-btw-add-ipsecme-
ike-03 (work in progress), May 2021.
[I-D.ietf-add-ddr]
Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", draft-ietf-
add-ddr-02 (work in progress), July 2021.
[I-D.ietf-add-dnr]
Boucadair, M., Reddy, T., Wing, D., Cook, N., and T.
Jensen, "DHCP and Router Advertisement Options for the
Discovery of Network-designated Resolvers (DNR)", draft-
ietf-add-dnr-02 (work in progress), May 2021.
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[INS] The Unicode Consortium, "Vodafone Foundation Instant
Schools for Sub-Saharan Africa",
<https://www.vodafone.com/about/vodafone-foundation/focus-
areas/instant-schools>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
<https://www.rfc-editor.org/info/rfc6950>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<https://www.rfc-editor.org/info/rfc7149>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8598] Pauly, T. and P. Wouters, "Split DNS Configuration for the
Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 8598, DOI 10.17487/RFC8598, May 2019,
<https://www.rfc-editor.org/info/rfc8598>.
Authors' Addresses
Tirumaleswar Reddy
Akamai
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
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Dan Wing
Citrix Systems, Inc.
4988 Great America Pkwy
Santa Clara, CA 95054
USA
Email: danwing@gmail.com
Kevin Smith
Vodafone Group
One Kingdom Street
London
UK
Email: kevin.smith@vodafone.com
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