GEOPRIV M. Thomson Internet-Draft J. Winterbottom Intended status: Standards Track Andrew Expires: October 3, 2009 April 1, 2009 Discovering the Local Location Information Server (LIS) draft-ietf-geopriv-lis-discovery-09 Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 3, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract Discovery of the correct Location Information Server (LIS) in the local access network is necessary for devices that wish to acquire location information from the network. A method is described for the Thomson & Winterbottom Expires October 3, 2009 [Page 1] Internet-Draft LIS Discovery April 2009 discovery of a LIS. Dynamic Host Configuration Protocol (DHCP) options for IP versions 4 and 6 are defined that specify a URI for a LIS in the local access network. An alternative method that uses URI-enabled NAPTR (U-NAPTR) is described for use where the DHCP option is unsuccessful. Table of Contents 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 1.1. DHCP Discovery . . . . . . . . . . . . . . . . . . . . . . 3 1.2. U-NAPTR Discovery . . . . . . . . . . . . . . . . . . . . 3 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. LIS Discovery Using DHCP . . . . . . . . . . . . . . . . . . . 4 2.1. DHCPv4 LIS URI Option . . . . . . . . . . . . . . . . . . 4 2.2. DHCPv6 LIS URI Option . . . . . . . . . . . . . . . . . . 5 3. U-NAPTR for LIS Discovery . . . . . . . . . . . . . . . . . . 6 3.1. Determining a Domain Name . . . . . . . . . . . . . . . . 7 4. Overall Discovery Procedure . . . . . . . . . . . . . . . . . 7 4.1. Residential Gateways . . . . . . . . . . . . . . . . . . . 8 4.2. Virtual Private Networks (VPNs) . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6.1. Registration of DHCPv4 and DHCPv6 LIS URI Option Codes . . 10 6.2. Registration of a Location Server Application Service Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Registration of a Location Server Application Protocol Tag for HELD . . . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . . 13 Thomson & Winterbottom Expires October 3, 2009 [Page 2] Internet-Draft LIS Discovery April 2009 1. Introduction and Overview The location of a device is a useful and sometimes necessary part of many services. A Location Information Server (LIS) is responsible for providing that location information to devices with an access network. The LIS uses knowledge of the access network and its physical topology to generate and serve location information to devices. Each access network requires specific knowledge about topology. Therefore, it is important to discover the LIS that has the specific knowledge necessary to locate a device. That is, the LIS that serves the current access network. Automatic discovery is important where there is any chance of movement outside a single access network. Reliance on static configuration can lead to unexpected errors if a device moves between access networks. This document describes DHCP options and DNS records that a device can use to discover a LIS. The product of a discovery process, such as the one described in this document, is the address of the service. In this document, the result is an http: or https: URI, which identifies a LIS. The URI result from the discovery process is suitable for location configuration only; that is, the device MUST dereference the URI using the process described in HELD [I-D.ietf-geopriv-http-location-delivery]. URIs discovered in this way are not "location URIs" [I-D.ietf-geopriv-lbyr-requirements]; dereferencing one of them provides the location of the requester only. Devices MUST NOT embed these URIs in fields in other protocols designed to carry the location of the device. 1.1. DHCP Discovery DHCP ([RFC2131], [RFC3315]) is a commonly used mechanism for providing bootstrap configuration information allowing a device to operate in a specific network environment. The bulk of DHCP information is largely static; consisting of configuration information that does not change over the period that the device is attached to the network. Physical location information might change over this time, however the address of the LIS does not. Thus, DHCP is suitable for configuring a device with the address of a LIS. 1.2. U-NAPTR Discovery Where DHCP is not available, the DNS might be able to provide a URI. This document describes a method that uses URI-enabled NAPTR Thomson & Winterbottom Expires October 3, 2009 [Page 3] Internet-Draft LIS Discovery April 2009 (U-NAPTR) [RFC4848], a Dynamic Delegation Discovery Service (DDDS) profile that supports URI results. For the LIS discovery DDDS application, an Application Service tag "LIS" and an Application Protocol tag "HELD" are created and registered with the IANA. Taking a domain name, this U-NAPTR application uses the two tags to determine the LIS URI. 1.3. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. This document also uses the term "device" to refer to an end host, or client consistent with its use in HELD. In HELD and RFC3693 [RFC3693] parlance, the Device is also the Target. The terms "access network" refers to the network that a device connects to for Internet access. The "access network provider" is the entity that operates the access network. This is consistent with the definition in [I-D.ietf-geopriv-l7-lcp-ps] which combines the Internet Access Provider (IAP) and Internet Service Provider (ISP). The access network provider is responsible for allocating the device a public IP address and for directly or indirectly providing a LIS service. 2. LIS Discovery Using DHCP DHCP allows the access network provider to specify the address of a LIS as part of network configuration. If the device is able to acquire a LIS URI using DHCP then this URI is used directly; the U-NAPTR process is not necessary if this option is provided. This document registers a DHCP option for a LIS URI for both IPv4 and IPv6. An "https:" LIS URI that is a product of U-NAPTR MUST be authenticated using the domain name method described in Section 3.1 of RFC 2818 [RFC2818]. 2.1. DHCPv4 LIS URI Option This section defines a DHCP for IPv4 (DHCPv4) option for the address of a LIS. Thomson & Winterbottom Expires October 3, 2009 [Page 4] Internet-Draft LIS Discovery April 2009 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LIS_URI | Length | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . LIS URI . . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: DHCPv4 LIS URI Option LIS_URI: The IANA assigned option number (TBD). [[IANA/RFC-Editor Note: Please replace TBD with the assigned DHCPv4 option code.]] Length: The length of the entire LIS URI option in octets. LIS URI: The address of the LIS. The URI MUST NOT be terminated by a zero octet. The DHCPv4 version of this URI SHOULD NOT exceed 255 octets in length, but MAY be extended by concatenating multiple option values if necessary, as described in [RFC3396]. 2.2. DHCPv6 LIS URI Option This section defines a DHCP for IPv6 (DHCPv6) option for the address of a LIS. The DHCPv6 option for this parameter is similarly formatted to the DHCPv4 option. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_LIS_URI | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . LIS URI . . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: DHCPv6 LIS URI Option OPTION_LIS_URI: The IANA assigned option number (TBD). [[IANA/ RFC-Editor Note: Please replace TBD with the assigned DHCPv6 option code.]] Length: The length of the LIS URI option in octets. Thomson & Winterbottom Expires October 3, 2009 [Page 5] Internet-Draft LIS Discovery April 2009 The semantics and format of the remainder of the LIS URI option are identical to the DHCPv4 option, except for the larger allowance for URI length granted by the 16 bit length field. DHCPv6 prohibits concatenation of option values. 3. U-NAPTR for LIS Discovery U-NAPTR resolution for a LIS takes a domain name as input and produces a URI that identifies the LIS. This process also requires an Application Service tag and an Application Protocol tag, which differentiate LIS-related NAPTR records from other records for that domain. Section 6.2 defines an Application Service tag of "LIS", which is used to identify the location service for a particular domain. The Application Protocol tag "HELD", defined in Section 6.3, is used to identify a LIS that understands the HELD protocol [I-D.ietf-geopriv-http-location-delivery]. The NAPTR records in the following example demonstrate the use of the Application Service and Protocol tags. Iterative NAPTR resolution is used to delegate responsibility for the LIS service from "zonea.example.net." and "zoneb.example.net." to "outsource.example.com.". zonea.example.net. ;; order pref flags IN NAPTR 100 10 "" "LIS:HELD" ( ; service "" ; regex outsource.example.com. ; replacement ) zoneb.example.net. ;; order pref flags IN NAPTR 100 10 "" "LIS:HELD" ( ; service "" ; regex outsource.example.com. ; replacement ) outsource.example.com. ;; order pref flags IN NAPTR 100 10 "u" "LIS:HELD" ( ; service "!*.!https://lis.example.org:4802/?c=ex!" ; regex . ; replacement ) Figure 3: Sample LIS:HELD Service NAPTR Records Details for the "LIS" Application Service tag and the "HELD" Thomson & Winterbottom Expires October 3, 2009 [Page 6] Internet-Draft LIS Discovery April 2009 Application Protocol tag are included in Section 6. An "https:" LIS URI that is a product of U-NAPTR MUST be authenticated using the domain name method described in Section 3.1 of RFC 2818 [RFC2818]. 3.1. Determining a Domain Name The U-NAPTR discovery method described requires a domain name as input. This document does not specify how that domain name is acquired by a device. If a device knows one or more domain names that might be used for discovery, it is able to attempt to use each domain name as input to the U-NAPTR discovery process. Static configuration of a device is possible if a domain name is known to work for this purpose. A fully qualified domain name (FQDN) for the device might be provided by a DHCP server ([RFC4702] for DHCPv4, [RFC4704] for DHCPv6). DHCPv4 option 15 [RFC2131] could also be used as a source of a domain name suffix for the device. If DHCP and any of these options are available, these values could be used as input the U-NAPTR procedure; however, implementers need to be aware that many DHCP servers do not provide a sensible value for these options. Therefore, this method of discovery SHOULD be given lesser precedence than methods that are based on more explicit assurances. 4. Overall Discovery Procedure The individual components of discovery are combined into a single discovery procedure. Some networks maintain a topology analogous to an onion and are comprised of layers, or segments, separating devices from the Internet through intermediate networks. Applying the individual discovery methods in an order that favours a physically proximate LIS over a remote LIS is preferred. A device MUST support DHCP discovery, where applicable. Devices SHOULD support U-NAPTR discovery unless no input domain names can be determined. The following process ensures a greater likelihood of a LIS in close physical proximity being discovered: 1. Request the DHCP LIS URI Option for each network interface. 2. Use U-NAPTR to discover a LIS URI using all known domain names. 3. Use a statically configured LIS URI. Thomson & Winterbottom Expires October 3, 2009 [Page 7] Internet-Draft LIS Discovery April 2009 A device that has multiple network interfaces could potentially be served by a different access network on each interface, each with a different LIS. The device SHOULD attempt to discover the LIS applicable to each network interface, stopping when a LIS is successfully discovered on any interface. A device that discovers a LIS URI MUST attempt to verify that the LIS is able to provide location information. For the HELD protocol, the device MUST make a location request to the LIS. If - at any time - the LIS responds to a request with the "notLocatable" error code (see Section 4.3.2 of [I-D.ietf-geopriv-http-location-delivery]), the device MUST continue or restart the discovery process. A device SHOULD NOT make further requests to a LIS that provides a "notLocatable" error until its network attachment changes, or it discovers the LIS on an alternative network interface. DHCP discovery MUST be attempted before any other discovery method. This allows the network access provider a direct and explicit means of configuring a LIS address. Alternative methods are only specified as a means to discover a LIS where the DHCP infrastructure does not support the LIS URI option. This document does not mandate any particular source for the domain name that is used as input to U-NAPTR. Static configuration MAY be used if all other discovery methods fail. Note however, that if a device has moved from its customary location, static configuration might indicate a LIS that is unable to provide accurate location information. The product of the LIS discovery process is an "https:" or "http:" URI. Nothing distinguishes this URI from other URIs with the same scheme, aside from the fact that it is the product of this process. Only URIs produced by the discovery process can be used for location configuration using HELD. URIs that are not a product of LIS discovery MUST NOT be used for location configuration. 4.1. Residential Gateways The process described in this document is known to not work in a very common deployment scenario. A fixed wireline scenario is described in more detail in Section 3.1 of [I-D.ietf-geopriv-l7-lcp-ps]. In this fixed wireline environment an intervening residential gateway exists between the device and the access network. If the residential gateway does not provide this option to the devices it serves, those devices are unable to discover a LIS. Support of this specification by residential gateways ensures that Thomson & Winterbottom Expires October 3, 2009 [Page 8] Internet-Draft LIS Discovery April 2009 the devices they serve are able to acquire location information. In most cases the residential gateway configures the devices it serves using DHCP. When DHCP is used, the residential gateway MUST provide the devices it serves with a LIS URI option. In order to provide a sensible value for this option, the residential gateway MUST either: 1. act as a LIS and provide location information to the devices that it serves, or 2. discover a LIS on its external interface and relay this information to devices. In either case, the residential gateway provides a LIS URI option to devices. 4.2. Virtual Private Networks (VPNs) LIS discovery over a VPN network interface SHOULD NOT be performed. A LIS discovered in this way is unlikely to have the information necessary to determine an accurate location. Not all interfaces connected to a VPN can be detected by devices or the software running on them. A LIS MUST NOT provide location information in response to requests that it can identify as originating from a device on the remote end of a VPN tunnel, unless it is able to accurately determine location. The "notLocatable" HELD error code can be used to indicate to a device that discovery has revealed an unsuitable LIS. This ensures that even if a device discovers a LIS over the VPN, it does not rely on a LIS that is unable to provide accurate location information. 5. Security Considerations The primary attack against the methods described in this document is one that would lead to impersonation of a LIS. The LIS is responsible for providing location information and this information is critical to a number of network services; furthermore, a device does not necessarily have a prior relationship with a LIS. Several methods are described here that can limit the probablity of, or provide some protection against, such an attack. The address of a LIS is usually well-known within an access network; therefore, interception of messages does not introduce any specific concerns. An attacker that is able to modify or spoof messages from a DHCP server could provide a falsified LIS URI that a device would be able to use to successfully authenticate the LIS. Preventing DHCP Thomson & Winterbottom Expires October 3, 2009 [Page 9] Internet-Draft LIS Discovery April 2009 messages from being modified or spoofed by attackers is necessary if this information is to be relied upon. Physical or link layer security are commonplace methods that can reduce the possibility of such an attack within an access network; alternatively, DHCP authentication [RFC3118] can provide a degree of protection against modification or spoofing. An attacker could attempt to compromise the U-NAPTR resolution. A more thorough description of the security considerations for U-NAPTR applications is included in [RFC4848]. In addition to considerations related to U-NAPTR, it is important to recognize that the output of U-NAPTR discovery is entirely dependent on its input. An attacker who can control the domain name is therefore able to control the final URI. A LIS that is identified by an "http:" URI cannot be authenticated. Use of HTTP also does not meet requirements in HELD for confidentiality and integrity. If an "http:" URI is the product of DHCP or U-NAPTR discovery, this leaves devices vulnerable to several attacks. Lower layer protections, such as layer 2 traffic separation might provide some guarantees. 6. IANA Considerations 6.1. Registration of DHCPv4 and DHCPv6 LIS URI Option Codes The IANA has assigned an option code of (TBD) for the DHCPv4 option for a LIS URI, as described in Section 2.1 of this document. The IANA has assigned an option code of (TBD) for the DHCPv6 option for a LIS URI, as described in Section 2.2 of this document. 6.2. Registration of a Location Server Application Service Tag This section registers a new S-NAPTR/U-NAPTR Application Service tag for a LIS, as mandated by [RFC3958]. Application Service Tag: LIS Intended usage: Identifies a service that provides a device with its location information. Defining publication: RFCXXXX Related publications: HELD [I-D.ietf-geopriv-http-location-delivery] Thomson & Winterbottom Expires October 3, 2009 [Page 10] Internet-Draft LIS Discovery April 2009 Contact information: The authors of this document Author/Change controller: The IESG 6.3. Registration of a Location Server Application Protocol Tag for HELD This section registers a new S-NAPTR/U-NAPTR Application Protocol tag for the HELD [I-D.ietf-geopriv-http-location-delivery] protocol, as mandated by [RFC3958]. Application Service Tag: HELD Intended Usage: Identifies the HELD protocol. Applicable Service Tag(s): LIS Terminal NAPTR Record Type(s): U Defining Publication: RFCXXXX Related Publications: HELD [I-D.ietf-geopriv-http-location-delivery] Contact Information: The authors of this document Author/Change Controller: The IESG 7. Acknowledgements The authors would like to thank Leslie Daigle for her work on U-NAPTR; Peter Koch for feedback on how not to use DNS for discovery; Andy Newton for constructive suggestions with regards to document direction; Hannes Tschofenig and Richard Barnes for input and reviews; Dean Willis for constructive feedback. 8. References 8.1. Normative References [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Thomson & Winterbottom Expires October 3, 2009 [Page 11] Internet-Draft LIS Discovery April 2009 Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3396] Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002. [RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host Configuration Protocol (DHCP) Client Fully Qualified Domain Name (FQDN) Option", RFC 4702, October 2006. [RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option", RFC 4704, October 2006. [RFC4848] Daigle, L., "Domain-Based Application Service Location Using URIs and the Dynamic Delegation Discovery Service (DDDS)", RFC 4848, April 2007. [I-D.ietf-geopriv-http-location-delivery] Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP Enabled Location Delivery (HELD)", draft-ietf-geopriv-http- location-delivery-13 (work in progress), February 2009. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Thomson & Winterbottom Expires October 3, 2009 [Page 12] Internet-Draft LIS Discovery April 2009 Levels", BCP 14, RFC 2119, March 1997. 8.2. Informative References [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC3958] Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, January 2005. [I-D.ietf-geopriv-l7-lcp-ps] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements", draft-ietf- geopriv-l7-lcp-ps-09 (work in progress), February 2009. [I-D.ietf-geopriv-lbyr-requirements] Marshall, R., "Requirements for a Location-by-Reference Mechanism", draft-ietf- geopriv-lbyr-requirements- 07 (work in progress), February 2009. Thomson & Winterbottom Expires October 3, 2009 [Page 13] Internet-Draft LIS Discovery April 2009 Authors' Addresses Martin Thomson Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU Phone: +61 2 4221 2915 EMail: martin.thomson@andrew.com URI: http://www.andrew.com/ James Winterbottom Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU Phone: +61 2 4221 2938 EMail: james.winterbottom@andrew.com URI: http://www.andrew.com/ Thomson & Winterbottom Expires October 3, 2009 [Page 14]