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rfc:rfc4097

Network Working Group M. Barnes, Ed. Request for Comments: 4097 Nortel Networks Category: Informational June 2005

      Middlebox Communications (MIDCOM) Protocol Evaluation

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 (2005).

Abstract

 This document provides an evaluation of the applicability of SNMP
 (Simple Network Management Protocol), RSIP (Realm Specific Internet
 Protocol), Megaco, Diameter, and COPS (Common Open Policy Service) as
 the MIDCOM (Middlebox Communications) protocol.  A summary of each of
 the proposed protocols against the MIDCOM requirements and the MIDCOM
 framework is provided.  Compliancy of each of the protocols against
 each requirement is detailed.  A conclusion summarizes how each of
 the protocols fares in the evaluation.

Table of Contents

 Overview..........................................................  2
 Conventions Used in This Document.................................  3
 1.  Protocol Proposals............................................  3
     1.1.  SNMP....................................................  3
     1.2.  RSIP....................................................  5
     1.3.  Megaco..................................................  7
     1.4.  Diameter................................................  8
     1.5.  COPS.................................................... 10
 2.  Item Level Compliance Evaluation.............................. 11
     2.1.  Protocol Machinery...................................... 11
     2.2.  Protocol Semantics...................................... 20
     2.3.  General Security Requirements........................... 27
 3.  Conclusions................................................... 29
 4.  Security Considerations....................................... 30
 5.  References.................................................... 31
     5.1.  Normative References.................................... 31
     5.2.  Informative References.................................. 33
 6.  Acknowledgements.............................................. 33

Barnes Informational [Page 1] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Appendix A - SNMP Overview........................................ 34
 Appendix B - RSIP with Tunneling.................................. 35
 Appendix C - Megaco Modeling Approach............................. 37
 Appendix D - Diameter IPFilter Rule............................... 39
 Contributors ..................................................... 42

Overview

 This document provides an evaluation of the applicability of SNMP
 (Simple Network Management Protocol), RSIP (Realm Specific Internet
 Protocol), Megaco, Diameter and COPS (Common Open Policy Service) as
 the MIDCOM (Middlebox Communications) protocol.  This evaluation
 provides overviews of the protocols and general statements of
 applicability based upon the MIDCOM framework [2] and requirements
 [1] documents.
 The process for the protocol evaluation was fairly straightforward as
 individuals volunteered to provide an individual document evaluating
 a specific protocol.  Thus, some protocols that might be considered
 as reasonably applicable as the MIDCOM protocol are not evaluated in
 this document since there were no volunteers to champion the work.
 The individual protocol documents for which there were volunteers
 were submitted for discussion on the list with feedback being
 incorporated into an updated document.  The updated versions of these
 documents formed the basis for the content of this WG document.
 Section 1 contains a list of the proposed protocols submitted for the
 purposes of the protocol evaluation with some background information
 on the protocols and similarities and differences with regards to the
 applicability to the framework [2] provided.
 Section 2 provides the item level evaluation of the proposed
 protocols against the Requirements [1].
 Section 3 provides a summary of the evaluation.  A table containing a
 numerical breakdown for each of the protocols, with regards to its
 applicability to the requirements, for the following categories is
 provided: Fully met, Partially met through the use of extensions,
 Partially met through other changes to the protocol, or Failing to be
 met.  This summary is not meant to provide a conclusive statement of
 the suitability of the protocols, but rather to provide information
 to be considered as input into the overall protocol decision process.
 In order for this document to serve as a complete evaluation of the
 protocols, some of the background information and more detailed
 aspects of the proposals documenting enhancements and applications of
 the protocols to comply with the MIDCOM framework and requirements
 are included in Appendices.

Barnes Informational [Page 2] RFC 4097 MIDCOM Protocol Evaluation June 2005

Conventions Used in this Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119 [4].

1. Protocol Proposals

 The following protocols were submitted to the MIDCOM WG for
 consideration:
 o  SNMP
 o  RSIP
 o  Megaco
 o  Diameter
 o  COPS
 The following provides an overview of each of the protocols and the
 applicability of each protocol to the MIDCOM framework.

1.1. SNMP

 This section provides a general statement with regards to the
 applicability of SNMP as the MIDCOM protocol.  A general overview and
 some specific details of SNMP are provided in Appendix A.  This
 evaluation of SNMP is specific to SNMPv3, which provides the security
 required for MIDCOM usage.  SNMPv1 and SNMPv2c would be inappropriate
 for MIDCOM since they have been declared Historic, and because their
 messages have only trivial security.  Some specifics with regards to
 existing support for NAT and Firewall Control are provided in section
 1.1.2.  The differences between the SNMP framework and the MIDCOM
 framework are addressed in section 1.1.3.

1.1.1. SNMP General Applicability

 The primary advantages of SNMPv3 are that it is a mature, well
 understood protocol, currently deployed in various scenarios, with
 mature toolsets available for SNMP managers and agents.
 Application intelligence is captured in MIB modules, rather than in
 the messaging protocol.  MIB modules define a data model of the
 information that can be collected and configured for a managed
 functionality.  The SNMP messaging protocol transports the data in a
 standardized format without needing to understand the semantics of
 the data being transferred.  The endpoints of the communication
 understand the semantics of the data.

Barnes Informational [Page 3] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Partly due to the lack of security in SNMPv1 and SNMPv2c, and partly
 due to variations in configuration requirements across vendors, few
 MIB modules have been developed that enable standardized
 configuration of managed devices across vendors.  Since monitoring
 can be done using only a least-common-denominator subset of
 information across vendors, many MIB modules have been developed to
 provide standardized monitoring of managed devices.  As a result,
 SNMP has been used primarily for monitoring rather than for
 configuring network nodes.
 SNMPv3 builds upon the design of widely-deployed SNMPv1 and SNMPv2c
 versions.  Specifically, SNMPv3 shares the separation of data
 modeling (MIBs) from the protocol to transfer data, so all existing
 MIBs can be used with SNMPv3.  SNMPv3 also uses the SMIv2 standard,
 and it shares operations and transport with SNMPv2c.  The major
 difference between SNMPv3 and earlier versions is the addition of
 strong message security and controlled access to data.
 SNMPv3 uses the architecture detailed in RFC 3411 [5], where all SNMP
 entities are capable of performing certain functions, such as the
 generation of requests, response to requests, the generation of
 asynchronous notifications, the receipt of notifications, and the
 proxy-forwarding of SNMP messages.  SNMP is used to read and
 manipulate virtual databases of managed-application-specific
 operational parameters and statistics, which are defined in MIB
 modules.

1.1.2. SNMP Existing Support for NAT and Firewall Control

 For configuring NATs, a NAT MIB module [16] has been developed.  The
 NAT MIB module meets all of the MIDCOM requirements concerning NAT
 control with the exception of grouping of policy rules (requirement
 2.2.3.).  In order to support this, an additional grouping table in
 the NAT MIB module is required.
 Existing work for firewall control with SNMP only considered the
 monitoring of firewalls and not the configuration.  Further work is
 required towards the development of MIBs for configuring firewalls.

1.1.3. Architectural Differences between SNMP and MIDCOM

 The SNMP management framework provides functions equivalent to those
 defined by the MIDCOM framework, although there are a few
 architectural differences.
 Traditionally, SNMP entities have been called Manager and Agent.
 Manager and agent are now recognized as entities designed to support
 particular configurations of SNMPv3 functions.  A traditional manager

Barnes Informational [Page 4] RFC 4097 MIDCOM Protocol Evaluation June 2005

 is an entity capable of generating requests and receiving
 notifications, and a traditional agent is an entity capable of
 responding to requests and generating notifications.  The SNMP use of
 the term agent is different from its use in the MIDCOM framework: The
 SNMP Manager corresponds to the MIDCOM agent and the SNMP Agent
 corresponds to the MIDCOM PDP.  The SNMP evaluation assumes that the
 MIDCOM PDP (SNMP Agent) is physically part of the middlebox, which is
 allowed by the MIDCOM framework as described in section 6.0 of [2].
 Thus, for the purpose of this evaluation, the SNMP agent corresponds
 to the Middlebox.
 While this evaluation is based on the assumption that the SNMP agent
 corresponds to the middlebox, SNMP does not force such a restriction.
 Proxy means many things to many people.  SNMP can be deployed using
 intermediate entities to forward messages, or to help distribute
 policies to the middlebox, similar to the proxy capabilities of the
 other candidate protocols.  Since proxy adds configuration and
 deployment complexity and is not necessary to meet the specified
 MIDCOM requirements, the use of a proxy agent or mid-level manager is
 not considered in this evaluation.  Further details on SNMP proxy
 capabilities are provided in Appendix A.
 Although the SNMP management framework does not have the concept of a
 session, session-like associations can be established through the use
 of managed objects.  In order to implement the MIDCOM protocol based
 on SNMP, a MIDCOM MIB module is required.  All requests from the
 MIDCOM agent to the Middlebox would be performed using write access
 to managed objects defined in the MIDCOM MIB module.  Replies to
 requests are signaled by the Middlebox (SNMP agent), by modifying the
 managed objects.  The MIDCOM agent (SNMP manager) can receive this
 information by reading or polling, if required, the corresponding
 managed object.

1.2. RSIP

 The RSIP framework and detailed protocol are defined in RFC 3102 [17]
 and RFC 3103 [18] respectively.

1.2.1. Framework Elements in Common to MIDCOM and RSIP

 The following framework elements are common to MIDCOM and RSIP listed
 by their MIDCOM names, with the RSIP name indicated in parenthesis:
 o  Hosts
 o  Applications
 o  Middleboxes (RSIP gateways)
 o  Private domain (private realm)

Barnes Informational [Page 5] RFC 4097 MIDCOM Protocol Evaluation June 2005

 o  External domain (public realm)
 o  Middlebox communication protocol (RSIP)
 o  MIDCOM agent registration (host registration)
 o  MIDCOM session (RSIP session)
 o  MIDCOM Filter (local / remote address and port number(s) pairs)

1.2.2. MIDCOM Framework Elements Not Supported by RSIP

 The following MIDCOM framework elements are not supported by RSIP:
 o  Policy actions and rules.  RSIP always implicitly assumes a permit
    action.  To support MIDCOM, a more general and explicit action
    parameter would have to be defined.  RSIP requests specifying
    local / remote address and port number(s) pairs would have to be
    extended to include an action parameter, in MIDCOM rules.
 o  MIDCOM agents.  RSIP makes no distinction between applications and
    agents; address assignment operations can be performed equally by
    applications and agents.
 o  Policy Decision Points.  RSIP assumes that middleboxes grant or
    deny requests with reference to a policy known to them; the policy
    could be determined jointly by the middlebox and a policy decision
    point; such joint determination is not addressed by the RSIP
    framework, nor is it specifically precluded.

1.2.3. RSIP Framework Elements Not Supported by MIDCOM

 The following elements are unique to the RSIP framework.  If RSIP
 were adopted as the basis for the MIDCOM protocol, they could be
 added to the MIDCOM framework:
 o  RSIP client: that portion of the application (or agent) that talks
    to the RSIP gateway using RSIP.
 o  RSIP server: that portion of an RSIP gateway that talks to
    applications using RSIP.
 o  Realm Specific Address IP (RSA-IP) and Realm Specific Address and
    Port IP (RSAP-IP): RSIP distinguishes between filters that include
    all ports on an IP address and those that do not.
 o  Demultiplexing Fields: Any set of packet header or payload fields
    that an RSIP gateway uses to route an incoming packet to an RSIP
    host.  RSIP allows a gateway to perform, and an application to
    control, packet routing to hosts in the private domain based on
    more than IP header fields.

Barnes Informational [Page 6] RFC 4097 MIDCOM Protocol Evaluation June 2005

 o  Host-to-middlebox tunnels: RSIP assumes that data communicated
    between a private realm host and a public realm host is
    transferred through the private realm by a tunnel between the
    inner host and the middle box, where it is converted to and from
    native IP based communications to the public realm host.

1.2.4. Comparison of MIDCOM and RSIP Frameworks

 RSIP with tunneling, has the advantage that the public realm IP
 addresses and port numbers are known to the private realm host
 application, thus no translation is needed for protocols such as SDP,
 the FTP control protocol, RTSP, SMIL, etc.  However, this does
 require that an RSIP server and a tunneling protocol be implemented
 in the middlebox and an RSIP client and the tunneling protocol be
 implemented in the private realm host.  The host modifications can
 generally be made without modification to the host application or
 requiring the implementation of a host application agent.  This is
 viewed as a significant advantage over NAT (Network Address
 Translation).
 Further details on the evaluation of RSIP with regards to tunneling
 in the context of NAT support are available in Appendix B of this
 document.

1.3. Megaco

1.3.1. Megaco Architectural Model

 Megaco is a master-slave, transaction-oriented protocol defined in
 RFC 3015 [20] in which Media Gateway Controllers (MGC) control the
 operation of Media Gateways (MG).  Originally designed to control IP
 Telephony gateways, it is used between an application-unaware device
 (the Media Gateway) and an intelligent entity (the Media Gateway
 Controller) having application awareness.
 The Megaco model includes the following key concepts:
 1. Terminations: Logical entities on the MG that act as sources or
    sink of packet streams.  A termination can be physical or
    ephemeral and is associated with a single MGC.
 2. Context: An association between Terminations for sharing media
    between the Terminations.  Terminations can be added, subtracted
    from a Context and can be moved from one Context to another.  A
    Context and all of its Terminations are associated with a single
    MGC.

Barnes Informational [Page 7] RFC 4097 MIDCOM Protocol Evaluation June 2005

 3. Virtual Media Gateways: A physical MG can be partitioned into
    multiple virtual MGs allowing multiple Controllers to interact
    with disjoint sets of Contexts/Terminations within a single
    physical device.
 4. Transactions/Messages: Each Megaco command applies to one
    Termination within a Context and generates a unique response.
    Commands may be replicated implicitly so that they act on all
    Terminations of a given Context through wildcarding of Termination
    identifiers.  Multiple commands addressed to different Contexts
    can be grouped in a Transaction structure.  Similarly, multiple
    Transactions can be concatenated into a Message.
 5. Descriptors/Properties: A Termination is described by a number of
    characterizing parameters or Properties, which are grouped in a
    set of Descriptors that are included in commands and responses.
 6. Events and signals: A Termination can be programmed to perform
    certain actions or to detect certain events and notify the Agent.
 7. Packages: Packages are groups of properties, events, etc.
    associated with a Termination.  Packages are simple means of
    extending the protocol to serve various types of devices or
    Middleboxes.

1.3.2. Comparison of the Megaco and MIDCOM Architectural Frameworks

 In the MIDCOM architecture, the Middlebox plays the role of an
 application-unaware device being controlled by the application-aware
 Agent.  In the Megaco architecture, the Media Gateway controller
 serves a role similar to the MIDCOM Agent (MA) and the Media Gateway
 serves a role similar to the Middlebox (MB).  One major difference
 between the Megaco model and the MIDCOM protocol requirements is that
 MIDCOM requires that the MIDCOM Agent establish the session.
 Whereas, the Megaco definition is that a MG (Middlebox) establishes
 communication with an MGC (MIDCOM Agent).

1.4. Diameter

1.4.1. Diameter Architecture

 Diameter is designed to support AAA for network access.  It is meant
 to operate through networks of Diameter nodes, which both act upon
 and route messages toward their final destinations.  Endpoints are
 characterized as either clients, which perform network access
 control, or servers, which handle authentication, authorization and
 accounting requests for a particular realm.  Intermediate nodes
 perform relay, proxy, redirect, and translation services.  Design

Barnes Informational [Page 8] RFC 4097 MIDCOM Protocol Evaluation June 2005

 requirements for the protocol include robustness in the face of
 bursty message loads and server failures, resistance to specific DOS
 attacks and protection of message contents, and extensibility
 including support for vendor-specific attributes and message types.
 The protocol is designed as a base protocol in RFC 3588 [24] to be
 supported by all implementations, plus extensions devoted to specific
 applications.  Messages consist of a header and an aggregation of
 "Attribute-Value Pairs (AVPs)", each of which is a tag-length-value
 construct.  The header includes a command code, which determines the
 processing of the message and what other AVP types must or may be
 present.  AVPs are strongly typed.  Some basic and compound types are
 provided by the base protocol specification, while others may be
 added by application extensions.  One of the types provided in the
 base is the IPFilterRule, which may be sufficient to express the
 Policy Rules that MIDCOM deals with.
 Messaging takes the form of request-answer exchanges.  Some exchanges
 may take multiple round-trips to complete.  The protocol is
 connection-oriented at both the transport and application levels.  In
 addition, the protocol is tied closely to the idea of sessions, which
 relate sequences of message exchanges through use of a common session
 identifier.  Each application provides its own definition of the
 semantics of a session.  Multiple sessions may be open
 simultaneously.

1.4.2. Comparison of Diameter With MIDCOM Architectural Requirements

 The MIDCOM Agent does not perform the functions of a Diameter client,
 nor does the Middlebox support the functions of a Diameter server.
 Thus the MIDCOM application would introduce two new types of
 endpoints into the Diameter architecture.  Moreover, the MIDCOM
 requirements do not at this time imply any type of intermediate node.
 A general assessment might be that Diameter meets and exceeds MIDCOM
 architectural requirements, however the connection orientation may be
 too heavy for the number of relationships the Middlebox must support.
 Certainly the focus on extensibility, request-response messaging
 orientation, and treatment of the session, are all well-matched to
 what MIDCOM needs.  At this point, MIDCOM is focused on simple
 point-to-point relationships, so the proxying and forwarding
 capabilities provided by Diameter are not needed.  Most of the
 commands and AVPs defined in the base protocol are also surplus to
 MIDCOM requirements.

Barnes Informational [Page 9] RFC 4097 MIDCOM Protocol Evaluation June 2005

1.5. COPS

 Overall, COPS, defined in RFC 2748 [25], and COPS-PR, defined in RFC
 3084 [26], have similar compliancy with regards to the MIDCOM
 protocol requirements.  In this document, references to COPS are
 generally applicable to both COPS and COPS-PR.  However, COPS-PR is
 explicitly identified to meet two of the requirements.  The only
 other major difference between COPS-PR and COPS, as applied to the
 MIDCOM protocol, would be the description of the MIDCOM policy rule
 attributes with COPS-PR MIDCOM PIB attributes rather than COPS MIDCOM
 client specific objects.

1.5.1. COPS Protocol Architecture

 COPS is a simple query and response protocol that can be used to
 exchange policy information between a policy server (Policy Decision
 Point or PDP) and its clients (Policy Enforcement Points or PEPs).
 COPS was defined to be a simple and extensible protocol.  The main
 characteristics of COPS include the following:
 1. The protocol employs a client/server model.  The PEP sends
    requests, updates, and deletions to the remote PDP and the PDP
    returns decisions back to the PEP.
 2. The protocol uses TCP as its transport protocol for reliable
    exchange of messages between policy clients and a server.
 3. The protocol is extensible in that it is designed to leverage
    self-identifying objects and can support diverse client specific
    information without requiring modification of the COPS protocol.
 4. The protocol was created for the general administration,
    configuration, and enforcement of policies.
 5. COPS provides message level security for authentication, replay
    protection, and message integrity.  COPS can make use of existing
    protocols for security such as IPSEC [22] or TLS [21] to
    authenticate and secure the channel between the PEP and the PDP.
 6. The protocol is stateful in two main aspects:
   (1) Request/Decision state is shared and kept synchronized in a
       transactional manner between client and server.  Requests from
       the client PEP are installed or remembered by the remote PDP
       until they are explicitly deleted by the PEP.  At the same
       time, Decisions from the remote PDP can be generated
       asynchronously at any time for a currently installed request
       state.

Barnes Informational [Page 10] RFC 4097 MIDCOM Protocol Evaluation June 2005

   (2) State from various events (Request/Decision pairs) may be
       inter-associated.  The server may respond to new queries
       differently because of previously installed, related
       Request/Decision state(s).
 7. The protocol is also stateful in that it allows the server to push
    configuration information to the client, and then allows the
    server to remove such state from the client when it is no longer
    applicable.

1.5.2. Comparison of COPS and the MIDCOM Framework

 In the MIDCOM framework, the Middlebox enforces the policy controlled
 by an application-aware Agent.  Thus, when compared to the COPS
 architecture, the Middlebox serves as the PEP (COPS Client) and the
 MIDCOM Agent serves as the PDP (COPS Policy Server).  One major
 difference between the COPS protocol model and the MIDCOM protocol
 requirements is that MIDCOM requires that the MIDCOM Agent establish
 the session.  Whereas, the COPS definition is that a PEP (Middlebox)
 establishes communication with a PDP (MIDCOM Agent).

2. Item Level Compliance Evaluation

 This section contains a review of the protocol's level of compliance
 to each of the MIDCOM Requirements [1].  The following key will be
 used to identify the level of compliancy of each of the individual
 protocols:
 T =  Total Compliance.  Meets the requirement fully.
 P+ = Partial Compliance+.  Fundamentally meets the requirement
      through the use of extensions (e.g., packages, additional
      parameters, etc).
 P =  Partial Compliance.  Meets some aspect of the requirement,
      however, the necessary changes require more than an extension
      and/or are inconsistent with the design intent of the
      protocol.
 F =  Failed Compliance.  Does not meet the requirement.

2.1. Protocol Machinery

 This section describes the compliancy of the proposed protocols
 against the protocol machinery requirements from section 2.1 of the
 requirements document [1].  A short description of each of the
 protocols is provided to substantiate the evaluation.

Barnes Informational [Page 11] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.1.1. Ability to Establish Association Between Agent and Middlebox.

 SNMP: T, RSIP: P+, Megaco: P, Diameter: T, COPS: P
 SNMP:  SNMPv3 provides mutual authentication at the user level
    (where the user can be an application or a host if desired) via
    shared secrets.  Each authenticated principal is associated with a
    group that has access rights that control the principals ability
    to perform operations on specific subsets of data.  Failure to
    authenticate can generate a SNMP notification (administrator
    configurable choice).
 RSIP: RSIP allows sessions to be established between middleboxes
    and applications and MIDCOM agents.  Authorization credentials
    would have to be added to the session establishment request to
    allow the middlebox to authorize the session requestor.
 Megaco: There is a directionality component implicit in this
    requirement in that the MA initiates the establishment of the
    authorized session.  Megaco defines this association to be
    established in the opposite direction, i.e., the Middlebox(MG)
    initiates the establishment.  If this restriction is not
    considered, then Megaco makes the syntax and semantics available
    for the endpoint to initiate the connection.
 Diameter: Although this is out of scope, the Diameter specification
    describes several ways to discover a peer.  Having done so, a
    Diameter node establishes a transport connection (TCP, TLS, or
    SCTP) to the peer.  The two peers then exchange Capability
    Exchange Request/Answer messages to identify each other and
    determine the Diameter applications each supports.
    If the connection between two peers is lost, Diameter prescribes
    procedures whereby it may be re-established.  To ensure that loss
    of connectivity is detected quickly, Diameter provides the
    Device-Watchdog Request/Answer messages, to be used when traffic
    between the two peers is low.
    Diameter provides an extensive state machine to govern the
    relationship between two peers.
 COPS: COPS does not meet the directionality part of the
    requirement.  The definition of COPS allows a PEP (Middlebox) to
    establish communication with a PDP (MIDCOM Agent).  However,
    nothing explicitly prohibits a PDP from establishing communication

Barnes Informational [Page 12] RFC 4097 MIDCOM Protocol Evaluation June 2005

    with a PEP.  The PEP could have local policies dictating what
    action to take when it is contacted by an unknown PDP.  These
    actions, defined in the local policies, would ensure the proper
    establishment of an authorized association.

2.1.2. Agent Can Relate to Multiple Middleboxes

 SNMP: T, RSIP: P, Megaco: T, Diameter: T, COPS: T
 SNMP:  An SNMP manager can communicate simultaneously with several
    Middleboxes.
 RSIP: RSIP sessions are identified by their IP source and
    destination addresses and their TCP / UDP port numbers.  Thus each
    RSIP client can communicate with multiple servers, and each server
    can communicate with multiple clients.  However, RSIP did not
    explicitly include agents in its design.  The architecture and
    semantics of RSIP messages do not preclude agents, thus the RSIP
    architecture could certainly be extended to explicitly include
    agents; therefore RSIP is deemed partially compliant to this
    requirement.
 Megaco: Megaco allows an MA to control several Middleboxes.  Each
    message carries an identifier of the endpoint that transmitted the
    message allowing the recipient to determine the source.
 Diameter: Diameter allows connection to more than one peer (and
    encourages this for improved reliability).  Whether the Diameter
    connection state machine is too heavy to support the number of
    connections needed is a matter for discussion.
 COPS: COPS PDPs are designed to communicate with several PEPs.

2.1.3. Middlebox Can Relate to Multiple Agents

 SNMP: T, RSIP: P, Megaco: T, Diameter: T, COPS: T
 SNMP:  An SNMP agent can communicate with several SNMP managers
    Simultaneously.
 RSIP: Refer to 2.1.2.
 Megaco: Megaco has the concept of Virtual Media Gateways (VMG),
    allowing multiple MGCs to communicate simultaneously with the same
    MG.  Applying this model to MIDCOM would allow the same middlebox
    (MG) to have associations with multiple MIDCOM Agents (MGCs).

Barnes Informational [Page 13] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Diameter: Diameter allows connection to more than one peer and
    encourages this for improved reliability.  Whether the Diameter
    connection state machine is too heavy to support the number of
    connections needed is a matter for discussion.  The Middlebox and
    Agent play symmetric roles as far as Diameter peering is
    concerned.
 COPS: The COPS-PR framework specifies that a PEP should have a
    unique PDP in order to achieve effective policy control.  The
    COPS-PR protocol would allow the scenario whereby a PEP
    establishes communication with multiple PDPs by creating a COPS
    client instance per PDP.

2.1.4. Deterministic Outcome When Multiple Requests are Presented to

      the Middlebox Simultaneously
 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  While the architectural design of SNMP can permit race
    conditions to occur, there are mechanisms defined as part of the
    SNMPv3 standard, such as view-based access control and advisory
    locking that can be used to prevent the conditions, and MIB
    modules may also contain special functionality, such as RMONs
    OwnerString, to prevent conflicts.  Deterministic behavior of SNMP
    agents when being accessed by multiple managers is important for
    several management applications and supported by SNMP.
 RSIP: All RSIP requests are defined to be atomic.  Near simultaneous
    requests are executed as is they were sequential.
 Megaco: Megaco supports the concept of VMGs to make these
    interactions deterministic and to avoid resource access conflicts.
    Each VMG has a single owner, in a MGC, and there can be no overlap
    between the sets of Terminations belonging to multiple VMGs.  The
    Megaco protocol messages also include the identifier of the
    sending entity, so that the MG can easily determine to whom to
    send the response or asynchronously report certain events.
 Diameter: Diameter depends partly upon the transport protocol to
    provide flow control when the server becomes heavily loaded.  It
    also has application-layer messaging to indicate that it is too
    busy or out of space (Diameter_TOO_BUSY and Diameter_OUT_OF_SPACE
    result codes).
 COPS: COPS has built-in support for clear state and policy
    instances.  This would allow the creation of well-behaved MIDCOM
    state machines.

Barnes Informational [Page 14] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.1.5. Known and Stable State

 SNMP: T, RSIP: T, Megaco: T, Diameter: P, COPS: T
 SNMP:  Requests are atomic in SNMP.  MIB modules can define which
    data is persistent across reboots, so a known startup state can be
    established.  The manager can poll the agent to determine the
    current state.
 RSIP: RSIP assumes that on middlebox start-up no sessions are
    defined, and thus no allocations have been made.  In effect, all
    resources are released upon restart after failure.
 Megaco: Megaco has extensive audit capabilities to synchronize
    states between the MG and the MGC.  Megaco also provides the MGC
    with the ability to do mass resets, as well as individual resets.
    The MGC can always release resources in the MG.  The MG can also
    initiate the release of resources by the MGC.
 Diameter: Diameter documentation does not discuss the degree of
    atomicity of message processing, so this would have to be
    specified in the MIDCOM extension.
 COPS: The COPS protocol maintains synchronized states between
    Middleboxes and MA hence all the states are known on both sides.

2.1.6. Middlebox Status Report

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  The status of a middlebox can be reported using asynchronous
    communications, or via polling.
 RSIP: All RSIP client requests have explicit server responses.
    Additionally, a client may explicitly request server status using
    a QUERY request.
 Megaco: Megaco has extensive audit capabilities for the MG to
    report status information to the MGC.  It can also report some
    status updates using the ServiceChange command.
 Diameter: Diameter provides a number of response codes by means of
    which a server can indicate error conditions reflecting status of
    the server as a whole.  The Disconnect-Peer-Request provides a
    means in the extreme case to terminate a connection with a peer
    gracefully, informing the other end about the reason for the
    disconnection.

Barnes Informational [Page 15] RFC 4097 MIDCOM Protocol Evaluation June 2005

 COPS: The COPS Report message is designed to indicate any
    asynchronous conditions/events.

2.1.7. Middlebox Can Generate Unsolicited Messages

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  SNMPv3 supports both confirmed and unconfirmed asynchronous
    notifications.
 RSIP: An RSIP server will send an unsolicited DE_REGISTER_RESPONSE
    to force an RSIP host to relinquish all of its bindings and
    terminate its relationship with the RSIP gateway.  An RSIP server
    can send an asynchronous ERROR_RESPONSE to indicate less severe
    conditions.
 Megaco: Megaco supports the asynchronous notification of events
    using the Notify command.
 Diameter: The Diameter protocol permits either peer in a connection
    to originate transactions.  Thus the protocol supports Middlebox-
    originated messages.
 COPS: The COPS Report message is designed to indicate any
    asynchronous conditions/events.

2.1.8. Mutual Authentication

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP: SNMPv3 meets this requirement.  SNMPv3 supports user
    authentication and explicitly supports symmetric secret key
    encryption between MIDCOM agent (SNMP manager) and Middlebox (SNMP
    agent), thus supporting mutual authentication.  The default
    authentication and encryption methods are specified in RFC 3414
    [11] (MD5, SHA-1, and DES).  Different users at the same
    management application (MIDCOM agent) can authenticate themselves
    with different authentication and encryption methods, and
    additional methods can be added to SNMPv3 entities as needed.
 RSIP: This requirement can be met by operating RSIP over IPSec as
    described in RFC 3104 [19].  The RSIP framework recommends all
    communication between an RSIP host and gateway be authenticated.
    Authentication, in the form of a message hash appended to the end
    of each RSIP protocol packet, can serve to authenticate the RSIP
    host and gateway to one another, provide message integrity, and

Barnes Informational [Page 16] RFC 4097 MIDCOM Protocol Evaluation June 2005

    avoid replay attacks with an anti-replay counter.  However, the
    message hash and replay counter parameters would need to be
    defined for the RSIP protocol.
 Megaco: Megaco provides for the use of IPSec [22] for all security
    mechanisms including mutual authentication, integrity check and
    encryption.  Use of IKE is recommended with support of RSA
    signatures and public key encryption.
 Diameter: The Diameter base protocol assumes that messages are
    secured by using either IPSec or TLS [21].  Diameter requires that
    when using the latter, peers must mutually authenticate
    themselves.
 COPS: COPS has built-in message level security for authentication,
    replay protection, and message integrity.  COPS can also use TLS
    or IPSec.

2.1.9. Termination of session by either party

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP: Each SNMPv3 message is authenticated and authorized, so each
    message could be considered to have its own session, which
    automatically terminates after processing.  Processing may be
    stopped for a number of reasons, such as security, and a response
    is sent.
    Either peer may stop operating, and be unavailable for further
    operations.  The authentication and/or authorization parameters of
    a principal may be changed between operations if desired, to
    prevent further authentication or authorization for security
    reasons.
    Additionally, managed objects can be defined for realizing
    sessions that persist beyond processing of a single message.  The
    MIB module would need to specify the responsibility for cleanup of
    the objects following normal/abnormal termination.
 RSIP: An RSIP client may terminate a session with a
    DE_REGISTER_REQUEST.  An RSIP server may terminate a session with
    an unsolicited DE_REGISTER_RESPONSE, and then respond to
    subsequent requests on the session with a REGISTER_FIRST error.
 Megaco: The Megaco protocol allows both peers to terminate the
    association with proper reason code.

Barnes Informational [Page 17] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Diameter: Either peer in a connection may issue a Disconnect-Peer-
    Request to end the connection gracefully.
 COPS: COPS allows both the PEP and PDP to terminate a session.

2.1.10. Indication of Success or Failure

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP: Each operation request has a corresponding response message
    that contains an error status to indicate success or failure.  For
    complex requests that the middlebox cannot complete immediately,
    the corresponding MIB module may be designed to also provide
    asynchronous notifications of the success or failure of the
    complete transaction, and/or may provide pollable objects that
    indicate the success or failure of the complete transaction.  For
    example, see ifAdminStatus and ifOperStatus in RFC 2863 [28].
 RSIP: All RSIP requests result in a paired RSIP response if the
    request was successful or an ERROR_RESPONSE if the request was not
    successful.
 Megaco: Megaco defines a special descriptor called an Error
    descriptor that contains the error code and an optional
    explanatory string.
 Diameter: Every Diameter request is matched by a response, and this
    response contains a result code as well as other information.
 COPS: The COPS Report message directly fulfills this requirement.

2.1.11. Version Interworking

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP: SNMP has a separation of the protocol to carry data, and the
    data that defines additional management functionality.  Additional
    functionality can be added easily through MIBs.  Capability
    exchange in SNMP is usually uni-directional.  Managers can query
    the middlebox (SNMP agent) to determine which MIBs are supported.
    In addition, multiple message versions can be supported
    simultaneously, and are identified by a version number in the
    message header.
 RSIP: Each RSIP message contains a version parameter.
 Megaco: Version interworking and negotiation are supported both for
    the protocol and any extension Packages.

Barnes Informational [Page 18] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Diameter: The Capabilities Exchange Request/Answer allows two peers
    to determine information about what each supports, including
    protocol version and specific applications.
 COPS: The COPS protocol can carry a MIDCOM version number and
    capability negotiation between the COPS client and the COPS
    server.  This capability negotiation mechanism allows the COPS
    client and server to communicate the supported
    features/capabilities.  This would allow seamless version
    interworking.

2.1.12. Deterministic Behaviour in the Presence of Overlapping

       Rules
 SNMP: T, RSIP: T, Megaco: P, Diameter: T, COPS: T
 SNMP: Rulesets would be defined in MIBs.  The priority of rulesets,
    and the resolution of conflict, can be defined in the MIB module
    definition.  The SNMPConf policy MIB defines mechanisms to achieve
    deterministic behavior in the presence of overlapping rule sets.
 RSIP: All requests for allocation of IP addresses, or ports or both
    resulting in rule overlap are rejected by an RSIP server with a
    LOCAL_ADDR_INUSE error.
 Megaco: This is met with the help of a model that separates Megaco
    protocol elements from the overlapping Policy rules (see Appendix
    C).  However, new behavior for the Megaco protocol elements needs
    to be specified as part of a new MIDCOM specific Package.
 Diameter: The IPFilterRule type specification, which would probably
    be used as the type of a Policy Rule AVP, comes with an extensive
    semantic description providing a deterministic outcome, which the
    individual Agent cannot know unless it knows all of the Policy
    Rules installed on the Middlebox.  Rules for the appropriate
    direction are evaluated in order, with the first matched rule
    terminating the evaluation.  Each packet is evaluated once.  If no
    rule matches, the packet is dropped if the last rule evaluated was
    a permit, and passed if the last rule was a deny.  The
    IPFilterRule format and further details on its applicability to
    this requirement are provided in Appendix D.
 COPS: The COPS protocol provides transactional-based communication
    between the PEP and PDP, hence the behavior is totally
    deterministic provided the middlebox state machine is designed
    correctly.  The COPS protocol features encourage and support good
    state machine design.

Barnes Informational [Page 19] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.2. Protocol Semantics

 This section contains the individual protocols as evaluated against
 the protocol semantic requirements from section 2.2 of the
 requirements document [1].  A short description of each of the
 protocols is provided to substantiate the evaluation.

2.2.1. Extensibility

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP: Extensibility is a basic feature of the SNMP management
    Framework.
 RSIP: All RSIP messages consist of three mandatory fields (protocol
    version, message type, and message length) and a sequence of
    parameterType / length / value 3-tuples.  New messages may be
    defined by defining new values for the message type field.  New
    parameter types may be defined, and existing messages may be
    extended, by defining new parameterType values.  If new messages,
    parameters, or both are added in a non-backward compatible way, a
    new value of the protocol version field may be defined.  This may
    be desirable even of the additions are backward compatible.
 Megaco: Megaco is easily extensible through new Packages, which
    allow definition of new attributes and behavior of a Termination.
 Diameter: Diameter provides a great deal of flexibility for
    extensions, including allowance for vendor-defined commands and
    AVPs and the ability to flag each AVP as must-understand or
    ignorable if not understood.
 COPS: The COPS protocol is extensible, since it was designed to
    separate the Protocol from the Policy Control Information.

2.2.2. Support of Multiple Middlebox Types

 SNMP: T, RSIP: P+, Megaco: T, Diameter: P+, COPS: T
 SNMP: SNMP explicitly supports managing different device types with
    different capabilities.  First the managed object called
    sysObjectID from basic MIB-II [3] identifies the type of box.  For
    boxes with variable capabilities, SNMP can check the availability
    of corresponding MIBs.

Barnes Informational [Page 20] RFC 4097 MIDCOM Protocol Evaluation June 2005

 RSIP: All types of middleboxes are supported so long as the ruleset
    action is permit.  Other actions would require the definition of a
    new RSIP message parameter with values for permit and the other
    desired actions.
 Megaco: Megaco can support multiple Middlebox types on the same
    interface either by designing the properties representing the
    Policy Rules to provide this support, or by using multiple
    terminations in the same session, each representing one type of
    action.  In the latter case, the Megaco Context can be used as a
    convenient means of managing the related terminations as a group.
    However, the inherent idea of flow between terminations of a
    context is irrelevant and would have to be discarded.
 Diameter: Any necessary additional AVPs or values must be specified
    as part of the MIDCOM application extension (see <2.2.8> below).
 COPS: COPS allows a PDP to provide filters and actions to multiple
    PEP functions through a single COPS session.

2.2.3. Ruleset Groups

 SNMP: T, RSIP: P+, Megaco: T, Diameter: T, COPS: T
 SNMP: This requirement can be realized via the SNMP management
    framework by an appropriate definition of a MIB module.  The
    SNMPConf WG has already defined an SNMP Policy MIB that permits
    the definitions of policy rulesets and grouping of rulesets.
 RSIP: RSIP currently only allows one IP address, or address and
    port range, to be assigned to a bind-ID.  RSIP could implement
    rulesets as required by adding an optional bind-ID parameter to
    the ASSIGN_REQUESTs to extend an existing ruleset rather than
    creating a new one.  Similarly, the FREE_REQUESTs would have to be
    extended by adding optional, local and remote, address and port
    parameters.
 Megaco: The Megaco context can be used to group terminations to be
    managed together.  For example, all of the terminations, each
    representing an instantiation of a Policy Rule, can be deleted in
    one command by doing a wildcarded Subtract from the context.
    However, the inherent idea of media flows between terminations of
    a context would be irrelevant in this application of the protocol.
 Diameter: Diameter allows message syntax definitions where multiple
    instances of the same AVP (for example, a Policy Rule AVP whose
    syntax and low-level semantics are defined by the IPFilterRule
    type definition) may be present.  If a tighter grouping is

Barnes Informational [Page 21] RFC 4097 MIDCOM Protocol Evaluation June 2005

    required, the set of Diameter base types includes the Grouped
    type.  MIDCOM can choose how to make use of these capabilities to
    meet the ruleset group requirement when defining its application
    extension to the Diameter protocol.
 COPS: The COPS-PR Handle State may be used to associate the set of
    closely related policy objects.  As the Middlebox learns
    additional requirements, the Middlebox adds these resource
    requirements under the same handle ID, which constitutes the
    required aggregation.

2.2.4. Lifetime Extension

 SNMP: P+, RSIP: T, Megaco: T, Diameter: T, COPS: P+
 SNMP: This requirement can be realized via the SNMP management
    framework by an appropriate definition of a MIB module.  The
    SNMPConf WG has developed a Policy MIB module that includes a
    pmPolicySchedule object with a modifiable lifetime.
 RSIP: A client may request an explicit lease time when a request is
    made to assign one or more IP addresses, ports or both.  The
    server may grant the requested lease time, or assign one if none
    was requested.  Subsequently, the lease time may be extended if a
    client's EXTEND_REQUEST is granted by the server.
 Megaco: The MG can report the imminent expiry of a policy rule to
    the MGC, which can then extend or delete the corresponding
    Termination.
 Diameter: The Diameter concept of a session includes the session
    lifetime, grace period, and lifetime extension.  It may make sense
    to associate the Diameter session with the lifetime of a MIDCOM
    Policy Rule, in which case support for lifetime extension comes
    ready-made.
 COPS: COPS allows a PDP to send unsolicited decisions to the PEP.
    However, the unsolicited events will be relevant to the COPS
    MIDCOM specific client or the MIDCOM specific PIB which needs to
    be defined.  This would allow the PDP to extend the lifetime of an
    existing ruleset.

Barnes Informational [Page 22] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.2.5. Handling of Mandatory/Optional Nature of Unknown Attributes

 SNMP: T, RSIP: T, Megaco: P+, Diameter: P+, COPS: T
 SNMP: Unknown attributes in a read operation are flagged as
    exceptions in the Response message, but the rest of the read
    succeeds.  In a write operation (a SET request), all attributes
    are validated before the write is performed.  If there are unknown
    attributes, the request fails and no writes are done.  Unknown
    attributes are flagged as exceptions in the Response message, and
    the error status is reported.
 RSIP: All options of all requests are fully specified.  Not
    understood parameters must be reported by an ERROR_RESPONSE with
    an EXTRA_PARM error value, with the entire request otherwise
    ignored.
 Megaco: Megaco entities provide Error codes in response messages.
    If a command marked "Optional" in a transaction fails, the
    remaining commands will continue.  However, the specified
    requirement deals with rules of processing properties that need
    definition in new Package.
 Diameter: Indication of the mandatory or optional status of AVPs is
    fully supported, provided it is enabled in the AVP definition.  No
    guidance is imposed regarding the return of diagnostic information
    for optional AVPs.
 COPS: COPS provides for the exchange of capabilities and
    limitations between the PEP and PDP to ensure well-known outcomes
    are understood for scenarios with unknown attributes.  There is
    also clear error handling for situations when the request is
    rejected.

2.2.6. Actionable Failure Reasons

 SNMP: T, RSIP: P+, Megaco: T, Diameter: T, COPS: T
 SNMP: The SNMPv3 protocol returns error codes and exception codes
    in Response messages, to permit the requestor to modify their
    request.  Errors and exceptions indicate the attribute that caused
    the error, and an error code identifies the nature of the error
    encountered.
    If desired, a MIB can be designed to provide additional data about
    error conditions either via asynchronous notifications or polled
    objects.

Barnes Informational [Page 23] RFC 4097 MIDCOM Protocol Evaluation June 2005

 RSIP: RSIP defines a fairly large number of very specific error
    values.  It is anticipated that additional error values will also
    have to be defined along with the new messages and parameters
    required for MIDCOM.
 Megaco: The MG can provide Error codes in response messages
    allowing the MGC to modify its behavior.  Megaco uses transaction
    identifiers for correlation between a response and a command.  If
    the same transaction id is received more than once, the receiving
    entity silently discards the message, thus providing some
    protection against replay attacks.
 Diameter: Diameter provides an extensive set of failure reasons in
    the base protocol.
 COPS: COPS uses an error object to identify a particular COPS
    protocol error.  The error sub-code field may contain additional
    detailed COPS client (MIDCOM Middlebox) specific error codes.

2.2.7. Multiple Agents Operating on the Same Ruleset.

 SNMP: T, RSIP: P, Megaco: P, Diameter: T, COPS: P
 SNMP: The SNMP framework supports multiple managers working on the
    same managed objects.  The View-based Access Control Model (VACM,
    RFC 3415 [14]) even offers means to customize the access rights of
    different managers in a fine-grained way.
 RSIP: RSIP neither explicitly permits nor precludes an operation on
    a binding by a host that had not originally create the binding.
    However, to support this requirement, the RSIP semantics must be
    extended to explicitly permit any authorized host to request
    operations on a binding; this does not require a change to the
    protocol.
 Megaco: If the Megaco state machine on the Middle Box is decoupled
    from the Middle Box policy rule management, this requirement can
    be met with local policies on the Middle Box.  However, this
    violates the spirit of the Megaco protocol, thus Megaco is
    considered partially compliant to this requirement.
 Diameter: The Diameter protocol, as currently defined, would allow
    multiple agents to operate on the same ruleset.
 COPS: It is possible to use COPS to operate the same resource with
    multiple agents.  An underlying resource management function,
    separate from the COPS state machine, on the Middlebox will handle
    the arbitration when resource conflicts happen.

Barnes Informational [Page 24] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.2.8. Transport of Filtering Rules

 SNMP: P+, RSIP: P+, Megaco: P+, Diameter: P+, COPS: P+
 SNMP: This requirement can be met by an appropriate definition of a
    MIDCOM MIB module.  SMI, the language used for defining MIB
    modules, is flexible enough to allow the implementation of a MIB
    module to meet the semantics of this requirement.
 RSIP: To support this requirement, a new optional enumeration
    parameter, transportProtocol, can be added to the RSIP
    ASSIGN_REQUESTs.  When the parameter is included, the binding
    created applies only to the use of the bound addresses and ports,
    by the specific transportProtocol.  When the parameter is not
    included, the binding applies to the use of all the bound
    addresses and ports, by any transport protocol, thus maintaining
    backward compatibility with the current definition of RSIP.
 Megaco: Megaco protocol can meet this requirement by defining a new
    property for the transport of filtering rules.
 Diameter: While Diameter defines the promising IPFilterRule data
    type (see 2.1.12 above), there is no existing message, which would
    convey this to a Middlebox along with other required MIDCOM
    attributes.  A new MIDCOM application extension of Diameter would
    have to be defined.
 COPS: The COPS protocol can meet this requirement by using a COPS
    MIDCOM specific client or a MIDCOM specific PIB.

2.2.9. Mapped Port Parity

 SNMP: P+, RSIP: P+, Megaco: P+, Diameter: P+, COPS: P+
 SNMP: This requirement can be met by an appropriate definition of a
    MIDCOM MIB module.
 RSIP: To support this requirement, a new optional boolean
    parameter, portOddity, can be added to the RSIP ASSIGN_REQUESTs.
    If the parameter is TRUE, the remote port number of the binding
    created would have the same oddity as the local port.  If the
    parameter is not specified, or is FALSE, the remote port's oddity
    is independent of the local port's oddity, thus maintaining
    backward compatibility with the current definition of RSIP.
 Megaco: Megaco can be easily extended using a MIDCOM specific
    Package to support this feature.

Barnes Informational [Page 25] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Diameter: This capability is not part of the current IPFilterRule
    type definition.  Rather than modify the IPFilterRule type, MIDCOM
    could group it with other AVPs which add the missing information.
 COPS: The COPS protocol has all the flexibility to meet this
    requirement by using a COPS MIDCOM specific client or a MIDCOM
    specific PIB.

2.2.10. Consecutive Range of Port Numbers

 SNMP: P+, RSIP: T, Megaco: P+, Diameter: P+, COPS: P+
 SNMP: This requirement can be met by an appropriate definition of a
    MIDCOM MIB module.  SMI, the language used for defining MIB
    modules, is flexible enough to allow the implementation of a MIB
    module to meet the semantics of this requirement.
 RSIP: The ports parameter of the RSIP ASSIGN_REQUESTs specifically
    allows multiple, consecutive port numbers to be specified.
 Megaco: Megaco can be easily extended using a MIDCOM specific
    Package to support this feature.
 Diameter: This capability is not part of the current IPFilterRule
    type definition.  Rather than modify the IPFilterRule type, MIDCOM
    could group it with other AVPs which add the missing information.
 COPS: The COPS protocol has all the flexibility to meet this
    requirement by using a COPS MIDCOM specific client or a MIDCOM
    specific PIB.

2.2.11. More Precise Rulesets Contradicting Overlapping Rulesets

 SNMP: P+, RSIP: P+, Megaco: P+, Diameter: T, COPS: P+
 SNMP: This requirement can be met by an appropriate definition of a
    MIDCOM MIB module.
 RSIP: To support this requirement, a new optional boolean
    parameter, overlapOK, can be added to the RSIP ASSIGN_REQUESTs.
    If the parameter is TRUE, the binding may overlap with an existing
    binding.  If the parameter is unspecified, or is FALSE, the
    binding will not overlap with an existing binding, thus
    maintaining backward compatibility with the current definition of
    RSIP.

Barnes Informational [Page 26] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Megaco: This requirement would be met if the policy in the
    Middlebox allows contradictory, overlapping policy rules to be
    installed.
 Diameter: Allowed by the IPFilterRule semantics described in
    Appendix D.
 COPS: The COPS protocol has all the flexibility to meet this
    requirement by using a COPS MIDCOM specific client or a MIDCOM
    specific PIB.

2.3. General Security Requirements

 This section contains the individual protocols as evaluated against
 the General Security requirements from section 2.3 of the
 requirements document [1].  A short description of each of the
 protocols is provided to substantiate the evaluation.

2.3.1. Message Authentication, Confidentiality and Integrity

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  SNMPv3 includes the User-based Security Model (USM,
    RFC 3414 [11]), which defines three standardized methods for
    providing authentication, confidentiality, and integrity.
    Additionally, USM has specific built-in mechanisms for preventing
    replay attacks including unique protocol engine IDs, timers and
    counters per engine and time windows for the validity of messages.
 RSIP: This requirement can be met by operating RSIP over IPSec.  The
    RSIP framework recommends all communication between an RSIP host
    and gateway be authenticated.  Authentication, in the form of a
    message hash appended to the end of each RSIP protocol packet, can
    serve to authenticate the RSIP host and gateway to one another,
    provide message integrity, and avoid replay attacks with an anti-
    replay counter.  However, the message hash and replay counter
    parameters would need to be defined for the RSIP protocol.
 Megaco: Megaco provides for these functions with the combined usage
    of IPSEC [22] or TLS [21].
 Diameter: Diameter relies on either IPSEC or TLS for these
    functions.
 COPS: COPS has built-in message level security for authentication,
    replay protection, and message integrity.  COPS can also use TLS
    or IPSec, thus reusing existing security mechanisms that have
    interoperated in the markets.

Barnes Informational [Page 27] RFC 4097 MIDCOM Protocol Evaluation June 2005

2.3.2. Optional Confidentiality Protection

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  SNMPv3 includes the User-based Security Model, which defines
    three standardized methods for providing authentication,
    confidentiality, and integrity, and is open to add further
    methods.  The method to use can be optionally chosen.
 RSIP: Refer to 2.3.1.
 Megaco: Refer to 2.3.1
 Diameter: Implementation support of IPSEC ESP (RFC 2406 [23]) in
    Diameter applications is not optional.  Deployment of either IPSEC
    or TLS is optional.
 COPS: Refer to 2.3.1.

2.3.3. Operate Across Untrusted Domains

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  The User-based Security Model of SNMPv3 defines three
    standardized methods for providing authentication,
    confidentiality, and integrity, and it is open to add further
    methods.  These methods operate securely across untrusted domains.
 RSIP: Refer to 2.3.1.
 Megaco: Refer to 2.3.1.
 Diameter: The Diameter specification [24] recommends the use of
    TLS [21] across untrusted domains.
 COPS: Refer to 2.3.1

2.3.4. Mitigates Replay Attacks on Control Messages

 SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
 SNMP:  The User-based Security Model for SNMPv3 has specific built-
    in mechanisms for preventing replay attacks including unique
    protocol engine IDs, timers and counters per engine and time
    windows for the validity of messages.
 RSIP: Refer to 2.3.1

Barnes Informational [Page 28] RFC 4097 MIDCOM Protocol Evaluation June 2005

 Megaco: Megaco commands and responses include matching transaction
    identifiers.  The recipient receiving the same transaction id
    multiple times would discard the message, thus providing some
    protection against replay attacks.  If even stronger protection
    against replay attack is needed, Megaco provides for the use of
    IPSec or TLS.
 Diameter: Diameter requires that implementations support the replay
    protection mechanisms of IPSEC.
 COPS: Refer to 2.3.1

3. Conclusions

 The overall statistics with regards to the number of Fully Compliant,
 Partially Compliant (P+ and P) and Failing Compliancy requirements
 for each of the protocols is summarized in table 1.
               T            P+           P            F
 -----------------------------------------------------------------
 SNMP          22           5            0            0
 RSIP          17           7            3            0
 Megaco        19           5            3            0
 Diameter      21           5            1            0
 COPS          20           5            2            0
               Table 1: Totals across all Requirements
 In considering the P+ category of compliancy, an important aspect is
 the mechanism for support of extensibility.  The extension mechanism
 provided by SNMP and COPS-PR using MIBs and PIBs respectively,
 provides extensions with no impact to the protocol.  Diameter
 extensions require protocol changes, thus has a higher impact,
 although the extensions can be handled by other Diameter entities
 without being understood.  Megaco's extension mechanisms of packages
 also requires protocol changes that must be understand by both
 sending and receiving entities, also being considered higher impact.
 The RSIP extension mechanism has the largest impact on the existing
 protocol and is based upon defining the necessary new parameters.
 The SNMP management framework meets all the specified MIDCOM protocol
 requirements with the appropriate design of a MIDCOM MIB module.
 SNMP is a proven technology with stable and proven development tools,
 already has extensions defined to support NAT configuration and
 policy-based management.  SNMPv3 is a full standard, is more mature
 and has undergone more validation than the other protocols in

Barnes Informational [Page 29] RFC 4097 MIDCOM Protocol Evaluation June 2005

 the evaluation, and has been deployed to manage large-scale real-
 world networks (e.g., DOCSIS cable modem networks).  The
 applicability of SNMP to the MIDCOM framework has a restriction in
 that it assumes the MIDCOM PDP is part of the Middlebox.
 RSIP fully meets many of the MIDCOM requirements.  However, it does
 require additions and extensions to meet several of the requirements.
 RSIP would also require several framework elements to be added to the
 MIDCOM framework as identified in section 1.2.3.  In addition, the
 tunneling required for RSIP as described in section 1.2.4, results in
 RSIP not being acceptable by the WG as the MIDCOM protocol.
 Megaco fully meets most of the key requirements for the MIDCOM
 Protocol.  Additional extensions in the form of a new Termination /
 Package definition would be required for MIDCOM to meet several of
 the requirements.  In order to meet the remaining requirements,
 modeling the underlying Middlebox resources (e.g., filters, policy
 rules) as separate elements from the Megaco entities might allow the
 usage of the protocol as-is, satisfying some of the resource access
 control requirements.
 The Diameter evaluation indicated a good overall fit.  Some partially
 met requirements were identified that could be addressed by a new
 application extension.  However, the Diameter architecture may be too
 heavy for the MIDCOM application and clearly much of the Diameter
 base is not needed.  In addition, Diameter is the only protocol, at
 the time of this evaluation, for which the RFCs had not yet been
 published.  Other than these reservations, the protocol is a good fit
 to MIDCOM requirements.
 The COPS evaluation indicates that the protocol meets the majority of
 the MIDCOM protocol requirements by using the protocol's native
 extension techniques, with COPS-PR being explicitly required to meet
 requirements 2.1.3 and 2.2.3.  In order to fully satisfy one
 partially met requirement, 2.1.1, the COPS model would need to allow
 a PDP to establish communication with a PEP.  While not explicitly
 prohibited by the COPS model, this would require additions, in the
 form of local policy, to ensure the proper establishment of an
 authorized association.

4. Security Considerations

 Security considerations for the MIDCOM protocol are covered by the
 comparison against the specific Security requirements in the MIDCOM
 requirements document [1] and are specifically addressed by section
 2.1.8 and section 2.3.

Barnes Informational [Page 30] RFC 4097 MIDCOM Protocol Evaluation June 2005

5. References

5.1. Normative References

 [1]  Swale, R., Mart, P., Sijben, P., Brim, S., and  M. Shore,
      "Middlebox Communications (MIDCOM) Protocol Requirements", RFC
      3304, August 2002.
 [2]  Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and A.
      Rayhan, "Middlebox Communications Architecture and Framework",
      RFC 3303, August 2002.
 [3]  Rose, M. and K. McCloghrie, "Management Information Base for
      Network Management of TCP/IP-based internets: MIB-II", STD 17,
      RFC 1213, March 1991.
 [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [5]  Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for
      Describing SNMP Management Frameworks", STD 62, RFC 3411,
      December 2002.
 [6]  McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Structure of
      Management Information Version 2 (SMIv2)", STD 58, RFC 2578,
      April 1999.
 [7]  McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Textual
      Conventions for SMIv2", STD 58, RFC 2579, April 1999.
 [8]  McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Conformance
      Statements for SMIv2", STD 58, RFC 2580, April 1999.
 [9]  Presuhn, R. (Ed.), "Transport Mappings for the Simple Network
      Management Protocol (SNMP)", STD 62, RFC 3417, December 2002.
 [10] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message
      Processing and Dispatching for the Simple Network Management
      Protocol (SNMP)", STD 62, RFC 3412, December 2002.
 [11] Blumenthal, U. and B. Wijnen, "User-based Security Model(USM)
      for version 3 of the Simple Network Management Protocol
      (SNMPv3)", STD 62, RFC 3414, December 2002.
 [12] Presuhn, R. (Ed.), "Version 2 of the Protocol Operations for the
      Simple Network Management Protocol (SNMP)", STD 62, RFC 3416,
      December 2002.

Barnes Informational [Page 31] RFC 4097 MIDCOM Protocol Evaluation June 2005

 [13] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications", STD
      62, RFC 3413, December 2002.
 [14] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access
      Control Model (VACM) for the Simple Network Management Protocol
      (SNMP)", STD 62, RFC 3415, December 2002.
 [15] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction
      to Version 3 of the Internet-Standard Network Management
      Framework", RFC 3410, December 2002.
 [16] Rohit, R., Srisuresh, P., Raghunarayan, R., Pai, N., and C.
      Wang, "Definitions of Managed Objects for Network Address
      Translators (NAT)", RFC 4008, March 2005.
 [17] Borella, M., Lo, J., Grabelsky, D., and G. Montenegro, "Realm
      Specific IP: Framework", RFC 3102, October 2001.
 [18] Borella, M., Grabelsky, D., Lo, J., and  K. Taniguchi, "Realm
      Specific IP: Protocol Specification", RFC 3103, October 2001.
 [19] Montenegro, G. and M. Borella, "RSIP Support for End-to-end
      Ipsec", RFC 3104, October 2001.
 [20] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosen, B., and
      J. Segers, "Megaco Protocol Version 1.0", RFC 3015, October
      2001.
 [21] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
      2246, January 1999.
 [22] Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [23] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload",
      RFC 2406, November 1998.
 [24] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
      "Diameter Base Protocol", RFC 3588, September 2003.
 [25] Durham, D. (Ed.), Boyle, J., Cohen, R., Herzog, S., Rajan, R.,
      and A. Sastry, "The COPS (Common Open Policy Service) Protocol",
      RFC 2748, January 2000.
 [26] Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie, K.,
      Herzog, S., Reichmeyer, F., Yavatkar, R., and A. Smith, "COPS
      Usage for Policy Provisioning", RFC 3084, March 2001.

Barnes Informational [Page 32] RFC 4097 MIDCOM Protocol Evaluation June 2005

5.2. Informative References

 [27] Raz, D., Schoenwalder, J., and B. Sugla, "An SNMP Application
      Level Gateway for Payload Address Translation", RFC 2962,
      October 2000.
 [28] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
      RFC 2863, June 2000.

6. Acknowledgements

 The editor would like to acknowledge the constructive feedback
 provided by Joel M. Halpern on the individual protocol evaluation
 contributions.  In addition, a thanks to Elwyn Davies, Christopher
 Martin, Bob Penfield, Scott Brim and Martin Stiemerling for
 contributing to the mailing list discussion on the document content.

Barnes Informational [Page 33] RFC 4097 MIDCOM Protocol Evaluation June 2005

Appendix A - SNMP Overview

 The SNMP Management Framework presently consists of five major
 components:
 o  An overall architecture, described in RFC 3411 [5].  A more
    detailed introduction and applicability statements for the SNMP
    Management Framework can be found in RFC 3410 [15].
 o  Mechanisms for describing and naming objects and events for the
    purpose of management.  The current version of this Structure of
    Management Information (SMI) is called SMIv2 and described in RFC
    2578 [6], RFC 2579 [7] and RFC 2580 [8].
 o  Message protocols for transferring management information.  The
    current version of the message protocol is called SNMPv3 and
    described in RFC 3412 [10], RFC 3414 [11] and RFC 3417 [9].
 o  Protocol operations for accessing management information.  The
    current version of the protocol operations and associated PDU
    formats is described in RFC 3416 [12].
 o  A set of fundamental applications described in RFC 3413 [13] and
    the view-based access control mechanism described in RFC 3415
    [14].
 Managed objects are accessed via a virtual information store, termed
 the Management Information Base or MIB.  Objects in the MIB are
 defined using the mechanisms defined in the SMI.

A.1 SNMPv3 Proxy Forwarding

 SNMPv3 proxy forwarding (RFC 3413 [13]) provides a standardized
 mechanism to configure an intermediate node to forward SNMP messages.
 A command generating entity sends requests to a proxy forwarding
 entity that forwards the request to a third entity.
 One SNMP entity may serve both functions as the SNMP agent to monitor
 and configure the node on which it is resident, and as an
 intermediate node in a proxy relationship to permit monitoring and
 configuration of additional entities.
 Each entity is identified by a unique engineID value, specifically to
 support proxy between addressing domains and/or trust domains.  An
 SNMPv3 message contains two engineIDs- one to identify the database
 to be used for message security, and one to identify the source (or
 target) of the contained data.  Message security is applied between
 the originator and the proxy, and then between the proxy and the

Barnes Informational [Page 34] RFC 4097 MIDCOM Protocol Evaluation June 2005

 end-target.  The PDU contains the engineID of the node whose data is
 contained in the message, which passes end-to-end, unchanged by the
 proxy.
 SNMPv3 proxy was designed to provide a standard SNMP approach to
 inserting an intermediate node in the middle of communications for a
 variety of scenarios.  SNMPv3 proxy can support crossing addressing
 domains, such as IPv4 and IPv6, crossing SNMP version domains, such
 as SNMPv3 and SNMPv1, crossing security mechanism domains, such as
 DES and AES, and for providing a single point of management contact
 for a subset of the network, such as managing a private network
 through a NAT device or a VPN endpoint.

A.2 Proxies Versus Application Level Gateways

 Proxies are generally preferred to Application Level Gateways for
 SNMP.  ALGs typically modify the headers and content of messages.
 SNMP is a protocol designed for troubleshooting network (mis-)
 configurations.  Because an operator needs to understand the actual
 configuration, the translation of addresses within SNMP data causes
 confusion, hiding the actual configuration of a managed device from
 the operator.  ALGs also introduce security vulnerabilities, and
 other complexities related to modifying SNMP data.
 SNMP Proxies can modify message headers without modifying the
 contained data.  This avoids the issues associated with translating
 the payload data, while permitting application level translation of
 addresses.
 The issues of ALGs versus proxies for SNMP Payload Address
 Translation are discussed at length in RFC 2962 [27].

Appendix B - RSIP with Tunneling

 NAT requires ALGs (Application Layer Gateways) in middleboxes without
 MIDCOM, and application modifications or agents for middleboxes with
 MIDCOM.
 Support for NAT without tunneling could easily be added to the RSIP
 control protocol.  NAT would be defined as a new, null tunnel type.
 Support for the NAT null tunnels could be implemented in hosts, or in
 applications or application agents.
 If support for NAT null tunnels were implemented in hosts, no
 modifications to applications would be required, and no application
 agents or ALGs would be required.  This has obvious advantages.  In
 addition to the NAT null tunnel, the host would have to implement an
 RSIP / MIDCOM client (or a STUN client) and the middlebox would have

Barnes Informational [Page 35] RFC 4097 MIDCOM Protocol Evaluation June 2005

 to implement an RSIP / MIDCOM server, or a STUN server would have to
 be available _beyond_ the middlebox.  Note that the STUN client /
 server approach may not work with all types of middleboxes.
 If support for NAT null tunnels were NOT implemented in hosts, then
 applications would have to be modified, or application agents or ALGs
 would have to be implemented.  This has the advantage over tunnels
 (whether null or not) of not requiring modification to hosts, but
 would require the modification of host applications or the
 implementation of application agents, both of which would include an
 RSIP / MIDCOM client, and the implementation of an RSIP/MIDCOM server
 in the middlebox.  Again, in some situations, STUN could be used
 instead of RSIP / MIDCOM.
 Tunneled or not, an RSIP / MIDCOM server is needed in the middlebox.
 Tunneled, the host needs to be modified, but not the application.
 Untunneled, an agent must be added or the application must be
 modified, but there would be no host modifications.  The
 advantages/disadvantages of tunneling would need to be evaluated in
 considering RSIP.

Barnes Informational [Page 36] RFC 4097 MIDCOM Protocol Evaluation June 2005

Appendix C - Megaco Modeling Approach

 To model the Middlebox functions such as firewall, NAT etc., a new
 Middlebox Termination type needs to be defined within Megaco.  If
 policy-rule overlap or modification by multiple Agents is NOT
 required, then a policy rule is equivalent to a Termination (see
 Figure 1).  The various components of a Policy rule such as filter,
 action, life-time, creator etc. are described as various properties
 of a Termination.  Use of the Virtual Media Gateway (VMG) concept
 allows for conflict-free interaction of multiple MA's with the same
 MB.
               +-------+             +-------+
               |  MA-1 |             |  MA-2 |
               |       |             |       |
               +-------+     |IF2    +-------+
                   |         |          |
     +-------------|---------|----------|-----------+
     |     +---------+       | +-------------+      |
 IF1 |VMG1 | +--+    |       | | +--+  +--+  |VMG2  |IF3
 ----------| |Tx|-------+    +---|Ty|--|Tz|----------------
     |     | +--+    |  |      | +--+  +--+  |      |
     | ....|         |  |      +-------------+      |
     |     +---------+  |                           |
     |                  +---------------------------------
     | Middlebox                                    | IF4
     +----------------------------------------------+
                            Tx: Termination x = Policy rule x
                            Ty: Termination y = Policy rule y
                            Tz: Termination z = Policy rule z
                            MA: MIDCOM Agent
                            IF: Interface
                        Figure 1.

Barnes Informational [Page 37] RFC 4097 MIDCOM Protocol Evaluation June 2005

 If it is required to allow multiple agents manipulate the same
 Middlebox resource (e.g., a Policy rule or a filter), the latter
 needs to be kept separate from the Termination (the Policy rule is
 manipulated by the MA by manipulating the properties of the
 associated Termination).  For example, if overlapping policy rule
 manipulation is required, then a Termination shall be associated with
 a single policy rule, but a policy rule may be associated with more
 than one Termination.  Thus, a Termination can share a policy rule
 with another Termination, or have a policy rule partially overlapping
 with that of another Termination.  This model allows two MAs,
 controlling two distinct Terminations (see Figure 2), manipulate the
 same or overlapping policy rules.  In Figure 2, policy rules 1 and 2
 are overlapping and they are shared by MA-1 and MA-2.
               +-------+             +-------+
               |  MA-1 |             |  MA-2 |
               |       |             |       |
               +-------+     |IF2    +-------+
                   |         |          |          MB
     +-------------|---------|----------|-----------+
     |       +-----------+   | +-------------+      |
 IF1 |VMG1   |     +--+  |   | | +--+  +--+  |VMG2  |IF3
 ------------------|Ty|----+ +---|Tx|--|Tz|----------------
     |       |     +--+  | |   | +--+  +--+  |      |
     | ....  |       |   | |   +--/------\---+      |
     |       +-------|---+ |     /        \         |
     |               |     +----/----------\------------------
     |            +------+----+------+   +------+   |IF4
     |            |Policy1 Policy2   |   |Policy|   |
     |            |    |      |      |   |  3   |   |
     |            +----+------+------+   +------+   |
     +----------------------------------------------+
                      Tx: Termination x
                      Ty: Termination y
                      Tz: Termination z
                      MA: MIDCOM Agent
                      IF: Interface
                      MB: Middlebox
                         Figure 2.
 This requires that the Agent and the Middlebox adhere to the
 following principles:
 (1) Only one Termination has read/write access to a filter at any
     time.

Barnes Informational [Page 38] RFC 4097 MIDCOM Protocol Evaluation June 2005

 (2) When the policy rule is being modified by a new agent (i.e., not
     the one that created the policy) the Middlebox makes a policy
     decision and decides whether to accept the requested modification
     or not.  In the case the modification is accepted the initial
     MIDCOM agent may be notified.

Appendix D - Diameter IPFilter Rule

 The IPFilterRule format is derived from the OctetString AVP Base
 Format.  It uses the UTF-8 encoding and has the same requirements as
 the UTF8String.  Packets may be filtered based on the following
 information that is associated with it:
    Direction                          (in or out)
    Source and destination IP address  (possibly masked)
    Protocol
    Source and destination port        (lists or ranges)
    TCP flags
    IP fragment flag
    IP options
    ICMP types
 Rules for the appropriate direction are evaluated in order, with the
 first matched rule terminating the evaluation.  Each packet is
 evaluated once.  If no rule matches, the packet is dropped if the
 last rule evaluated was a permit, and passed if the last rule was a
 deny.
 IPFilterRule filters MUST follow the format:
 action dir proto from src to dst [options]
 action       permit - Allow packets that match the rule.
              deny   - Drop packets that match the rule.
 dir          "in" is from the terminal, "out" is to the
              terminal.
 proto        An IP protocol specified by number.  The "ip"
              keyword means any protocol will match.
 src and dst  <address/mask> [ports]

Barnes Informational [Page 39] RFC 4097 MIDCOM Protocol Evaluation June 2005

              The <address/mask> may be specified as:
              ipno       An IPv4 or IPv6 number in dotted-
                         quad or canonical IPv6 form.  Only
                         this exact IP number will match the
                         rule.
              ipno/bits  An IP number as above with a mask
                         width of the form 1.2.3.4/24.  In
                         this case, all IP numbers from
                         1.2.3.0 to 1.2.3.255 will match.
                         The bit width MUST be valid for the
                         IP version and the IP number MUST
                         NOT have bits set beyond the mask.
                         For a match to occur, the same IP
                         version must be present in the
                         packet that was used in describing
                         the IP address.  To test for a
                         particular IP version, the bits part
                         can be set to zero.  The keyword
                         "any" is 0.0.0.0/0 or the IPv6
                         equivalent.  The keyword "assigned"
                         is the address or set of addresses
                         assigned to the terminal.  For IPv4,
                         a typical first rule is often
                         "deny in ip! assigned"
              The sense of the match can be inverted by
              preceding an address with the not modifier (!),
              causing all other addresses to be matched
              instead.  This does not affect the selection of
              port numbers.
              With the TCP, UDP and SCTP protocols, optional
              ports may be specified as:
                      {port|port-port}[,ports[,...]]
              The '-' notation specifies a range of ports
              (including boundaries).
              Fragmented packets that have a non-zero offset
              (i.e., not the first fragment) will never match
              a rule that has one or more port
              specifications.  See the frag option for
              details on matching fragmented packets.

Barnes Informational [Page 40] RFC 4097 MIDCOM Protocol Evaluation June 2005

 options:
    frag    Match if the packet is a fragment and this is not
            the first fragment of the datagram.  frag may not
            be used in conjunction with either tcpflags or
            TCP/UDP port specifications.
    ipoptions spec
            Match if the IP header contains the comma
            separated list of options specified in spec.  The
            supported IP options are:
            ssrr (strict source route), lsrr (loose source
            route), rr (record packet route) and ts
            (timestamp).  The absence of a particular option
            may be denoted with a '!'.
    tcpoptions spec
            Match if the TCP header contains the comma
            separated list of options specified in spec.  The
            supported TCP options are:
            mss (maximum segment size), window (tcp window
            advertisement), sack (selective ack), ts (rfc1323
            timestamp) and cc (rfc1644 t/tcp connection
            count).  The absence of a particular option may
            be denoted with a '!'.
    established
            TCP packets only.  Match packets that have the RST
            or ACK bits set.
    setup   TCP packets only.  Match packets that have the SYN
            bit set but no ACK bit.
    tcpflags spec
            TCP packets only.  Match if the TCP header
            contains the comma separated list of flags
            specified in spec.  The supported TCP flags are:
            fin, syn, rst, psh, ack and urg.  The absence of a
            particular flag may be denoted with a '!'.  A rule
            that contains a tcpflags specification can never
            match a fragmented packet that has a non-zero
            offset.  See the frag option for details on
            matching fragmented packets.

Barnes Informational [Page 41] RFC 4097 MIDCOM Protocol Evaluation June 2005

    icmptypes types
            ICMP packets only.  Match if the ICMP type is in
            the list types.  The list may be specified as any
            combination of ranges or individual types
            separated by commas.  Both the numeric values and
            the symbolic values listed below can be used.  The
            supported ICMP types are:
            echo reply (0), destination unreachable (3),
            source quench (4), redirect (5), echo request
            (8), router advertisement (9), router
            solicitation (10), time-to-live exceeded (11), IP
            header bad (12), timestamp request (13),
            timestamp reply (14), information request (15),
            information reply (16), address mask request (17)
            and address mask reply (18).
 There is one kind of packet that the access device MUST always
 discard, that is an IP fragment with a fragment offset of one.  This
 is a valid packet, but it only has one use, to try to circumvent
 firewalls.
 An access device that is unable to interpret or apply a deny rule
 MUST terminate the session.  An access device that is unable to
 interpret or apply a permit rule MAY apply a more restrictive rule.
 An access device MAY apply deny rules of its own before the supplied
 rules, for example to protect the access device owner's
 infrastructure.
 The rule syntax is a modified subset of ipfw(8) from FreeBSD, and the
 ipfw.c code may provide a useful base for implementations.

Contributors

 The following identifies the key contributors who provided the
 primary content for this document in the form of individual documents
 for each protocol:
 RSIP:
    Jim Renkel
 SNMP:
    Juergen Quittek
    NEC Europe Ltd.
    EMail: quittek@ccrle.nec.de

Barnes Informational [Page 42] RFC 4097 MIDCOM Protocol Evaluation June 2005

    David Harrington
    Co-chair SNMPv3 WG
    EMail: dbh@enterasys.com
 Megaco:
    Sanjoy Sen
    Cedric Aoun
    Nortel
    EMail: cedric.aoun@nortel.com
    Tom Taylor
    Nortel
    EMail: taylor@nortel.com
 Diameter:
    Tom Taylor
    Nortel
    EMail:  taylor@nortel.com
 COPS:
    Cedric Aoun
    Nortel
    EMail: cedric.aoun@nortel.com
    Kwok-Ho Chan
    Nortel
    EMail: khchan@nortel.com
    Louis-Nicolas Hamer
    Reinaldo Penno
    EMail: rpenno@juniper.net
    Sanjoy Sen

Author's Address

 Mary Barnes
 Nortel
 2201 Lakeside Blvd.
 Richardson, TX USA
 Phone:  1-972-684-5432
 EMail:  mary.barnes@nortel.com

Barnes Informational [Page 43] RFC 4097 MIDCOM Protocol Evaluation June 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 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.

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 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
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 might or might not be available; nor does it represent that it has
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 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 The IETF invites any interested party to bring to its attention any
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet
 gement

Barnes Informational [Page 44]

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