Network Working Group B. Carpenter (ed) Internet-Draft IBM Intended status: Informational October 12, 2006 Expires: April 15, 2007 Design issues for protocol extensions draft-carpenter-extension-recs-00 Status of this Memo 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 she becomes aware will be disclosed, in accordance with 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 on April 15, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document discusses issues related to the extensibility of IETF protocols, with a focus on the architectural design considerations involved. Concrete case study examples are included. Carpenter (ed) Expires April 15, 2007 [Page 1] Internet-Draft Design issues for protocol extensions October 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Interoperability . . . . . . . . . . . . . . . . . . . . . 3 1.2. Use of Registered Values . . . . . . . . . . . . . . . . . 4 2. Principles and Guidelines for Robust Extensions . . . . . . . 4 2.1. Achieving Interoperability . . . . . . . . . . . . . . . . 4 2.2. When is an Extension Minor? . . . . . . . . . . . . . . . 5 2.3. Specific Risks with Major Extensions . . . . . . . . . . . 6 3. Considerations for the Base Protocol . . . . . . . . . . . . . 6 4. Running Code Must Run Right . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 8. Change log [RFC Editor: please remove this section] . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 9 A.1. Already documented cases . . . . . . . . . . . . . . . . . 10 A.2. RADIUS Extensions . . . . . . . . . . . . . . . . . . . . 10 A.3. RSVP Extensions . . . . . . . . . . . . . . . . . . . . . 11 A.4. TLS Extensions . . . . . . . . . . . . . . . . . . . . . . 11 A.5. L2TP Extensions . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Carpenter (ed) Expires April 15, 2007 [Page 2] Internet-Draft Design issues for protocol extensions October 2006 1. Introduction For the origins of this draft, please see the Acknowledgements section. Authorship will be updated. When an initial protocol design is extended, there is always a risk of introducing interoperability defects, security defects, etc., along with the additional functionality. This risk is especially high if the extension is performed by a different team than the original designers, who may stray outside implicit design constraints or assumptions. This document aims to describe technical guidelines for protocol extensions that will minimize such risks. Although written in general terms, it is largely aimed at people considering extending an IETF protocol, whether as an IETF activity or elsewhere. This document is informative. Formal procedures for extending IETF protocols are discussed in [I-D.carpenter-protocol-extensions]. IETF protocols typically include mechanisms whereby they can be extended in the future. It is of course a good principle to design extensiblity into protocols; one common definition of a successful protocol is one that becomes widely used in ways not originally anticipated. Well-designed extensibility mechanisms facilitate the evolution of protocols and help make it easier to roll-out incremental changes in an interoperable fashion. At the same time, experience has shown that extensibility features should be limited to what is clearly necessary when the protocol is developed and any later extensions should be done carefully and with a full understanding of the base protocol, existing implementations, and current operational practice. 1.1. Interoperability Designers of extensions must assume the high likelihood of a specific system using the extension having to interoperate with other people's Internet systems; experience shows that software is often used outside the particular special environment it was originally intended for. Thus, an extension will lead to interoperability failures unless the extended protocol correctly supports all mandatory and optional features of the unextended base protocol, and implementations of the base protocol operate correctly in the presence of the extensions. Another aspect is that that mechanisms included to allow the extension of protocols must not be used to create incompatible forks in development instead. Ideally, the protocol mechanisms for extension and versioning should be sufficiently well described that Carpenter (ed) Expires April 15, 2007 [Page 3] Internet-Draft Design issues for protocol extensions October 2006 compatibility can be assessed later. Thus we observe that a key requirement for interoperable extension design is that the base protocol must be well designed for interoperability. This is further discussed below. Finally, it should be noted that protocol variations - specifications that look very similar to the original but are actually different - are of course even more harmful to interoperability than extensions. In general, such variations should be avoided. If they cannot be avoided, as many of the following considerations as possible should be applied, to minimize the damage to interoperability. 1.2. Use of Registered Values An extension is often likely to make use of additional values added to an existing IANA registry (in many cases, simply by adding a new "TLV" (type-length-value) field). To avoid conflicting usage of the same value, it is essential that all new values are properly registered by the applicable procedures, including expert review where applicable (see BCP 26, [RFC2434]). 2. Principles and Guidelines for Robust Extensions This document makes explicit some guiding principles based on the community's experience with extensibility mechanisms. One of the key principles is that protocols should not be made more extensible than clearly necessary at inception, and that proposed extensions should be reviewed by subject-matter experts familiar with the protocol itself and how it is used in currently deployed systems. The formal aspects of this are covered in [I-D.carpenter-protocol-extensions]. 2.1. Achieving Interoperability The importance of extending protocols only in carefully thought-out ways is driven by the overall goal of acheiving good interoperability. Good interoperability stems from a number of factors, including: o having a well-written spec, that makes clear and precise what an implementor needs to implement and what impact each individual operation (e.g., a message sent to a peer) will have when invoked. However, while necessary, a well-written spec is not by itself sufficient to result in good interoperability. o learning lessons from deployment, including understanding what current implementations do and how a proposed extension will interact with deployed systems. Carpenter (ed) Expires April 15, 2007 [Page 4] Internet-Draft Design issues for protocol extensions October 2006 o having an adequate transition story for deploying the new extension. What impact will the proposed extension have on implementations that do not understand it? Is there a way to negotiate or determine the capabilities of a peer? o being architecturally compatible with the base protocol. For example, does the extension make use of features as envisioned by the original protocol designers, or is a new mechanism being invented? o respecting underlying architectural or security assumptions (including those that may not be well-documented, those that may have arison as a result of operational experience, or those that only became understood after the original protocol was published). o will the proposed extension (or its proposed usage) operationally stress existing implementations or the underlying protocol itself if widely deployed? o some protocols have become critical components of the Internet infrastructure. Does the proposed extension (or its proposed usage) have the potential for negatively impacting such infrastructure to the point where explicit steps would be appropriate to firewall existing uses from new ones? o does the proposed extension extend the data model in a major way? Does the extension fundamentally change basic assumptions about data handling within the protocol? For example, do the extensions reverse the flow of data, allow formerly static parameters to be changed on the fly, add new data types or change assumptions relating to the frequency of reads/writes? o can the extended protocol negotiate with an unextended partner to find a common subset of useful functions? 2.2. When is an Extension Minor? The protocol is designed to carry such opaque data and no changes to the underlying base protocol are needed to carry a new type of data. Moreover, no changes are required to existing and currently deployed implementations of the underlying protocol unless they want to make use of the new data type. Using the existing protocol to carry a new type of opaque data will not impact existing implementations or cause operational problems. Examples of minor extensions include the DHC vendor-specific option, the enterprise OID tree for MIB modules, vnd. MIME types, and some classes of (non-critical) certification extensions. Such extensions can safely be made with minimal IETF coordination and are indicated by having an IANA Considerations that allows assignments of code points with minimal overhead (e.g., First Come First Served) [RFC2434]. Carpenter (ed) Expires April 15, 2007 [Page 5] Internet-Draft Design issues for protocol extensions October 2006 2.3. Specific Risks with Major Extensions Major extensions have some or all of the following characteristics: o Change or extend the way in which the basic underlying protocol works, e.g., by changing the semantics of existing PDUs or defining new message types that require implementation changes in existing and deployed implementations of the protocols, even if they do not want to make use of the new functions or data types. o Change basic architectural assumptions about the protocol that have been an assumed part of the protocol and its implementations. o Lead to new uses of the protocol in ways not originally intended or investigated, potentially leading to operational and other difficulties when deployed, even in cases where the "on-the-wire" format has not changed. For example, the overall quantity of traffic the protocol is expected to carry might go up substantially, typical packet sizes may increase compared to existing deployments, simple implementation algorithms that are widely deployed may not scale sufficiently or otherwise be up to the new task at hand, etc. All of these lead directly to a need for extremely close attention to backward compatibility with implementations of the unextended protocol, and to the inadvertent introduction of security or operational exposures. 3. Considerations for the Base Protocol Ideally, the document that defines a base protocol's extension mechanisms will include guidance to future extension writers that help them use extension mechanisms properly. It may also be possible to define classes of extensions that need little or no review, while other classes need wide review. The specific details will necessarily be technology-specific. As mentioned above, any mechanism for extension by versioning must include provisions to ensure interoperability, or at least clean failure modes. Imagine someone creating a protocol and using a "version" field and populating it with a value (1, let's say), but giving no information about what would happen when a new version number appears in it. That's bad protocol design and description; it should be clear what the expectation is and how you test it (e.g. 1.X is compatible but 2 or greater is not expected to be). Protocols commonly include one or more "reserved" fields, clearly intended for future extensions. It is good practice to specify the value to be inserted in such a field by the sender (typically zero) and the action to be taken by the receiver when seeing some other Carpenter (ed) Expires April 15, 2007 [Page 6] Internet-Draft Design issues for protocol extensions October 2006 value (typically no action). If this is not done, future implementation of new values in the reserved field may break old software. Similarly, protocols should carefully specify how receivers should react to unknown TLVs etc., such that failures occur only when that is truly the desired result. Protocols that permit easy extensions with minimal or no review, make it likely that unreviewed extensions will be deployed and used in practice. Consequently, protocols should not be made more extensible than clearly necessary at inception, and the process for defining new extensibility mechanisms must ensure that adequate review of proposed extensions will take place before widespread adoption. In practice, this means First Come First Served [RFC2434] and similar policies should be used very carefully, as they imply minimal or no review. In order to increase the likelihood that minor extensions are truly minor, protocol documents should provide guidelines explaining how they should be done. For example, even though DHCP carries opaque data, defining a new option using completely unstructured data may lead to an option that is (unnecessarily) hard for clients and servers to process. In contrast, using widely-supported encoding formats leads to better interoperability [XXX need ref]. Similarly, SNMP MIB guidelines exist for defining the MIB objects that SNMP carries [RFC4181]. Documents defining IETF protocols should carefully analyze and identify which protocol components can be extended safely with minimal or no community review and which need community review, and then write appropriate IANA considerations sections that ensure the appropriate level of community review prior to the assignment of numbers. For example, the definition of additional data formats that can be carried may require no review, while the addition of new protocol message types might require a Standards Track action [RFC2434]. Finally, the use of version numbers should be carefully specified in order to favour interoperability or clean failure modes. In a number of cases, there is a need for explicit guidance relating to extensions beyond what is encapsulated in the IANA considerations section of the base specification. The usefulness of [RFC4181] would appear to suggest that protocols whose data model is likely to be widely extended (particularly using vendor-specific elements) need a Design Guidelines document specifically addressing extensions. 4. Running Code Must Run Right Experience shows that it is insufficient to correctly specify extensibility and backwards compatibility in an RFC. It is also of importance that every implementation must fully respect the Carpenter (ed) Expires April 15, 2007 [Page 7] Internet-Draft Design issues for protocol extensions October 2006 compatibility mechanisms; if not, non-interoperable pairs of implementations may arise. The TLS case study below shows how important this may be. 5. Security Considerations An extension must not introduce new security risks without also providing an adequate counter-measure, and in particular it must not inadvertently defeat security measures in the unextended protocol. Thus, the security analysis for an extension needs to be as thorough as for the original protocol - effectively it needs to be a regression analysis to check that the extension doesn't inadvertently invalidate the original security model. 6. IANA Considerations This draft requires no action by IANA. 7. Acknowledgements This document is heavily based on an earlier draft under a different title by Scott Bradner and Thomas Narten. That draft stated: The initial version of this document was put together by the IESG in 2002. Since then, it has been reworked in response to feedback from John Loughney, Henrik Levkowetz, Mark Townsley, Randy Bush, Bernard Aboba and others. Valuable comments and suggestions were made by Jari Arkko, Ted Hardie, Loa Andersson... The text on TLS experience was contributed by Yngve Pettersen. This document was produced using the xml2rfc tool [RFC2629]. 8. Change log [RFC Editor: please remove this section] draft-carpenter-extension-recs-00: original version, 2006-10-12. Derived from draft-iesg-vendor-extensions-02.txt dated 2004-06-04 by focussing on architectural issues; the more procedural issues in that draft were moved to another document. 9. References Carpenter (ed) Expires April 15, 2007 [Page 8] Internet-Draft Design issues for protocol extensions October 2006 9.1. Normative References [I-D.carpenter-protocol-extensions] Carpenter, B., "Procedures for protocol extensions and variations", draft-carpenter-protocol-extensions-04 (work in progress), October 2006. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC3427] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J., and B. Rosen, "Change Process for the Session Initiation Protocol (SIP)", BCP 67, RFC 3427, December 2002. [RFC3932] Alvestrand, H., "The IESG and RFC Editor Documents: Procedures", BCP 92, RFC 3932, October 2004. [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB Documents", BCP 111, RFC 4181, September 2005. 9.2. Informative References [I-D.andersson-rtg-gmpls-change] Andersson, L. and A. Farrel, "Change Process for Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Protocols and Procedures", draft-andersson-rtg-gmpls-change-04 (work in progress), October 2006. [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June 1999. [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. Appendix A. Examples [This is mainly raw material from the old draft, not yet edited except for minimal reformatting from nroff to xml2rfc.] This section discusses some specific examples, as it is not always immediately clear what constitutes a major extension. Carpenter (ed) Expires April 15, 2007 [Page 9] Internet-Draft Design issues for protocol extensions October 2006 A.1. Already documented cases There are certain documents that specify a change process for specific IETF protocols: The SIP change process [RFC3427] The (G)MPLS change process [I-D.andersson-rtg-gmpls-change] It is relatively common for MIBs, which are all in effect extensions of the SMI data model, to be defined or extended outside the IETF. BCP 111 [RFC4181] offers detailed guidance for authors and reviewers. A.2. RADIUS Extensions The RADIUS [RFC2865] protocol was designed to be extensible via addition of Attributes to a Data Dictionary on the server, without requiring code changes. However, this extensibility model assumed that Attributes would conform to a limited set of data types and that vendor extensionns would be limited to use by vendors in situations in which interoperability was not required. Recent developments have stretched those assumptions. [RFC2865] Section 6.2 defines a mechanism for Vendor-Specific extensions (Attribute 26), and states that use: "... should be encouraged instead of allocation of global attribute types, for functions specific only to one vendor's implementation of RADIUS, where no interoperability is deemed useful." However, in practice usage of Vendor-Specific Attributes (VSAs) has been considerably broader than this; in particular, VSAs have been used by SDOs to define their extensions to the RADIUS protocol. This has caused a number of problems. Since the VSA mechanism was not designed for interoperability, VSAs do not contain a "mandatory" bit. As a result, RADIUS clients and servers may not know whether it is safe to ignore unknown attributes. For example, [RFC2865] Section 5 states: "A RADIUS server MAY ignore Attributes with an unknown Type. A RADIUS client MAY ignore Attributes with an unknown Type." However, in the case where the VSAs pertain to security (e.g. Filters) it may not be safe to ignore them, since [RFC2865] also states: "A NAS that does not implement a given service MUST NOT implement the RADIUS attributes for that service. For example, a NAS that is unable to offer ARAP service MUST NOT implement the RADIUS attributes Carpenter (ed) Expires April 15, 2007 [Page 10] Internet-Draft Design issues for protocol extensions October 2006 for ARAP. A NAS MUST treat a RADIUS access-accept authorizing an unavailable service as an access-reject instead." Since it was not envisaged that multi-vendor VSA implementations would need to interoperate, [RFC2865] does not define the data model for VSAs, and allows multiple subattributes to be included within a single Attribute of type 26. However, this enables VSAs to be defined which would not be supportable by current implementations if placed within the standard RADIUS attribute space. This has caused problems in standardizing widely deployed VSAs. In addition to extending RADIUS by use of VSAs, SDOs have also defined new values of the Service-Type attribute in order to create new RADIUS commands. Since [RFC2865] defined Service-Type values as being allocated First Come, First Served (FCFS), this essentially enabled new RADIUS commands to be allocated without IETF review. This oversight has since been fixed in [RFC3575]. A.3. RSVP Extensions TBD A.4. TLS Extensions The Secure Sockets Layer (SSL) v2 protocol was developed by Netscape to be used to secure online transactions on the Internet. It was later replaced by SSL v3, also developed by Netscape [[check this, AFAIK IETF was, to some extent involved]]. SSL v3 was then further developed by the IETF as the Transport Layer Security (TLS) protocol. The SSL v3 protocol was designed to be expanded in several ways, which have been inherited by TLS: o New versions o New cipher suites o Compression o Expanded handshake messages o New record types o New handshake messages The protocol also defines how implementations should handle unknown extensions. Of the above extension methods, new versions and expanded handshake messages have caused the most problems, although it is also known that some implementations may have had problems when encountering unknown record types and handshake messages unexpectedly in test situations. Carpenter (ed) Expires April 15, 2007 [Page 11] Internet-Draft Design issues for protocol extensions October 2006 The new version support in SSL/TLS includes a capability to define new versions of the protocol, while allowing newer implementations to communicate with older implementations. As part of this functionality some Key Exchange methods include functionality to prevent version roll-back attacks. The experience with this upgrade functionality in SSL and TLS is decidely mixed. o SSL v2 and SSL v3/TLS are not compatible. It is possible to use SSL v2 protocol messages to intiate a SSL v3/TLS connection, but it is not possible to communicate with a SSL v2 implementation using SSL v3/TLS protocol messages. o There are implementations that refuse to accept handshakes using newer versions of the protocol than they support. o There are other implementations that accepts newer versions, but have implemented the version rollback protection incorrectly. The SSL v2 problem have forced clients to use SSL v3 and TLS clients to continue to use SSL v2 Client Hellos for their initial handshake with almost all servers until 2006, much longer than would have been desirable, in order to interoperate with old servers. The problem with incorrect handling of newer versions has also forced many clients to actually disable the newer protocol versions, either by default, or by automatically disabling the functionality, to be able to connect to such servers. Effectively, this means that the version rollback protection in SSL and TLS is currently non-existent, opening the possibility for attacks should one of the older version prove to be vulnerable to a feasible man-in-the-middle attack. SSL v3 and TLS also permitted expansion of the Client Hello and Server Hello handshake messages. This functionality was fully defined by the introduction of TLS Extensions, which makes it possible to add new functionality to the handshake, such as the name of the server the client is connecting to, request certificate status information, indicate Certificate Authority support, maximum record length, etc. Several of these extensions also introduces new handshake messages. It has turned out that many SSL v3 and TLS implementations that do not support TLS Extensions, did not, as specified in the protocols, ignore the unknown extensions, but instead failed to establish connections. Several of the implementations behaving in this manner are used by high profile Internet sites, such as online banking sites, and this has caused a significant delay in the deployment of clients supporting TLS Extensions, and several of the clients that have Carpenter (ed) Expires April 15, 2007 [Page 12] Internet-Draft Design issues for protocol extensions October 2006 enabled support are using heuristics that allow them to disable the functionality when they detect a problem. Looking forward, the protocol version problem, in particular, can cause future security problem for the TLS protocol. The strength of the Digest algorithms (MD5 and SHA-1) used by SSL and and TLS is weakening, and work is underway to define TLS 1.2 which will permit new methods to be used in the protocol instead of the currently used methods. If MD5 and SHA-1 weaken to the point where it is feasible to mount successful attacks against older SSL and TLS versions, the current error recovery used by clients would become a security vulnerability. The lesson to be drawn from this experience is that it isn't sufficient to design extensibility carefully; it must also be implemented carefully by every implementer, without exception. A.5. L2TP Extensions L2TP [L2TP] carries Attribute-Value Pairs (AVPs), with most AVPs having no semantics to the L2TP protocol itself. However, it should be noted that L2TP message types are identified by a Message Type AVP (Attribute Type 0) with specific AVP values indicating the actual message type. Thus, extensions relating to Message Type AVPs would likely be considered major extensions. L2TP also provides for Vendor-Specific AVPs. Because everything in L2TP is encoded using AVPs, it would be easy to define vendor- specific AVPs that would be considered major extensions. L2TP also provides for a "mandatory" bit in AVPs. Recipients of L2TP messages containing AVPs they do not understand but that have the mandatory bit set, are expected to reject the message and terminate the tunnel or session the message refers to. This leads to interesting interoperability issues, because a sender can include a vendor-specific AVP with the M-bit set, which then cause the recipient to not interoperate with the sender. This sort of behavior is counter to the IETF ideals, as implementations of the IETF standard should interoperate successfully with other implementations and not require the implementation of non-IETF extensions in order to interoperate successfully. Section 4.2 of the L2TP specification [L2TP] includes specific wording on this point, though there was significant debate at the time as to whether such language was by itself sufficient. Fortunately, it does not appear that the above concerns have been a problem in practice. At the time of this writing, the authors are unaware of the existance of vendor-specific AVPs that also set the Carpenter (ed) Expires April 15, 2007 [Page 13] Internet-Draft Design issues for protocol extensions October 2006 M-bit. Author's Address Brian Carpenter (ed) IBM 8 Chemin de Blandonnet 1214 Vernier, Switzerland Email: brc@zurich.ibm.com Carpenter (ed) Expires April 15, 2007 [Page 14] Internet-Draft Design issues for protocol extensions October 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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. 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. Intellectual Property 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Carpenter (ed) Expires April 15, 2007 [Page 15]