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Network Working Group                                        R. P. SwaleRequest for Comments: 3304                          BTexact TechnologiesCategory: Informational                                       P. A. Mart                                                  Marconi Communications                                                               P. Sijben                                                     Lucent Technologies                                                                 S. Brim                                                                M. Shore                                                           Cisco Systems                                                             August 2002Middlebox Communications (midcom) Protocol RequirementsStatus 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.Swale, et al.                Informational                      [Page 1]

RFC 3304                  Midcom Requirements                August 20022.  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 machinery2.1.1.   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.Swale, et al.                Informational                      [Page 2]

RFC 3304                  Midcom Requirements                August 20022.1.5.   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.Swale, et al.                Informational                      [Page 3]

RFC 3304                  Midcom Requirements                August 20022.1.10.   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 Semantics2.2.1.   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).Swale, et al.                Informational                      [Page 4]

RFC 3304                  Midcom Requirements                August 2002   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.Swale, et al.                Informational                      [Page 5]

RFC 3304                  Midcom Requirements                August 20022.2.8.   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 Requirements2.3.1.   The Midcom protocol must provide for message authentication,   confidentiality, and integrity.Swale, et al.                Informational                      [Page 6]

RFC 3304                  Midcom Requirements                August 20022.3.2.   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 inBCP-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 insection 2.3.Swale, et al.                Informational                      [Page 7]

RFC 3304                  Midcom Requirements                August 20025.  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",RFC1889, 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:  richard.swale@bt.com   Paul Sijben   Lucent Technologies EMEA BV   Huizen   Netherlands   EMail: paul.sijben@picopoint.com   Philip Mart   Marconi Communications Ltd.   Edge Lane   Liverpool   United Kingdom   EMail: philip.mart@marconi.com   Scott Brim   Cisco Systems   146 Honness Lane   Ithaca, NY 14850   EMail: sbrim@cisco.com   Melinda Shore   Cisco Systems   809 Hayts Road   Ithaca, NY 14850   EMail: mshore@cisco.comSwale, et al.                Informational                      [Page 8]

RFC 3304                  Midcom Requirements                August 2002Full 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.Swale, et al.                Informational                      [Page 9]