This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 983
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.


   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.

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


   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.


   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.


   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.


   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.


   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.


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


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

   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.


   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].


   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.


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

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


   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.


   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

2.2.  Midcom Protocol Semantics


   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.


   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).

   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.


   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.


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


   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.


   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.


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


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

   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.


   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"


   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.


   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

2.3.  General Security Requirements


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


   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.


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


   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

4.  Security Considerations

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

5.  Normative References

      [MCFW]    Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A. and 
             A.  Rayhan, "Middlebox communication architecture and
             framework", RFC 3303, August 2002.
EID 983 (Verified) is as follows:

Section: 5

Original Text:

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

Corrected Text:

   [MCFW]    Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A. and
             A.  Rayhan, "Middlebox communication architecture and
             framework", RFC 3303, August 2002.
from pending
[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: Paul Sijben Lucent Technologies EMEA BV Huizen Netherlands EMail: Philip Mart Marconi Communications Ltd. Edge Lane Liverpool United Kingdom EMail: Scott Brim Cisco Systems 146 Honness Lane Ithaca, NY 14850 EMail: Melinda Shore Cisco Systems 809 Hayts Road Ithaca, NY 14850 EMail: Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.