Geopriv WG James Polk Internet-Draft Cisco Systems Intended status: Standards Track (PS) Sept 14, 2009 Expires: March 14, 2010 Dynamic Host Configuration Protocol (DHCP) IPv4 and IPv6 Option for a Location Uniform Resource Identifier (URI) draft-ietf-geopriv-dhcp-lbyr-uri-option-06 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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Polk Expires March 14, 2010 [Page 1] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 Legal This documents and the information contained therein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Abstract This document creates a Dynamic Host Configuration Protocol (DHCP) Option for transmitting a client's geolocation Uniform Resource Identifier (URI) of a client, which can be dereferenced in a separate transaction by the client or an entity the client sends this URI to. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Format of the DHCP LuriElement Option . . . . . . . . . . . . 4 2.1. Overall Format of LuriElement Option in IPv4 . . . . . 5 2.2. Overall Format of LuriElement Option in IPv6 . . . . . 5 2.3. LuriElement Format for both IPv4 and IPv6 . . . . . . . 6 3. DHC Option Operation . . . . . . . . . . . . . . . . . . . . 7 3.1 Architectural Assumptions . . . . . . . . . . . . . . . . 8 3.2 Harmful URIs and URLs . . . . . . . . . . . . . . . . . . 9 3.3 Valid Location URI Schemes or Types . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. Normative References . . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 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]. Polk Expires March 14, 2010 [Page 2] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 1. Introduction This document creates a Dynamic Host Configuration Protocol (DHCP) Option for transmitting a client's geolocation Uniform Resource Identifier (URI). The DHCP implementation of the client can then make this location information available to upper layer protocols for their usage. This location URI points a Location Server [ID-LBYR-REQ] which has the geolocation of the client (through means not defined in this document). In this scenario, the DHCP client is a Geopriv Target (i.e., the entity whose geolocation is associated by the location URI). Applications using upper layer protocols within the Target can then choose to deference this location URI and/or transmit the URI to another entity as a means of conveying where the Target is located. Dereferencing a location URI is described in [ID-SIP-LOC]. Conveying a location URI is also described in [ID-SIP-LOC]. Session Initiation Protocol (SIP) is not the only protocol that can dereference a location URI; there is also HTTP-Enabled Location Delivery (HELD) [ID-HELD-DEREF]. Having a location URI has advantages over having a PIDF-LO, especially when a target's location changes. With a location URI, when a target moves, the location URI does not change (at least within the same domain). It can still be given out as the reference to the Target's current location. The opposite is true if the location is conveyed by value in a message. Once the Target moves, the previously given location is no longer valid, and it the Target wants to inform another entity about its location, it has to send the PIDF-LO to the location recipient (again). A Location Server (LS) stores the Target's location as a presence document, called a Presence Information Date Format - Location Object (PIDF-LO), defined in RFC 4119 [RFC4119]. The Location Server is the entity contacted during the act of dereferencing a Target's location. If the dereferencing entity has permission, defined in [ID-GEO-POL], the location of the target will be received. The LS will grant permission to location inquires based on the rules established by a Rule Holder [RFC3693]. The LS has the ability to challenge any request for a target's location, thereby providing additive security properties before location revelation. A problem exists within existing RFCs that provide location to the UA ([RFC3825] and [RFC4776]). These DHCP Options for geolocation values require an update of the entire location information (LI) every time a client moves. Not all clients will move frequently, but some will. Refreshing location values every time a client moves does not scale in certain networks/environments, such as IP-based cellular networks, enterprise networks or service provider networks with mobile endpoints. An 802.11 based access network is one example of this. Constantly updating LCI to endpoints might not scale in mobile (residential or enterprise or municipal) networks in Polk Expires March 14, 2010 [Page 3] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 which the client is moving through more than one network attachment point, perhaps as a person walks or drives with their client down a neighborhood street or apartment complex or a shopping center or through a municipality (that has IP connectivity as a service). If the client were provided a location URI reference to retain and hand out when it wants or needs to convey its location (in a protocol other than DHCP), a location URI that would not change as the client's location changes (within a domain), scaling issues would be significantly reduced to needing an update of the location URI only when a client changes administrative domains - which is much less often. This delivery of an indirect location has the added benefit of not using up valuable or limited bandwidth to the client with the constant updates. It also relieves the client from having to determine when it has moved far enough to consider asking for a refresh of its location. In enterprise networks, if a known location is assigned to each individual Ethernet port in the network, a device that attaches to the network a wall-jack (directly associated with a specific Ethernet Switch port) will be associated with a known location via a unique circuit-ID that's used by the RAIO Option defined in RFC 3046 [RFC3046]. This assumes wall-jacks have an updated wiremap database. RFC 3825 and RFC 4776 would return an LCI value of location. This document specifies how a location URI is returned using DHCP. Behind the DHCP server, in the backend of the network, via the (logical entity of an) LS has a PIDF-LO to be dereferenced with a location URI. If local configuration has the requirement of only assigning unique location URIs to each client, then unique location URIs will be given out, though they will all have the same location at the record, relieving the backend Sighter or LS from individually maintaining each location independently. This Option can be useful in IEEE 802.16e connected endpoints or IP cellular endpoints. The location URI Option can be configured as a client if there is a router, such as a residential home gateway, with the ability to communicate to downstream endpoints as a server. How an LS responds to a dereference request can vary, and a policy established by a Ruleholder [RFC3693] for a Location Target as to what type of challenge(s) is to be used, how strong a challenge is used or how precise the location information is given to a Location Recipient (LR). All of this is outside the scope of this document (since this will not be accomplished using DHCP). This document IANA registers the new IPv4 and IPv6 DHC Options for a location URI. 2. Format of the DHCP LuriElement Option Polk Expires March 14, 2010 [Page 4] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 2.1 Overall Format of LuriElement Option in IPv4 The LuriElement Option format for IPv4 is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code XXX | Length=XX | Ver | Resv | . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . LuriElements... ... . (see Section 2.3 for details) ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. IPv4 Fields for this LuriElement Option Code XXX: The code for this DHCPv4 option (IANA assigned). Length=XX: The length of this option, counted in bytes - not counting the Code and Length bytes. This is a variable length Option, therefore the length value will change based on the length of the URI within the Option. Ver: (4 bits) The version of this Option. This document defines version 1 of this Option. Resv: (4 bits) reserved for future use. LuriElement: see Section 2.3 for details 2.2 Overall Format of LuriElement Option in IPv6 The LuriElement Option format for IPv6 is as follows: 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-code | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver | Resv | . +---------------+ . . LuriElements... . . (see Section 2.3 for details) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. IPv6 fields of this LuriElement Option option-code: The code for this DHCPv6 option (IANA assigned). option-len: The length of this option, counted in bytes - not counting the Code and Length bytes. This is a variable Polk Expires March 14, 2010 [Page 5] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 length Option, therefore the length value will change based on the shape within the Option. Ver: See above (Section 2.1). This will specify version 1. Resv: See above (Section 2.1). LuriElement: see below (Section 2.3 for details). 2.3 LuriElement Format for both IPv4 and IPv6 The LuriElement, in both DHCPv4 and DHCPv6, have the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LuriType | LuriLength | LuriValue ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3. LuriElement Format for both IPv4 and IPv6 LuriType: A one-byte identifier of the data location value. LuriLength: The length, in bytes, of the LuriValue, not including the LuriLength field itself, up to a maximum of 255 bytes. LuriValue: The LuriElement value, as described in detail below. The LuriValue is always in UTP-8. The LuriTypes this document defines (and IANA registers) for a point are: LuriType=1 Location URI - This is the URI pointing at the location record where the PIDF-LO resides which indicates the location of the Location Target. LuriType=2 Valid-For - The time, in seconds, this URI is to be considered Valid for dereferencing. The timer associated with this LuriType starts upon receipt of this Option. The LuriType=2 (Valid-For) indicates how long, in seconds, the client is to consider this LuriType=1 (location URI) valid before performing a refresh of this Option, with a refreshed LuriType=2 (Valid-For) value. A Location URI refresh SHOULD be done the normal DHCP refresh rate, or necessitated by this timer, perhaps with the client only requesting this Option be refreshed. Polk Expires March 14, 2010 [Page 6] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 If the LuriType=2 (Valid-For) timer is received (solicited or unsolicited), it is RECOMMENDED that the client refresh the Location URI when the (Valid-For) counter value has reaches the halfway point. For example, if 16000 was the initial value of the LuriType=2 (Valid-For) value, when 8000 seconds have passed, the Option SHOULD be refreshed. The LuriType=2 (Valid-For) is not mandated for use by this document. However, its presence MUST NOT cause any error in handling the location URI (i.e., if not understood, it MUST be ignored). This Option format is highly extensible. Additional LuriType types created MUST be done so through IANA registration with peer review and an RFC. 3. DHC Option Operation The [RFC3046] RAIO MUST be utilized to provide the appropriate indication to the DHCP Server where this DISCOVER or REQUEST message came from, in order to supply the correct response. That said, this Option SHOULD NOT be in a DISCOVER message, because there is zero knowledge by the client of which Server will answer. Caution SHOULD always be used involving the creation of large Options, meaning that this Option MAY need to be in its own INFORM, OPTION or ACK message. It is RECOMMENDED to avoid building URIs, with any parameters, larger than what a single DHCP response can be. However, if a message is larger than 255 bytes, concatenation is allowed, per RFC 3396 [RFC3396]. Per [RFC2131], subsequent LuriElement Options, which are non-concatenated, overwrite the previous value. Location URIs MUST NOT reveal identity information of the user of the device, since DHCP is a cleartext delivery protocol. For example, location URIs such as sips:34LKJH534663J54@example.com are to be done, providing no identity information, rather than a location URI such as this sips:aliceisat123mainstalanta@example.com In the element of a PIDF-LO document, there is an 'entity' attribute that identities what entity *this* document (including the associated location) refers to. It is up to the PIDF-LO generator, either Location Server or an application in the endpoint, to insert the identity in the 'entity' attribute. This Polk Expires March 14, 2010 [Page 7] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 can be seen in [RFC4119]. The entity= discussion is orthogonal to the identification information contained within the location URI. This Option is used only for communications between a DHCP client and a DHCP server. It can be solicited (requested) by the client, or it can be pushed by the server without a request for it. DHCP Options not understood are ignored. A DHCP server supporting this Option might or might not have the location of a client. If a server does not have a client's location, but needs to provide this Location URI Option to a client (for whatever reason), an LS is contacted. This server-to-LS transaction is not DHCP, therefore it is out of scope of this document. The deference of a target's location URI would not involve DHCP, but an application layer protocol, such as SIP or HTTP, therefore dereferencing is out of scope of this document. In the case of residential gateways being DHCP servers, they usually perform as DHCP clients in a hierarchical fashion up into a service provider's network DHCP server(s), or learn what information to provide via DHCP to residential clients through a protocol, such as PPP. In these cases, the location URI would likely indicate the residence's civic address to all wired or wireless clients within that residence. 3.1 Architectural Assumptions The following assumptions have been made for use of this LuriElement Option for a client to learn its location URI (in no particular order): o Any user control (what [RFC3693] calls a 'Ruleholder') for access to the dereferencing step is assumed to be out of scope of this document. An example authorization policy is in [ID-GEO-POL]. o The authorization vs. possession security model can be found in [ID-LBYR-REQ], describing what is expected in each model of operation. It should be assumed that a location URI attained using DHCP will operate under an authorization model. This means possessing the location URI does not give that entity the right to view the PIDF-LO of the target whose location is indicated in a presence document. The dereference transaction will be, in many environments, challenged by the Location Server. The nature of this challenge is out of scope of this document. o This document does not prevent some environments from operating in a possession model, for example - tightly controlled enterprise networks, but this operation SHOULD NOT be assumed to exist as a matter of local policy. The costs associated with authorization vs. possession models are discussed in Section 3.3.2 of [ID-GEO-RA]. Polk Expires March 14, 2010 [Page 8] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 3.2 Harmful URIs and URLs There are, in fact, some types of URIs that are not good to receive, due to security concerns. For example, any URLs that can have scripts, such as "data:" URLs, and some "HTTP:" URLs that go to web pages that have scripts. Therefore, o URIs received via this Option SHOULD NOT be sent to a general-browser to connect to a web page, because they could have harmful scripts. o This Option SHOULD NOT contain "data:" URLs, because they could contain harmful scripts. Instead of listing all the types of URIs and URLs that can be misused or potentially have harmful affects, Section 3.3 IANA registers acceptable location URI schemes (or types). 3.3 Valid Location URI Schemes or Types This section specifies which URI types are acceptable as a location URI scheme (or type) for this DHCP Option: 1. sip: 2. sips: 3. pres: These location URI types are IANA registered in Section 4.2 of this document. 4. IANA Considerations 4.1 The IPv4 Option number for this Option This document IANA registers this IPv4 Option number XXX (to be assigned by IANA once this document becomes an RFC). 4.2 The IPv6 Option-Code for this Option This document IANA registers this IPv6 Option-Code XXX (to be assigned by IANA once this document becomes an RFC). 4.3 The Version number for this Option This document IANA registers the version number 1 of this Option. Polk Expires March 14, 2010 [Page 9] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 4.4 IANA Considerations for Acceptable Location URI Types IANA is requested to create a new registry for acceptable location URI types. The following 3 URI types are registered by this document: 1. sip: 2. sips: 3. pres: Any additional location URI types to be defined for use via this DHC Option need to be created and IANA registered with peer review and an RFC. 4.5 IANA Considerations for LuriTypes IANA is requested to create a new registry for acceptable location types defined in Section 3.2 of this document, arranged similar to this: +------------+----------------------------------------+-----------+ | LuriType | Name | Reference | +------------+----------------------------------------+-----------+ | 1 | Location URI | RFC XXXX* | | 2 | Valid-For | RFC XXXX* | +------------+----------------------------------------+-----------+ * RFC XXXX is to be replaced with this document's RFC-Editor RFC number. Additions to this list require a standards track RFC. 5. Security Considerations Where critical decisions might be based on the value of this location URI option, DHCP authentication in [RFC3118] SHOULD be used to protect the integrity of the DHCP options. A real concern with RFC 3118 it is that not widely deployed because it requires pre-shared keys to successfully work (i.e., in the client and in the server). Most implementations do not accommodate this. DHCP, initially, is a broadcast request (a client looking for a server), and a unicast response (answer from a server) type of protocol. It is not secure in a practical sense. In today's infrastructures, DHCP will be primarily used over a wired, switched Ethernet network, requiring physical access to within a wire to gain access. Further, within an 802.11 wireless network, the 802.11 specs offer layer 2 security mechanisms to prevent a location URI Polk Expires March 14, 2010 [Page 10] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 from being learned by an unauthorized entity. That said, having the location URI does not mean an unauthorized entity has the location of a client. The location URI still needs to be dereferenced to learn the location of the client. This dereferencing function, which is not done using DHCP, is done by requesting the location record at a Location Server, which can challenge each request it receives based on the policy provided by the Ruleholder. The Ruleholder, as defined in RFC 3693, configures the authentication and authorization policies for the location revelation of a Target. This includes giving out more or less precise location information in a response, therefore it can answer a bad-hat, but not allow it from learning exactly where a client is. Penetrating an LS is supposed to be hard, and hopefully vendors that implement an LS accomplish this goal. As to the concerns about the location URI itself, as stated in the document here (in Section 3), it MUST NOT have any user identifying information in the URI user-part/string itself. The location URI also needs to be hard to guess that it belongs to a specific user. When implementing a DHC server that will serve clients across an uncontrolled network, one should consider the potential security risks therein. 6. Acknowledgements Thanks to James Winterbottom, Marc Linsner, Roger Marshall and Robert Sparks for their useful comments. And to Lisa Dusseault for her concerns about the types of URIs that can cause harm. To Richard Barnes for inspiring a more robust Security Considerations section. To Hannes Tschofenig and Ted Hardie for riding me to comply with their concerns, including a good scrubbing of the nearly final doc. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. Polk Expires March 14, 2010 [Page 11] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001. [RFC3261] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, May 2002. [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [RFC3396] T. Lemon, S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002 [RFC4119] J. Peterson, "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005 7.2. Informative References [ID-SIP-LOC] J. Polk, B. Rosen, "SIP Location Conveyance", "work in progress", July 2009 [ID-HELD-DEREF] J. Winterbottom, H. Tschofenig, H. Schulzrinne, M. Thomson, M. Dawson, "A Location Dereferencing Protocol Using HELD", "work in progress", July 2009 [RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host Configuration Protocol Option for Coordinate-based Location Configuration Information", RFC 3825, July 2004 [RFC4776] H. Schulzrinne, " Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration Information ", RFC 4776, November 2006 [ID-LBYR-REQ] R. Marshall, "Requirements for a Location-by-Reference Mechanism", "work in progress", Feb 2009 [RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk, "Geopriv Requirements", RFC 3693, February 2004 [ID-GEO-POL] H. Schulzrinne, H. Tschofenig, J. Morris, J. Cuellar, J. Polk, "Geolocation Policy: A Document Format for Expressing Privacy Preferences for Location Information", "work in progress", Feb 2009 [ID-GEO-RA] J. Peterson, T. Hardie, J. Morris, " Implications of 'retransmission-allowed' for SIP Location Conveyance", "work in progress", March 2009 Polk Expires March 14, 2010 [Page 12] Internet-Draft Geopriv DHCP Location URI Option Sept 2009 Authors' Address James Polk 3913 Treemont Circle Colleyville, Texas 76034 USA Email: jmpolk@cisco.com Polk Expires March 14, 2010 [Page 13]