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RFC 3897 - Open Pluggable Edge Services (OPES) Entities and End

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Network Working Group                                          A. Barbir
Request for Comments: 3897                               Nortel Networks
Category: Informational                                   September 2004

             Open Pluggable Edge Services (OPES) Entities
                      and End Points Communication

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).


   This memo documents tracing and non-blocking (bypass) requirements
   for Open Pluggable Edge Services (OPES).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . .  2
   2.  OPES System  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.  Tracing Requirements . . . . . . . . . . . . . . . . . . . . .  3
       3.1.  Traceable entities . . . . . . . . . . . . . . . . . . .  3
       3.2.  System requirements  . . . . . . . . . . . . . . . . . .  5
       3.3.  Processor requirements . . . . . . . . . . . . . . . . .  5
       3.4.  Callout server requirements  . . . . . . . . . . . . . .  5
   4.  Bypass (Non-blocking feature) Requirements . . . . . . . . . .  6
       4.1.  Bypassable entities  . . . . . . . . . . . . . . . . . .  7
       4.2.  System requirements  . . . . . . . . . . . . . . . . . .  8
       4.3.  Processor requirements . . . . . . . . . . . . . . . . .  8
       4.4.  Callout server requirements  . . . . . . . . . . . . . .  9
   5.  Protocol Binding . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Compliance Considerations  . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
       8.1.  Tracing security considerations  . . . . . . . . . . . . 10
       8.2.  Bypass security considerations . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       9.1.  Normative References . . . . . . . . . . . . . . . . . . 12
       9.2.  Informative References . . . . . . . . . . . . . . . . . 13
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13

   11. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 13
   12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   The Open Pluggable Edge Services (OPES) architecture [1] 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.

   This work specifies OPES tracing and bypass functionality.  The
   architecture document [1] requires that tracing is supported in-band.
   This design goal limits the type of application protocols that OPES
   can support.  The details of what a trace record can convey are also
   dependent on the choice of the application level protocol.  For these
   reasons, this work only documents requirements for OPES entities that
   are needed to support traces and bypass functionality.  The task of
   encoding tracing and bypass features is application protocol
   specific.  Separate documents will address HTTP and other protocols.

   The architecture does not prevent implementers from developing out-
   of-band protocols and techniques to address tracing and bypass.  Such
   protocols are out of scope of the current work.

1.1.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119 [2].
   When used with the normative meanings, these keywords will be all
   uppercase.  Occurrences of these words in lowercase comprise normal
   prose usage, with no normative implications.

2.  OPES System

   This section provides a definition of OPES System.  This is needed in
   order to define what is traceable (or bypassable) in an OPES Flow.

   Definition: An OPES System is a set of all OPES entities authorized
   by either the data provider or the data consumer application to
   process a given application message.

   The nature of the authorization agreement determines if authority
   delegation is transitive (meaning an authorized entity is authorized
   to include other entities).

   If specific authority agreements allow for re-delegation, an OPES
   system can be formed by induction.  In this case, an OPES system
   starts with entities directly authorized by a data provider (or a
   data consumer) application.  The OPES system then includes any OPES
   entity authorized by an entity that is already in the OPES system.
   The authority delegation is always viewed in the context of a given
   application message.

   An OPES System is defined on an application message basis.  Having an
   authority to process a message does not imply being involved in
   message processing.  Thus, some OPES system members may not
   participate in processing of a message.  Similarly, some members may
   process the same message several times.

   The above definition implies that there can be no more than two OPES
   systems [Client-side and server-side OPES systems can process the
   same message at the same time] processing the same message at a given
   time.  This is based on the assumption that there is a single data
   provider and a single data consumer as far as a given application
   message is concerned.

   For example, consider a Content Delivery Network (CDN) delivering an
   image on behalf of a busy web site.  OPES processors and services,
   which the CDN uses to adapt and deliver the image, comprise an OPES
   System.  In a more complex example, an OPES System would contain
   third party OPES entities that the CDN engages to perform adaptations
   (e.g., to adjust image quality).

3.  Tracing Requirements

   The definition of OPES trace and tracing are given next.

      OPES trace: application message information about OPES entities
      that adapted the message.

      OPES tracing: the process of creating, manipulating, or
      interpreting an OPES trace.

   Note that the above trace definition assumes in-band tracing.  This
   dependency can be removed if desired.  Tracing is performed on per
   message basis.  Trace format is dependent on the application protocol
   that is being adapted.  A traceable entity can appear multiple times
   in a trace (for example, every time it acts on a message).

3.1.  Traceable entities

   This section focuses on identifying traceable entities in an OPES

   Tracing information provides an "end" with information about OPES
   entities that adapted the data.  There are two distinct uses of OPES
   traces.  First, a trace enables an "end" to detect the presence of
   OPES System.  Such "end" should be able to see a trace entry, but
   does not need to be able to interpret it beyond identification of the
   OPES System and location of certain required OPES-related disclosures
   (see Section 3.2).

   Second, the OPES System administrator is expected to be able to
   interpret the contents of an OPES trace.  The trace can be relayed to
   the administrator by an "end" without interpretation, as opaque data
   (e.g., a TCP packet or an HTTP message snapshot).  The administrator
   can use the trace information to identify the participating OPES
   entities.  The administrator can use the trace to identify the
   applied adaptation services along with other message-specific

   Since the administrators of various OPES Systems can have various
   ways of looking into tracing, they require the freedom in what to put
   in trace records and how to format them.

   At the implementation level, for a given trace, an OPES entity
   involved in handling the corresponding application message is
   traceable or traced if information about it appears in that trace.
   This work does not specify any order to that information.  The order
   of information in a trace can be OPES System specific or can be
   defined by application bindings documents.

   OPES entities have different levels of traceability requirements.

   o  An OPES System MUST add its entry to the trace.
   o  An OPES processor SHOULD add its entry to the trace.
   o  An OPES service MAY add its entry to the trace.
   o  An OPES entity MAY delegate addition of its trace entry to another
      OPES entity.  For example, an OPES System can have a dedicated
      OPES processor for adding System entries; an OPES processor can
      use a callout service to manage all OPES trace manipulations
      (since such manipulations are OPES adaptations).

   In an OPES context, a good tracing approach is similar to a trouble
   ticket ready for submission to a known address.  The address is
   printed on the ticket.  The trace in itself is not necessarily a
   detailed description of what has happened.  It is the responsibility
   of the operator to decode trace details and to resolve the problems.

3.2  System requirements

   The following requirements document actions when forming an OPES
   System trace entry:

   o  OPES system MUST include its unique identification in its trace
      entry.  Here, uniqueness scope is all OPES Systems that may adapt
      the message being traced.
   o  An OPES System MUST define its impact on inter- and intra-document
      reference validity.
   o  An OPES System MUST include information about its privacy policy,
      including identity of the party responsible for setting and
      enforcing the policy.
   o  An OPES System SHOULD include information that identifies, to the
      technical contact, the OPES processors involved in processing the
   o  When providing required information, an OPES System MAY use a
      single URI to identify a resource containing several required
      items.  For example, an OPES System can point to a single web page
      with a reference to System privacy policy and technical contact

   This specification does not define the meaning of the terms privacy
   policy, policy enforcement, or reference validity or technical
   contact and contains no requirements regarding encoding, language,
   format, or any other aspects of that information.  For example, a URI
   used for an OPES System trace entry may look like "http://
   www.examplecompany.com/opes/?client=example.com" where the identified
   web page is dynamically generated and contains the all OPES System
   information required above.

3.3.  Processor requirements

   The following requirements document actions when forming an OPES
   System trace entry:

   o  OPES processor SHOULD add its unique identification to the trace.
      Here, uniqueness scope is the OPES System containing the

3.4.  Callout server requirements

   In an OPES system, it is the task of an OPES processor to add trace
   records to application messages.  The OPES System administrator
   decides if and under what conditions callout servers may add trace
   information to application messages.

4.  Bypass (Non-blocking feature) Requirements

   IAB recommendation (3.3) [6] requires that the OPES architecture does
   not prevent a data consumer application from retrieving non-OPES
   version of content from a data provider application, provided that
   the non-OPES content exists.  IAB recommendation (3.3) suggests that
   the Non-blocking feature (bypass) be used to bypass faulty OPES
   intermediaries (once they have been identified, by some method).

   In addressing IAB consideration (3.3), one need to specify what
   constitutes non-OPES content.  In this work the definition of "non-
   OPES" content is provider dependent.  In some cases, the availability
   of "non-OPES" content can be a function of the internal policy of a
   given organization that has contracted the services of an OPES
   provider.  For example, Company A has as contract with an OPES
   provider to perform virus checking on all e-mail attachments.  An
   employee X of Company A can issue a non-blocking request for the
   virus scanning service.  The request could be ignored by the OPES
   provider since it contradicts its agreement with Company A.

   The availability of non-OPES content can be a function of content
   providers (or consumers or both) policy and deployment scenarios [5].
   For this reason, this work does not attempt to define what is an OPES
   content as opposed to non-OPES content.  The meaning of OPES versus
   non-OPES content is assumed to be determined through various
   agreements between the OPES provider, data provider and/or data
   consumer.  The agreement determines what OPES services can be
   bypassed and in what order (if applicable).

   This specification documents bypassing of an OPES service or a group
   of services identified by a URI.  In this context, to "bypass the
   service" for a given application message in an OPES Flow means to
   "not invoke the service" for that application message.  A bypass URI
   that identifies an OPES system (processor) matches all services
   attached to that OPES system (processor).  However, bypassing of OPES
   processors and OPES Systems themselves requires non-OPES mechanisms
   and is out of this specification scope.  A bypass request an
   instruction to bypass, usually embedded in an application message.

   The current specification does not provide for a good mechanism that
   allow and "end" to specify to "bypass this service but only if it is
   a part of that OPES system" or "bypass all services of that OPES
   system but not of this OPES system".  Furthermore, if an OPES
   processor does not know for sure that a bypass URI does not match its
   service, it must bypass that service.

   If no non-OPES content is available without the specified service,
   the bypass request for that service must be ignored.  This design
   implies that it may not be possible to detect non-OPES content
   existence or to detect violations of bypass rules in the environments
   where the tester does not know whether non-OPES content exists.  This
   design assumes that most bypass requests are intended for situations
   where serving undesirable OPES content is better than serving an
   error message that no preferred non-OPES content exists.

   Bypass feature is to malfunctioning OPES services as HTTP "reload"
   request is to malfunctioning HTTP caches.  The primary purpose of the
   bypass is to get usable content in the presence of service failures
   and not to provide the content consumer with more information on what
   is going on.  OPES trace should be used for the latter instead.

   While this work defines a "bypass service if possible" feature, there
   are other related bypass features that can be implemented in OPES
   and/or in application protocols being adapted.  For example, a
   "bypass service or generate an error" or "bypass OPES entity or
   generate an error".  Such services would be useful for debugging
   broken OPES systems and may be defined in other OPES specifications.
   This work concentrates on documenting a user-level bypass feature
   addressing direct IAB concerns.

4.1.  Bypassable entities

   In this work, the focus is on developing a bypass feature that allows
   a user to instruct the OPES System to bypass some or all of its
   services.  The collection of OPES services that can be bypassed is a
   function of the agreement of the OPES provider with either (or both)
   the content provider or the content consumer applications.  In the
   general case, a bypass request is viewed as a bypass instruction that
   contains a URI that identifies an OPES entity or a group of OPES
   entities that perform a service (or services) to be bypassed.  An
   instruction may contain more than one such URI.  A special wildcard
   identifier can be used to represent all possible URIs.

   In an OPES Flow, a bypass request is processed by each involved OPES
   processor.  This means that an OPES processor examines the bypass
   instruction and if non-OPES content is available, the processor then
   bypasses the indicated services.  The request is then forwarded to
   the next OPES processor in the OPES Flow.  The next OPES processor
   would then handle all bypass requests, regardless of the previous
   processor actions.  The processing chain continues throughout the
   whole processors that are involved in the OPES Flow.

4.2.  System requirements

   In an OPES System, bypass requests are generally client centric
   (originated by the data consumer application) and go in the opposite
   direction of tracing requests.  This work requires that the bypass
   feature be performed in-band as an extension to an application
   specific protocol.  Non-OPES entities should be able to safely ignore
   these extensions.  The work does not prevent OPES Systems from
   developing their own out of band protocols.

   The following requirements apply for bypass feature as related to an
   OPES System (the availability of a non-OPES content is a

   o  An OPES System MUST support a bypass feature.  This means that the
      OPES System bypasses services whose URIs are identified by an OPES
   o  An OPES System MUST provide OPES version of the content if non-
      OPES version is not available.

   In order to facilitate the debugging (or data consumer user
   experience) of the bypass feature in an OPES System, it would be
   beneficial if non-bypassed entities included information related to
   why they ignored the bypass instruction.  It is important to note
   that in some cases the tracing facility itself may be broken and the
   whole OPES System (or part) may need to be bypassed through the issue
   of a bypass instruction.

4.3.  Processor requirements

   Bypass requirements for OPES processors are (the availability of a
   non-OPES content is a precondition):

   o  OPES processor SHOULD be able to interpret and process a bypass
      instruction.  This requirement applies to all bypass instructions,
      including those that identify unknown-to-recipient services.
   o  OPES processors MUST forward bypass request to the next
      application hop provided that the next hop speaks application
      protocol with OPES bypass support.
   o  OPES processor SHOULD be able to bypass it's service(s) execution.

   OPES processors that know how to process and interpret a bypass
   instruction have the following requirements:

   o  The recipient of a bypass instruction with a URI that does not
      identify any known-to-recipient OPES entity MUST treat that URI as
      a wildcard identifier (meaning bypass all applicable services).

4.4.  Callout server requirements

   In an OPES system, it is the task of an OPES processor to process
   bypass requests.  The OPES System administrator decides if and under
   what conditions callout servers process bypass requests.

5.  Protocol Binding

   The task of encoding tracing and bypass features is application
   protocol specific.  Separate documents will address HTTP and other
   protocols.  These documents must address the ordering of trace
   information as needed.

6.  Compliance Considerations

   This specification defines compliance for the following compliance
   subjects: OPES System, processors, entities and callout servers.

   A compliance subject is compliant if it satisfies all applicable
   "MUST" and "SHOULD" level requirements.  By definition, to satisfy a
   "MUST" level requirement means to act as prescribed by the
   requirement; to satisfy a "SHOULD" level requirement means to either
   act as prescribed by the requirement or have a reason to act
   differently.  A requirement is applicable to the subject if it
   instructs (addresses) the subject.

   Informally, compliance with this document means that there are no
   known "MUST" violations, and all "SHOULD" violations are conscious.
   In other words, a "SHOULD" means "MUST satisfy or MUST have a reason
   to violate".  It is expected that compliance claims are accompanied
   by a list of unsupported SHOULDs (if any), in an appropriate format,
   explaining why preferred behavior was not chosen.

   Only normative parts of this specification affect compliance.
   Normative parts are: parts explicitly marked using the word
   "normative", definitions, and phrases containing unquoted capitalized
   keywords from RFC 2119 [2].  Consequently, examples and illustrations
   are not normative.

7.  IANA Considerations

   This specification contains no IANA considerations.  Application
   bindings MAY contain application-specific IANA considerations.

8.  Security Considerations

   Security considerations for OPES are documented in [4].  Policy and
   authorization issues are documented in [3].  It is recommended that
   designers consult these documents before reading this section.

   This document is a requirement document for tracing and bypass
   feature.  The requirements that are stated in this document can be
   used to extend an application level protocol to support these
   features.  As such, the work has security precautions.

8.1.  Tracing security considerations

   The tracing facility for OPES architecture is implemented as a
   protocol extension.  Inadequate implementations of the tracing
   facility may defeat safeguards built into the OPES architecture.  The
   tracing facility by itself can become a target of malicious attacks
   or used to lunch attacks on an OPES System.

   Threats caused by or against the tracing facility can be viewed as
   threats at the application level in an OPES Flow.  In this case, the
   threats can affect the data consumer and the data provider

   Since tracing information is a protocol extension, these traces can
   be injected in the data flow by non-OPES entities.  In this case,
   there are risks that non-OPES entities can be compromised in a
   fashion that threat the overall integrity and effectiveness of an
   OPES System.  For example, a non-OPES proxy can add fake tracing
   information into a trace.  This can be done in the form of wrong, or
   unwanted, or non existent services.  A non-OPES entity can inject
   large size traces that may cause buffer overflow in a data consumer
   application.  The same threats can arise from compromised OPES
   entities.  An attacker can control an OPES entity and inject wrong,
   or very large trace information that can overwhelm an end or the next
   OPES entity in an OPES flow.  Similar threats can result from bad
   implementations of the tracing facility in trusted OPES entities.

   Compromised tracing information can be used to launch attacks on an
   OPES System that give the impression that unwanted content
   transformation was performed on the data.  This can be achieved by
   inserting wrong entity (such OPES processor) identifiers.  A
   compromised trace can affect the overall message integrity structure.
   This can affect entities that use message header information to
   perform services such as accounting, load balancing, or reference-
   based services.

   Compromised trace information can be used to launch DoS attacks that
   can overwhelm a data consumer application or an OPES entity in an
   OPES Flow.  Inserting wrong tracing information can complicate the
   debugging tasks performed by system administrator during trouble
   shooting of OPES System behavior.

   As a precaution, OPES entities ought to be capable of verifying that
   the inserted traces are performed by legal OPES entities.  This can
   be done as part of the authorization and authentication face.  Policy
   can be used to indicate what trace information can be expected from a
   peer entity.  Other application level related security concerns can
   be found in [4].

8.2.  Bypass security considerations

   The bypass facility for OPES architecture is implemented as a
   protocol extension.  Inadequate implementations of the bypass
   facility may defeat safeguards built into the OPES architecture.  The
   bypass facility by itself can become a target of malicious attacks or
   used to lunch attacks on an OPES System.

   Threats caused by or against the bypass facility can be viewed as
   threats at the application level in an OPES Flow.  In this case, the
   threats can affect the data consumer and the data provider

   There are risks for the OPES System by non-OPES entities, whereby,
   these entities can insert bypass instructions into the OPES Flow.
   The threat can come from compromised non-OPES entities.  The threat
   might affect the overall integrity and effectiveness of an OPES
   System.  For example, a non-OPES proxy can add bypass instruction to
   bypass legitimate OPES entities.  The attack might result in
   overwhelming the original content provider servers, since the attack
   essentially bypass any load balancing techniques.  In addition, such
   an attack is also equivalent to a DoS attack, whereby, a legitimate
   data consumer application may not be able to access some content from
   a content provider or its OPES version.

   Since an OPES Flow may include non-OPES entities, it is susceptible
   to man-in-the-middle attacks, whereby an intruder may inject bypass
   instructions into the data path.  These attacks may affect content
   availability or disturb load balancing techniques in the network.

   The above threats can also arise by compromised OPES entities.  An
   intruder can compromise an OPES entities and then use man-in-the-
   middle techniques to disturb content availability to a data consumer
   application or overload a content provider server (essentially, some
   form of a DoS attack).

   Attackers can use the bypass instruction to affect the overall
   integrity of the OPES System.  The ability to introduce bypass
   instructions into a data flow may effect the accounting of the OPES
   System.  It may also affect the quality of content that is delivered
   to the data consumer applications.  Similar threats can arise from
   bad implementations of the bypass facility.

   Inconsistent or selective bypass is also a threat.  Here, one end can
   try to bypass a subset of OPES entities so that the resulting content
   is malformed and crashes or compromises entities that process that
   content (and expect that content to be complete and valid).  Such
   exceptions are often not tested because implementers do not expect a
   vital service to disappear from the processing loop.

   Other threats can arise from configuring access control policies for
   OPES entities.  It is possible that systems implementing access
   controls via OPES entities may be incorrectly configured to honor
   bypass and, hence, give unauthorized access to intruders.

   Tap bypass can also be a threat.  This is because systems
   implementing wiretaps via OPES entities may be incorrectly configured
   to honor bypass and, hence, ignore (leave undetected) traffic with
   bypass instructions that should have been tapped or logged.  It is
   also possible for one end to bypass services such as virus scanning
   at the receiving end.  This threat can be used by hackers to inject
   viruses throughout the network.  Following an IETF policy on
   Wiretapping [7], OPES communication model does not consider
   wiretapping requirements.  Nevertheless, the documented threat is
   real, not obvious, and OPES technology users operating in wiretapping
   or similar logging environments should be aware of it.

   Other application level related security concerns can be found in

9.  References

9.1.  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]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [4]  Barbir, A., Batuner, O., Srinivas, B., Hofmann, M., and H.
        Orman, "Security Threats and Risks for Open Pluggable Edge
        Services (OPES)", RFC 3837, August 2004.

9.2  Informative References

   [5]  Barbir A., Burger, E., Chen, R., McHenry, S., Orman, H., and R.
        Penno, "Open Pluggable Edge Services (OPES) Use Cases and
        Deployment Scenarios", RFC 3752, April 2004.

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

   [7]  IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May 2000.

10. Acknowledgements

   Several people has contributed to this work. Many thanks to: Alex
   Rousskov, Hilarie Orman, Oscar Batuner, Markus Huffman, Martin
   Stecher, Marshall Rose and Reinaldo Penno.

11. Author's Address

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

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

12. Full Copyright Statement

   Copyright (C) The Internet Society (2004).

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   retain all their rights.

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