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Network Working Group F. Adrangi Internet-Draft V. Lortz Expires:September 2,November 19, 2005 Intel F. Bari Cingular Wireless P. Eronen NokiaMarchMay 18, 2005 Identity selection hints for Extensible Authentication Protocol (EAP)draft-adrangi-eap-network-discovery-12draft-adrangi-eap-network-discovery-13 Status of this MemoThis document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667.By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or shebecomebecomes aware will be disclosed, in accordance withRFC 3668.Section 6 of 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 onSeptember 2,November 19, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The Extensible Authentication Protocol (EAP) is defined inRFC 3748.[RFC3748]. This document defines a mechanism that allows an access network toAdrangi, et al. Expires September 2, 2005 [Page 1] Internet-Draft Identity selection hints for EAP March 2005provide identity selection hints to an EAP peer. The purpose is to assist the EAP peer in selecting an appropriate Network Access Adrangi, et al. Expires November 19, 2005 [Page 1] Internet-Draft Identity selection hints for EAP May 2005 Identifier(NAI)(NAI). This is useful in situations where the peer does not receive a lower layer indication of what network it is connecting to, or when there is no direct roaming relationship between the access network and the peer's home network. Inthisthe latter case, authentication is typically accomplished via a mediating network such as a roaming consortium or broker. The mechanism defined in this document is limited in its scalability. It is intended for access networks that have a small to moderate number of direct roaming partners. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Relationship with other specifications . . . . . . . . . . 3 1.2 Applicability . . . . . . . . . . . . . . . . . . . . . . 31.21.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Implementation requirements . . . . . . . . . . . . . . . . .45 2.1 Packet format . . . . . . . . . . . . . . . . . . . . . .56 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . .67 4. Security considerations . . . . . . . . . . . . . . . . . . .67 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 6. Appendix - Delivery Options . . . . . . . . . . . . . . . . .78 7. References . . . . . . . . . . . . . . . . . . . . . . . . . .1112 7.1 Normative references . . . . . . . . . . . . . . . . . . .1112 7.2 Informative references . . . . . . . . . . . . . . . . . .1112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .1213 Intellectual Property and Copyright Statements . . . . . . . .1314 Adrangi, et al. ExpiresSeptember 2,November 19, 2005 [Page 2] Internet-Draft Identity selection hints for EAPMarchMay 2005 1. Introduction The Extensible Authentication Protocol (EAP) is defined in [RFC3748]. An EAP peer (hereafter, also referred to as the peer)canmay haveseveral setsmultiple credentials. Where the lower layer does not provide an indication ofcredentials, andwhich network it is connecting to, or where its home network may have roaming relationships with several mediatingnetworks. In some cases,networks, the peer may be uncertain which Network Access Identity (NAI) to include in an EAP-Response/Identity.The Extensible Authentication Protocol (EAP) is defined in [RFC3748].This document defines a mechanism that allows the access network to provide an EAP peer with identity selection hints, including information about its roaming relationships. This information is sent to the peer in an EAP-Request/Identity message by appending it after the displayable message and a NUL character.One possible application for thisThis mechanismis to help an EAPmay assist the peerperformin selecting a credential and associated NAI, or in formatting the NAIdecoration[rfc2486bis] to facilitate routing of AAA messages to the home AAA server. If there are severalpossiblemediatingnetworks,networks available, the peer canuse this method toinfluence which one is used. Exactly how the selection is made by the peer depends largely on the peer's local policy and configuration, and is outside the scope of this document. For example, the peer could decide to use one of its other identities, decide to switch to another access network, or attempt to reformat its NAI [rfc2486bis] to assist in proper AAA routing. The exact client behaviour is described by standard bodies using this specification such as 3GPP [TS 24.234]. Section 2 describes the required behavior ofimplementations of this Specification,implementations, including thepacketformat forstructuring and presentingidentityhint informationhints. 1.1 Relationship with other specifications This document specifies behavior of RADIUS proxies that handle EAP messages. This includes the specification of the behavior of proxies in response to anEAP peer. 1.1unknown realm within the User-Name(1) attribute of an Access-Request containing one or EAP-Message attributes. This document, which depends on NAI "decoration" specified in [rfc2486bis], assumes a source routing model for determination of the roaming relationship path, and therefore affects the behavior of RADIUS proxies in roaming situations. 1.2 ApplicabilityThe identityIdentity hints aretypicallyusefulonly when there's too much ambiguity for an access network toin situations where the peer cannot determinehowwhich credentials toroute the AAA packet.use, or where there may be multiple Adrangi, et al. Expires November 19, 2005 [Page 3] Internet-Draft Identity selection hints for EAP May 2005 alternative routes by which an access network can reach a home network. This canhappen, for instance,occur when access networkshave contracts withsupport multiple roaming consortiums but do not have a full list of the home networks reachable through them. In such scenarios,a limited number ofidentity hints (e.g., a list of roaming partners of the access network) can be providedby the mechanismto enable the EAP peer to influencerouting of AAA packets.route selection, using the NAI [RFC2486bis] to specify the desired source route. The immediate application of the proposed mechanism is in 3GPP systems interworking with WLANs [TS 23.234] and [TS 24.234]. Theroaming partner informationnumber of hints that can be providedviaby this mechanism isAdrangi, et al. Expires September 2, 2005 [Page 3] Internet-Draft Identity selection hints for EAP March 2005limited by thelink layer MTU size.EAP MTU. For example, assumingan average of20 octets perroaming partner / home network informationhint andthe link layeran EAP MTUsizeof 1096,the approximate numbera maximum of 50 roaming partnersthatcan beadvertised would be 50. The scalability limitationadvertised. Scaling limitations imposed by thelink layerEAP MTUsizeshould be taken intoconsiderationaccount when deploying this solution. Since this mechanism relies on information provided in the EAP- Request/Identity packet, it is necessary for the peer to select a point of attachment prior to obtaining identity hints. Where there are multiple point of attachment available, the mechanism defined in this specification does not allow the peer to utilize the identity hints in making a decision about which point of attachment to select. In roaming situations, this can require the peer to try multiple points of attachment before it finds a compatible one, increasing handoff latency. This document isalsorelated to the general network discovery and selection problem described in [netsel-problem]. The proposed mechanism described in this document solves only a part of the problem in [netsel-problem]. IEEE 802.11 is also looking into more comprehensive and long-term solutions for network discovery and selection.1.21.3 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]. NAI Network Address Identifier [rfc2486bis]. Decorated NAI An NAIwith additional information for influencing AAA routing. Please refer tospecifying a source route. See [rfc2486bis] section 2.7of [rfc2486bis]forits construction.more information. Adrangi, et al. Expires November 19, 2005 [Page 4] Internet-Draft Identity selection hints for EAP May 2005 NAI Realm Realm portion of an NAI [rfc2486bis]. 2. Implementation requirementsAn EAP peer implementing this specification MUST be able to receive an identity hint in an initial EAP-Request/Identity, or in a subsequent EAP-Request/Identity.The EAP authenticator MAY send an identity hint to the peer in the initial EAP-Request/Identity. If the identity hint is not sent initially (such as when the authenticator does not support this specification), thenifthe EAP peer may select the wrong NAI. If the localEAP-awareAAAproxy/serverproxy does not have a default route configured, then it may find that the User-Name(1) attribute in the request contains a realm for which there is no corresponding route. As noted in [RFC2607], Section 5.1: "Proxies are frequently used to implement policy in roaming situations. Proxies implementingthis specification receivespolicy MAY reply directly to Access-Requests without forwarding the request. When replying directly to anAAA Request packetAccess-Request, the proxy MUST reply either with anunknown realm, it SHOULDAccess-Reject or an Access-Challenge packet. A proxy MUST NOT reply directly with anEAP-Request/Identity containingAccess-Accept." Where no route is found, existing AAA proxies will typically send an Access-Reject. However, where the request contains an EAP-Message attribute, AAA proxies implementing this specification should instead reply with a challenge including an identity hint. For example,in case of RADIUS,ifthe EAP-awarea RADIUSproxy/server [RFC3579]proxy receives an Access-Requestpacketwith an EAP-Message attribute and a User-Name(1) attribute containing an unknownrealm in the UserName(1) attribute, thenrealm, itcanSHOULD reply with an Access-Challenge with an EAP- Message attribute encapsulating an EAP-Request/Identity packet containing an identityhint withinhint, rather than anAccess-Challenge packet.Access-Reject. See "option 3" in the appendix for the message flow diagram. If the peer responds with an EAP-Response/Identity containing anAdrangi, et al. Expires September 2, 2005 [Page 4] Internet-Draft Identity selection hints for EAP March 2005unknown realm after the local AAAproxy/serverproxy sends an identity hint, thenthe local AAA proxy/server MUST respond with an EAP Failure packet. Thea local AAA proxy/server implementing this specification MUST eventually send an Access-Reject containing an EAP-Failure. Prior to doing so it MAYalsosend an Access-Challenge containing an EAP-Notification message providing the reason for the failure priorNotification, in order tothe EAP Failure packet. Whenprovide anIdentity hint is sent by a AAA proxy/server,explanation for theAAA proxy/ server MUST be ablefailure. In order to determineifwhether an identity hint hadpreviouslybeensent by it to the EAP peer. When RADIUS is used,previously sent, the State(24) attribute defined in [RFC2865] can beused to achieve this.used. As noted in [RFC3748], Section 3.1, the minimum EAP MTU size is 1020 octets. EAP does not support fragmentation of EAP-Request/Identity messages, so the maximum length of the identity hint information is limited by the link MTU. Adrangi, et al. Expires November 19, 2005 [Page 5] Internet-Draft Identity selection hints for EAP May 2005 2.1 Packet format The Identity hint information is placed after the displayable string and a NUL character in the EAP-Request/Identity. The following ABNF [RFC2234] defines an NAIRealms attribute for presenting the identity hint information. The attribute's value consists of a set of realm names separated by a semicolon. identity-request-data = [ displayable-string ] "%x00" [ Network-Info ] displayable-string = *CHAR Network-Info = "NAIRealms=" realm-list Network-Info =/ 1*OCTET ",NAIRealms=" realm-list Network-Info =/ "NAIRealms=" realm-list "," 1*OCTET Network-Info =/ 1*OCTET ",NAIRealms=" realm-list "," 1*OCTET realm-list = realm / ( realm-list ";" realm ) The "OCTET" and "CHAR" rules are defined in [RFC2234] and the "realm" rule is defined in [rfc2486bis]. A sample hex dump of an EAP-Request/Identity packet is shown below.Adrangi, et al. Expires September 2, 2005 [Page 5] Internet-Draft Identity selection hints for EAP March 200501 ; Code: Request 00 ; Identifier: 0 00 43 ; Length: 67 octets 01 ; Type: Identity 48 65 6c 6c 6f 21 00 4e ; "Hello!\0NAIRealms=example.com;mnc014. 41 49 52 65 61 6c 6d 73 ; mcc310.3gppnetwork.org" 3d 69 73 70 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d 3b 6d 6e 63 30 31 34 2e 6d 63 63 33 31 30 2e 33 67 70 70 6e 65 74 77 6f 72 6b 2e 6f 72 67 The Network-Info can contain a NAIRealms list in addition to proprietary information. The proprietary information can be placed before or after NAIRealms list. To extract NAIRealms list, an implementation can either find the "NAIRealms=" immediately after the NUL or seek forward to find ",NAIRealms" somewhere in the string. The realms data ends either at the first "," or at the end of the string, whichever comes first. Adrangi, et al. Expires November 19, 2005 [Page 6] Internet-Draft Identity selection hints for EAP May 2005 3. IANA Considerations This document does not define any new namespaces to be managed by IANA, and does not require any assignments in existing namespaces. 4. Security considerations Identity hint information is delivered inside an EAP-Request/Identity before the authentication conversation begins. Therefore, it can be modified by an attacker. The NAIRealms attribute therefore MUST be treated as a hint by the peer. Unauthenticated hints may result in peers inadvertently revealing additional identities, thus compromising privacy. Since the EAP- Response/Identity is sent in the clear, this vulnerability already exists. This vulnerability can be addressed via method-specific identity exchanges. Similarly, in a situation where the peer has multiple identities to choose from, an attacker can use a forged hint to convince the peer to choose an identity bound to a weak EAP method. Requiring the use of strong EAP methods can protect against this. A similar issue already exists with respect to unprotected link layer advertisements such as 802.11 SSIDs. If the identity hint is used to select a mediating network, existing EAP methods may not provide a way for the home AAA server to verifyAdrangi, et al. Expires September 2, 2005 [Page 6] Internet-Draft Identity selection hints for EAP March 2005that the mediating network selected by the peer was actually used. Any information revealed either from the network or client sides before authentication has occurred can be seen as a security risk. For instance, revealing the existence of a network that uses a weak authentication method can make it easier for attackers to discover that such network is accessible. Therefore, the consent of the network being advertised in the hints is required before such hints can be sent. 5. Acknowledgements The authors would specially like to thank Jari Arkko, Bernard Aboba, and Glen Zorn for their help in scoping the problem, for reviewing the draft work in progress and for suggesting improvements to it. The authors would also like to acknowledge and thank Adrian Buckley, Blair Bullock, Jose Puthenkulam, Johanna Wild, Joe Salowey, Marco Spini, Simone Ruffino, Mark Grayson, Mark Watson, and Avi Lior for their support, feedback and guidance during the various stages of this work. Adrangi, et al. Expires November 19, 2005 [Page 7] Internet-Draft Identity selection hints for EAP May 2005 6. Appendix - Delivery Options Although the delivery options are described in the context of IEEE 802.11 access networks, they are also applicable to other access networks that use EAP [RFC3748] for authentication and use the NAI format [rfc2486bis] for identifying users. The options assume that the AAA protocol in use is RADIUS [RFC2865]. However, Diameter [RFC3588] could also be used instead of RADIUS without introducing significant architectural differences. The main difference amongst the options is which entity in the access network creates the EAP-Request/Identity. For example, the role of EAP server may be played by the EAP authenticator (where an initial EAP-Request/Identity is sent with an identity hint) or a RADIUS proxy/server (where the NAI Realm is used for forwarding). The RADIUS proxy/server acts only on the RADIUS UserName(1) attribute and does not have to parse the EAP-Message attribute. Option 1: Initial EAP-Request/Identity from access point In typical IEEE 802.11 wireless LANs, the initial EAP-Request/ Identity is sent by the access point (i.e., EAP authenticator). In the simplest case, the identity hint information is simply included in this request, as shown below.Adrangi, et al. Expires September 2, 2005 [Page 7] Internet-Draft Identity selection hints for EAP March 2005EAP Access Point local RADIUS home RADIUS Peer proxy/server server | 1. EAP | | | | Request/Identity | | | | (NAIRealms) | | | |<------------------| | | | 2. EAP | | | | Response/Identity| | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | | Response/Identity)| | | |------------------->| | | | | 4.Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | | |<-------------------EAP conversation ----------------------->| Adrangi, et al. Expires November 19, 2005 [Page 8] Internet-Draft Identity selection hints for EAP May 2005 Current access points do not support this mechanism, so other options may be preferable. This option can also require configuring the identity hint information in a potentially large number of access points, which may be problematic if the information changes often. Option 2: Initial EAP-Request/Identity from local RADIUS proxy/server This is similar to Option 1, but the initial EAP-Request/Identity is created by the local RADIUS proxy/server instead of the access point. Once a peer associates with an access network AP using IEEE 802.11 procedures, the AP sends an EAP-Start message [RFC3579] within a RADIUS Access-Request. The access network RADIUS server can then send the EAP-Request/Identity containing the identity hint information.Adrangi, et al. Expires September 2, 2005 [Page 8] Internet-Draft Identity selection hints for EAP March 2005EAP Access Point local RADIUS home RADIUS Peer proxy/server server | | 1. Access-Request | | | | (EAP-Start) | | | |------------------->| | | | 2.Access-Challenge | | | | (EAP | | | | Request/Identity | | | | with NAIRealms) | | | |<-------------------| | | 3. EAP | | | | Request/Identity | | | | (NAIRealms) | | | |<------------------| | | | 4. EAP | | | | Response/Identity | | | |------------------>| | | | | 5. Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | | 6. Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | | |<------------------- EAP conversation ---------------------->| This option can work with current access points if they support the EAP-Start message. Adrangi, et al. Expires November 19, 2005 [Page 9] Internet-Draft Identity selection hints for EAP May 2005 Option 3: Subsequent EAP-Request/Identity from local RADIUS proxy/ server In the third option, the access point sends the initial EAP-Request/ Identity without any hint information. The peer then responds with an EAP-Response/Identity, which is forwarded to the local RADIUS proxy/server. If the RADIUS proxy/server cannot route the message based on the identity provided by the peer, it sends a second EAP- Request/Identity containing the identity hint information. Adrangi, et al. ExpiresSeptember 2,November 19, 2005 [Page9]10] Internet-Draft Identity selection hints for EAPMarchMay 2005 EAP Access Point local RADIUS home RADIUS Peer Proxy/Server server | | | | | 1. EAP | | | | Request/Identity | | | | (w/o NAIRealms) | | | |<------------------| | | | 2. EAP | | | | Response/Identity | | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | 4.Access-Challenge | | | | (EAP | | | | Request/Identity | | | | with NAIRealms) | | | |<-------------------| | | 5. EAP | | | | Request/Identity | | | | (NAIRealms) | | | |<------------------| | | | 6. EAP | | | | Response/Identity | | | |------------------>| | | | | 7. Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | | | ======================Failure due to unknown realm============= | | | | | | 7a.Access-Reject | | | | (EAP-Failure) | | | |<-------------------| | | 7b. EAP | | | | Failure | | | |<------------------| | | ================================================================ | | | | | | | 8. Access-Request | | | | (EAP | | | | Response/Identity) | | | |------------------->| | | | | |<-------------------- EAP conversation --------------------->| Adrangi, et al. ExpiresSeptember 2,November 19, 2005 [Page10]11] Internet-Draft Identity selection hints for EAPMarchMay 2005 This option does not require changes to existing NASes, so it may be preferable in many environments. 7. References 7.1 Normative references [rfc2486bis] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network Access Identifier", draft-ietf-radext-rfc2486bis-05 (work in progress), July 2004. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy Implementation in Roaming", RFC 2607, June 1999. 7.2 Informative references [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [netsel-problem] Arkko, J. and B. Aboba, "Network Discovery and Selection Problem", draft-ietf-eap-netsel-problem-02 (work in progress), July 2004. [TS 23.234] "3GPP System to Wireless Local Area Network (WLAN) interworking. Stage 2. (www.3gpp.org)", Release 6 3GPP/ WLAN Stage 2 Specification TS 23.234. [TS 24.234] "3GPP System to Wireless Local Area Network (WLAN) interworking. Stage 3. (www.3gpp.org)", Release 6 3GPP/ WLAN Stage 2 Specification TS 24.234. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Adrangi, et al. Expires November 19, 2005 [Page 12] Internet-Draft Identity selection hints for EAP May 2005 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,Adrangi, et al. Expires September 2, 2005 [Page 11] Internet-Draft Identity selection hints for EAP March 2005"Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. Authors' Addresses Farid Adrangi Intel Corporation 2111 N.E. 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503-712-1791 Email: farid.adrangi@intel.com Victor Lortz Intel Corporation 2111 N.E. 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503-264-3253 Email: victor.lortz@intel.com Farooq Bari Cingular Wireless 7277 164th Avenue N.E. Redmond, WA 98052 USA Phone: +1 425-580-5526 Email: farooq.bari@cingular.com Pasi Eronen Nokia Research Center P.O. Box 407 FIN-00045 Nokia Group Finland Email: pasi.eronen@nokia.com Adrangi, et al. ExpiresSeptember 2,November 19, 2005 [Page12]13] Internet-Draft Identity selection hints for EAPMarchMay 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY 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 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Adrangi, et al. ExpiresSeptember 2,November 19, 2005 [Page13]14] ----