GEOPRIV M. Thomson
Internet-Draft J. Winterbottom
Intended status: Standards Track Andrew
Expires: October 3, 2009 April 1, 2009
Discovering the Local Location Information Server (LIS)
draft-ietf-geopriv-lis-discovery-09
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 3, 2009.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
Discovery of the correct Location Information Server (LIS) in the
local access network is necessary for devices that wish to acquire
location information from the network. A method is described for the
Thomson & Winterbottom Expires October 3, 2009 [Page 1]
Internet-Draft LIS Discovery April 2009
discovery of a LIS. Dynamic Host Configuration Protocol (DHCP)
options for IP versions 4 and 6 are defined that specify a URI for a
LIS in the local access network. An alternative method that uses
URI-enabled NAPTR (U-NAPTR) is described for use where the DHCP
option is unsuccessful.
Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3
1.1. DHCP Discovery . . . . . . . . . . . . . . . . . . . . . . 3
1.2. U-NAPTR Discovery . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. LIS Discovery Using DHCP . . . . . . . . . . . . . . . . . . . 4
2.1. DHCPv4 LIS URI Option . . . . . . . . . . . . . . . . . . 4
2.2. DHCPv6 LIS URI Option . . . . . . . . . . . . . . . . . . 5
3. U-NAPTR for LIS Discovery . . . . . . . . . . . . . . . . . . 6
3.1. Determining a Domain Name . . . . . . . . . . . . . . . . 7
4. Overall Discovery Procedure . . . . . . . . . . . . . . . . . 7
4.1. Residential Gateways . . . . . . . . . . . . . . . . . . . 8
4.2. Virtual Private Networks (VPNs) . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. Registration of DHCPv4 and DHCPv6 LIS URI Option Codes . . 10
6.2. Registration of a Location Server Application Service
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.3. Registration of a Location Server Application Protocol
Tag for HELD . . . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Thomson & Winterbottom Expires October 3, 2009 [Page 2]
Internet-Draft LIS Discovery April 2009
1. Introduction and Overview
The location of a device is a useful and sometimes necessary part of
many services. A Location Information Server (LIS) is responsible
for providing that location information to devices with an access
network. The LIS uses knowledge of the access network and its
physical topology to generate and serve location information to
devices.
Each access network requires specific knowledge about topology.
Therefore, it is important to discover the LIS that has the specific
knowledge necessary to locate a device. That is, the LIS that serves
the current access network. Automatic discovery is important where
there is any chance of movement outside a single access network.
Reliance on static configuration can lead to unexpected errors if a
device moves between access networks.
This document describes DHCP options and DNS records that a device
can use to discover a LIS.
The product of a discovery process, such as the one described in this
document, is the address of the service. In this document, the
result is an http: or https: URI, which identifies a LIS.
The URI result from the discovery process is suitable for location
configuration only; that is, the device MUST dereference the URI
using the process described in HELD
[I-D.ietf-geopriv-http-location-delivery]. URIs discovered in this
way are not "location URIs" [I-D.ietf-geopriv-lbyr-requirements];
dereferencing one of them provides the location of the requester
only. Devices MUST NOT embed these URIs in fields in other protocols
designed to carry the location of the device.
1.1. DHCP Discovery
DHCP ([RFC2131], [RFC3315]) is a commonly used mechanism for
providing bootstrap configuration information allowing a device to
operate in a specific network environment. The bulk of DHCP
information is largely static; consisting of configuration
information that does not change over the period that the device is
attached to the network. Physical location information might change
over this time, however the address of the LIS does not. Thus, DHCP
is suitable for configuring a device with the address of a LIS.
1.2. U-NAPTR Discovery
Where DHCP is not available, the DNS might be able to provide a URI.
This document describes a method that uses URI-enabled NAPTR
Thomson & Winterbottom Expires October 3, 2009 [Page 3]
Internet-Draft LIS Discovery April 2009
(U-NAPTR) [RFC4848], a Dynamic Delegation Discovery Service (DDDS)
profile that supports URI results.
For the LIS discovery 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.
1.3. 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 also uses the term "device" to refer to an end host, or
client consistent with its use in HELD. In HELD and RFC3693
[RFC3693] parlance, the Device is also the Target.
The terms "access network" refers to the network that a device
connects to for Internet access. The "access network provider" is
the entity that operates the access network. This is consistent with
the definition in [I-D.ietf-geopriv-l7-lcp-ps] which combines the
Internet Access Provider (IAP) and Internet Service Provider (ISP).
The access network provider is responsible for allocating the device
a public IP address and for directly or indirectly providing a LIS
service.
2. LIS Discovery Using DHCP
DHCP allows the access network provider to specify the address of a
LIS as part of network configuration. If the device is able to
acquire a LIS URI using DHCP then this URI is used directly; the
U-NAPTR process is not necessary if this option is provided.
This document registers a DHCP option for a LIS URI for both IPv4 and
IPv6. An "https:" LIS URI that is a product of U-NAPTR MUST be
authenticated using the domain name method described in Section 3.1
of RFC 2818 [RFC2818].
2.1. DHCPv4 LIS URI Option
This section defines a DHCP for IPv4 (DHCPv4) option for the address
of a LIS.
Thomson & Winterbottom Expires October 3, 2009 [Page 4]
Internet-Draft LIS Discovery April 2009
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LIS_URI | Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. LIS URI .
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DHCPv4 LIS URI Option
LIS_URI: The IANA assigned option number (TBD). [[IANA/RFC-Editor
Note: Please replace TBD with the assigned DHCPv4 option code.]]
Length: The length of the entire LIS URI option in octets.
LIS URI: The address of the LIS. The URI MUST NOT be terminated by
a zero octet.
The DHCPv4 version of this URI SHOULD NOT exceed 255 octets in
length, but MAY be extended by concatenating multiple option
values if necessary, as described in [RFC3396].
2.2. DHCPv6 LIS URI Option
This section defines a DHCP for IPv6 (DHCPv6) option for the address
of a LIS. The DHCPv6 option for this parameter is similarly
formatted to the DHCPv4 option.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_LIS_URI | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. LIS URI .
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DHCPv6 LIS URI Option
OPTION_LIS_URI: The IANA assigned option number (TBD). [[IANA/
RFC-Editor Note: Please replace TBD with the assigned DHCPv6
option code.]]
Length: The length of the LIS URI option in octets.
Thomson & Winterbottom Expires October 3, 2009 [Page 5]
Internet-Draft LIS Discovery April 2009
The semantics and format of the remainder of the LIS URI option
are identical to the DHCPv4 option, except for the larger
allowance for URI length granted by the 16 bit length field.
DHCPv6 prohibits concatenation of option values.
3. 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 6.2 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 6.3, is used to
identify a LIS that understands the HELD protocol
[I-D.ietf-geopriv-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.net." and "zoneb.example.net." to
"outsource.example.com.".
zonea.example.net.
;; order pref flags
IN NAPTR 100 10 "" "LIS:HELD" ( ; service
"" ; regex
outsource.example.com. ; replacement
)
zoneb.example.net.
;; order pref flags
IN NAPTR 100 10 "" "LIS:HELD" ( ; service
"" ; regex
outsource.example.com. ; replacement
)
outsource.example.com.
;; order pref flags
IN NAPTR 100 10 "u" "LIS:HELD" ( ; service
"!*.!https://lis.example.org:4802/?c=ex!" ; regex
. ; replacement
)
Figure 3: Sample LIS:HELD Service NAPTR Records
Details for the "LIS" Application Service tag and the "HELD"
Thomson & Winterbottom Expires October 3, 2009 [Page 6]
Internet-Draft LIS Discovery April 2009
Application Protocol tag are included in Section 6.
An "https:" LIS URI that is a product of U-NAPTR MUST be
authenticated using the domain name method described in Section 3.1
of RFC 2818 [RFC2818].
3.1. Determining a Domain Name
The U-NAPTR discovery method described requires a domain name as
input. This document does not specify how that domain name is
acquired by a device. If a device knows one or more domain names
that might be used for discovery, it is able to attempt to use each
domain name as input to the U-NAPTR discovery process. Static
configuration of a device is possible if a domain name is known to
work for this purpose.
A fully qualified domain name (FQDN) for the device might be provided
by a DHCP server ([RFC4702] for DHCPv4, [RFC4704] for DHCPv6).
DHCPv4 option 15 [RFC2131] could also be used as a source of a domain
name suffix for the device. If DHCP and any of these options are
available, these values could be used as input the U-NAPTR procedure;
however, implementers need to be aware that many DHCP servers do not
provide a sensible value for these options. Therefore, this method
of discovery SHOULD be given lesser precedence than methods that are
based on more explicit assurances.
4. Overall Discovery Procedure
The individual components of discovery are combined into a single
discovery procedure. Some networks maintain a topology analogous to
an onion and are comprised of layers, or segments, separating devices
from the Internet through intermediate networks. Applying the
individual discovery methods in an order that favours a physically
proximate LIS over a remote LIS is preferred.
A device MUST support DHCP discovery, where applicable. Devices
SHOULD support U-NAPTR discovery unless no input domain names can be
determined.
The following process ensures a greater likelihood of a LIS in close
physical proximity being discovered:
1. Request the DHCP LIS URI Option for each network interface.
2. Use U-NAPTR to discover a LIS URI using all known domain names.
3. Use a statically configured LIS URI.
Thomson & Winterbottom Expires October 3, 2009 [Page 7]
Internet-Draft LIS Discovery April 2009
A device that has multiple network interfaces could potentially be
served by a different access network on each interface, each with a
different LIS. The device SHOULD attempt to discover the LIS
applicable to each network interface, stopping when a LIS is
successfully discovered on any interface.
A device that discovers a LIS URI MUST attempt to verify that the LIS
is able to provide location information. For the HELD protocol, the
device MUST make a location request to the LIS. If - at any time -
the LIS responds to a request with the "notLocatable" error code (see
Section 4.3.2 of [I-D.ietf-geopriv-http-location-delivery]), the
device MUST continue or restart the discovery process. A device
SHOULD NOT make further requests to a LIS that provides a
"notLocatable" error until its network attachment changes, or it
discovers the LIS on an alternative network interface.
DHCP discovery MUST be attempted before any other discovery method.
This allows the network access provider a direct and explicit means
of configuring a LIS address. Alternative methods are only specified
as a means to discover a LIS where the DHCP infrastructure does not
support the LIS URI option.
This document does not mandate any particular source for the domain
name that is used as input to U-NAPTR.
Static configuration MAY be used if all other discovery methods fail.
Note however, that if a device has moved from its customary location,
static configuration might indicate a LIS that is unable to provide
accurate location information.
The product of the LIS discovery process is an "https:" or "http:"
URI. Nothing distinguishes this URI from other URIs with the same
scheme, aside from the fact that it is the product of this process.
Only URIs produced by the discovery process can be used for location
configuration using HELD. URIs that are not a product of LIS
discovery MUST NOT be used for location configuration.
4.1. Residential Gateways
The process described in this document is known to not work in a very
common deployment scenario. A fixed wireline scenario is described
in more detail in Section 3.1 of [I-D.ietf-geopriv-l7-lcp-ps]. In
this fixed wireline environment an intervening residential gateway
exists between the device and the access network. If the residential
gateway does not provide this option to the devices it serves, those
devices are unable to discover a LIS.
Support of this specification by residential gateways ensures that
Thomson & Winterbottom Expires October 3, 2009 [Page 8]
Internet-Draft LIS Discovery April 2009
the devices they serve are able to acquire location information. In
most cases the residential gateway configures the devices it serves
using DHCP. When DHCP is used, the residential gateway MUST provide
the devices it serves with a LIS URI option. In order to provide a
sensible value for this option, the residential gateway MUST either:
1. act as a LIS and provide location information to the devices that
it serves, or
2. discover a LIS on its external interface and relay this
information to devices.
In either case, the residential gateway provides a LIS URI option to
devices.
4.2. Virtual Private Networks (VPNs)
LIS discovery over a VPN network interface SHOULD NOT be performed.
A LIS discovered in this way is unlikely to have the information
necessary to determine an accurate location.
Not all interfaces connected to a VPN can be detected by devices or
the software running on them. A LIS MUST NOT provide location
information in response to requests that it can identify as
originating from a device on the remote end of a VPN tunnel, unless
it is able to accurately determine location. The "notLocatable" HELD
error code can be used to indicate to a device that discovery has
revealed an unsuitable LIS. This ensures that even if a device
discovers a LIS over the VPN, it does not rely on a LIS that is
unable to provide accurate location information.
5. Security Considerations
The primary attack against the methods described in this document is
one that would lead to impersonation of a LIS. The LIS is
responsible for providing location information and this information
is critical to a number of network services; furthermore, a device
does not necessarily have a prior relationship with a LIS. Several
methods are described here that can limit the probablity of, or
provide some protection against, such an attack.
The address of a LIS is usually well-known within an access network;
therefore, interception of messages does not introduce any specific
concerns.
An attacker that is able to modify or spoof messages from a DHCP
server could provide a falsified LIS URI that a device would be able
to use to successfully authenticate the LIS. Preventing DHCP
Thomson & Winterbottom Expires October 3, 2009 [Page 9]
Internet-Draft LIS Discovery April 2009
messages from being modified or spoofed by attackers is necessary if
this information is to be relied upon. Physical or link layer
security are commonplace methods that can reduce the possibility of
such an attack within an access network; alternatively, DHCP
authentication [RFC3118] can provide a degree of protection against
modification or spoofing.
An attacker could attempt to compromise the U-NAPTR resolution. A
more thorough description of the security considerations for U-NAPTR
applications is included in [RFC4848]. In addition to considerations
related to U-NAPTR, it is important to recognize that the output of
U-NAPTR discovery is entirely dependent on its input. An attacker
who can control the domain name is therefore able to control the
final URI.
A LIS that is identified by an "http:" URI cannot be authenticated.
Use of HTTP also does not meet requirements in HELD for
confidentiality and integrity. If an "http:" URI is the product of
DHCP or U-NAPTR discovery, this leaves devices vulnerable to several
attacks. Lower layer protections, such as layer 2 traffic separation
might provide some guarantees.
6. IANA Considerations
6.1. Registration of DHCPv4 and DHCPv6 LIS URI Option Codes
The IANA has assigned an option code of (TBD) for the DHCPv4 option
for a LIS URI, as described in Section 2.1 of this document.
The IANA has assigned an option code of (TBD) for the DHCPv6 option
for a LIS URI, as described in Section 2.2 of this document.
6.2. 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 device with its
location information.
Defining publication: RFCXXXX
Related publications: HELD [I-D.ietf-geopriv-http-location-delivery]
Thomson & Winterbottom Expires October 3, 2009 [Page 10]
Internet-Draft LIS Discovery April 2009
Contact information: The authors of this document
Author/Change controller: The IESG
6.3. Registration of a Location Server Application Protocol Tag for
HELD
This section registers a new S-NAPTR/U-NAPTR Application Protocol tag
for the HELD [I-D.ietf-geopriv-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: RFCXXXX
Related Publications: HELD [I-D.ietf-geopriv-http-location-delivery]
Contact Information: The authors of this document
Author/Change Controller: The IESG
7. Acknowledgements
The authors would like to thank Leslie Daigle for her work on
U-NAPTR; Peter Koch for feedback on how not to use DNS for discovery;
Andy Newton for constructive suggestions with regards to document
direction; Hannes Tschofenig and Richard Barnes for input and
reviews; Dean Willis for constructive feedback.
8. References
8.1. Normative References
[RFC2131] Droms, R., "Dynamic Host
Configuration Protocol",
RFC 2131, March 1997.
[RFC2818] Rescorla, E., "HTTP Over
TLS", RFC 2818, May 2000.
[RFC3315] Droms, R., Bound, J.,
Volz, B., Lemon, T.,
Thomson & Winterbottom Expires October 3, 2009 [Page 11]
Internet-Draft LIS Discovery April 2009
Perkins, C., and M.
Carney, "Dynamic Host
Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315,
July 2003.
[RFC3396] Lemon, T. and S. Cheshire,
"Encoding Long Options in
the Dynamic Host
Configuration Protocol
(DHCPv4)", RFC 3396,
November 2002.
[RFC4702] Stapp, M., Volz, B., and
Y. Rekhter, "The Dynamic
Host Configuration
Protocol (DHCP) Client
Fully Qualified Domain
Name (FQDN) Option",
RFC 4702, October 2006.
[RFC4704] Volz, B., "The Dynamic
Host Configuration
Protocol for IPv6 (DHCPv6)
Client Fully Qualified
Domain Name (FQDN)
Option", RFC 4704,
October 2006.
[RFC4848] Daigle, L., "Domain-Based
Application Service
Location Using URIs and
the Dynamic Delegation
Discovery Service (DDDS)",
RFC 4848, April 2007.
[I-D.ietf-geopriv-http-location-delivery] Barnes, M., Winterbottom,
J., Thomson, M., and B.
Stark, "HTTP Enabled
Location Delivery (HELD)",
draft-ietf-geopriv-http-
location-delivery-13 (work
in progress),
February 2009.
[RFC2119] Bradner, S., "Key words
for use in RFCs to
Indicate Requirement
Thomson & Winterbottom Expires October 3, 2009 [Page 12]
Internet-Draft LIS Discovery April 2009
Levels", BCP 14, RFC 2119,
March 1997.
8.2. Informative References
[RFC3118] Droms, R. and W. Arbaugh,
"Authentication for DHCP
Messages", RFC 3118,
June 2001.
[RFC3693] Cuellar, J., Morris, J.,
Mulligan, D., Peterson,
J., and J. Polk, "Geopriv
Requirements", RFC 3693,
February 2004.
[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.
[I-D.ietf-geopriv-l7-lcp-ps] Tschofenig, H. and H.
Schulzrinne, "GEOPRIV
Layer 7 Location
Configuration Protocol;
Problem Statement and
Requirements", draft-ietf-
geopriv-l7-lcp-ps-09 (work
in progress),
February 2009.
[I-D.ietf-geopriv-lbyr-requirements] Marshall, R.,
"Requirements for a
Location-by-Reference
Mechanism", draft-ietf-
geopriv-lbyr-requirements-
07 (work in progress),
February 2009.
Thomson & Winterbottom Expires October 3, 2009 [Page 13]
Internet-Draft LIS Discovery April 2009
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/
Thomson & Winterbottom Expires October 3, 2009 [Page 14]
