GEOPRIV M. Thomson
Internet-Draft J. Winterbottom
Intended status: Standards Track Andrew
Expires: September 24, 2009 March 23, 2009
Discovering the Local Location Information Server (LIS)
draft-ietf-geopriv-lis-discovery-08
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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
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. Additional DHCP options are
provided that enable authentication of the indicated LIS. 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 . . . . . . . . . . . . . . . . . . . . 4
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. LIS Discovery Using DHCP . . . . . . . . . . . . . . . . . . . 5
2.1. DHCPv4 LIS URI Option . . . . . . . . . . . . . . . . . . 5
2.2. DHCPv6 LIS URI Option . . . . . . . . . . . . . . . . . . 5
2.3. LIS Authentication . . . . . . . . . . . . . . . . . . . . 6
2.3.1. Alternative Certificates . . . . . . . . . . . . . . . 7
2.3.2. Sub-Option Codes . . . . . . . . . . . . . . . . . . . 8
2.3.3. Authentication Algorithm Summary . . . . . . . . . . . 9
2.3.4. DHCPv4 LIS Certificate Fingerprint Option . . . . . . 10
2.3.5. DHCPv6 LIS Certificate Fingerprint Option . . . . . . 11
3. U-NAPTR for LIS Discovery . . . . . . . . . . . . . . . . . . 13
3.1. Determining a Domain Name . . . . . . . . . . . . . . . . 14
4. Overall Discovery Procedure . . . . . . . . . . . . . . . . . 15
4.1. Virtual Private Networks (VPNs) . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6.1. Registration of DHCPv4 and DHCPv6 LIS URI Option Codes . . 18
6.2. Registration of DHCPv4 and DHCPv6 LIS Certificate
Fingerprint Option Codes . . . . . . . . . . . . . . . . . 18
6.3. Creation of Registry for LIS Certificate Fingerprint
Sub-Option Codes . . . . . . . . . . . . . . . . . . . . . 18
6.4. Registration of a Location Server Application Service
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.5. Registration of a Location Server Application Protocol
Tag for HELD . . . . . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . . 21
8.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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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 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.
A second DHCP option is defined that enables the authentication of a
LIS based on a fingerprint of the X.509 certificate [RFC5280] it
presents. Use of this option provides an alternative to the
authentication defined in HELD that relies on the domain name of the
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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
(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.
A domain name is the crucial input to the U-NAPTR resolution process.
Section 3.1 of this document describes several methods for deriving
an appropriate domain name.
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.
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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 DHCP options for a LIS URI for both IPv4 and
IPv6. A second option for both DHCP versions is also registered to
convey a fingerprint of the certificate expected to be used by the
LIS.
2.1. DHCPv4 LIS URI Option
This section defines a DHCP for IPv4 (DHCPv4) option for the address
of a LIS.
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.
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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.
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.
2.3. LIS Authentication
HTTP over TLS [RFC2818] describes how a host is authenticated based
on an expected domain name using public key infrastructure. Relying
exclusively on a domain name for authentication is not appropriate
for a LIS, since the domain name associated with the access network
might not be known. Indeed, it is often inappropriate to attempt to
assign any particular domain name to an access network.
This specification defines an alternative means of establishing an
expected identity for the server that uses a certificate fingerprint.
One or more fingerprints for the server certificate used by the LIS
is included in a second DHCP option. The device uses the fingerprint
information provided by the DHCP server to authenticate the LIS when
it establishes a TLS session. The domain name MUST NOT be used to
authenticate the LIS if a non-empty fingerprint information option is
provided.
This fingerprint option is of particular use for private networks
where authentication based on domain name is either infeasible or not
desirable.
The LIS certificate fingerprint option uses a format of "sub-
options", that allows for the inclusion of multiple fingerprint
values. Each "sub-option" includes a fingerprint generated by a
different cryptographic hash algorithm. The "sub-option" code
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indicates the hash algorithm used for generating the fingerprint.
Each hash algorithm is identified by the assigned code from the IANA
registry "TLS HashAlgorithm Registry" established in [RFC5246].
The use of sub-options provides a means to upgrade hash functions
without affecting backward compatibility. New hash algorithms can be
used without affecting devices that do not yet support the algorithm.
A device MUST use the first fingerprint that it supports. If any
supported fingerprint does not match, the LIS MUST be considered
unauthenticated. If none of the specified hash algorithms are
supported by the device, it MUST consider the LIS to be
unauthenticated.
A fingerprint is generated or checked by applying a cryptographic
hash function to the DER-encoded certificate. Implementations MUST
support the SHA-1 algorithm, using a sub-option code of 2.
A device SHOULD request the LIS certificate fingerprint option at the
same time as the LIS URI option. Without the LIS certificate
fingerprint option a device cannot authenticate the LIS; absence of
this option prevents authentication.
An access network operator is able to nominate authentication based
on a domain name by omitting fingerprints. If an empty option is
provided, the device MUST authenticate the server using the default
method for the applicable URI scheme. For https: URIs, the
authentication described in Section 3.1 of RFC 2818 [RFC2818] MUST be
used if the LIS certificate fingerprint option is empty.
The certificate fingerprint can be ignored if the LIS URI indicates a
protocol that does not support exchange of certificates (such as
http:). Such a LIS cannot be authenticated using this option. The
LIS certificate fingerprint option MUST be empty if no means of
achieving authentication is available.
Note: Whether the device goes on to use the information provided by
an unauthenticated LIS depends on device policy. A device might
choose to continue with discovery using different network
interfaces or methods before falling back to an unauthenticated
LIS.
2.3.1. Alternative Certificates
There is a need to renew certificates as they expire. Around the
time that a certificate is replaced, DHCP configuration identifying
the certificate fingerprint might become invalid. Therefore, to
prevent , or where circumstances require that the LIS function is
served by multiple hosts, there is a need to allow for alternative
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certificates. Authentication based on a fingerprint of a single
certificate fails around the time that a certificate is replaced, or
if there is a need for alternative servers that use different
certificates.
A sub-option code of 0 indicates that the sub-option contains a
certificate serial number. The value of the sub-option is the
integer value in network byte order. All subsequent fingerprint
values until the next occurence of sub-option 0 apply only to
certificates with the given serial number.
This method means that ordering of sub-options is signficant. All
fingerprint values after a certificate serial number apply to
certificates with that serial number only. The DHCP server MUST NOT
include fingerprint values before the first serial number, if a
serial number is used. Serial numbers can be omitted if there is
only one valid certificate.
Note that serial number alone is not a guarantee of uniqueness.
There is small probability that two different certificate issuers
could provide the same serial number with the same fingerprint. If
re-issue of the certificate is not viable, selection of a different
hash function might remove the collision.
2.3.2. Sub-Option Codes
The LIS certificate fingerprint option use sub-option codes that
identify the hash function that is used to generate the fingerprint.
A value of 0 indicates that the sub-option contains a certificate
serial number.
The following list is the current state of the "TLS HashAlgorithm
Registry" established in [RFC5246] and maintained by the IANA. As
additional values are added to the registry, these MAY be used as
option.
0: (serial number) This code indicates that the sub-option contains a
certificate serial number.
1: The sub-option contains a fingerprint generated using the MD5 hash
algorithm.
2: A fingerprint generated using SHA-1.
3: A fingerprint generated using SHA-224.
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4: A fingerprint generated using SHA-256.
5: A fingerprint generated using SHA-384.
6: A fingerprint generated using SHA-512.
The sub-option code of 0 corresponds to the "none" value in the "TLS
HashAlgorithm Registry"; sub-option codes 1 through 6 correspond to
the same value.
Sub-option 0 contains a long integer value in network byte order.
This value is compared numerically. Negative and zero values are
possible (see [RFC5280]), and are expressed in twos complement;
therefore, the most significant bit of the first octet is interpreted
as having a negative value. This value could be up to 20 octets in
size. Note that the sub-option does not contain values encoded using
the distinguished encoding rules (DER).
2.3.3. Authentication Algorithm Summary
Once a device acquires the LIS URI option and the LIS certificate
fingerprint option, it is able to authenticate a LIS. Assuming that
the LIS URI indicates use of TLS, the device establishes a TLS
session and acquires a certificate from the LIS.
The LIS certificate fingerprint option is either empty, or it
contains a set of fingerprints. The set of fingerprints is either
divided into groups based on certificate serial number, or all of the
fingerprints describe the same certificate using different hash
algorithms. This is shown in Figure 3.
Without serial numbers With serial numbers
<hash> : <value> <serial> : <hash> : <value>
<hash> : <value> : <hash> : <value>
... <serial> : <hash> : <value>
: <hash> : <value>
...
Figure 3: LIS Certificate Fingerprint Option Structure
If the LIS certificate fingerprint option is empty, the LIS is
authenticated using the domain name indicated in its offered
certificate, using the mechanism described in Section 3.1 of
[RFC2818].
If the LIS certificate fingerprint option contains data, the LIS is
authenticated based on a fingerprint of its certificate. If multiple
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certificates are indicated using serial numbers, the first sub-option
contains the serial numbers sub-option (code 0).
No serial numbers: The device matches the certificate fingerprint it
calculates from the LIS certificate against any of the fingerprint
sub-options.
Serial numbers: The device matches the certificate fingerprint it
calculates against a fingerprint sub-option that follows a serial
number sub-option containing the certificate serial number.
If no match can be found, the LIS is not authenticated.
2.3.4. DHCPv4 LIS Certificate Fingerprint Option
This section defines a DHCP for IPv4 (DHCPv4) option for LIS
certificate fingerprints.
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_CERT_FP | Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. Fingerprint-Sub-Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DHCPv4 LIS Certificate Fingerprint Option
LIS_CERT_FP: 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 certificate fingerprint option
in octets.
Fingerprint-Sub-Options: A series of one or more sub-options, as
shown in Figure 5.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Option | Length | Fingerprint-Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: DHCPv4 LIS Certificate Fingerprint Sub-Option
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Sub-Option: A code that identifies the hash algorithm used to
generate the fingerprint, or a certificate serial number. The set
of codes are defined in Section 2.3.2.
Length: The length, in octets of the "Fingerprint-Value" sub-option.
Fingerprint-Value: The octet values of the certificate fingerprint
(or a certificate serial number for sub-option 0). An invalid
fingerprint is not equivalent to no fingerprint. If the length of
this field does not match the expected length of the hash function
output, the fingerprint MUST be considered invalid.
DHCPv4 option concatenation [RFC3396] SHOULD be avoided, but is
permitted if long values are required. The sub-options described in
this document do not require any more than 255 octets to express
fully, so concatenation of sub-options is not necessary.
2.3.5. DHCPv6 LIS Certificate Fingerprint Option
This section defines a DHCP for IPv6 (DHCPv6) option for LIS
certificate fingerprints. 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_CERT_FP | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Fingerprint-Sub-Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: DHCPv6 LIS Certificate Fingerprint Option
OPTION_LIS_CERT_FP: 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 certificate fingerprint option in
octets.
Fingerprint-Sub-Options: A series of one or more sub-options, as
shown in Figure 7.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Option | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Fingerprint-Value .
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: DHCPv6 LIS Certificate Fingerprint Sub-Option
The semantics of the DHCPv6 LIS certificate fingerprint sub-options
are identical to the DHCPv4 option except that concatenation is
neither required nor permitted. Length fields are 16 bits in length;
therefore, concatenation is not needed to accomodate values longer
than 255 octets. DHCPv6 prohibits concatenation of option values.
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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 6.4 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 6.5, 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 8: Sample LIS:HELD Service NAPTR Records
Details for the "LIS" Application Service tag and the "HELD"
Application Protocol tag are included in Section 6.
U-NAPTR MUST only be used if the DHCP LIS URI option is not
available.
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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 of the domain
names assigned to it, it MAY attempt to use each domain name as
input. 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.
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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 hosts
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 host MUST support DHCP discovery and MAY support U-NAPTR discovery.
The process described in this document is known to not work in a very
common deployment scenario, namely the fixed wired environment
described in Section 3.1 of [I-D.ietf-geopriv-l7-lcp-ps].
Alternative methods of discovery to address this limitation are
likely.
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.
A host that has multiple network interfaces could potentially be
served by a different access network on each interface, each with a
different LIS. The host SHOULD attempt to discover the LIS
applicable to each network interface, stopping when a LIS is
successfully discovered on any interface.
A host that discovers a LIS URI MUST attempt to verify that the LIS
is able to provide location information. For the HELD protocol, the
host MUST make a location request to the LIS. If the LIS responds to
this request with the "notLocatable" error code (see Section 4.3.2 of
[I-D.ietf-geopriv-http-location-delivery]), the host MUST continue
the discovery process and not make further requests to that LIS on
that 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. Alternative methods for
determining the domain name MAY be used.
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Static configuration MAY be used if all other discovery methods fail.
Note however, that if a host has moved from its customary location,
static configuration might indicate a LIS that is unable to provide a
location.
The product of the LIS discovery process is an http: or https: 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. 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.
Since not all interfaces connected to a VPN can be detected by
devices, 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 interface. This ensures that even if a host
discovers a LIS over the VPN, it does not rely on a LIS that is
unable to provide accurate location information. The exception to
this is where the LIS and host are able to determine a location
without access network support.
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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 host 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.
Section 2.3 describes how a LIS is authenticated by devices, using
either certificate fingerprints or a domain name certificate. This
mechanism relies on the integrity of the information provided by the
DHCP server.
An attacker that is able to modify or spoof messages from a DHCP
server could provide a falsified LIS URI and certificate fingerprint
options that a device would be able to use to successfully
authenticate the LIS. Preventing DHCP 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 this is entirely dependent on its input.
An attacker who can control the domain name is therefore able to
control the final URI.
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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 DHCPv4 and DHCPv6 LIS Certificate Fingerprint
Option Codes
The IANA has assigned an option code of (TBD) for the DHCPv4 option
for LIS certificate fingerprints, as described in Section 2.3.4 of
this document.
The IANA has assigned an option code of (TBD) for the DHCPv6 option
for LIS certificate fingerprints, as described in Section 2.3.5 of
this document.
6.3. Creation of Registry for LIS Certificate Fingerprint Sub-Option
Codes
The IANA has created a registry entitled "DHCP Certificate
Fingerprint Sub-Option Codes" that contains codes identifying the
sub-option codes used for the DHCPv4 and DHCPv6 LIS certificate
fingerprint option. This registry is a sub-registry of "Dynamic Host
Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP)
Parameters".
The registry contains the following fields for each registration:
Sub-Option Code: The numerical value of the sub-option code. Values
from 0 through 255 (decimal) apply to DHCPv4 and DHCPv6. Values
from 256 to 65535 only apply to the DHCPv6 option.
Semantics: The name of the hash algorithm that the sub-option
represents, or a reference to the document defining specific
semantics.
TLS HashAlgorithm Code: For sub-options that refer to hash
algorithms, the code used in the "TLS HashAlgorithm Registry".
The initial values for this registry are included in Section 2.3.2 of
this document.
This registry operates under the "Specification Required" rule
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[RFC5226]. For hash algorithms, the only specification required is
the specification referenced in the "TLS HashAlgorithm Registry".
6.4. 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: RFCXXXX
Related publications: HELD [I-D.ietf-geopriv-http-location-delivery]
Contact information: The authors of this document
Author/Change controller: The IESG
6.5. 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
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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; Pasi Eronen for the
certificate fingerprint concept; Ralph Droms, David W. Hankins,
Damien Neil, and Bernie Volz for DHCP option format.
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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., 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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[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 Levels", BCP 14, RFC 2119, March 1997.
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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.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[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.
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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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