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Internet Engineering Task Force (IETF)                          D. Lopez
Request for Comments: 8329                                Telefonica I+D
Category: Informational                                         E. Lopez
ISSN: 2070-1721                                       Curveball Networks
                                                               L. Dunbar
                                                            J. Strassner
                                                                R. Kumar
                                                        Juniper Networks
                                                           February 2018

         Framework for Interface to Network Security Functions


   This document describes the framework for Interface to Network
   Security Functions (I2NSF) and defines a reference model (including
   major functional components) for I2NSF.  Network Security Functions
   (NSFs) are packet-processing engines that inspect and optionally
   modify packets traversing networks, either directly or in the context
   of sessions to which the packet is associated.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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RFC 8329                     I2NSF Framework               February 2018

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  I2NSF Reference Model . . . . . . . . . . . . . . . . . . . .   5
     3.1.  I2NSF Consumer-Facing Interface . . . . . . . . . . . . .   6
     3.2.  I2NSF NSF-Facing Interface  . . . . . . . . . . . . . . .   6
     3.3.  I2NSF Registration Interface  . . . . . . . . . . . . . .   7
   4.  Threats Associated with Externally Provided NSFs  . . . . . .   8
   5.  Avoiding NSF Ossification . . . . . . . . . . . . . . . . . .   9
   6.  The Network Connecting I2NSF Components . . . . . . . . . . .  10
     6.1.  Network Connecting I2NSF Users and the I2NSF Controller .  10
     6.2.  Network Connecting the I2NSF Controller and NSFs  . . . .  10
     6.3.  Interface to vNSFs  . . . . . . . . . . . . . . . . . . .  11
     6.4.  Consistency . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  I2NSF Flow Security Policy Structure  . . . . . . . . . . . .  13
     7.1.  Customer-Facing Flow Security Policy Structure  . . . . .  13
     7.2.  NSF-Facing Flow Security Policy Structure . . . . . . . .  14
     7.3.  Differences from ACL Data Models  . . . . . . . . . . . .  16
   8.  Capability Negotiation  . . . . . . . . . . . . . . . . . . .  16
   9.  Registration Considerations . . . . . . . . . . . . . . . . .  17
     9.1.  Flow-Based NSF Capability Characterization  . . . . . . .  17
     9.2.  Registration Categories . . . . . . . . . . . . . . . . .  18
   10. Manageability Considerations  . . . . . . . . . . . . . . . .  21
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     13.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

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1.  Introduction

   This document describes the framework for Interface to Network
   Security Functions (I2NSF) and defines a reference model (including
   major functional components) for I2NSF.  This includes an analysis of
   the threats implied by the deployment of Network Security Functions
   (NSFs) that are externally provided.  It also describes how I2NSF
   facilitates implementing security functions in a technology- and
   vendor-independent manner in Software-Defined Networking (SDN) and
   Network Function Virtualization (NFV) environments, while avoiding
   potential constraints that could limit the capabilities of NSFs.

   I2NSF use cases [RFC8192] call for standard interfaces for users of
   an I2NSF system (e.g., applications, overlay or cloud network
   management system, or enterprise network administrator or management
   system) to inform the I2NSF system which I2NSF functions should be
   applied to which traffic (or traffic patterns).  The I2NSF system
   realizes this as a set of security rules for monitoring and
   controlling the behavior of different traffic.  It also provides
   standard interfaces for users to monitor flow-based security
   functions hosted and managed by different administrative domains.

   [RFC8192] also describes the motivation and the problem space for an
   Interface to Network Security Functions system.

2.  Conventions Used in This Document

   This memo does not propose a protocol standard, and the use of words
   such as "should" follow their ordinary English meaning and not that
   for normative languages defined in [RFC2119] [RFC8174].

2.1.  Acronyms

   The following acronyms are used in this document:

      DOTS: Distributed Denial-of-Service Open Threat Signaling
      IDS: Intrusion Detection System
      IoT: Internet of Things
      IPS: Intrusion Protection System
      NSF: Network Security Function

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2.2.  Definitions

   The following terms, which are used in this document, are defined in
   the I2NSF terminology document [I2NSF-TERMS]:

      I2NSF Consumer
      I2NSF NSF-Facing Interface
      I2NSF Policy Rule
      I2NSF Producer
      I2NSF Registration Interface
      I2NSF Registry
      Interface Group
      Intrusion Detection System
      Intrusion Protection System
      Network Security Function

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3.  I2NSF Reference Model

   Figure 1 shows a reference model (including major functional
   components and interfaces) for an I2NSF system.  This figure is drawn
   from the point of view of the Network Operator Management System;
   hence, this view does not assume any particular management
   architecture for either the NSFs or how the NSFs are managed (on the
   developer's side).  In particular, the Network Operator Management
   System does not participate in NSF data-plane activities.

       |  I2NSF User (e.g., Overlay Network Mgmt, Enterprise   |
       |  Network Mgmt, another network domain's mgmt, etc.)   |
                            |  I2NSF Consumer-Facing Interface
                            |              I2NSF
               +------------+---------+ Registration  +-------------+
               | Network Operator Mgmt|  Interface    | Developer's |
               |        System        | < --------- > | Mgmt System |
               +----------------+-----+               +-------------+
                                | I2NSF NSF-Facing Interface
           |               |                 |               |
       +---+---+       +---+---+         +---+---+       +---+---+
       | NSF-1 |  ...  | NSF-m |         | NSF-1 |  ...  | NSF-m |  ...
       +-------+       +-------+         +-------+       +-------+

        Developer Mgmt System A           Developer Mgmt System B

                      Figure 1: I2NSF Reference Model

   When defining I2NSF Interfaces, this framework adheres to the
   following principles:

   o  It is agnostic of network topology and NSF location in the network

   o  It is agnostic of provider of the NSF (i.e., independent of the
      way that the provider makes an NSF available, as well as how the
      provider allows the NSF to be managed)

   o  It is agnostic of any vendor-specific operational, administrative,
      and management implementation; hosting environment; and form
      factor (physical or virtual)

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   o  It is agnostic to NSF control-plane implementation (e.g.,
      signaling capabilities)

   o  It is agnostic to NSF data-plane implementation (e.g.,
      encapsulation capabilities)

   In general, all I2NSF Interfaces should require at least mutual
   authentication and authorization for their use.  Other security and
   privacy considerations are specified in Section 11.

3.1.  I2NSF Consumer-Facing Interface

   The I2NSF Consumer-Facing Interface is used to enable different users
   of a given I2NSF system to define, manage, and monitor security
   policies for specific flows within an administrative domain.  The
   location and implementation of I2NSF policies are irrelevant to the
   consumer of I2NSF policies.

   Some examples of I2NSF Consumers include:

   o  A video-conference network manager that needs to dynamically
      inform the underlay network to allow, rate-limit, or deny flows
      (some of which are encrypted) based on specific fields in the
      packets for a certain time span.

   o  Enterprise network administrators and management systems that need
      to request their provider network to enforce specific I2NSF
      policies for particular flows.

   o  An IoT management system sending requests to the underlay network
      to block flows that match a set of specific conditions.

3.2.  I2NSF NSF-Facing Interface

   The I2NSF NSF-Facing Interface (NSF-Facing Interface for short) is
   used to specify and monitor flow-based security policies enforced by
   one or more NSFs.  Note that the I2NSF Management System does not
   need to use all features of a given NSF, nor does it need to use all
   available NSFs.  Hence, this abstraction enables NSF features to be
   treated as building blocks by an NSF system; thus, developers are
   free to use the security functions defined by NSFs independent of
   vendor and technology.

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   Flow-based NSFs [RFC8192] inspect packets in the order that they are
   received.  Note that all Interface Groups require the NSF to be
   registered using the Registration Interface.  The interface to flow-
   based NSFs can be categorized as follows:

   1.  NSF Operational and Administrative Interface: an Interface Group
       used by the I2NSF Management System to program the operational
       state of the NSF; this also includes administrative control
       functions.  I2NSF Policy Rules represent one way to change this
       Interface Group in a consistent manner.  Since applications and
       I2NSF Components need to dynamically control the behavior of
       traffic that they send and receive, much of the I2NSF effort is
       focused on this Interface Group.

   2.  Monitoring Interface: an Interface Group used by the I2NSF
       Management System to obtain monitoring information from one or
       more selected NSFs.  Each interface in this Interface Group could
       be a query- or a report-based interface.  The difference is that
       a query-based interface is used by the I2NSF Management System to
       obtain information, whereas a report-based interface is used by
       the NSF to provide information.  The functionality of this
       Interface Group may also be defined by other protocols, such as
       SYSLOG and DOTS.  The I2NSF Management System may take one or
       more actions based on the receipt of information; this should be
       specified by an I2NSF Policy Rule.  This Interface Group does NOT
       change the operational state of the NSF.

   This document uses the flow-based paradigm to develop the NSF-Facing
   Interface.  A common trait of flow-based NSFs is in the processing of
   packets based on the content (e.g., header/payload) and/or context
   (e.g., session state and authentication state) of the received
   packets.  This feature is one of the requirements for defining the
   behavior of I2NSF.

3.3.  I2NSF Registration Interface

   NSFs provided by different vendors may have different capabilities.
   In order to automate the process of utilizing multiple types of
   security functions provided by different vendors, it is necessary to
   have a dedicated interface for vendors to define the capabilities of
   (i.e., register) their NSFs.  This interface is called the I2NSF
   Registration Interface.

   An NSF's capabilities can be either pre-configured or retrieved
   dynamically through the I2NSF Registration Interface.  If a new
   function that is exposed to the consumer is added to an NSF, then the
   capabilities of that new function should be registered in the I2NSF

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   Registry via the I2NSF Registration Interface, so that interested
   management and control entities may be made aware of them.

4.  Threats Associated with Externally Provided NSFs

   While associated with a much higher flexibility, and in many cases a
   necessary approach given the deployment conditions, the usage of
   externally provided NSFs implies several additional concerns in
   security.  The most relevant threats associated with a security
   platform of this nature are:

   o  An unknown/unauthorized user can try to impersonate another user
      that can legitimately access external NSF services.  This attack
      may lead to accessing the I2NSF Policy Rules and applications of
      the attacked user and/or generating network traffic outside the
      security functions with a falsified identity.

   o  An authorized user may misuse assigned privileges to alter the
      network traffic processing of other users in the NSF underlay or

   o  A user may try to install malformed elements (e.g., I2NSF Policy
      Rules or configuration files) to directly take control of an NSF
      or the whole provider platform.  For example, a user may exploit a
      vulnerability on one of the functions or may try to intercept or
      modify the traffic of other users in the same provider platform.

   o  A malicious provider can modify the software (e.g., the operating
      system or the specific NSF implementation) to alter the behavior
      of one or more NSFs.  This event has a high impact on all users
      accessing NSFs, since the provider has the highest level of
      privileges controlling the operation of the software.

   o  A user that has physical access to the provider platform can
      modify the behavior of the hardware/software components or the
      components themselves.  For example, the user can access a serial
      console (most devices offer this interface for maintenance
      reasons) to access the NSF software with the same level of
      privilege of the provider.

   The use of authentication, authorization, accounting, and audit
   mechanisms is recommended for all users and applications to access
   the I2NSF environment.  This can be further enhanced by requiring
   attestation to be used to detect changes to the I2NSF environment by
   authorized parties.  The characteristics of these procedures will
   define the level of assurance of the I2NSF environment.

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5.  Avoiding NSF Ossification

   A basic tenet in the introduction of I2NSF standards is that the
   standards should not make it easier for attackers to compromise the
   network.  Therefore, in constructing standards for I2NSF Interfaces
   as well as I2NSF Policy Rules, it is equally important to allow
   support for specific functions, as this enables the introduction of
   NSFs that evolve to meet new threats.  Proposed standards for I2NSF
   Interfaces to communicate with NSFs, as well as I2NSF Policy Rules to
   control NSF functionality, should not:

   o  Narrowly define NSF categories, or their roles, when implemented
      within a network.  Security is a constantly evolving discipline.
      The I2NSF framework relies on an object-oriented information
      model, which provides an extensible definition of NSF information
      elements and categories; it is recommended that implementations
      follow this model.

   o  Attempt to impose functional requirements or constraints, either
      directly or indirectly, upon NSF developers.  Implementations
      should be free to realize and apply NSFs in a way that best suits
      the needs of the applications and environment using them.

   o  Be a limited lowest common denominator approach, where interfaces
      can only support a limited set of standardized functions, without
      allowing for developer-specific functions.  NSFs, interfaces, and
      the data communicated should be extensible, so that they can
      evolve to protect against new threats.

   o  Be seen as endorsing a best common practice for the implementation
      of NSFs; rather, this document describes the conceptual structure
      and reference model of I2NSF.  The purpose of this reference model
      is to define a common set of concepts in order to facilitate the
      flexible implementation of an I2NSF system.

   To prevent constraints on NSF developers' creativity and innovation,
   this document recommends flow-based NSF interfaces to be designed
   from the paradigm of processing packets in the network.  Flow-based
   NSFs are ultimately packet-processing engines that inspect packets
   traversing networks, either directly or in the context of sessions in
   which the packet is associated.  The goal is to create a workable
   interface to NSFs that aids in their integration within legacy, SDN,
   and/or NFV environments, while avoiding potential constraints that
   could limit their functional capabilities.

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6.  The Network Connecting I2NSF Components

6.1.  Network Connecting I2NSF Users and the I2NSF Controller

   As a general principle, in the I2NSF environment, users directly
   interact with the I2NSF Controller.  Given the role of the I2NSF
   Controller, a mutual authentication of users and the I2NSF Controller
   is required.  I2NSF does not mandate a specific authentication
   scheme; it is up to the users to choose available authentication
   schemes based on their needs.

   Upon successful authentication, a trusted connection between the user
   and the I2NSF Controller (or an endpoint designated by it) will be
   established.  This means that a direct, physical point-to-point
   connection, with physical access restricted according to access
   control, must be used.  All traffic to and from the NSF environment
   will flow through this connection.  The connection is intended not
   only to be secure but trusted in the sense that it should be bound to
   the mutual authentication between the user and the I2NSF Controller,
   as described in [I2NSF-ATTESTATION].  The only possible exception is
   when the required level of assurance is lower (see Section 4.1 of
   [I2NSF-ATTESTATION]), in which case the user must be made aware of
   this circumstance.

6.2.  Network Connecting the I2NSF Controller and NSFs

   Most likely, the NSFs are not directly attached to the I2NSF
   Controller; for example, NSFs can be distributed across the network.
   The network that connects the I2NSF Controller with the NSFs can be
   the same network that carries the data traffic, or it can be a
   dedicated network for management purposes only.  In either case,
   packet loss could happen due to failure, congestion, or other

   Therefore, the transport mechanism used to carry management data and
   information must be secure.  It does not have to be a reliable
   transport; rather, a transport-independent reliable messaging
   mechanism is required, where communication can be performed reliably
   (e.g., by establishing end-to-end communication sessions and by
   introducing explicit acknowledgement of messages into the
   communication flow).  Latency requirements for control message
   delivery must also be evaluated.  Note that monitoring does not
   require reliable transport.

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   The network connection between the I2NSF Controller and NSFs can rely
   on either:

   o  Open environments, where one or more NSFs can be hosted in one or
      more external administrative domains that are reached via secure
      external network connections.  This requires more restrictive
      security control to be placed over the I2NSF Interface.  The
      information over the I2NSF Interfaces shall be exchanged by using
      the trusted connection described in Section 6.1, or

   o  Closed environments, where there is only one administrative
      domain.  Such environments provide a more **isolated** environment
      but still communicate over the same set of I2NSF Interfaces
      present in open environments (see above).  Hence, the security
      control and access requirements for closed environments are the
      same as those for open environments.

   The network connection between the I2NSF Controller and NSFs will use
   the trusted connection mechanisms described in Section 6.1.
   Following these mechanisms, the connections need to rely on the use
   of properly verified peer identities (e.g., through an
   Authentication, Authorization, and Accounting (AAA) framework).  The
   implementations of identity management functions, as well as the AAA
   framework, are out of scope for I2NSF.

6.3.  Interface to vNSFs

   There are some unique characteristics in interfacing to virtual NSFs

   o  There could be multiple instantiations of one single NSF that has
      been distributed across a network.  When different instantiations
      are visible to the I2NSF Controller, different policies may be
      applied to different instantiations of an individual NSF (e.g., to
      reflect the different roles that each vNSF is designated for).
      Therefore, it is recommended that Roles, in addition to the use of
      robust identities, be used to distinguish between different
      instantiations of the same vNSF.  Note that this also applies to
      physical NSFs.

   o  When multiple instantiations of one single NSF appear as one
      single entity to the I2NSF Controller, the I2NSF Controller may
      need to get assistance from other entities in the I2NSF Management
      System and/or delegate the provisioning of the multiple
      instantiations of the (single) NSF to other entities in the I2NSF
      Management System.  This is shown in Figure 2 below.

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   o  Policies enforced by one vNSF instance may need to be retrieved
      and moved to another vNSF of the same type when user flows are
      moved from one vNSF to another.

   o  Multiple vNSFs may share the same physical platform.

   o  There may be scenarios where multiple vNSFs collectively perform
      the security policies needed.

                          |    I2NSF Controller    |
                                   ^        ^
                                   |        |
                       +-----------+        +------------+
                       |                                 |
                       v                                 v
    + - - - - - - - - - - - - - - - +  + - - - - - - - - - - - - - - - +
    |  NSF-A  +--------------+      |  |  NSF-B  +--------------+      |
    |         | NSF Manager  |      |  |         | NSF Manager  |      |
    |         +--------------+      |  |         +--------------+      |
    | + - - - - - - - - - - - - - + |  | + - - - - - - - - - - - - - + |
    | |+---------+     +---------+| |  | |+---------+     +---------+| |
    | || NSF-A#1 | ... | NSF-A#n || |  | || NSF-B#1 | ... | NSF-B#m || |
    | |+---------+     +---------+| |  | |+---------+     +---------+| |
    | |         NSF-A cluster     | |  | |          NSF-B cluster    | |
    | + - - - - - - - - - - - - - + |  | + - - - - - - - - - - - - - + |
    + - - - - - - - - - - - - - - - +  + - - - - - - - - - - - - - - - +

            Figure 2: Cluster of NSF Instantiations Management

6.4.  Consistency

   There are three basic models of consistency:

   o  centralized, which uses a single manager to impose behavior

   o  decentralized, in which managers make decisions without being
      aware of each other (i.e., managers do not exchange information)

   o  distributed, in which managers make explicit use of information
      exchange to arrive at a decision

   This document does NOT make a recommendation on which of the above
   three models to use.  I2NSF Policy Rules, coupled with an appropriate
   management strategy, is applicable to the design and integration of
   any of the above three consistency models.

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7.  I2NSF Flow Security Policy Structure

   Even though security functions come in a variety of form factors and
   have different features, provisioning to flow-based NSFs can be
   standardized by using policy rules.

   In this version of I2NSF, policy rules are limited to imperative
   paradigms.  I2NSF is using an Event-Condition-Action (ECA) policy,

   o  An Event clause is used to trigger the evaluation of the Condition
      clause of the I2NSF Policy Rule.

   o  A Condition clause is used to determine whether or not the set of
      Actions in the I2NSF Policy Rule can be executed or not.

   o  An Action clause defines the type of operations that may be
      performed on this packet or flow.

   Each of the above three clauses are defined to be Boolean clauses.
   This means that each is a logical statement that evaluates to either

   The above concepts are described in detail in [I2NSF-CAPABILITIES].

7.1.  Customer-Facing Flow Security Policy Structure

   This layer is for the user's network management system to express and
   monitor the needed flow security policies for their specific flows.

   Some customers may not have the requisite security skills to express
   security requirements or policies that are precise enough to
   implement in an NSF.  These customers may instead express
   expectations (e.g., goals or intent) of the functionality desired by
   their security policies.  Customers may also express guidelines, such
   as which types of destinations are (or are not) allowed for certain
   users.  As a result, there could be different levels of content and
   abstractions used in Service Layer policies.  Here are some examples
   of more abstract security policies that can be developed based on the
   I2NSF-defined Customer-Facing Interface:

   o  Enable Internet access for authenticated users

   o  Any operation on a HighValueAsset must use the corporate network

   o  The use of FTP from any user except the CxOGroup must be audited

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   o  Streaming media applications are prohibited on the corporate
      network during business hours

   o  Scan email for malware detection; protect traffic to corporate
      network with integrity and confidentiality

   o  Remove tracking data from Facebook [website = *.facebook.com]

   One flow policy over the Customer-Facing Interface may need multiple
   NSFs at various locations to achieve the desired enforcement.  Some
   flow security policies from users may not be granted because of
   resource constraints.  [I2NSF-DEMO] describes an implementation of
   translating a set of 1) user policies to flow policies and 2) flow
   policies to individual NSFs.

   I2NSF will first focus on user policies that can be modeled as
   closely as possible to the flow security policies used by individual
   NSFs.  An I2NSF user flow policy should be similar in structure to
   the structure of an I2NSF Policy Rule, but with more of a user-
   oriented expression for the packet content, the context, and other
   parts of an ECA policy rule.  This enables the user to construct an
   I2NSF Policy Rule without having to know the exact syntax of the
   desired content (e.g., actual tags or addresses) to match in the
   packets.  For example, when used in the context of policy rules over
   the Client-Facing Interface:

   o  An Event can be "the client has passed the AAA process"

   o  A Condition can be matching the user identifier or from specific
      ingress or egress points

   o  An Action can be establishing an IPsec tunnel

7.2.  NSF-Facing Flow Security Policy Structure

   The NSF-Facing Interface is to pass explicit rules to individual NSFs
   to treat packets, as well as methods to monitor the execution status
   of those functions.

   Here are some examples of Events over the NSF-Facing Interface:

   o  time == 08:00

   o  notification that a NSF state changes from standby to active

   o  user logon or logoff

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   Here are some examples of Conditions over the NSF-Facing Interface:

   o  Packet content values that look for one or more packet headers,
      data from the packet payload, bits in the packet, or data that are
      derived from the packet.

   o  Context values that are based on measured and/or inferred
      knowledge, which can be used to define the state and environment
      in which a managed entity exists or has existed.  In addition to
      state data, this includes data from sessions, direction of the
      traffic, time, and geo-location information.  State refers to the
      behavior of a managed entity at a particular point in time.
      Hence, it may refer to situations in which multiple pieces of
      information that are not available at the same time must be
      analyzed.  For example, tracking established TCP connections
      (connections that have gone through the initial three-way

   Actions to individual flow-based NSFs include:

   o  Actions performed on ingress packets, such as pass, drop, rate
      limiting, and mirroring.

   o  Actions performed on egress packets, such as invoke signaling,
      tunnel encapsulation, packet forwarding, and/or transformation.

   o  Applying a specific functional profile or signature -- e.g., an
      IPS Profile, a signature file, an anti-virus file, or a URL
      filtering file.  Many flow-based NSFs utilize profile and/or
      signature files to achieve more effective threat detection and
      prevention.  It is not uncommon for an NSF to apply different
      profiles and/or signatures for different flows.  Some profiles/
      signatures do not require any knowledge of past or future
      activities, while others are stateful and may need to maintain
      state for a specific length of time.

   The functional profile or signature file is one of the key properties
   that determine the effectiveness of the NSF and is mostly NSF
   specific today.  The rulesets and software interfaces of I2NSF aim to
   specify the format to pass profile and signature files while
   supporting specific functionalities of each.

   Policy consistency among multiple security function instances is very
   critical because security policies are no longer maintained by one
   central security device; instead, they are enforced by multiple
   security functions instantiated at various locations.

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7.3.  Differences from ACL Data Models

   Policy rules are very different from Access Control Lists (ACLs).  An
   ACL is NOT a policy.  Rather, policies are used to manage the
   construction and life cycle of an ACL.

   [ACL-YANG] has defined rules for ACLs supported by most routers/
   switches that forward packets based on their L2, L3, or sometimes L4
   headers.  The actions for ACLs include Pass, Drop, or Redirect.

   The functional profiles (or signatures) for NSFs are not present in
   [ACL-YANG] because the functional profiles are unique to specific
   NSFs.  For example, most IPS/IDS implementations have their
   proprietary functions/profiles.  One of the goals of I2NSF is to
   define a common envelope format for exchanging or sharing profiles
   among different organizations to achieve more effective protection
   against threats.

   The "packet content matching" of the I2NSF policies should not only
   include the matching criteria specified by [ACL-YANG] but also the
   L4-L7 fields depending on the NSFs selected.

   Some flow-based NSFs need matching criteria that include the context
   associated with the packets.  This may also include metadata.

   The I2NSF "actions" should extend the actions specified by [ACL-YANG]
   to include applying statistics functions, threat profiles, or
   signature files that clients provide.

8.  Capability Negotiation

   It is very possible that the underlay network (or provider network)
   does not have the capability or resources to enforce the flow
   security policies requested by the overlay network (or enterprise
   network).  Therefore, it is required that the I2NSF system support
   dynamic discovery capabilities, as well as a query mechanism, so that
   the I2NSF system can expose appropriate security services using I2NSF
   capabilities.  This may also be used to support negotiation between a
   user and the I2NSF system.  Such dynamic negotiation facilitates the
   delivery of the required security service(s).  The outcome of the
   negotiation would feed the I2NSF Management System, which would then
   dynamically allocate appropriate NSFs (along with any resources
   needed by the allocated NSFs) and configure the set of security
   services that meet the requirements of the user.

   When an NSF cannot perform the desired provisioning (e.g., due to
   resource constraints), it must inform the I2NSF Management System.
   The protocol needed for this security function/capability negotiation

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   may be somewhat correlated to the dynamic service parameter
   negotiation procedure described in [RFC7297].  The Connectivity
   Provisioning Profile (CPP) template, even though currently covering
   only connectivity requirements, includes security clauses such as
   isolation requirements and non-via nodes.  Hence, it could be
   extended as a basis for the negotiation procedure.  Likewise, the
   companion Connectivity Provisioning Negotiation Protocol (CPNP) could
   be a candidate for the negotiation procedure.

   "Security-as-a-Service" would be a typical example of the kind of
   (CPP-based) negotiation procedures that could take place between a
   corporate customer and a service provider.  However, more security-
   specific parameters have to be considered.

   [I2NSF-CAPABILITIES] describes the concepts of capabilities in

9.  Registration Considerations

9.1.  Flow-Based NSF Capability Characterization

   There are many types of flow-based NSFs.  Firewall, IPS, and IDS are
   the commonly deployed flow-based NSFs.  However, the differences
   among them are definitely blurring, due to more powerful technology,
   integration of platforms, and new threats.  Basic types of flow-based
   NSFs include:

   o  Firewall -- A device or a function that analyzes packet headers
      and enforces policy based on protocol type, source address,
      destination address, source port, destination port, and/or other
      attributes of the packet header.  Packets that do not match policy
      are rejected.  Note that additional functions, such as logging and
      notification of a system administrator, could optionally be
      enforced as well.

   o  IDS (Intrusion Detection System) -- A device or function that
      analyzes packets, both header and payload, looking for known
      events.  When a known event is detected, a log message is
      generated detailing the event.  Note that additional functions,
      such as notification of a system administrator, could optionally
      be enforced as well.

   o  IPS (Intrusion Prevention System) -- A device or function that
      analyzes packets, both header and payload, looking for known
      events.  When a known event is detected, the packet is rejected.
      Note that additional functions, such as logging and notification
      of a system administrator, could optionally be enforced as well.

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   Flow-based NSFs differ in the depth of packet header or payload they
   can inspect, the various session/context states they can maintain,
   and the specific profiles and the actions they can apply.  An example
   of a session is as follows: allowing outbound connection requests and
   only allowing return traffic from the external network.

9.2.  Registration Categories

   Developers can register their NSFs using packet content matching
   categories.  The Inter-Domain Routing (IDR) Flow Specification
   [RFC5575] has specified 12 different packet header matching types.

   IP Flow Information Export (IPFIX) data [IPFIX-D] defines IP flow
   information and mechanisms to transmit such information.  This
   includes flow attributes as well as information about the metering
   and exporting processes.  Such information may be stored in an IPFIX
   registry [IPFIX-R].  As such, IPFIX information should be considered
   when defining categories of registration information.

   More packet content matching types have been proposed in the IDR WG.
   I2NSF should reuse the packet matching types being specified as much
   as possible.  More matching types might be added for flow-based NSFs.

   Figures 3-6 below list the applicable packet content categories that
   can be potentially used as packet matching types by flow-based NSFs:

        |         Packet Content Matching Capability Index          |
        | Layer 2       | Layer 2 header fields:                    |
        | Header        |            Source                         |
        |               |            Destination                    |
        |               |            s-VID                          |
        |               |            c-VID                          |
        |               |            Ethertype                      |
        | Layer 3       | Layer 3 header fields:                    |
        |               |            protocol                       |
        | IPv4 Header   |            dest port                      |
        |               |            src port                       |
        |               |            src address                    |
        |               |            dest address                   |
        |               |            dscp                           |
        |               |            length                         |
        |               |            flags                          |
        |               |            ttl                            |

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        | IPv6 Header   |                                           |
        |               |            protocol/nh                    |
        |               |            src port                       |
        |               |            dest port                      |
        |               |            src address                    |
        |               |            dest address                   |
        |               |            length                         |
        |               |            traffic class                  |
        |               |            hop limit                      |
        |               |            flow label                     |
        |               |            dscp                           |
        | Layer 4       | Layer 4 header fields:                    |
        | TCP           |            Port                           |
        | SCTP          |            syn                            |
        | DCCP          |            ack                            |
        |               |            fin                            |
        |               |            rst                            |
        |               |          ? psh                            |
        |               |          ? urg                            |
        |               |          ? window                         |
        |               |            sockstress                     |
        |               | Note: bitmap could be used to             |
        |               |   represent all the fields                |
        | UDP           |                                           |
        |               |            flood abuse                    |
        |               |            fragment abuse                 |
        |               |            Port                           |
        | HTTP layer    |                                           |
        |               |          | hash collision                 |
        |               |          | http - get flood               |
        |               |          | http - post flood              |
        |               |          | http - random/invalid url      |
        |               |          | http - slowloris               |
        |               |          | http - slow read               |
        |               |          | http - r-u-dead-yet (rudy)     |
        |               |          | http - malformed request       |
        |               |          | http - xss                     |
        |               |          | https - ssl session exhaustion |

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        | IETF PCP      | Configurable                              |
        |               | Ports                                     |
        | IETF TRAM     | profile                                   |

           DCCP:  Datagram Congestion Control Protocol
           PCP:   Port Control Protocol
           TRAM:  TURN Revised and Modernized, where TURN stands for
                  Traversal Using Relays around NAT

            Figure 3: Packet Content Matching Capability Index

        |             Context Matching Capability Index             |
        | Session       |   Session State,                          |
        |               |   Bidirectional State                     |
        | Time          |   Time span                               |
        |               |   Time occurrence                         |
        | Events        |   Event URL, variables                    |
        | Location      |   Text string, GPS coords, URL            |
        | Connection    |   Internet (unsecured), Internet          |
        |   Type        |   (secured by VPN, etc.), Intranet, ...   |
        | Direction     |   Inbound, Outbound                       |
        | State         |   Authentication State                    |
        |               |   Authorization State                     |
        |               |   Accounting State                        |
        |               |   Session State                           |

          These fields are used to provide context information for
          I2NSF Policy Rules to make decisions on how to handle
          traffic.  For example, GPS coordinates define the location
          of the traffic that is entering and exiting an I2NSF
          system; this enables the developer to apply different
          rules for ingress and egress traffic handling.

                Figure 4: Context Matching Capability Index

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        |                  Action Capability Index                  |
        | Ingress port  |   SFC header termination,                 |
        |               |   VxLAN header termination                |
        |               |   Pass                                    |
        | Actions       |   Deny                                    |
        |               |   Mirror                                  |
        |               |   Simple Statistics: Count (X min; Day;..)|
        |               |   Client-Specified Functions: URL         |
        | Egress        |   Encap SFC, VxLAN, or other header       |

          SFC:  Service Function Chaining

                     Figure 5: Action Capability Index

        |                 Functional Profile Index                  |
        | Profile types |   name, type, or flexible                 |
        |               |                                           |
        | Signature     |   Profile/signature URL command for the   |
        |               |   I2NSF Controller to enable/disable      |

                    Figure 6: Functional Profile Index

10.  Manageability Considerations

   Management of NSFs include:

   o  Life-cycle management and resource management of NSFs

   o  Configuration of devices, such as address configuration, device
      internal attributes configuration, etc.

   o  Signaling

   o  Policy rules provisioning

   Currently, I2NSF only focuses on the policy rule provisioning part.

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11.  Security Considerations

   The configuration, control, and monitoring of NSFs provide access to
   and information about security functions that are critical for
   delivering network security and for protecting end-to-end traffic.
   Therefore, it is important that the messages that are exchanged
   within this architecture utilize a trustworthy, robust, and fully
   secure communication channel.  The mechanisms adopted within the
   solution space must include proper secure communication channels that
   are carefully specified for carrying the controlling and monitoring
   information between the NSFs and their management entity or entities.
   The threats associated with remotely managed NSFs are discussed in
   Section 4, and solutions must address those concerns.

   This framework is intended for enterprise users, with or without
   cloud service offerings.  Privacy of users must be provided by using
   existing standard mechanisms, such as encryption; anonymization of
   data should also be done if possible (depending on the transport
   used).  Such mechanisms require confidentiality and integrity.

12.  IANA Considerations

   This document has no IANA actions.

13.  References

13.1.  Normative References

   [IPFIX-D]  "IP Flow Information Export (ipfix)",

   [IPFIX-R]  IANA, "IP Flow Information Export (IPFIX) Entities",

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,

   [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
              Connectivity Provisioning Profile (CPP)", RFC 7297,
              DOI 10.17487/RFC7297, July 2014,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

13.2.  Informative References

              Jethanandani, M., Huang, L., Agarwal, S., and D. Blair,
              "Network Access Control List (ACL) YANG Data Model", Work
              in Progress, draft-ietf-netmod-acl-model-15, January 2018.

              Pastor, A., Lopez, D., and A. Shaw, "Remote Attestation
              Procedures for Network Security Functions (NSFs) through
              the I2NSF Security Controller", Work in Progress,
              draft-pastor-i2nsf-nsf-remote-attestation-02, September

              Xia, L., Strassner, J., Basile, C., and D. Lopez,
              "Information Model of NSFs Capabilities", Work in
              Progress, draft-i2nsf-capability-00, September 2017.

              Xie, Y., Xia, L., and J. Wu, "Interface to Network
              Security Functions Demo Outline Design", Work in
              Progress, draft-xie-i2nsf-demo-outline-design-00, April

              Hares, S., Strassner, J., Lopez, D., Xia, L., and H.
              Birkholz, "Interface to Network Security Functions (I2NSF)
              Terminology", Work in Progress, draft-ietf-i2nsf-
              terminology-05, January 2018.

   [RFC8192]  Hares, S., Lopez, D., Zarny, M., Jacquenet, C., Kumar, R.,
              and J. Jeong, "Interface to Network Security Functions
              (I2NSF): Problem Statement and Use Cases", RFC 8192,
              DOI 10.17487/RFC8192, July 2017,

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   This document includes significant contributions from Christian
   Jacquenet (Orange), Seetharama Rao Durbha (Cablelabs), Mohamed
   Boucadair (Orange), Ramki Krishnan (Dell), Anil Lohiya (Juniper
   Networks), Joe Parrott (BT), Frank Xialing (Huawei), and XiaoJun
   Zhuang (China Mobile).

   Some of the results leading to this work have received funding from
   the European Union Seventh Framework Programme (FP7/2007-2013) under
   grant agreement no. 611458.

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Authors' Addresses

   Diego R. Lopez
   Telefonica I+D
   Editor Jose Manuel Lara, 9
   Seville,   41013

   Email: diego.r.lopez@telefonica.com

   Edward Lopez
   Curveball Networks
   Chantilly, Virginia
   United States of America

   Email: ed@curveballnetworks.com

   Linda Dunbar
   Huawei Technologies
   United States of America

   Email: Linda.Dunbar@huawei.com

   John Strassner
   Huawei Technologies
   Santa Clara, CA
   United States of America

   Email: John.sc.Strassner@huawei.com

   Rakesh Kumar
   Juniper Networks
   United States of America

   Email: rakeshkumarcloud@gmail.com

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