Network Working Group                                        R. P. Swale
Request for Comments: 3304                          BTexact Technologies
Category: Informational                                       P. A. Mart
                                                 Marconi Communications
                                                              P. Sijben
                                                    Lucent Technologies
                                                                S. Brim
                                                               M. Shore
                                                          Cisco Systems
                                                            August 2002


       Middlebox Communications (midcom) Protocol Requirements

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 (2002).  All Rights Reserved.

Abstract

  This document specifies the requirements that the Middlebox
  Communication (midcom) protocol must satisfy in order to meet the
  needs of applications wishing to influence the middlebox function.
  These requirements were developed with a specific focus on network
  address translation and firewall middleboxes.

1.  Introduction

  This document is one of two developed by the Middlebox Communication
  (midcom) working group to address the requirements and framework for
  a protocol between middleboxes and "midcom agents."  This document
  presents midcom requirements; [MCFW] presents the context and
  framework.  [MCFW] also presents terminology and definitions and
  should be read in tandem with this one.

  These requirements were developed by examining the midcom framework
  and extracting requirements, both explicit and implicit, that
  appeared there.







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2.  Requirements

  Each requirement is presented as a statement, followed by brief
  explanatory material as appropriate.  Terminology is defined in
  [MCFW].  There may be overlap between requirements.

2.1.  Protocol machinery

2.1.1.

  The Midcom protocol must enable a Midcom agent requiring the services
  of a middlebox to establish an authorized association between itself
  and the middlebox.

  This states that the protocol must allow the middlebox to identify an
  agent requesting services and make a determination as to whether or
  not the agent will be permitted to do so.

2.1.2.

  The Midcom protocol must allow a Midcom agent to communicate with
  more than one middlebox simultaneously.

  In any but the most simple network, an agent is likely to want to
  influence the behavior of more than one middlebox.  The protocol
  design must not preclude the ability to do this.

2.1.3.

  The Midcom protocol must allow a middlebox to communicate with more
  than one Midcom agent simultaneously.

  There may be multiple instances of a single application or multiple
  applications desiring service from a single middlebox, and different
  agents may represent them.  The protocol design must not preclude the
  ability to do so.

2.1.4.

  Where a multiplicity of Midcom Agents are interacting with a given
  middlebox, the Midcom protocol must provide mechanisms ensuring that
  the overall behavior is deterministic.

  This states that the protocol must include mechanisms for avoiding
  race conditions or other situations in which the requests of one
  agent may influence the results of the requests of other agents in an
  unpredictable manner.




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2.1.5.

  The Midcom protocol must enable the middlebox and any associated
  Midcom agents to establish a known and stable state.  This must
  include the case of power failure, or other failure, where the
  protocol must ensure that any resources used by a failed element can
  be released.

  This states that the protocol must provide clear identification for
  requests and results and that protocol operations must be atomic with
  respect to the midcom protocol.

2.1.6.

  The middlebox must be able to report its status to a Midcom agent
  with which it is associated.

2.1.7.

  The protocol must support unsolicited messages from middlebox to
  agent, for reporting conditions detected asynchronously at the
  middlebox.

  It may be the case that exceptional conditions or other events at the
  middlebox (resource shortages, intrusion mitigation) will cause the
  middlebox to close pinholes or release resources without consulting
  the associated Midcom agent.  In that event, the protocol must allow
  the middlebox to notify the agent.

2.1.8.

  The Midcom protocol must provide for the mutual authentication of
  Midcom agent and middlebox to one another.

  In addition for the more obvious need for the Midcom agent to
  authenticate itself to the middlebox, there are some attacks against
  the protocol which can be mitigated by having the middlebox
  authenticate to the agent.  See [MCFW].

2.1.9.

  The Midcom protocol must allow either the Midcom agent or the
  middlebox to terminate the Midcom session between a Midcom Agent and
  a middlebox.  This allows either entity to close the session for
  maintenance, security, or other reasons.






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2.1.10.

  A Midcom agent must be able to determine whether or not a request was
  successful.

  This states that a middlebox must return a success or failure
  indication to a request made by an agent.

2.1.11.

  The Midcom protocol must contain version interworking capabilities to
  enable subsequent extensions to support different types of middlebox
  and future requirements of applications not considered at this stage.

  We assume that there will be later revisions of this protocol.  The
  initial version will focus on communication with firewalls and NATs,
  and it is possible that the protocol will need to be modified, as
  support for other middlebox types is added.  These version
  interworking capabilities may include (but are not limited to) a
  protocol version number.

2.1.12.

  It must be possible to deterministically predict the behavior of the
  middlebox in the presence of overlapping rules.

  The protocol must preclude nondeterministic behavior in the case of
  overlapping rulesets, e.g. by ensuring that some known precedence is
  imposed.

2.2.  Midcom Protocol Semantics

2.2.1.

  The syntax and semantics of the Midcom protocol must be extensible to
  allow the requirements of future applications to be adopted.

  This is related to, but different from, the requirement for
  versioning support.  As support for additional middlebox types is
  added there may be a need to add new message types.

2.2.2.

  The Midcom protocol must support the ability of an agent to install a
  ruleset that governs multiple types of middlebox actions (e.g.
  firewall and NAT).





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  This states that a the protocol must support rules and actions for a
  variety of types of middleboxes.  A Midcom agent ought to be able to
  have a single Midcom session with a middlebox and use the Midcom
  interface on the middlebox to interface with different middlebox
  functions on the same middlebox interface.

2.2.3.

  The protocol must support the concept of a ruleset group comprising a
  multiple of individual rulesets to be treated as an aggregate.

  Applications using more than one data stream may find it more
  convenient and more efficient to be able to use single messages to
  tear down, extend, and manipulate all middlebox rulesets being used
  by one instance of the application.

2.2.4.

  The protocol must allow the midcom agent to extend the lifetime of an
  existing ruleset that otherwise would be deleted by the middlebox.

2.2.5.

  If a peer does not understand an option, it must be clear whether the
  action required is to proceed without the unknown attribute being
  taken into account or the request is to be rejected.  Where
  attributes may be ignored if not understood, a means may be provided
  to inform the client about what has been ignored.

  This states that failure modes must be robust, providing sufficient
  information for the agent or middlebox, to be able to accommodate the
  failure or to retry with a new option that is more likely to succeed.

2.2.6.

  To enable management systems to interact with the Midcom environment,
  the protocol must include failure reasons that allow the Midcom Agent
  behavior to be modified as a result of the information contained in
  the reason.  Failure reasons need to be chosen such that they do not
  make an attack on security easier.

2.2.7.

  The Midcom protocol must not preclude multiple authorized agents from
  working on the same ruleset.






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2.2.8.

  The Midcom protocol must be able to carry filtering rules, including
  but not limited to the 5-tuple, from the midcom agent to the
  middlebox.

  By "5-tuple", we refer to the standard <source address, source port,
  destination address, destination port, transport protocol> tuple.
  Other filtering elements may be carried, as well.

2.2.9.

  When the middlebox performs a port mapping function, the protocol
  should allow the Midcom agent to request that the external port
  number have the same oddity as the internal port.

  This requirement is to support RTP and RTCP [RFC1889] "oddity"
  requirements.

2.2.10.

  When the middlebox performs a port mapping function, the protocol
  should allow the Midcom agent to request that a consecutive range of
  external port numbers be mapped to consecutive internal ports.  This
  requirement is to support RTP and RTCP "sequence" requirements.

2.2.11.

  It should be possible to define rulesets that contain a more specific
  filter spec than an overlapping ruleset.  This should allow agents to
  request actions for the subset that contradict those of the
  overlapping set.

  This should allow a Midcom agent to request to a Midcom server
  controlling a firewall function that a subset of the traffic that
  would be allowed by the overlapping ruleset be specifically
  disallowed.

2.3.  General Security Requirements

2.3.1.

  The Midcom protocol must provide for message authentication,
  confidentiality, and integrity.







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2.3.2.

  The Midcom protocol must allow for optional confidentiality
  protection of control messages.  If provided, the mechanism should
  allow a choice in the algorithm to be used.

2.3.3.

  The Midcom protocol must operate across un-trusted domains, between
  the Midcom agent and middlebox in a secure fashion.

2.3.4.

  The Midcom protocol must define mechanisms to mitigate replay attacks
  on the control messages.

3. Intellectual Property

  The IETF takes no position regarding the validity or scope of any
  intellectual property or other rights that might be claimed to
  pertain to the implementation or use other technology described in
  this document or the extent to which any license under such rights
  might or might not be available; neither does it represent that it
  has made any effort to identify any such rights.  Information on the
  IETF's procedures with respect to rights in standards-track and
  standards-related documentation can be found in BCP-11.  Copies of
  claims of rights made available for publication 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 Secretariat.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights which may cover technology that may be required to practice
  this standard.  Please address the information to the IETF Executive
  Director.

4.  Security Considerations

  The security requirements for a midcom protocol are discussed in
  section 2.3.









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5.  Normative References

  [MCFW]    Srisuresh, S., Kuthan, J., Rosenberg, J., Molitor, A. and
            A.  Rayhan, "Middlebox communication architecture and
            framework", RFC 3303, Date.*

  [RFC1889] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
            "RTP: A Transport Protocol for Real-Time Applications", RFC
            1889, January 1996.

6.  Informative References

  [RFC2026] Bradner, S. "The Internet Standards Process -- Revision 3",
            BCP 9, RFC 2026. October 1996.

Authors' Addresses

  Richard Swale
  BTexact Technologies
  Callisto House
  Adastral Park
  Ipswich United Kingdom
  EMail:  [email protected]

  Paul Sijben
  Lucent Technologies EMEA BV
  Huizen
  Netherlands
  EMail: [email protected]

  Philip Mart
  Marconi Communications Ltd.
  Edge Lane
  Liverpool
  United Kingdom
  EMail: [email protected]

  Scott Brim
  Cisco Systems
  146 Honness Lane
  Ithaca, NY 14850
  EMail: [email protected]

  Melinda Shore
  Cisco Systems
  809 Hayts Road
  Ithaca, NY 14850
  EMail: [email protected]



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Full Copyright Statement

  Copyright (C) The Internet Society (2002).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
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  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
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  The limited permissions granted above are perpetual and will not be
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  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

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



















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