GEOPRIV M. Thomson
Internet-Draft J. Winterbottom
Intended status: Standards Track Andrew
Expires: June 13, 2008 December 11, 2007
Discovering the Local Location Information Server (LIS)
draft-ietf-geopriv-lis-discovery-00.txt
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Copyright (C) The IETF Trust (2007).
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Abstract
A method is described for the discovery of a Location Information
Server. The method consists of attempting to use a Dynamic Host
Configuration Protocol (DHCP) option, followed by a URI-enabled NAPTR
(U-NAPTR). DHCP options are defined for both IPv4 and IPv6 DHCP.
This document also defines a U-NAPTR Application Service for a LIS,
with a specific Application Protocol for the HTTP Enabled Location
Delivery (HELD) protocol.
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 . . . . . . . . . . . . . . . . . . . 5
2.1. DHCPv4 Option for a LIS Address . . . . . . . . . . . . . 5
2.2. DHCPv6 Option for a LIS Address . . . . . . . . . . . . . 5
3. U-NAPTR for LIS Discovery . . . . . . . . . . . . . . . . . . 7
4. Determining the Access Network Domain Name . . . . . . . . . . 8
4.1. DHCP Domain Name Option . . . . . . . . . . . . . . . . . 8
4.2. Reverse DNS . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Determining an External IP Address . . . . . . . . . . 9
5. Discovery Order . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Virtual Private Networks (VPNs) . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. Registration of DHCPv4 and DHCPv6 Option Codes . . . . . . 14
7.2. Registration of a Location Server Application Service
Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3. Registration of a Location Server Application Protocol
Tag for HELD . . . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Residential Broadband LIS Discovery Example . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . . . 23
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1. Introduction and Overview
Discovering a Location Information Server (LIS) is an important part
of the location acquisition process. The LIS is an access network
service that needs to be discovered before it can be used. This
document describes a method that a host can use to discover a URI for
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 a URI, which identifies a LIS. A URI permits
identification of a LIS that includes information about protocols and
other supplementary information.
The discovery process requires that the host first attempt LIS
discovery using Dynamic Host Configuration protocol (DHCP). If DHCP
is not available, or the option is not supported by the network, the
host attempts to discover the LIS using the DNS and URI-enabled
Naming Authority Pointer (U-NAPTR). Finally, the host can rely on
proprietary methods for determining the address of the LIS, including
static configuration.
1.1. DHCP Discovery
DHCP ([RFC2131], [RFC3315]) is a commonly used mechanism for
providing bootstrap configuration information allowing a host 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 host 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 host 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.
For DNS methods, alternative discovery techniques SRV records
[RFC2782] or Straightforward NAPTR (S-NAPTR) [RFC3958] provide an
indication of a service for a domain, but these methods cannot be
used; SRV and S-NAPTR only permit the return of a hostname and port,
not a URI. URI-enabled NAPTR (U-NAPTR) [RFC4848], which is based on
S-NAPTR, describes a method of applying the Dynamic Delegation
Discovery Service (DDDS) for 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.
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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.
1.3. 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 "host" to refer to an end host. In
RFC3693 [RFC3693] parlance, the host is the Device, which might also
be the Target.
The terms "access network" refers to the network that a host 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 host an
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. This document registers DHCP
options for a LIS address for both IPv4 and IPv6.
2.1. DHCPv4 Option for a LIS Address
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 | URI ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| URI ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DHCPv4 LIS URI Option
LIS_URI: The IANA assigned option number (TBD).
Length: The length of the URI in octets.
URI: The address of the LIS. This URI SHOULD NOT be more than 253
bytes in length, but MAY be extended by concatenating multiple
option values, as described in [RFC3396]. The URI MUST NOT be
NULL terminated.
2.2. DHCPv6 Option for a LIS Address
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| URI ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DHCPv6 LIS URI Option
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OPTION_LIS_URI: The IANA assigned option number (TBD).
Length: The length of the URI in octets.
URI: The address of the LIS. The URI MUST NOT be NULL terminated.
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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 7.2 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 7.3, 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.com." and "zoneb.example.com." to
"outsource.example.com.".
zonea.example.com.
;; order pref flags
IN NAPTR 100 10 "" "LIS:HELD" ( ; service
"" ; regex
outsource.example.com. ; replacement
)
zoneb.example.com.
;; 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.outsource.example.com/!" ; 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 7.
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4. Determining the Access Network Domain Name
The U-NAPTR discovery method described in Section 3 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 is 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 to determine
additional domain names. Reattempting with different methods is
particularly applicable when NAT is used, as is shown in
Section 4.2.1.
4.1. 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 for IPv6 provides a single domain name suffix that can be used
in the same manner, as a described in
[I-D.ietf-dhc-dhcpv6-opt-dnsdomain].
Alternatively, a fully qualified domain name (FQDN) for the host
might be provided by the server ([RFC4702] for DHCPv4, [RFC4704] for
DHCPv6). This domain name is used as input to the U-NAPTR resolution
and is obtained from the FQDN by removing the first label. If the
host has provided a fully qualified domain name using this option, it
SHOULD NOT be used - the domain known to the host might not be the
same as that of the access network.
Either DHCP method SHOULD be attempted first if DHCP is available.
Note that this method is only attempted if the LIS address option is
not available.
4.2. 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
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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 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.
4.2.1. 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.
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4.2.1.1. 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.
UPnP defines a method for discovering UPnP-enabled hosts in a
network; the host does not need any prior configuration to employ
this method.
4.2.1.2. STUN
A host can use the Session Traversal Utilities for NAT (STUN)
[I-D.ietf-behave-rfc3489bis] to determine a public IP address. The
host uses the "Binding Request" message and the resulting
"XOR-MAPPED-ADDRESS" parameter that is returned in the response.
Using STUN requires cooperation from a publicly accessible STUN
server. The host also requires configuration information that
identifies the STUN server, or a domain name that can be used for
STUN server discovery.
4.2.1.3. 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. HTTP proxies render this method
unusable; in particular, transparent HTTP proxies might affect the
results of this method without the knowledge of the host. Such
services already exist on the public Internet.
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5. Discovery Order
The previous sections described a set of procedures that allow a
device to determine the LIS associated with the local access network.
Some networks maintain a topology analogous to an onion and are
comprised of layers, or segments, separating hosts from the Internet
through intermediate networks. It is best therefore for a host to
discover the LIS logically closest to it, and this can best be done
by applying the discovery techniques in the following order:
1. DHCP LIS URI Option
2. DNS U-NAPTR Discovery, using the domain name from:
1. DHCP Domain Name Option
2. Reverse DNS, using the hosts IP address from:
1. the local network interface and immediate network segment
2. the network segment adjacent to the immediate segment, as
revealed by UPnP
3. the public Internet, as revealed by STUN; or the network
segment where the STUN server resides
(4.) any network segment, as revealed by other method
3. Static configuration
DHCP discovery MUST be attempted before DNS discovery. This allows
the network access provider a direct and explicit means of
configuring a LIS address. DNS discovery is used as a failsafe,
providing a means to discover a LIS where the DHCP infrastructure
does not support the LIS URI option.
Static host configuration MAY be used to provide a LIS address if
both DHCP and DNS 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. User
interaction is NOT RECOMMENDED; the discovery process is not easily
diagnosed by a user.
LIS discovery through DNS requires the host to determine the domain
name of the local access network. Where DHCP is available, the DHCP
domain name option (Section 4.1) can be used to provide this
information. If the domain name cannot be determined from DHCP, or
the resulting domain name fails to yield a valid LIS address then
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reverse DNS is used.
The discovery procedure assumes that the correct LIS is in a network
segment that is closer to the host. Each network segment between the
host and LIS decreases the chance that the LIS is able to correctly
determine a location for the host.
Discovery methods follow an order of precedence. The exception is
for alternative methods of determining the hosts IP address in each
network segment; precedence is given to addresses in the network
segments closer to the host. Therefore, the host MUST attempt to use
the IP address assigned to its local network interface before
attempting to determine its IP address. Precedence is given to
methods, like UPnP that provide an IP address in adjacent network
segments. Methods for determining addresses on the public Internet
are given lower precedence.
To claim compliance with this document, a host MUST support both DHCP
discovery and U-NAPTR discovery. Further, the host MUST support
retrieval of domain name from DHCP and reverse DNS, using a local
interface address, UPnP and STUN. Additional methods for determining
the IP address of the host in different network segments are
optional.
5.1. Virtual Private Networks (VPNs)
Where a host has multiple network interfaces the host MAY
independently discover the LIS corresponding to the access networks
reached by each network interface. Resolving which LIS to contact
for location information is a host application issue.
LIS discovery over a VPN network interface SHOULD NOT be performed
since such a LIS does not have the physical presence generally
necessary to determine location. However, since not all VPN
interfaces can be detected by hosts, a LIS SHOULD NOT respond to
requests originating from a VPN pool. 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.
TBD: Is there an advantage in providing a HELD error code that
indicates that the host has reached the LIS over a VPN?
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6. 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.
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.
An attacker could attempt to compromise the U-NAPTR resolution. A
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 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.
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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7. IANA Considerations
7.1. Registration of DHCPv4 and DHCPv6 Option Codes
The IANA is requested to assign an option code for the DHCPv4 option
for a LIS address, as described in Section 2.1 of this document.
The IANA is requested to assign an option code for the DHCPv6 option
for a LIS address, as described in Section 2.2 of this document.
7.2. 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 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
7.3. 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
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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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8. 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; Andy Newton for constructive suggestions with regards to
document direction; Hannes Tschofenig for input and reviews.
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9. References
9.1. 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.
[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.
[I-D.ietf-behave-rfc3489bis]
Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-13 (work in progress),
November 2007.
[I-D.ietf-dhc-dhcpv6-opt-dnsdomain]
Yan, R., "Domain Suffix Option for DHCPv6",
draft-ietf-dhc-dhcpv6-opt-dnsdomain-04 (work in progress),
June 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
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February 2000.
[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.
[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-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-06 (work in
progress), November 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-03 (work in
progress), November 2007.
[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. Residential Broadband LIS Discovery Example
This example shows how LIS discovery using U-NAPTR and DNS might be
performed in a residential broadband scenario. The assumed network
topology for this network is shown in Figure 4.
__________ __________
+----------------+ ( ) ( )
| NAT | ( ACCESS ) ( )
| (Home Router) |-------( NETWORK )-------( INTERNET )
| 192.0.2.75 | ( my.isp.net ) ( )
+----------------+ ( ) ( )
| ---------- ----------
| :
| :
+----------------+ +-----------------+
| DEVICE | | VOICE SERVICE |
| | | PROVIDER (VSP) |
| 192.168.0.55 | | STUN SERVER |
+----------------+ +-----------------+
Figure 4: Example Network Topology
In this example, the host sits behind a home router that includes a
NAT function. The host is assigned an address from the private
192.168.x.x address range, in this case 192.168.0.55. The outbound
IP address provided to the home router is public and and belongs to
the my.isp.net domain; in this example the home router is assigned
192.0.2.75, which is also given the domain name 192-0-2-
75.my.isp.net.
In this example, several methods are not possible due to the
configuration of the devices and network. The DHCP server on the
home router does not support the LIS URI option, and a domain name is
not configured on the router. In addition to this, the UPnP service
on home router is disabled. Therefore, the host attempts these
methods and is unsuccessful.
The example first covers the unsuccessful attempts to discover the
LIS, followed by a successful application of DNS discovery based on
an address provided by a STUN server. In this situation, the STUN
server is provided by a Voice Service Provider (VSP) that the owner
of the host purchases a voice service from. The address of the STUN
server is configured on the host. The VSP is a separate entity on
the public Internet with no relation to the access network provider.
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The sequence diagram below shows each of the failed attempts to
discover the LIS, followed by the successful discovery using the STUN
server, reverse DNS and the DNS discovery method.
+-------+ +--------+ +-----+ +-----+ +--------+
| HOST | | HOME | | DNS | | LIS | | STUN |
| | | ROUTER | | | | | | SERVER |
+---+---+ +----+---+ +--+--+ +--+--+ +---+----+
| | | | |
1 +--- DHCPINFORM -->| | | |
| | | | |
2 |<---- DHCPACK ----+ | | |
| | | | |
3 +------- DNS: PTR ------------->| | |
| 55.0.168.192.in-addr.arpa. | | |
| | | | |
4 |<------ DNS: no domain --------+ | |
| | | | |
5 +----- UPnP: ----->| | | |
| ssdp:discover | | | |
| | | | |
6 | (no response) | | | |
| | | | |
7 +---------------- STUN: Binding Request --------------->|
| | | | |
8 |<------- STUN: XOR-MAPPED-ADDRESS = (192.0.2.75) ------+
| | | | |
9 +------- DNS: PTR ------------->| | |
| 75.2.0.192.in-addr.arpa. | | |
| | | | |
10 |<--- 192-0-2-205.my.isp.net ---+ | |
| | | | |
11 +--- DNS: NAPTR my.isp.net ---->| | |
| | | | |
12 |<--- https://lis.my.isp.net/ --+ | |
| | | | |
13 +-------- HELD: locationRequest ----------->| |
| | | | |
. . . . .
Figure 5: LIS Discovery Sequence
1. The host makes a DHCP request for the LIS URI option. To reduce
the overall time required in case the LIS URI is unknown, the
host also requests the domain name option.
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2. The DHCP server (in the home router) responds but does not have
either datum. Therefore, the host is unable to use the DHCP
method, or use the domain name to perform U-NAPTR discovery.
3. The host then attempts reverse DNS based on its IP address
(192.168.0.55). The host makes a DNS PTR request for
"55.0.168.192.in-addr.arpa."
4. The DNS server has no knowledge of the private network segment
and so indicates that there is no such domain.
5. The host then must determine its address in a different network
segment. It first attempts to discover this using UPnP. The
host broadcasts a UPnP discovery message, attempting to locate a
UPnP capable device that supports the WANIPConnection profile.
6. There are no UPnP devices on the network and the UPnP discovery
message is unanswered.
7. The host contacts a STUN server, which is configured on the
host. It sends a Binding Request to the STUN server.
8. The STUN server responds to the Binding Request, including the
XOR-MAPPED-ADDRESS parameter. The host decodes this parameter,
which reveals the IP address of the home router: 192.0.2.75.
9. The host requests the domain name assigned to 192.0.2.75. It
makes a DNS PTR request to "75.2.0.192.in-addr.arpa."
10. The DNS server indicates that 192.0.2.75 is assigned the name
"192-0-2-75.my.isp.net."
11. The host removes the host part of the domain name and makes a
DNS NAPTR request for the domain "my.isp.net."
12. The DNS server provides all NAPTR records for the "my.isp.net."
domain. The host finds the record with a service tag of
"LIS:HELD" and retrieves the URI from the regexp field. The URI
of the LIS is found to be "https://lis.my.isp.net/".
13. The host sends a HELD "locationRequest" to the LIS.
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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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Thomson & Winterbottom Expires June 13, 2008 [Page 23]
