GEOPRIV M. Thomson
Internet-Draft J. Winterbottom
Intended status: Standards Track Andrew
Expires: October 25, 2009 April 23, 2009
Discovering the Local Location Information Server (LIS)
draft-ietf-geopriv-lis-discovery-10
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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
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discovery of a LIS in the access network serving a device. Dynamic
Host Configuration Protocol (DHCP) options for IP versions 4 and 6
are defined that specify a domain name. This domain name is then
used as input to a URI-enabled NAPTR (U-NAPTR) resolution process.
Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3
1.1. Discovery Procedure Overview . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. LIS Discovery Procedure . . . . . . . . . . . . . . . . . . . 4
2.1. Residential Gateways . . . . . . . . . . . . . . . . . . . 5
2.2. Virtual Private Networks (VPNs) . . . . . . . . . . . . . 6
3. Access Network Domain Name DHCP Option . . . . . . . . . . . . 6
3.1. Domain Name Encoding . . . . . . . . . . . . . . . . . . . 7
3.2. Access Network Domain Name DHCPv4 Option . . . . . . . . . 7
3.3. Access Network Domain Name DHCPv6 Option . . . . . . . . . 8
4. U-NAPTR Resolution of a LIS URI . . . . . . . . . . . . . . . 8
4.1. Determining a Domain Name . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6.1. Registration of DHCPv4 and DHCPv6 Option Codes . . . . . . 11
6.2. Registration of a Location Server Application Service
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3. Registration of a Location Server Application Protocol
Tag for HELD . . . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
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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 a process that a device can use to discover a
LIS. This process uses a DHCP option and the DNS. The product of
this discovery process 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. Discovery Procedure Overview
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.
This document defines a DHCP option that produces a domain name that
identifies the local access network in Section 3.
Section 4 describes a method that uses URI-enabled NAPTR (U-NAPTR)
[RFC4848], a Dynamic Delegation Discovery Service (DDDS) profile that
produces a URI for the LIS. The input to this process is provided by
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the DHCP option.
For the LIS discovery DDDS application, an Application Service tag
"LIS" and an Application Protocol tag "HELD" are created and
registered with the IANA. Based on the domain name, this U-NAPTR
application uses the two tags to determine a URI for a LIS that
supports the HELD protocol.
1.2. 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 Procedure
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.
The LIS discovery procedure follows the following process:
1. Acquire the access network domain name DHCP option (Section 3).
This process might be repeated for each of the network interfaces
on the device. Domain names acquired from other sources might
also be added.
2. Apply U-NAPTR resolution (Section 4) to discover a LIS URI.
The U-NAPTR process is applied using each of the domain names as
input.
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3. Verify that the LIS is able to provide location information.
The first URI that results in a successful response from the LIS
is used.
A device MUST support discovery using the access network domain name
DHCP option (Section 3) as input to U-NAPTR resolution (Section 4).
Other domain names MAY be used, as described in Section 4.1.
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 verifies the URI by making 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.
Static configuration of a domain name or a LIS URI MAY be used if all
other discovery methods fail. Note 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 for HELD 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.
2.1. 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
the devices they serve are able to acquire location information. In
many 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 an access network domain name DHCP option
suitable for LIS discovery. In order to provide a useful value for
this option, the residential gateway MUST either:
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o acquire an access network domain name from the access network
provider (possibly using DHCP) and pass the resulting value to
devices; or
o discover a LIS on its external interface, then provide devices
with the domain name that was used to successfully discover the
LIS; or
o explicitly include configuration that refers to a particular LIS.
In either case, the residential gateway provides an access network
domain name DHCP option to devices.
[I-D.ietf-dhc-container-opt] might be used by an access network
provider to convey configuration information to a residential gateway
for use by the devices it serves. Support and use of this option is
RECOMMENDED for both residential gateways and devices. Option values
found within the container MUST be used after values that are
directly in the DHCP response.
2.2. 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.
3. Access Network Domain Name DHCP Option
DHCP provides a direct means for the access network provider to
configure a device. The access network domain name option identifies
a domain name that is suitable for service discovery within the
access network. This domain name is used as input to the U-NAPTR
resolution process for LIS discovery.
The domain name provided in this option is one owned by the access
network operator. This domain name is intended for use in
discovering services within the access network.
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This document registers a DHCP option for the access network domain
name for both IPv4 and IPv6.
3.1. Domain Name Encoding
This section describes the encoding of the domain name used in the
DHCPv4 option defined in Section 3.2 and also used in the DHCPv6
option defined in Section 3.3.
The domain name is encoded according to Section 3.1 of [RFC1035].
Each label is represented as a one-octet length field followed by
that number of octets. Since every domain name ends with the null
label of the root, a domain name is terminated by a length byte of
zero. The high-order two bits of every length octet MUST be zero,
and the remaining six bits of the length field limit the label to 63
octets or less. To simplify implementations, the total length of a
domain name (i.e., label octets and label length octets) is
restricted to 255 octets or less.
3.2. Access Network Domain Name DHCPv4 Option
This section defines a DHCP for IPv4 (DHCPv4) option for the domain
name associated with the access network.
Code Len Access Network Domain Name
+-----+-----+-----+-----+-----+-----+-----+----
| TBD | n | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+----
Figure 1: Access Network Domain Name DHCPv4 Option
The values s1, s2, s3, etc. represent the domain name labels in the
domain name encoding. Note that the length field in the DHCPv4
option represents the length of the entire domain name encoding,
whereas the length fields in the domain name encoding (see Section 3)
is the length of a single domain name label.
Code: OPTION_V4_ACCESS_DOMAIN (TBD). [[IANA/RFC-Editor Note: Please
replace TBD with the assigned DHCPv4 option code, both here and in
Figure 1.]]
Length: The length of the entire access network domain name option
in octets.
Access Network Domain Name: The domain name associated with the
access network, encoded as described in Section 3.1.
A DHCPv4 client MAY request a LoST server domain name in a Parameter
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Request List option, as described in [RFC2131].
This option contains a single domain name and, as such, MUST contain
precisely one root label.
3.3. Access Network Domain Name DHCPv6 Option
This section defines a DHCP for IPv6 (DHCPv6) option for the domain
name associated with the access network. 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_V6_ACCESS_DOMAIN | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Access Network Domain Name .
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DHCPv6 Access Network Domain Name Option
option-code: OPTION_V6_ACCESS_DOMAIN (TBD). [[IANA/RFC-Editor Note:
Please replace TBD with the assigned DHCPv6 option code.]]
option-length: The length of the entire access network domain name
option in octets.
option-value: The access network domain name, encoded as described
in Section 3.1.
A DHCPv6 client MAY request a LoST server domain name in a Options
Request Option (ORO), as described in [RFC3315].
This option contains a single domain name and, as such, MUST contain
precisely one root label.
4. U-NAPTR Resolution of a LIS URI
U-NAPTR [RFC4848] 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 given domain. The
Application Protocol tag "HELD", defined in Section 6.3, is used to
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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"
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]. The domain name that is used in this
authentication is the one extracted from the URI, not the input to
the U-NAPTR resolution process.
4.1. Determining a Domain Name
The U-NAPTR resolution method described requires a domain name as
input. The access network domain name DHCP option (Section 3)
describes one source of this domain name.
If a device knows one or more alternative domain names that might be
used for discovery, it MAY repeat the U-NAPTR process using those
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domain names as input. For instance, static configuration of a
device might be used to provide a device with a domain name.
Alternative domain names MUST NOT be used unless the access network
domain name option is unsuccessful or where external information
indicates that a particular domain name is to be used. For instance,
domain names 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. However, these domain names could be provided without
considering their use for LIS discovery; therefore, many DHCP servers
do not provide a sensible value for these options.
5. Security Considerations
The address of a LIS is usually well-known within an access network;
therefore, interception of messages does not introduce any specific
concerns.
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. These methods MUST
be applied unless similar protections are in place, or in cases -
such as an emergency - where location information of dubious origin
is arguably better than none at all.
An attacker could attempt to compromise LIS discovery at any of three
stages:
1. providing a falsified domain name to be used as input to U-NAPTR
2. altering the DNS records used in U-NAPTR resolution
3. impersonation of the LIS
U-NAPTR is entirely dependent on its inputs. In falsifying a domain
name, an attacker avoids any later protections, bypassing them
entirely. To ensure that the access network domain name DHCP option
can be relied upon, preventing DHCP messages from being modified or
spoofed by attackers is necessary. 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.
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The domain name that is used to authenticated the LIS is the domain
name in the URI that is the result of the U-NAPTR resolution.
Therefore, if an attacker were able to modify or spoof any of the DNS
records used in the DDDS resolution, this URI could be replaced by an
invalid URI. The application of DNS security (DNSSEC) [RFC4033]
provides a means to limit attacks that rely on modification of the
DNS records used in U-NAPTR resolution. Security considerations
specific to U-NAPTR are described in more detail in [RFC4848].
An "https:" URI is authenticated using the method described in
Section 3.1 of [RFC2818]. The domain name used for this
authentication is the domain name in the URI resulting from U-NAPTR
resolution, not the input domain name as in [RFC3958]. Using the
domain name in the URI is more compatible with existing HTTP client
software, which authenticate servers based on the domain name in the
URI.
A LIS that is identified by an "http:" URI cannot be authenticated.
Use of unsecured HTTP also does not meet requirements in HELD for
confidentiality and integrity. If an "http:" URI is the product of
LIS discovery, this leaves devices vulnerable to several attacks.
Lower layer protections, such as layer 2 traffic separation might be
used to provide some guarantees.
6. IANA Considerations
6.1. Registration of DHCPv4 and DHCPv6 Option Codes
The IANA has assigned an option code of (TBD) for the DHCPv4 option
for an access network domain name option, as described in Section 3.2
of this document.
The IANA has assigned an option code of (TBD) for the DHCPv6 option
for an access network domain name option, as described in Section 3.3
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.
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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
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, Richard Barnes, and Joe Salowey for
input and reviews; Dean Willis for constructive feedback.
8. References
8.1. Normative References
[RFC1035] Mockapetris, P., "Domain
names - implementation and
specification", STD 13,
RFC 1035, November 1987.
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[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.,
Perkins, C., and M.
Carney, "Dynamic Host
Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315,
July 2003.
[RFC4033] Arends, R., Austein, R.,
Larson, M., Massey, D.,
and S. Rose, "DNS Security
Introduction and
Requirements", RFC 4033,
March 2005.
[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
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Location Delivery (HELD)",
draft-ietf-geopriv-http-
location-delivery-13 (work
in progress),
February 2009.
[I-D.ietf-dhc-container-opt] Droms, R., "Container
Option for Server
Configuration", draft-
ietf-dhc-container-opt-05
(work in progress),
March 2009.
[RFC2119] Bradner, S., "Key words
for use in RFCs to
Indicate Requirement
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),
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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.
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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