GEOPRIV M. Thomson
Internet-Draft J. Winterbottom
Intended status: Standards Track Andrew
Expires: April 16, 2007 October 13, 2006
U-NAPTR Discovery for HELD Services
draft-thomson-geopriv-held-unaptr-00.txt
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Copyright (C) The Internet Society (2006).
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Abstract
A method is described where URI-enabled NAPTR (U-NAPTR) is applied to
the discovery of a local Location Information Server (LIS). This
document defines an Application Service for a LIS, with a specific
Application Protocol for the HTTP Enabled Location Delivery (HELD)
protocol. This document also discusses several solutions that enable
this method where Network Address Translation (NAT) devices are
employed.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. U-NAPTR for LIS Discovery . . . . . . . . . . . . . . . . . . 4
3. Determining the Access Network Domain Name . . . . . . . . . . 5
3.1. DHCP Domain Name Option . . . . . . . . . . . . . . . . . 5
3.2. Reverse DNS . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Determining an External IP Address . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5.1. Registration of a Location Server Application Service
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Registration of a Location Server Application Protocol
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Normative References . . . . . . . . . . . . . . . . . . . 10
6.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
Discovering a Location Information Server (LIS) is an important part
of the location acquisition process. Discovery is used to establish
a relationship between a LIS and its client. This document describes
a method where the client uses the DNS to discover a URI for a LIS.
Unlike protocols that use TCP or UDP directly, HELD is built on a
higher layer protocol, which means that a LIS server requires more
specific identification that a hostname or hostname/port. URI-
enabled NAPTR (U-NAPTR) [I-D.daigle-unaptr] describes a
straightforward method of applying the Dynamic Delegation Discovery
Service (DDDS) for URI results.
This document describes how U-NAPTR resolution can be used to
discover the LIS URI. For this DDDS application, an Application
Service tag "LIS" and an Application Protocol tag "HELD" are created
and registered with the IANA. Taking a domain name, this U-NAPTR
application uses the two tags to determine the LIS URI.
Determining the domain name to be used is a critical part of the
resolution process. The second part of this document describes how a
domain name can be derived. Several methods are described that
address different scenarios.
1.1. Terminology
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 [RFC2119].
This document uses the terms "access network" to refer to the network
that a host connects to for Internet access. The "access network
provider" is the entity that operates the access network. The access
network provider is responsible for allocating the host an IP address
and for directly or indirectly providing a LIS service.
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2. U-NAPTR for LIS Discovery
U-NAPTR resolution for a LIS takes a domain name as input and
produces a URI that identifies the LIS. This process also requires
an Application Service tag and an Application Protocol tag, which
differentiate LIS-related NAPTR records from other records for that
domain.
Section 5.1 defines an Application Service tag of "LIS", which is
used to identify the location service for a particular domain. The
Application Protocol tag "HELD", defined in Section 5.2, is used to
identify a LIS that understands the HELD protocol
[I-D.winterbottom-http-location-delivery].
The NAPTR records in the following example demonstrate the use of the
Application Service and Protocol tags. Iterative NAPTR resolution is
used to delegate responsibility for the LIS service from
"zonea.example.com" and "zoneb.example.com" to "example.com".
zonea.example.com.
;; order pref flags
IN NAPTR 100 10 "" "LIS:HELD" ( ; service
"" ; regex
example.com. ; replacement
)
zoneb.example.com.
;; order pref flags
IN NAPTR 100 10 "" "LIS:HELD" ( ; service
"" ; regex
example.com. ; replacement
)
example.com.
;; order pref flags
IN NAPTR 100 10 "u" "LIS:HELD" ( ; service
"!*.!https://lis.example.com/!" ; regex
. ; replacement
)
Details for the "LIS" Application Service tag and the "HELD"
Application Protocol tag are included in Section 5.
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3. Determining the Access Network Domain Name
The U-NAPTR discovery method described in Section 2 requires that the
domain name applicable to the access network is known. An
unconfigured host might not have this information, therefore it must
determine this value before the U-NAPTR method can be attempted.
This section describes several methods for discovering a domain name
for the local access network. Each method should be attempted where
applicable until a domain name is derived. If a domain name is
successfully derived but that domain name does not produce any
U-NAPTR records, alternative methods can be attempted. Reattempting
with different methods is particularly applicable when NAT is used,
as is shown in Section 3.2.1.
3.1. DHCP Domain Name Option
For IP version 4, Dynamic Host Configuration Protocol (DHCP) option
15 [RFC2131] includes the domain name suffix for the host. If DHCP
and option 15 are available, this value should be used as input the
U-NAPTR procedure.
DHCP version 6 does not provide a single domain name suffix; instead
a fully qualified domain name (FQDN) for the client is provided in
option 39 [I-D.ietf-dhc-dhcpv6-fqdn]. The domain name used as input
to the U-NAPTR resolution is derived from the FQDN by removing the
first label.
Either DHCP method SHOULD be attempted first if DHCP is available.
3.2. Reverse DNS
DNS "PTR" records in the "in-addr.arpa." domain can be used to
determine the domain name of a host, and therefore, the name of the
domain for that host. The use of the "in-addr.arpa." domain is
described in [RFC1034] and results in the domain name of the host.
Likewise, IPv6 hosts use the "ip6.arpa." domain. In the majority of
cases, the domain part of this name (everything excluding the first
label) is also the domain name for the access network. Assuming that
this is true, this domain name can be used as input to the U-NAPTR
process.
For example, if the for "10.1.2.3" address, if the "PTR" record at
"3.2.1.10.in-addr.arpa." refers to "host.example.com", this results
in a U-NAPTR search for "example.com".
The DNS hierarchy does not necessarily directly map onto a network
topology (see [RFC4367]; therefore, this method MUST only be used for
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the domain name determined by removing the first label only. This
method assumes that the access network provider also provides the
reverse DNS record and they control the domain that is indicated in
the "PTR" record.
Furthermore, this method might not apply where a host is given a
domain name that is different from the domain name of the access
network. This might occur in some hosting configurations, such as
where a number of web server hosts, with widely varying domain names,
are co-located. From the above example, the access network provider
allocated "10.1.2.3" to the host; therefore, they also need to
control the DNS domain "example.com" and the associated NAPTR
records. DNS Security Extensions (DNSSEC) [RFC4033] provides a
cryptographic means of validating this association, through data
origin authentication.
3.2.1. Determining an External IP Address
Reverse DNS relies on knowing the IP address of a host within the
access domain. Initially, this SHOULD be attempted using the IP
address that is assigned to a local interface on the host. However,
when a NAT device is used, the IP address of the NAT device is
substituted for the source IP address. If a NAT device exists
between the host and the access network, the host does not have any
direct way to determine the IP address that it is effectively using
within the access network. The IP address of the NAT device and the
corresponding domain name can be used to discover the LIS.
In order to use reverse DNS in this configuration, the hosts need to
know the IP address that the NAT device uses. The following sections
describe some possible methods.
These methods are particularly useful in residential broadband
configurations. A large proportion of residential broadband services
employ a NAT device so that several hosts can share the same Internet
access. Since the network behind the NAT device are generally very
small, both in numbers and geographical area, it isn't necessary for
a LIS to operate within that network; the hosts are able to access a
LIS in the access network outside of the NAT device.
3.2.1.1. UPnP
If a NAT device complies with the Universal Plug and Play (UPnP)
specification [UPnP-IGD-WANIPConnection1], the WANIPConnection part
can be used to query the device for its public IP address. The
"GetExternalIPAddress" function provides the external address for a
particular network connection.
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UPnP defines a method for discovering UPnP-enabled hosts in a
network; the host does not need any prior configuration.
3.2.1.2. STUN
A host can use the Simple Traversal of UDP NATs (STUN)
[I-D.ietf-behave-rfc3489bis] to determine a public IP address.
"Binding Request" message and the resulting "MAPPED-ADDRESS" that is
returned in the response.
Using STUN requires cooperation from a publicly accessible STUN
server. A domain name needs to be configured at the host for STUN
server discovery.
3.2.1.3. Other Options
The source IP address in any IP packet can be used to determine the
public IP address of a host. While the STUN method uses a small part
of a more sophisticated protocol, this principle can be applied using
any other protocol. Like STUN, this method requires prior knowledge
of the publicly accessible server and the method that it supports.
For instance, a publicly accessible host could be configured to
respond to a UDP packet on a predefined port; the data of the
response could contain the source IP address that was in the request.
Alternatively, a HTTP server at a particular URL could be configured
to respond to a GET request with a "text/plain" body containing the
IP address of the requester. Note that transparent HTTP proxies
might affect the results of this method.
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4. Security Considerations
The primary attack against the methods described in this document is
one that would lead to impersonation of a LIS. An attacker could
attempt to compromise the U-NAPTR resolution. A description of the
security considerations for U-NAPTR applications is included in
[I-D.daigle-unaptr].
In addition to considerations related to U-NAPTR, it is important to
recognize that the output of this is entirely dependent on its input.
An attacker who can control the domain name can also control the
final URI. Because a number of methods are provided for determining
the domain name, a host implementation needs to consider attacks
against each of the methods that are used.
If DHCP is used, the integrity of DHCP options is limited by the
security of the channel over which they are provided. Physical
security and separation of DHCP messages from other packets are
commonplace methods that can reduce the possibility of attack within
an access network; alternatively, DHCP authentication [RFC3118] can
provide a degree of protection against modification.
Reverse DNS is subject to the maintenance of the "in-addr.arpa." or
"ip6.arpa." domain and the integrity of the results that it provides.
DNSSEC [RFC4033] provides some measures that can improve the
reliability of DNS results. In particular, DNSSEC SHOULD be applied
to ensure that the reverse DNS record and the resulting domain are
provided by the same entity before this method is used. Without this
assurance, the host cannot be certain that the access network
provider has provided the NAPTR record for the domain name that is
provided.
Hosts behind NAT devices are also subject to attacks when retrieving
their public IP address. [I-D.ietf-behave-rfc3489bis] describes some
means of mitigating this attack for STUN.
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5. IANA Considerations
5.1. Registration of a Location Server Application Service Tag
This section registers a new S-NAPTR/U-NAPTR Application Service tag
for a LIS, as mandated by [RFC3958].
Application Service Tag: LIS
Intended usage: Identifies a service that provides a host with its
location information.
Defining publication: XXXX
Related publications: HELD [I-D.winterbottom-http-location-delivery]
Contact information: The authors of this document
Author/Change controller: The IESG
5.2. Registration of a Location Server Application Protocol Tag
This section registers a new S-NAPTR/U-NAPTR Application Protocol tag
for the HELD [I-D.winterbottom-http-location-delivery] protocol, as
mandated by [RFC3958].
Application Service Tag: HELD
Intended Usage: Identifies the HELD protocol.
Applicable Service Tag(s): LIS
Terminal NAPTR Record Type(s): U
Defining Publication: XXXX
Related Publications: HELD [I-D.winterbottom-http-location-delivery]
Contact Information: The authors of this document
Author/Change Controller: The IESG
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6. References
6.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[I-D.daigle-unaptr]
Daigle, L., "Domain-based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", draft-daigle-unaptr-00 (work in progress),
June 2006.
[I-D.ietf-dhc-dhcpv6-fqdn]
Volz, B., "The DHCPv6 Client FQDN Option",
draft-ietf-dhc-dhcpv6-fqdn-05 (work in progress),
March 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC4367] Rosenberg, J. and IAB, "What's in a Name: False
Assumptions about DNS Names", RFC 4367, February 2006.
[I-D.ietf-behave-rfc3489bis]
Rosenberg, J., "Simple Traversal Underneath Network
Address Translators (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-04 (work in progress),
July 2006.
[I-D.winterbottom-http-location-delivery]
Winterbottom, J., "HTTP Enabled Location Delivery (HELD)",
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draft-winterbottom-http-location-delivery-03 (work in
progress), May 2006.
[UPnP-IGD-WANIPConnection1]
UPnP Forum, "Internet Gateway Device (IGD) Standardized
Device Control Protocol V 1.0: WANIPConnection:1 Service
Template Version 1.01 For UPnP Version 1.0", DCP 05-001,
Nov 2001.
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Appendix A. Acknowledgements
The authors would like to thank Leslie Daigle for her work on
U-NAPTR; Peter Koch for his feedback on the DNS aspects of this
document; and ...
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Authors' Addresses
Martin Thomson
Andrew
PO Box U40
Wollongong University Campus, NSW 2500
AU
Phone: +61 2 4221 2915
Email: martin.thomson@andrew.com
URI: http://www.andrew.com/
James Winterbottom
Andrew
PO Box U40
Wollongong University Campus, NSW 2500
AU
Phone: +61 2 4221 2938
Email: james.winterbottom@andrew.com
URI: http://www.andrew.com/
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