    Network Working Group                                          A. Barbir
    Request for Comments: 3837                               Nortel Networks
    Category: Informational                                       O. Batuner
                                                      Independent consultant
                                                                 B. Srinivas
                                                                       Nokia
                                                                  M. Hofmann
                                               Bell Labs/Lucent Technologies
                                                                    H. Orman
                                                   Purple Streak Development
                                                                 August 2004

       Security Threats and Risks for Open Pluggable Edge Services (OPES)

    Status of this Memo

       This memo provides information for the Internet community.  It does
       not specify an Internet standard of any kind.  Distribution of this
       memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (2004).

    Abstract

       The document investigates the security threats associated with the
       Open Pluggable Edge Services (OPES) and discusses the effects of
       security threats on the underlying architecture.  The main goal of
       this document is threat discovery and analysis.  The document does
       not specify or recommend any solutions.

    Barbir, et al.               Informational                      [Page 1]

    RFC 3837               Security Threats for OPES             August 2004

    Table of Contents

       1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       2.  OPES Data Flow Threats . . . . . . . . . . . . . . . . . . . .  4
           2.1.  OPES Flow Network Level Threats  . . . . . . . . . . . .  5
                 2.1.1.  Connection-Flow Denial-of-Service (DoS). . . . .  6
                 2.1.2.  Threats to Network Robustness. . . . . . . . . .  6
           2.2.  OPES Flow Application Level Threats. . . . . . . . . . .  6
                 2.2.1.  Unauthorized OPES Entities . . . . . . . . . . .  6
                 2.2.2.  Unauthorized Actions of legitimate OPES Entities  7
                 2.2.3.  Unwanted Content Transformations . . . . . . . .  7
                 2.2.4.  Corrupted Content  . . . . . . . . . . . . . . .  7
                 2.2.5.  Threats to Message Structure Integrity . . . . .  8
                 2.2.6.  Granularity of Protection  . . . . . . . . . . .  8
                 2.2.7.  Risks of Hop-by-Hop Protection . . . . . . . . .  8
                 2.2.8.  Threats to Integrity of Complex Data . . . . . .  8
                 2.2.9.  Denial of Service (DoS)  . . . . . . . . . . . .  9
                 2.2.10. Tracing and Notification Information . . . . . .  9
                 2.2.11. Unauthenticated Communication in OPES Flow . . .  9
       3.  Threats to Out-of-Band Data  . . . . . . . . . . . . . . . . .  9
           3.1.  Threats that Endanger the OPES Data Flow . . . . . . . . 10
           3.2.  Inaccurate Accounting Information  . . . . . . . . . . . 10
           3.3.  OPES Service Request Repudiation . . . . . . . . . . . . 11
           3.4.  Inconsistent Privacy Policy  . . . . . . . . . . . . . . 11
           3.5.  Exposure of Privacy Preferences  . . . . . . . . . . . . 11
           3.6.  Exposure of Security Settings  . . . . . . . . . . . . . 11
           3.7.  Improper Enforcement of Privacy and Security Policy  . . 11
           3.8.  DoS Attacks  . . . . . . . . . . . . . . . . . . . . . . 12
       4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
       5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
           5.1.  Normative References . . . . . . . . . . . . . . . . . . 12
           5.2.  Informative References . . . . . . . . . . . . . . . . . 12
       6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
       7.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
       8.  Full Copyright Statement . . . . . . . . . . . . . . . . . . . 14

    1.  Introduction

       The Open Pluggable Edge Services (OPES) [1] architecture enables
       cooperative application services (OPES services) between a data
       provider, a data consumer, and zero or more OPES processors.  The
       application services under consideration analyze and possibly
       transform application-level messages exchanged between the data
       provider and the data consumer.  The OPES processor can distribute
       the responsibility of service execution by communicating and
       collaborating with one or more remote callout servers.  The details
       of the OPES architecture can be found in [1].

    Barbir, et al.               Informational                      [Page 2]

    RFC 3837               Security Threats for OPES             August 2004

       Security threats with respect to OPES can be viewed from different
       angles.  There are security risks that affect content consumer
       applications, and those that affect the data provider applications.
       These threats affect the quality and integrity of data that the
       applications either produce or consume.  On the other hand, the
       security risks can also be categorized into trust within the system
       (i.e., OPES service providers) and protection of the system from
       threats imposed by outsiders such as hackers and attackers.  Insiders
       are those parties that are part of the OPES system.  Outsiders are
       those entities that are not participating in the OPES system.

       It must be noted that not everyone in an OPES delivery path is
       equally trusted.  Each OPES administrative trust domain must protect
       itself from all outsiders.  Furthermore, it may have a limited trust
       relationship with another OPES administrative domain for certain
       purposes.

       OPES service providers must use authentication as the basis for
       building trust relationships between administrative domains.
       Insiders can intentionally or unintentionally inflict harm and damage
       on the data consumer and data provider applications.  This can be
       through bad system configuration, execution of bad software or, if
       their networks are compromised, by inside or outside hackers.

       Depending on the deployment scenario, the trust within the OPES
       system is based on a set of transitive trust relationships between
       the data provider application, the OPES entities, and the data
       consumer application.  Threats to OPES entities can be at the OPES
       flow level and/or at the network level.

       In considering threats to the OPES system, the document will follow a
       threat analysis model that identifies the threats from the
       perspective of how they will affect the data consumer and the data
       provider applications.

       The main goal of this document is threat discovery and analysis.  The
       document does not specify or recommend any solutions.

       It is important to mention that the OPES architecture has many
       similarities with other so called overlay networks, specifically web
       caches and content delivery networks (CDN) (see [2], [4]).  This
       document focuses on threats that are introduced by the existence of
       the OPES processor and callout servers.  Security threats specific to
       content services that do not use the OPES architecture are considered
       out-of-scope of this document.  However, this document can be used as
       input when considering security implications for web caches and CDNs.

    Barbir, et al.               Informational                      [Page 3]

    RFC 3837               Security Threats for OPES             August 2004

       The document is organized as follows: Section 2 discusses threats to
       OPES data flow on the network and application level, section 3
       discusses threats to other parts of the system, and section 4
       discusses security considerations.

    2. OPES Data Flow Threats

       Threats to the OPES data flow can affect the data consumer and data
       provider applications.  At the OPES flow level, threats can occur at
       Policy Enforcement Points, and Policy Decision Points [3], and along
       the OPES flow path where network elements are used to process the
       data.

       A serious problem is posed by the very fact that the OPES
       architecture is based on widely adopted protocols (HTTP is used as an
       example).  The architecture document specifically requires that "the
       presence of an OPES processor in the data request/response flow SHALL
       NOT interfere with the operations of non-OPES aware clients and
       servers".  This greatly facilitates OPES' deployment, but on the
       other hand a vast majority of clients (browsers) will not be able to
       exploit any safeguards added as base protocol extensions.

       For the usual data consumer, who might have questions such as (Where
       does this content come from? Can I get it another way? What is the
       difference? Is it legitimate?).  Even if there are facilities and
       technical expertise present to pursue these questions, such thorough
       examination of each result is prohibitively expensive in terms of
       time and effort.  OPES-aware content providers may try to protect
       themselves by adding verification scripts and special page
       structures.  OPES-aware end users may use special tools.  In all
       other cases (non-OPES aware clients and servers) protection will rely
       on monitoring services and investigation of occasionally discovered
       anomalies.

       An OPES system poses a special danger as a possible base for
       classical man-in-the-middle attacks.  One of the reasons why such
       attacks are relatively rare is the difficulty in finding an
       appropriate base: a combination of a traffic interception point
       controlling a large flow of data and an application codebase running
       on a high-performance hardware with sufficient performance to analyze
       and possibly modify all passing data.  An OPES processor meets this
       definition.  This calls for special attention to protection measures
       at all levels of the system.

    Barbir, et al.               Informational                      [Page 4]

    RFC 3837               Security Threats for OPES             August 2004

       Any compromise of an OPES processor or remote callout server can have
       a ripple effect on the integrity of the affected OPES services across
       all service providers that use the service.  To mitigate this threat,
       appropriate security procedures and tools (e.g., a firewall) should
       be applied.

       Specific threats can exist at the network level and at the OPES data
       flow level.

    2.1.  OPES Flow Network Level Threats

       OPES processor and callout servers are susceptible to network level
       attacks from outsiders or from the networks of other OPES service
       providers (i.e., if the network of a contracted OPES service is
       compromised).

       The OPES architecture is based on common application protocols that
       do not provide strong guarantees of privacy, authentication, or
       integrity.  The IAB considerations [4] require that the IP address of
       an OPES processor be accessible to data consumer applications at the
       IP addressing level.  This requirement limits the ability of service
       providers to position the OPES processor behind firewalls and may
       expose the OPES processor and remote callout servers to network level
       attacks.  For example, the use of TCP/IP as a network level protocol
       makes OPES processors subject to many known attacks, such as IP
       spoofing and session stealing.

       The OPES system is also susceptible to a number of security threats
       that are commonly associated with network infrastructure.  These
       threats include snooping, denial of service, sabotage, vandalism,
       industrial espionage, and theft of service.

       There are best practice solutions to mitigate network level threats.
       It is recommended that the security of the OPES entities at the
       network level be enhanced using known techniques and methods that
       minimize the risks of IP spoofing, snooping, denial of service, and
       session stealing.

       At the OPES Flow level, connection-level security between the OPES
       processor and callout servers is an important consideration.  For
       example, it is possible to spoof the OPES processor or the remote
       callout server.  There are threats to data confidentiality between
       the OPES processor and the remote callout server in an OPES flow.

       The next subsections cover possible DoS attacks on an OPES processor,
       remote callout server or data consumer application, and network
       robustness.

    Barbir, et al.               Informational                      [Page 5]

    RFC 3837               Security Threats for OPES             August 2004

    2.1.1.  Connection-Flow Denial-of-Service (DoS)

       OPES processors, callout servers, and data consumer applications can
       be vulnerable to DoS attacks.  DoS attacks can be of various types.
       One example of a DoS attack is the overloading of OPES processors or
       callout servers by spurious service requests issued by a malicious
       node, which denies the legal data traffic the necessary resources to
       render service.  The resources include CPU cycles, memory, network
       interfaces, etc.  A Denial-of-Service attack can be selective,
       generic, or random in terms of which communication streams are
       affected.

       Distributed DoS is also possible when an attacker successfully
       directs multiple nodes over the network to initiate spurious service
       requests to an OPES processor (or callout server) simultaneously.

    2.1.2.  Threats to Network Robustness

       If OPES implementation violates end-to-end addressing principles, it
       could endanger the Internet infrastructure by complicating routing
       and connection management.  If it does not use flow-control
       principles for managing connections, or if it interferes with end-
       to-end flow control of connections that it did not originate, then it
       could cause Internet congestion.

       An implementation that violates the IAB requirement of explicit IP
       level addressing (for example, by adding OPES functional capabilities
       to an interception proxy) may defeat some of the protective
       mechanisms and safeguards built into the OPES architecture.

    2.2.  OPES Flow Application Level Threats

       At the content level, threats to the OPES system can come from
       outsiders or insiders.  The threat from outsiders is frequently
       intentional.  Threats from insiders can be intentional or accidental.
       Accidents may result from programming or configuration errors that
       result in bad system behavior.

       Application level problems and threats to the OPES systems are
       discussed below:

    2.2.1.  Unauthorized OPES Entities

       Although one party authorization is mandated by the OPES
       architecture, such authorization occurs out-of-band.  Discovering the
       presence of an OPES entity and verifying authorization requires
       special actions and may present a problem.

    Barbir, et al.               Informational                      [Page 6]

    RFC 3837               Security Threats for OPES             August 2004

       Adding notification and authorization information to the data
       messages (by using base protocol extensions) may help, especially if
       the data consumer's software is aware of such extensions.

    2.2.2.  Unauthorized Actions of Legitimate OPES Entities

       According to the OPES architecture, the authorization is not tightly
       coupled with specific rules and procedures triggered by the rules.
       Even if a requirement to approve each particular rule and procedure
       was set, it looks at least impractical, if not impossible, to request
       such permission from the end user.  Authorization granularity extends
       to transformation classes, but not to individual rules or
       transformations.  The actual rules and triggered procedures may
       (maliciously or due to a programming error) perform actions that they
       are not authorized for.

    2.2.3.  Unwanted Content Transformations

       An authorized OPES service may perform actions that do not adhere to
       the expectations of the party that gave the authorization for the
       service.  Examples may include ad flooding by a local ad insertion
       service or use of inappropriate policy by a content filtering
       service.

       On the other hand, an OPES entity acting on behalf of one party may
       perform transformations that another party deems inappropriate.
       Examples may include replacing ads initially inserted by the content
       provider or applying filtering transformations that change the
       meaning of the text.

    2.2.4.  Corrupted Content

       The OPES system may deliver outdated or otherwise distorted
       information due to programming problems or as a result of malicious
       attacks.  For example, a compromised server, instead of performing an
       OPES service, may inject bogus content.  Such an action may be an act
       of cyber-vandalism (including virus injection) or intentional
       distribution of misleading information (such as manipulations with
       financial data).

       A compromised OPES server or malicious entity in the data flow may
       introduce changes specifically intended to cause improper actions in
       the OPES server or callout server.  These changes may be in the
       message body, headers, or both.  This type of threat is discussed in
       more detail below.

    Barbir, et al.               Informational                      [Page 7]

    RFC 3837               Security Threats for OPES             August 2004

    2.2.5.  Threats to Message Structure Integrity

       An OPES server may add, remove, or delete certain headers in a
       request and/or response message (for example, to implement additional
       privacy protection or assist in content filtering).  Such changes may
       violate end-to-end integrity requirements or defeat services that use
       information provided in such headers (for example, some local
       filtering services or reference-based services).

    2.2.6.  Granularity of Protection

       OPES services have implicit permission to modify content.  However,
       the permissions generally apply only to portions of the content, for
       example, URL's between particular HTML tags, text in headlines, or
       URL's matching particular patterns.  In order to express such
       policies, one must be able to refer to portions of messages and to
       detect modifications to message parts.

       Because there is currently very little support for policies that are
       expressed in terms of message parts, it will be difficult to
       attribute any particular modification to a particular OPES processor,
       or to automatically detect policy violations.

       A fine-grained policy language should be devised, and it could be
       enforced using digital signatures.  This would avoid the problems
       inherent in hop-by-hop data integrity measures (see next section).

    2.2.7.  Risks of Hop-by-Hop Protection

       Generally, OPES services cannot be applied to data protected with
       end-to-end encryption methods because the decryption key cannot be
       shared with OPES processors without compromising the intended
       confidentiality of the data.  This means that if the endpoint
       policies permit OPES services, the data must either be transmitted
       without confidentiality protections or an alternative model to end-
       to-end encryption must be developed, one in which the confidentiality
       is guaranteed hop-by-hop.  Extending the end-to-end encryption model
       is out of scope of this work.

       OPES services that modify data are incompatible with end-to-end
       integrity protection methods, and this work will not attempt to
       define hop-by-hop integrity protection methods.

    2.2.8.  Threats to Integrity of Complex Data

       The OPES system may violate data integrity by applying inconsistent
       transformations to interrelated data objects or references within the
       data object.  Problems may range from a broken reference structure

    Barbir, et al.               Informational                      [Page 8]

    RFC 3837               Security Threats for OPES             August 2004

       (modified/missing targets, references to wrong locations or missing
       documents) to deliberate replacement/deletion/insertion of links that
       violate intentions of the content provider.

    2.2.9.  Denial of Service (DoS)

       The data consumer application may not be able to access data if the
       OPES system fails for any reason.

       A malicious or malfunctioning node may be able to block all traffic.
       The data traffic destined for the OPES processor (or callout server)
       may not be able to use the services of the OPES device.  The DoS may
       be achieved by preventing the data traffic from reaching the
       processor or the callout server.

    2.2.10.  Tracing and Notification Information

       Inadequate or vulnerable implementation of the tracing and
       notification mechanisms may defeat safeguards built into the OPES
       architecture.

       Tracing and notification facilities may become a target of malicious
       attack.  Such an attack may create problems in discovering and
       stopping other attacks.

       The absence of a standard for tracing and notification information
       may present an additional problem.  This information is produced and
       consumed by the independent entities (OPES servers/user agents/
       content provider facilities).  This calls for a set of standards
       related to each base protocol in use.

    2.2.11.  Unauthenticated Communication in OPES Flow

       There are risks and threats that could arise from unauthenticated
       communication between the OPES server and callout servers.  Lack of
       use of strong authentication between OPES processors and callout
       servers may open security holes whereby DoS and other types of
       attacks (see sections [2 and 3]) can be performed.

    3.  Threats to Out-of-Band Data

       The OPES architecture separates a data flow from a control
       information flow (loading rulesets, trust establishment, tracing,
       policy propagation, etc.).  There are certain requirements set for
       the latter, but no specific mechanism is prescribed.  This gives more
       flexibility for implementations, but creates more burden for
       implementers and potential customers to ensure that each specific

    Barbir, et al.               Informational                      [Page 9]

    RFC 3837               Security Threats for OPES             August 2004

       implementation meets all requirements for data security, entity
       authentication, and action authorization.

       In addition to performing correct actions on the OPES data flow, any
       OPES implementation has to provide an adequate mechanism to satisfy
       requirements for out-of-band data and signaling information
       integrity.

       Whatever the specific mechanism may be, it inevitably becomes subject
       to multiple security threats and possible attacks.  The way the
       threats and attacks may be realized depends on implementation
       specifics but the resulting harm generally falls into two categories:
       threats to OPES data flow and threats to data integrity.

       The specific threats are:

    3.1.  Threats that Endanger the OPES Data Flow

       Any weakness in the implementation of a security, authentication, or
       authorization mechanism may open the door to the attacks described in
       section 2.

       An OPES system implementation should address all these threats and
       prove its robustness and ability to withstand malicious attacks or
       networking and programming problems.

    3.2.  Inaccurate Accounting Information

       Collecting and reporting accurate accounting data may be vital when
       OPES servers are used to extend a business model of a content
       provider, service provider, or as a basis for third party service.
       The ability to collect and process accounting data is an important
       part of OPES' system functionality.  This functionality may be
       challenged by distortion or destruction of base accounting data
       (usually logs), processed accounting data, accounting parameters, and
       reporting configuration.

       As a result a data consumer may be inappropriately charged for
       viewing content that was not successfully delivered, or a content
       provider or independent OPES services provider may not be compensated
       for the services performed.

       The OPES system may use accounting information to distribute
       resources between different consumers or limit resource usage by a
       specific consumer.  In this case an attack on the accounting system
       (by distortion of data or issuing false configuration commands) may
       result in incorrect resource management and DoS by artificial
       resource starvation.

    Barbir, et al.               Informational                     [Page 10]

    RFC 3837               Security Threats for OPES             August 2004

    3.3.  OPES Service Request Repudiation

       An entity (producer or consumer) might make an authorized request and
       later claim that it did not make that request.  As a result, an OPES
       entity may be held liable for unauthorized changes to the data flow,
       or will be unable to receive compensation for a service.

       There should be a clear request that this service is required and
       there should be a clear course of action on behalf of all parties.
       This action should have a request, an action, a non-repudiable means
       of verifying the request, and a means of specifying the effect of the
       action.

    3.4.  Inconsistent Privacy Policy

       The OPES entities may have privacy policies that are not consistent
       with the data consumer application or content provider application.

       Privacy related problems may be further complicated if OPES entities,
       content providers, and end users belong to different jurisdictions
       with different requirements and different levels of legal protection.
       As a result, the end user may not be aware that he or she does not
       have the expected legal protection.  The content provider may be
       exposed to legal risks due to a  failure to comply with regulations
       of which he is not even aware.

    3.5.  Exposure of Privacy Preferences

       The OPES system may inadvertently or maliciously expose end user
       privacy settings and requirements.

    3.6.  Exposure of Security Settings

       There are risks that the OPES system may expose end user security
       settings when handling the request and responses.  The user data must
       be handled as sensitive system information and protected against
       accidental and deliberate disclosure.

    3.7.  Improper Enforcement of Privacy and Security Policy

       OPES entities are part of the content distribution system and as such
       take on certain obligations to support security and privacy policies
       mandated by the content producer and/or end user.  However there is a
       danger that these policies are not properly implemented and enforced.
       The data consumer application may not be aware that its protections
       are no longer in effect.

    Barbir, et al.               Informational                     [Page 11]

    RFC 3837               Security Threats for OPES             August 2004

       There is also the possibility of security and privacy leaks due to
       the accidental misconfiguration or, due to misunderstanding what
       rules are in effect for a particular user or request.

       Privacy and security related parts of the systems can be targeted by
       malicious attacks and the ability to withstand such attacks is of
       paramount importance.

    3.8.  DoS Attacks

       DoS attacks can be of various types.  One type of DoS attack takes
       effect by overloading the client.  For example, an intruder can
       direct an OPES processor to issue numerous responses to a client.
       There is also additional DoS risk from a rule misconfiguration that
       would have the OPES processor ignore a data consumer application.

    4.  Security Considerations

       This document discusses multiple security and privacy issues related
       to the OPES services.

    5.  References

    5.1.  Normative References

       [1]  Barbir, A., Penno, R., Chen, R., Hofmann, M., and H. Orman, "An
            Architecture for Open Pluggable Edge Services (OPES)", RFC 3835,
            August 2004.

       [2]  Barbir, A., Burger, E., Chen, R., McHenry, S., Orman, H., and R.
            Penno, "OPES Use Cases and Deployment Scenarios", RFC 3752,
            April 2004.

       [3] Barbir, A., Batuner, O., Beck, A., Chan, T., and H. Orman,
            "Policy, Authorization, and Enforcement Requirements of Open
            Pluggable Edge Services (OPES)", RFC 3838, August 2004.

    5.2.  Informative References

       [4]  Floyd, S. and L. Daigle, "IAB Architectural and Policy
            Considerations for Open Pluggable Edge Services", RFC 3238,
            January 2002.

    6.  Acknowledgements

       Many thanks to T. Chan (Nokia) and A. Beck (Lucent).

    Barbir, et al.               Informational                     [Page 12]

    RFC 3837               Security Threats for OPES             August 2004

    7.  Authors' Addresses

       Abbie Barbir
       Nortel Networks
       3500 Carling Avenue
       Nepean, Ontario  K2H 8E9
       Canada

       Phone: +1 613 763 5229
       EMail: abbieb@nortelnetworks.com

       Oskar Batuner
       Independent consultant

       EMail: batuner@attbi.com

       Bindignavile Srinivas
       Nokia
       5 Wayside Road
       Burlington, MA  01803
       USA

       EMail: bindignavile.srinivas@nokia.com

       Markus Hofmann
       Bell Labs/Lucent Technologies
       Room 4F-513
       101 Crawfords Corner Road
       Holmdel, NJ  07733
       US

       Phone: +1 732 332 5983
       EMail: hofmann@bell-labs.com

       Hilarie Orman
       Purple Streak Development

       EMail: ho@alum.mit.edu

    Barbir, et al.               Informational                     [Page 13]

    RFC 3837               Security Threats for OPES             August 2004

    8.  Full Copyright Statement

       Copyright (C) The Internet Society (2004).  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.

    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

    Barbir, et al.               Informational                     [Page 14]