



I2NSF Working Group                                             J. Jeong
Internet-Draft                                   Sungkyunkwan University
Intended status: Informational                                   S. Hyun
Expires: 4 October 2025                               Myongji University
                                                                  T. Ahn
                                                                      KT
                                                                S. Hares
                                                                  Huawei
                                                                D. Lopez
                                                          Telefonica I+D
                                                            2 April 2025


 Applicability of Interfaces to Network Security Functions to Network-
                        Based Security Services
                   draft-ietf-i2nsf-applicability-19

Abstract

   This document describes the applicability of Interface to Network
   Security Functions (I2NSF) to network-based security services in
   Network Functions Virtualization (NFV) environments, such as
   firewall, deep packet inspection, or attack mitigation engines.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 4 October 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.






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   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  I2NSF Framework . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Time-dependent Web Access Control Service . . . . . . . . . .   9
   5.  Intent-based Security Services  . . . . . . . . . . . . . . .  14
   6.  I2NSF Framework with SFC  . . . . . . . . . . . . . . . . . .  16
   7.  I2NSF Framework with SDN  . . . . . . . . . . . . . . . . . .  18
     7.1.  Firewall: Centralized Firewall System . . . . . . . . . .  20
     7.2.  Deep Packet Inspection: Centralized VoIP/VoLTE Security
           System  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.3.  Attack Mitigation: Centralized DDoS-attack Mitigation
           System  . . . . . . . . . . . . . . . . . . . . . . . . .  21
   8.  I2NSF Framework with NFV  . . . . . . . . . . . . . . . . . .  22
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     11.2.  Informative References . . . . . . . . . . . . . . . . .  27
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  28
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   Interface to Network Security Functions (I2NSF) defines a framework
   and interfaces for interacting with Network Security Functions
   (NSFs).  Note that an NSF is defined as software that provides a set
   of security-related services, such as (i) detecting unwanted
   activity, (ii) blocking or mitigating the effect of such unwanted
   activity in order to fulfill service requirements, and (iii)
   supporting communication stream integrity and confidentiality
   [RFC8329].

   The I2NSF framework allows heterogeneous NSFs developed by different
   security solution vendors to be used in the Network Functions
   Virtualization (NFV) environment [ETSI-NFV] by utilizing the
   capabilities of such NSFs through I2NSF interfaces such as Customer-



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   Facing Interface [consumer-facing-inf-dm] and NSF-Facing Interface
   [nsf-facing-inf-dm].  In the I2NSF framework, each NSF initially
   registers the profile of its own capabilities with the Security
   Controller (i.e., network operator management system [RFC8329]) of
   the I2NSF system via the Registration Interface
   [registration-inf-dm].  This registration enables an I2NSF User
   (i.e., network security administrator) to select and use the NSF to
   enforce a given security policy.  Note that Developer's Management
   System (DMS) is management software that provides a vendor's security
   service software as a Virtual Network Function (VNF) in an NFV
   environment (or middlebox in the legacy network) as an NSF, and
   registers the capabilities of an NSF into Security Controller via
   Registration Interface for a security service [RFC8329].

   Security Controller maintains the mapping between a capability and an
   NSF, so it can perform to translate a high-level security policy
   received from I2NSF User to a low-level security policy configured
   and enforced in an NSF [SPT].  Security Controller can monitor the
   states and security attacks in NSFs through NSF monitoring
   [nsf-monitoring-dm].

   This document illustrates the applicability of the I2NSF framework
   with five different scenarios:

   1.  The enforcement of time-dependent web access control.

   2.  The support of intent-based security services through I2NSF and
       Security Policy Translator [SPT].

   3.  The application of I2NSF to a Service Function Chaining (SFC)
       environment [RFC7665].

   4.  The integration of the I2NSF framework with Software-Defined
       Networking (SDN) [RFC7149] to provide different security
       functionality such as firewalls [opsawg-firewalls], Deep Packet
       Inspection (DPI), and Distributed Denial of Service (DDoS) attack
       mitigation.

   5.  The use of Network Functions Virtualization (NFV) [ETSI-NFV] as a
       supporting technology.

   The implementation of I2NSF in these scenarios has allowed us to
   verify the applicability and effectiveness of the I2NSF framework for
   a variety of use cases.







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2.  Terminology

   This document uses the terminology described in [RFC7665], [RFC7149],
   [ITU-T.Y.3300], [ONF-SDN-Architecture], [ITU-T.X.800],
   [NFV-Terminology], [RFC8329], and [RFC8329].  In addition, the
   following terms are defined below:

   *  Centralized DDoS-attack Mitigation System: A centralized mitigator
      that can establish and distribute access control policy rules into
      network resources for efficient DDoS-attack mitigation.

   *  Centralized Firewall System: A centralized firewall that can
      establish and distribute policy rules into network resources for
      efficient firewall management.

   *  Centralized VoIP Security System: A centralized security system
      that handles the security functions required for VoIP and VoLTE
      services.

   *  Firewall: A service function at the junction of two network
      segments that inspects some suspicious packets that attempt to
      cross the boundary.  It also rejects any packet that does not
      satisfy certain criteria for, for example, disallowed port numbers
      or IP addresses.

   *  Network Function: A functional block within a network
      infrastructure that has well-defined external interfaces and well-
      defined functional behavior.

   *  Network Functions Virtualization (NFV): A principle of separating
      network functions (or network security functions) from the
      hardware they run on by using virtual hardware abstraction.

   *  Network Security Function (NSF): Software that provides a set of
      security-related services.  Examples include detecting unwanted
      activity and blocking or mitigating the effect of such unwanted
      activity in order to fulfill service requirements.  The NSF can
      also help in supporting communication stream integrity and
      confidentiality.

   *  Security Policy Translator (SPT): Software that translates a high-
      level security policy for the Consumer-Facing Interface into a
      low-level security policy for the NSF-Facing Interface [SPT].  The
      SPT is a core part of the Security Controller in the I2NSF system.

   *  Service Function Chaining (SFC): The execution of an ordered set
      of abstract service functions (i.e., network functions) according
      to ordering constraints that must be applied to packets, frames,



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      and flows selected as a result of classification.  The implied
      order may not be a linear progression as the architecture allows
      for SFCs that copy to more than one branch, and also allows for
      cases where there is flexibility in the order in which service
      functions need to be applied [RFC7665].

   *  Software-Defined Networking (SDN): A set of techniques that
      enables to directly program, orchestrate, control, and manage
      network resources, which facilitates the design, delivery and
      operation of network services in a dynamic and scalable manner
      [ITU-T.Y.3300].

      +------------+
      | I2NSF User |
      +------------+
             ^
             | Consumer-Facing Interface
             v
   +-------------------+     Registration     +-----------------------+
   |Security Controller|<-------------------->|Developer's Mgmt System|
   +-------------------+      Interface       +-----------------------+
             ^
             | NSF-Facing Interface
             v
      +----------------+ +---------------+   +-----------------------+
      |      NSF-1     |-|     NSF-2     |...|         NSF-n         |
      |   (Firewall)   | | (Web Filter)  |   |(DDoS-Attack Mitigator)|
      +----------------+ +---------------+   +-----------------------+

                         Figure 1: I2NSF Framework

3.  I2NSF Framework

   This section summarizes the I2NSF framework as defined in [RFC8329].
   As shown in Figure 1, an I2NSF User can use security functions by
   delivering high-level security policies, which specify security
   requirements that the I2NSF user wants to enforce, to the Security
   Controller via the Consumer-Facing Interface (CFI)
   [consumer-facing-inf-dm].












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   The Security Controller receives and analyzes the high-level security
   policies from an I2NSF User, and identifies what types of security
   capabilities are required to meet these high-level security policies.
   The Security Controller then identifies NSFs that have the required
   security capabilities, and generates low-level security policies for
   each of the NSFs so that the high-level security policies are
   eventually enforced by those NSFs [SPT].  Finally, the Security
   Controller sends the generated low-level security policies to the
   NSFs via the NSF-Facing Interface (NFI) [nsf-facing-inf-dm].

   As shown in Figure 1, with a Developer's Management System (called
   DMS), developers (or vendors) inform the Security Controller of the
   capabilities of the NSFs through the Registration Interface (RI)
   [registration-inf-dm] for registering (or deregistering) the
   corresponding NSFs.  Note that the lifecycle management of NSF code
   from DMS (e.g., downloading of NSF modules and testing of NSF code)
   is out of scope for I2NSF.

   The Consumer-Facing Interface can be implemented with the Consumer-
   Facing Interface YANG data model [consumer-facing-inf-dm] using
   RESTCONF [RFC8040] which befits a web-based user interface for an
   I2NSF User to send a Security Controller a high-level security
   policy.  Data models specified by YANG [RFC6020] describe high-level
   security policies to be specified by an I2NSF User.  The data model
   defined in [consumer-facing-inf-dm] can be used for the I2NSF
   Consumer-Facing Interface.  Note that an inside attacker at the I2NSF
   User can misuse the I2NSF system so that the network system under the
   I2NSF system is vulnerable to security attacks.  To handle this type
   of threat, the Security Controller needs to monitor the activities of
   all the I2NSF Users as well as the NSFs through the I2NSF NSF
   monitoring functionality [nsf-monitoring-dm].  Note that the
   monitoring of the I2NSF Users is out of scope for I2NSF.

   The NSF-Facing Interface can be implemented with the NSF-Facing
   Interface YANG data model [nsf-facing-inf-dm] using NETCONF [RFC6241]
   which befits a command-line-based remote-procedure call for a
   Security Controller to configure an NSF with a low-level security
   policy.  Data models specified by YANG [RFC6020] describe low-level
   security policies for the sake of NSFs, which are translated from the
   high-level security policies by the Security Controller.  The data
   model defined in [nsf-facing-inf-dm] can be used for the I2NSF NSF-
   Facing Interface.

   The Registration Interface can be implemented with the Registration
   Interface YANG data model [registration-inf-dm] using NETCONF
   [RFC6241] which befits a command-line-based remote-procedure call for
   a DMS to send a Security Controller an NSF's capability information.
   Data models specified by YANG [RFC6020] describe the registration of



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   an NSF's capabilities to enforce security services at the NSF.  The
   data model defined in [registration-inf-dm] can be used for the I2NSF
   Registration Interface.

   The I2NSF framework can chain multiple NSFs to implement low-level
   security policies with the SFC architecture [RFC7665].

   The following sections describe different security service scenarios
   illustrating the applicability of the I2NSF framework.

  <i2nsf-cfi-policy
   xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cons-facing-interface">
    <name>sns_access</name>
    <rules>
      <name>block_sns_access_during_operation_time</name>
      <condition>
        <firewall>
          <source>employees</source>
        </firewall>
        <url-category>
          <url-name>sns-websites</url-name>
        </url-category>
        <context>
          <time>
            <start-date-time>2025-03-11T09:00:00.00Z</start-date-time>
            <end-date-time>2025-12-31T18:00:00.00Z</end-date-time>
            <period>
              <start-time>09:00:00Z</start-time>
              <end-time>18:00:00Z</end-time>
              <day>monday</day>
              <day>tuesday</day>
              <day>wednesday</day>
              <day>thursday</day>
              <day>friday</day>
            </period>
            <frequency>weekly</frequency>
          </time>
        </context>
      </condition>
      <action>
        <primary-action>
          <action>drop</action>
        </primary-action>
      </action>
    </rules>
  </i2nsf-cfi-policy>





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      Figure 2: A High-level Security Policy XML Document of a Time-
                             based Web Filter

   <i2nsf-security-policy
   xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-nsf-facing-interface">
    <name>sns_access</name>
    <rules>
     <name>block_sns_access_during_operation_time</name>
     <condition>
      <ipv6>
       <source-ipv6-network>2001:db8:1::/60</source-ipv6-network>
      </ipv6>
      <context>
       <time>
         <start-date-time>2025-03-11T09:00:00.00Z</start-date-time>
         <end-date-time>2025-12-31T18:00:00.00Z</end-date-time>
         <period>
           <start-time>09:00:00Z</start-time>
           <end-time>18:00:00Z</end-time>
           <day>monday</day>
           <day>tuesday</day>
           <day>wednesday</day>
           <day>thursday</day>
           <day>friday</day>
         </period>
         <frequency>weekly</frequency>
       </time>
      </context>
     </condition>
     <action>
      <advanced-action>
       <content-security-control>
         url-filtering
       </content-security-control>
      </advanced-action>
     </action>
    </rules>
   </i2nsf-security-policy>

      Figure 3: A Low-level Security Policy XML Document of a Firewall
                      NSF for a Time-based Web Filter










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   <i2nsf-security-policy
   xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-nsf-facing-interface">
    <name>sns_access</name>
    <rules>
     <name>block_sns_access_during_operation_time</name>
     <condition>
      <url-category>
       <user-defined>https://www.example.com/</user-defined>
       <user-defined>https://www.example.net/</user-defined>
       <user-defined>https://www.example.org/</user-defined>
      </url-category>
     </condition>
     <action>
      <packet-action>
       <egress-action>drop</egress-action>
      </packet-action>
     </action>
    </rules>
   </i2nsf-security-policy>

        Figure 4: A Low-level Security Policy XML Document of a Web
                    Filter NSF for Time-based Web Filter

4.  Time-dependent Web Access Control Service

   This service scenario assumes that an enterprise network
   administrator wants to control the employees' access to a particular
   Internet service (e.g., social networking service (SNS)) during
   business hours.  The following is an example high-level security
   policy rule for a web filter that the administrator requests: Block
   the employees' access to SNS websites from 9 AM (i.e., 09:00) to 6 PM
   (i.e., 18:00) on weekdays (from Monday to Friday) from March 11, 2025
   to December 31, 2025 by dropping their packets.  Figure 2 is a high-
   level security policy XML document of a time-based web filter that is
   sent from the I2NSF User to the Security Controller via the Consumer-
   Facing Interface [consumer-facing-inf-dm].

   The security policy name is "security_policy_for_blocking_sns" with
   the tag "name", and the security policy rule name is
   "block_access_to_sns_during_office_hours" with the tag "name".  The
   filtering event has the time span where the filtering start time is
   the time "09:00:00Z" (i.e., 9:00AM) with the tag "start-time", and
   the filtering end time is the time "18:00:00Z" (i.e., 6:00PM) with
   the tag "end-time".  The filtering condition has the source target of
   "employees" with the tag "source", and the destination target of
   "sns-websites" with the tag "url-name".





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   A high-level security policy XML document in Figure 2 is translated
   into two low-level security policy XML documents in Figure 3 and
   Figure 4 by the Security Policy Translator (SPT) [SPT] in the
   Security Controller.  These two low-level security policy XML
   documents are sent to a firewall NSF and a web filter NSF,
   respectively, by the Security Controller via the NSF-Facing Interface
   [nsf-facing-inf-dm].  On one hand, a firewall NSF performs IP address
   and port number inspection, and time checking for a packet for time-
   based web filtering.  On the other hand, a web filter NSF performs
   URL inspection for a packet for time-based web filtering.

   Assume that "employees" are IPv6 hosts whose IPv6 addresses are based
   on the prefix of 2001:db8:1::/60, as shown in Figure 3.  Also, assume
   that "sns-websites" includes https://www.example.com,
   https://www.example.net, and https://www.example.org, as shown in
   Figure 4.

   The source target can by translated by the SPT in the Security
   Controller to the IP addresses of computers (or mobile devices) used
   by the employees.  Refer to Section 5 for the detailed description of
   the SPT.  The destination target can also be translated by the SPT to
   the actual websites corresponding to the symbolic website name "sns-
   websites", and then either each website's URL or the corresponding IP
   address(es) can be used by both a firewall and a web filter.  The
   action is to "drop" the packets satisfying the above condition with
   the tag "action".

   After receiving the high-level security policy, the Security
   Controller identifies required security capabilities, e.g., IP
   address and port number inspection capabilities and URL inspection
   capability.  In this scenario, it is assumed that the IP address and
   port number inspection capabilities are required to check whether a
   received packet is an HTTP-session packet from an employee, which is
   part of an HTTP session generated by the employee.  The URL
   inspection capability is required to check whether the target URL of
   a received packet is one of the target websites (i.e.,
   www.example.com, www.example.net, and www.example.org) or not.

   The Security Controller maintains the security capabilities of each
   active NSF in the I2NSF system, which have been reported by the
   Developer's Management System via the Registration interface.  Based
   on this information, the Security Controller identifies NSFs that can
   perform the IP address and port number inspection and URL inspection
   through the security policy translation in Section 5.  In this
   scenario, it is assumed that a firewall NSF has the IP address and
   port number inspection capabilities and a web filter NSF has URL
   inspection capability.




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   The Security Controller may interoperate with an access control
   server in the enterprise network in order to retrieve the information
   (e.g., IP address in use, company identifier (ID), and role) of each
   employee that is currently using the network.  Based on the retrieved
   information, the Security Controller generates a low-level security
   policy to check whether the source IP address of a received packet
   matches any one being used by an employee.

   In addition, a low-level security policy's rule (shortly, low-level
   security rule) for a firewall NSF should be able to determine that a
   received packet uses either the HTTP protocol without Transport Layer
   Security (TLS) [RFC8446] or the HTTP protocol with TLS as HTTPS.  A
   low-level security policy's rule for a web filter checks that the
   target URL field of a received packet is equal to one of the target
   SNS websites (i.e., www.example.com, www.example.net, and
   www.example.org), or that the destination IP address of a received
   packet is an IP address corresponding to one of the SNS websites.
   Note that if HTTPS is used for an HTTP-session packet, the HTTP
   protocol header is encrypted, so the URL information may not be seen
   from the packet for the web filtering.  Thus, the IP address(es)
   corresponding to the target URL needs to be obtained from the
   certificate in TLS versions prior to 1.3 [RFC8446] or the Server Name
   Indication (SNI) in a TCP-session packet in TLS versions without the
   encrypted SNI [tls-esni].  Also, to obtain IP address(es)
   corresponding to a target URL, the DNS name resolution process can be
   observed through a packet capturing tool because the DNS name
   resolution will translate the target URL into IP address(es).  The IP
   addresses obtained through either TLS or DNS can be used by both a
   firewall and a web filter for whitelisting or blacklisting the TCP
   five-tuples of HTTP sessions.

   Finally, the Security Controller sends the low-level security policy
   of the IP address and port number inspection to the firewall NSF and
   the low-level security policy for URL inspection to the web filter
   NSF.

   The following describes how the time-dependent web access control
   service is enforced by the NSFs of firewall and web filter.

   1.  An employee tries to access one of the target SNS websites (i.e.,
       www.example.com, www.example.net, and www.example.org) during
       business hours, e.g., 10 AM.

   2.  The packet is forwarded from the employee's device to the
       firewall, and the firewall checks the source IP address and port
       number.  Now the firewall identifies the received packet is an
       HTTP-session packet from the employee.




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   3.  The firewall triggers the web filter to further inspect the
       packet, and the packet is forwarded from the firewall to the web
       filter.  The SFC architecture [RFC7665] can be utilized to
       support such packet forwarding in the I2NSF framework.

   4.  The web filter checks the received packet's target URL field or
       its destination IP address corresponding to the target URL, and
       detects that the packet is being sent to a server with the target
       URL (e.g., www.example.com).  The web filter then checks that the
       current time is within business hours.  If so, the web filter
       drops the packet, and consequently the employee's access to one
       of the SNS websites (i.e., www.example.com, www.example.net, and
       www.example.org) during business hours is blocked.






































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      +--------------------------------------------------+
      |                    I2NSF User                    |
      +------------------------+-------------------------+
                               | Consumer-Facing Interface
                               |
                   High-level Security Policy
                               |
      Security Controller      V
      +------------------------+--------------------------------+
      |  Security Policy       |                                |
      |  Translator            V                                |
      |  +---------------------+-----------------------------+  |
      |  |                     |                             |  |
      |  |                     V                             |  |
      |  |               +-----+-----+          +----------+ |  |
      |  |               |    Data   |          |Data Model| |  |
      |  |               | Extractor |          |  Mapper  | |  |
      |  |               +-----+-----+          +-----+----+ |  |
      |  | Extracted Data from |              Mapping |      |  |
      |  |   High-Level Policy V                Model V      |  |
      |  |               +-----+-----+           +----+---+  |  |
      |  |               |    Data   |<--------->| NSF DB |  |  |
      |  |               | Converter |           +--------+  |  |
      |  |               +-----+-----+                       |  |
      |  |                     |  Required Data for          |  |
      |  |                     V  Target NSFs                |  |
      |  |            +--------+---------+                   |  |
      |  |            | Policy Generator |                   |  |
      |  |            +--------+---------+                   |  |
      |  |                     |                             |  |
      |  |                     V                             |  |
      |  +---------------------+-----------------------------+  |
      |                        |                                |
      |                        V                                |
      +------------------------+--------------------------------+
                               | NSF-Facing Interface
                               |
                    Low-level Security Policy
                               |
                               V
      +------------------------+-------------------------+
      |                      NSF(s)                      |
      +--------------------------------------------------+

   Figure 5: Security Policy Translation and Enforcement in I2NSF System






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5.  Intent-based Security Services

   I2NSF aims at providing intent-based security services to configure
   specific security policies into NSFs with customer-friendly secuirty
   policies at a high level.  For example, when an I2NSF User submits a
   high-level security policy (e.g., web filtering as shown in Figure 2)
   to the Security Controller, the Security Policy Tranlator (SPT) [SPT]
   in the Security Controller will translate it into the correspondong
   two low-level security policies, as shown in Figure 3 and Figure 4.
   A security administrator using the I2NSF User can describe a security
   policy without the knowledge of the detailed information about
   subjects (e.g., source and destination) and objects (e.g., web
   traffic) of the security policy's rule(s).

   Figure 5 shows the security policy translation and enforcement in the
   I2NSF system [SPT].  As shown in Figure 5, an I2NSF User delivers a
   high-level security policy to the Security Controller using the
   Consumer-Facing Interface (denoted as CFI).  The high-level security
   policy is translated by the SPT in the Security Controller into the
   corresponding low-level security policy (or policies) which is
   understandable by target NSF(s).  The Security Controller delivers
   the low-level security policy (or policies) to the appropriate NSF(s)
   to enforce the policy's rule(s).

   The SPT consists of four modules for security policy translations
   such as Data Model Mapper, Data Extractor, Data Converter, and Policy
   Generator, as shown in Figure 5.  The Data Model Mapper creates a
   mapping model for mapping the elements between the YANG data model of
   Consumer-Facing Interface [consumer-facing-inf-dm] and the YANG data
   model of NSF-Facing Interface [nsf-facing-inf-dm] for the automation
   of security policy translation.  It stores the mapping model into the
   NSF Database (denoted as NSF DB).

   The Data Extractor extracts data from a high-level security policy
   delivered by the I2NSF User.  The data correspond to the leaf nodes
   in the YANG data model for the Consumer-Facing Interface.  In the
   high-level policy in Figure 2, the data are the tag values of a
   policy's "name", a rule's "name", "start-time", "end-time", a
   source's "source", a destination's "url-name", and "action".  That
   is, the tag values are "security_policy_for_blocking_sns",
   "block_access_to_sns_during_office_hours", "09:00:00Z", "18:00:00Z",
   "employees", "sns-websites", and "drop."

   The Data Converter converts the extracted high-level policy data
   received from the Data Extractor into the corresponding low-level
   policy data.  The low-level policy data have the capability
   information of NSFs to be selected as target NSFs for the required
   security service enforcement specified by the high-level security



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   policy.  The tag values in the extracted high-level policy data are
   replaced with the tag values in the low-level policy data, which are
   the leaf nodes of the YANG data model for the NSF-Facing Interface
   (denoted as NFI).  The value of each leaf node in CFI is translated
   into the value of the corresponding leaf node in NFI.  For example,
   "security_policy_for_blocking_sns" of a policy's name in CFI (in
   Figure 2) is translated into "sns_access" of a policy's name in NFI
   (in Figure 3).  The tag values of name, start-time, end-time, and
   action in CFI are mapped into the same values of name, start-time,
   end-time, and content-security-control (under advanced-action) in
   NFI, as shown in Figure 3.  However, the tag values of a source's
   source and a destination's url-name in CFI are translated into IP
   addresses (in Figure 3) and URLs (in Figure 4), respectively, for the
   sake of NFI.  That is, "employees" of CFI is translated into the IPv6
   prefix "2001:db8:1::/60" for the sake of NFI.  Also, "sns-websites"
   of CFI is translated into three URLs such as "www.example.com",
   "www.example.net", and "www.example.org" for the sake of NFI.  In
   addition to the data conversion, the Data Converter searches for
   appropriate NSFs having capabilities corresponding to the leaf nodes
   of the YANG data model for NFI.  For the data conversion and NSF
   search, an NSF DB can be consulted, as shown in Figure 5, because the
   NSF DB has the capability information of NSFs that the DMS(s)
   registered with the Security Controller using the Registration
   Interface.

   The Policy Generator generates a low-level security policy
   corresponding to the low-level policy data made by the Data Converter
   per a target NSF(s).  That is, the Policy Generator can build such
   low-level security policy XML documents like Figure 3 and Figure 4
   with the NSF DB because the NSF DB has the mapping information
   between the CFI YANG data model and the NFI YANG data model.

   Therefore, by allowing the I2NSF User to express its security policy
   without knowing the detailed information of entities for security
   policies, the I2NSF can efficiently support the intent-based security
   services with the help of the security policy translator along with
   the NSF DB.














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      +------------+
      | I2NSF User |
      +------------+
             ^
             | Consumer-Facing Interface
             v
   +-------------------+     Registration     +-----------------------+
   |Security Controller|<-------------------->|Developer's Mgmt System|
   +-------------------+      Interface       +-----------------------+
         ^       ^
         |       | NSF-Facing Interface
         |       |-------------------------
         |                                |
         | NSF-Facing Interface           |
   +-----v-----------+             +------v-------+
   |  +-----------+  |      ------>|     NSF-1    |
   |  |Classifier |  |      |      |  (Firewall)  |
   |  +-----------+  |      |      +--------------+
   |     +-----+     |<-----|      +--------------+
   |     | SFF |     |      |----->|     NSF-2    |
   |     +-----+     |      |      |     (DPI)    |
   +-----------------+      |      +--------------+
                            |             .
                            |             .
                            |             .
                            |      +-----------------------+
                            ------>|        NSF-n          |
                                   |(DDoS-Attack Mitigator)|
                                   +-----------------------+

                   Figure 6: An I2NSF Framework with SFC

6.  I2NSF Framework with SFC

   In the I2NSF architecture, an NSF can trigger an advanced security
   action (e.g., DPI or DDoS attack mitigation) on a packet based on the
   result of its own security inspection of the packet.  For example, a
   firewall triggers further inspection of a suspicious packet with DPI.
   For this advanced security action to be fulfilled, the suspicious
   packet should be forwarded from the current NSF to the successor NSF.
   SFC [RFC7665] is a technology that enables this advanced security
   action by steering a packet with multiple service functions (e.g.,
   NSFs), and this technology can be utilized by the I2NSF architecture
   to support the advanced security action.

   Figure 6 shows an I2NSF framework with the support of SFC.  As shown
   in the figure, SFC generally requires classifiers and service
   function forwarders (SFFs); classifiers are responsible for



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   determining which service function path (SFP) (i.e., an ordered
   sequence of service functions) a given packet should pass through,
   according to pre-configured classification rules, and SFFs perform
   forwarding the given packet to the next service function (e.g., NSF)
   on the SFP of the packet by referring to their forwarding tables.  In
   the I2NSF architecture with SFC, the Security Controller can take
   responsibilities of generating classification rules for classifiers
   and forwarding tables for SFFs.  By analyzing high-level security
   policies from I2NSF users, the Security Controller can construct SFPs
   that are required to meet the high-level security policies, generates
   classification rules of the SFPs, and then configures classifiers
   with the classification rules over NSF-Facing Interface so that
   relevant traffic packets can follow the SFPs.  Also, based on the
   global view of NSF instances available in the system, the Security
   Controller constructs forwarding tables, which are required for SFFs
   to forward a given packet to the next NSF over the SFP, and
   configures SFFs with those forwarding tables over NSF-Facing
   Interface.

   To trigger an advanced security action in the I2NSF architecture, the
   current NSF appends metadata describing the security capability
   required to the suspicious packet via a network service header (NSH)
   [RFC8300].  It then sends the packet to the classifier.  Based on the
   metadata information, the classifier searches an SFP which includes
   an NSF with the required security capability, changes the SFP-related
   information (e.g., service path identifier and service index
   [RFC8300]) of the packet with the new SFP that has been found, and
   then forwards the packet to the SFF.  When receiving the packet, the
   SFF checks the SFP-related information such as the service path
   identifier and service index contained in the packet and forwards the
   packet to the next NSF on the SFP of the packet, according to its
   forwarding table.



















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      +------------+
      | I2NSF User |
      +------------+
             ^
             | Consumer-Facing Interface
             v
   +-------------------+     Registration     +-----------------------+
   |Security Controller|<-------------------->|Developer's Mgmt System|
   +-------------------+      Interface       +-----------------------+
      ^     ^
      |     | NSF-Facing Interface
      |     v
      | +----------------+ +---------------+   +-----------------------+
      | |      NSF-1     |-|     NSF-2     |...|         NSF-n         |
      | |   (Firewall)   | |     (DPI)     |   |(DDoS-Attack Mitigator)|
      | +----------------+ +---------------+   +-----------------------+
      |
      |
      |                                                  SDN Network
   +--|----------------------------------------------------------------+
   |  V NSF-Facing Interface                                           |
   |  +----------------+                                               |
   |  | SDN Controller |                                               |
   |  +----------------+                                               |
   |           ^                                                       |
   |           | SDN Southbound Interface                              |
   |           v                                                       |
   |      +--------+ +------------+ +--------+       +--------+        |
   |      |Switch-1|-|  Switch-2  |-|Switch-3|.......|Switch-m|        |
   |      |        | |(Classifier)| | (SFF)  |       |        |        |
   |      +--------+ +------------+ +--------+       +--------+        |
   +-------------------------------------------------------------------+

               Figure 7: An I2NSF Framework with SDN Network

7.  I2NSF Framework with SDN

   This section describes an I2NSF framework with SDN for I2NSF
   applicability and use cases, such as firewall, deep packet
   inspection, and DDoS-attack mitigation functions.  SDN enables some
   packet filtering rules to be enforced in network forwarding elements
   (e.g., switch) by controlling their packet forwarding rules.  By
   taking advantage of this capability of SDN, it is possible to
   optimize the process of security service enforcement in the I2NSF
   system.  For example, for efficient firewall services, simple packet
   filtering can be performed by SDN forwarding elements (e.g.,
   switches), and complicated packet filtering based on packet payloads
   can be performed by a firewall NSF.  This optimized firewall using



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   both SDN forwarding elements and a firewall NSF is more efficient
   than a firewall where SDN forwarding elements forward all the packets
   to a firewall NSF for packet filtering.  This is because packets to
   be filtered out can be early dropped by SDN forwarding elements
   without consuming further network bandwidth due to the forwarding of
   the packets to the firewall NSF.

   Figure 7 shows an I2NSF framework [RFC8329] with SDN networks to
   support network-based security services.  In this system, the
   enforcement of security policy rules is divided into the SDN
   forwarding elements (e.g., a switch running as either a hardware
   middle box or a software virtual switch) and NSFs (e.g., a firewall
   running in a form of a VNF [ETSI-NFV]).  Note that NSFs are created
   or removed by the NFV Management and Orchestration (MANO)
   [ETSI-NFV-MANO], performing the lifecycle management of NSFs as VNFs.
   Refer to Section 8 for the detailed discussion of the NSF lifecycle
   management in the NFV MANO for I2NSF.  For security policy
   enforcement (e.g., packet filtering), the Security Controller
   instructs the SDN Controller via NSF-Facing Interface so that SDN
   forwarding elements can perform the required security services with
   flow tables under the supervision of the SDN Controller.

   As an example, let us consider two different types of security rules:
   Rule A is a simple packet filtering rule that checks only the IP
   address and port number of a given packet, whereas rule B is a time-
   consuming packet inspection rule for analyzing whether an attached
   file being transmitted over a flow of packets contains malware.  Rule
   A can be translated into packet forwarding rules of SDN forwarding
   elements and thus be enforced by these elements.  In contrast, rule B
   cannot be enforced by forwarding elements, but it has to be enforced
   by NSFs with anti-malware capability.  Specifically, a flow of
   packets is forwarded to and reassembled by an NSF to reconstruct the
   attached file stored in the flow of packets.  The NSF then analyzes
   the file to check the existence of malware.  If the file contains
   malware, the NSF drops the packets.

   In an I2NSF framework with SDN, the Security Controller can analyze
   given security policy rules and automatically determine which of the
   given security policy rules should be enforced by SDN forwarding
   elements and which should be enforced by NSFs.  If some of the given
   rules requires security capabilities that can be provided by SDN
   forwarding elements, then the Security Controller instructs the SDN
   Controller via NSF-Facing Interface so that SDN forwarding elements
   can enforce those security policy rules with flow tables under the
   supervision of the SDN Controller.  Or if some rules require security
   capabilities that cannot be provided by SDN forwarding elements but
   by NSFs, then the Security Controller instructs relevant NSFs to
   enforce those rules.



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   The distinction between software-based SDN forwarding elements and
   NSFs, which can both run as VNFs, may be necessary for some
   management purposes in this system.  Note that an SDN forwarding
   element (i.e., switch) is a specific type of VNF rather than an NSF
   because an NSF is for security services rather than for packet
   forwarding.  For this distinction, we can take advantage of the NFV
   MANO where there is a subsystem that maintains the descriptions of
   the capabilities each VNF can offer [ETSI-NFV-MANO].  This subsystem
   can determine whether a given software element (VNF instance) is an
   NSF or a virtualized SDN switch.  For example, if a VNF instance has
   anti-malware capability according to the description of the VNF, it
   could be considered as an NSF.  A VNF onboarding system
   [VNF-ONBOARDING] can be used as such a subsystem that maintains the
   descriptions of each VNF to tell whether a VNF instance is for an NSF
   or for a virtualized SDN switch.

   For the support of SFC in the I2NSF framework with SDN, as shown in
   Figure 7, network forwarding elements (e.g., switch) can play the
   role of either SFC Classifier or SFF, which are explained in
   Section 6.  Classifier and SFF have an NSF-Facing Interface with
   Security Controller.  This interface is used to update security
   service function chaining information for traffic flows.  For
   example, when it needs to update an SFP for a traffic flow in an SDN
   network, as shown in Figure 7, SFF (denoted as Switch-3) asks
   Security Controller to update the SFP for the traffic flow (needing
   another security service as an NSF) via NSF-Facing Interface.  This
   update lets Security Controller ask Classifier (denoted as Switch-2)
   to update the mapping between the traffic flow and SFP in Classifier
   via NSF-Facing Interface.

   The following subsections introduce three use cases from [RFC8192]
   for cloud-based security services: (i) firewall system, (ii) deep
   packet inspection system, and (iii) attack mitigation system.

7.1.  Firewall: Centralized Firewall System

   A centralized network firewall can manage each network resource and
   apply common rules to individual network elements (e.g., switch).
   The centralized network firewall controls each forwarding element,
   and firewall rules can be added or deleted dynamically.

   A time-based firewall can be enforced with packet filtering rules and
   a time span (e.g., work hours).  With this time-based firewall, a
   time-based security policy can be enforced, as explained in
   Section 4.  For example, employees at a company are allowed to access
   social networking service websites during lunch time or after work
   hours.




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7.2.  Deep Packet Inspection: Centralized VoIP/VoLTE Security System

   A centralized VoIP/VoLTE security system can monitor each VoIP/VoLTE
   flow and manage VoIP/VoLTE security rules, according to the
   configuration of a VoIP/VoLTE security service called VoIP Intrusion
   Prevention System (IPS).  This centralized VoIP/VoLTE security system
   controls each switch for the VoIP/VoLTE call flow management by
   manipulating the rules that can be added, deleted or modified
   dynamically.

   The centralized VoIP/VoLTE security system can cooperate with a
   network firewall to realize VoIP/VoLTE security service.
   Specifically, a network firewall performs the basic security check of
   an unknown flow's packet observed by a switch.  If the network
   firewall detects that the packet is an unknown VoIP call flow's
   packet that exhibits some suspicious patterns, then it triggers the
   VoIP/VoLTE security system for more specialized security analysis of
   the suspicious VoIP call packet.

7.3.  Attack Mitigation: Centralized DDoS-attack Mitigation System

   A centralized DDoS-attack mitigation can manage each network resource
   and configure rules to each switch for DDoS-attack mitigation (called
   DDoS-attack Mitigator) on a common server.  The centralized DDoS-
   attack mitigation system defends servers against DDoS attacks outside
   the private network, that is, from public networks
   [RFC8612][RFC8811].

   Servers are categorized into stateless servers (e.g., DNS servers)
   and stateful servers (e.g., web servers).  For DDoS-attack
   mitigation, the forwarding of traffic flows in switches can be
   dynamically configured such that malicious traffic flows are handled
   by the paths separated from normal traffic flows in order to minimize
   the impact of those malicious traffic on the servers.  This flow path
   separation can be done by a flow forwarding path management scheme
   [RFC8811][AVANT-GUARD].  This management should consider the load
   balance among the switches for the defense against DDoS attacks.

   So far this section has described the three use cases for network-
   based security services using the I2NSF framework with SDN networks.
   To support these use cases in the proposed data-driven security
   service framework, YANG data models described in
   [consumer-facing-inf-dm], [nsf-facing-inf-dm], and
   [registration-inf-dm] can be used as Consumer-Facing Interface, NSF-
   Facing Interface, and Registration Interface, respectively, along
   with RESTCONF [RFC8040] and NETCONF [RFC6241].





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                                                  +--------------------+
   +-------------------------------------------+  | ----------------   |
   |            I2NSF User (OSS/BSS)           |  | | NFV          |   |
   +------+------------------------------------+  | | Orchestrator +-+ |
          |  Consumer-Facing Interface            | -----+---------- | |
   +------|------------------------------------+  |      |           | |
   | -----+----------  (a)  -----------------  |  |  ----+-----      | |
   | |  Security    +-------+  Developer's  |  |  |  |        |      | |
   | |Controller(EM)|       |Mgmt System(EM)|  +-(b)-+ VNFM(s)|      | |
   | -----+----------       -----------------  |  |  |        |      | |
   |      |  NSF-Facing Interface              |  |  ----+-----      | |
   |  ----+-----    ----+-----    ----+-----   |  |      |           | |
   |  |NSF(VNF)|    |NSF(VNF)|    |NSF(VNF)|   |  |      |           | |
   |  ----+-----    ----+-----    ----+-----   |  |      |           | |
   |      |             |             |        |  |      |           | |
   +------|-------------|-------------|--------+  |      |           | |
          |             |             |           |      |           | |
   +------+-------------+-------------+--------+  |      |           | |
   |         NFV Infrastructure (NFVI)         |  |      |           | |
   | -----------    -----------    ----------- |  |      |           | |
   | | Virtual |    | Virtual |    | Virtual | |  |      |           | |
   | | Compute |    | Storage |    | Network | |  |      |           | |
   | -----------    -----------    ----------- |  |  ----+-----      | |
   | +---------------------------------------+ |  |  |        |      | |
   | |         Virtualization Layer          | +-----+ VIM(s) +------+ |
   | +---------------------------------------+ |  |  |        |        |
   | +---------------------------------------+ |  |  ----------        |
   | | -----------  -----------  ----------- | |  |                    |
   | | | Compute |  | Storage |  | Network | | |  |                    |
   | | | Hardware|  | Hardware|  | Hardware| | |  |                    |
   | | -----------  -----------  ----------- | |  |                    |
   | |          Hardware Resources           | |  |   NFV Management   |
   | +---------------------------------------+ |  | and Orchestration  |
   |                                           |  |       (MANO)       |
   +-------------------------------------------+  +--------------------+
   (a) = Registration Interface
   (b) = Ve-Vnfm Interface

   Figure 8: I2NSF Framework Implementation with respect to the NFV
                  Reference Architectural Framework

8.  I2NSF Framework with NFV

   This section discusses the implementation of the I2NSF framework
   using Network Functions Virtualization (NFV).






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   NFV is a promising technology for improving the elasticity and
   efficiency of network resource utilization.  In NFV environments,
   NSFs can be deployed in the forms of software-based virtual instances
   rather than physical appliances.  Virtualizing NSFs makes it possible
   to rapidly and flexibly respond to the amount of service requests by
   dynamically increasing or decreasing the number of NSF instances.
   Moreover, NFV technology facilitates flexibly including or excluding
   NSFs from multiple security solution vendors according to the changes
   on security requirements.  In order to take advantages of the NFV
   technology, the I2NSF framework can be implemented on top of an NFV
   infrastructure as show in Figure 8.

   Figure 8 shows an I2NSF framework implementation based on the NFV
   reference architecture that the European Telecommunications Standards
   Institute (ETSI) defines [ETSI-NFV].  The NSFs are deployed as VNFs
   in Figure 8.  The Developer's Management System (DMS) in the I2NSF
   framework is responsible for registering capability information of
   NSFs into the Security Controller.  However, those NSFs are created
   or removed by a virtual network function manager (VNFM) in the NFV
   MANO that performs the lifecycle management of VNFs.  Note that the
   lifecycle management of VNFs is out of scope for I2NSF.  The Security
   Controller controls and monitors the configurations (e.g., function
   parameters and security policy rules) of VNFs via the NSF-Facing
   Interface along with the NSF monitoring capability
   [nsf-facing-inf-dm][nsf-monitoring-dm].  Both the DMS and Security
   Controller can be implemented as the Element Managements (EMs) in the
   NFV architecture.  Finally, the I2NSF User can be implemented as OSS/
   BSS (Operational Support Systems/Business Support Systems) in the NFV
   architecture that provides interfaces for users in the NFV system.

   The operation procedure in the I2NSF framework based on the NFV
   architecture is as follows:

   1.  The VNFM has a set of virtual machine (VM) images of NSFs, and
       each VM image can be used to create an NSF instance that provides
       a set of security capabilities.  The DMS initially registers a
       mapping table of the ID of each VM image and the set of
       capabilities that can be provided by an NSF instance created from
       the VM image into the Security Controller.

   2.  If the Security Controller does not have any instantiated NSF
       that has the set of capabilities required to meet the security
       requirements from users, it searches the mapping table
       (registered by the DMS) for the VM image ID corresponding to the
       required set of capabilities.

   3.  The Security Controller requests the DMS to instantiate an NSF
       with the VM image ID via VNFM.



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   4.  When receiving the instantiation request, the VNFM first asks the
       NFV orchestrator for the permission required to create the NSF
       instance, requests the VIM to allocate resources for the NSF
       instance, and finally creates the NSF instance based on the
       allocated resources.

   5.  Once the NSF instance has been created by the VNFM, the DMS
       performs the initial configurations of the NSF instance and then
       notifies the Security Controller of the NSF instance.

   6.  After being notified of the created NSF instance, the Security
       Controller delivers low-level security policy rules to the NSF
       instance for policy enforcement.

   We can conclude that the I2NSF framework can be implemented based on
   the NFV architecture framework.  Note that the registration of the
   capabilities of NSFs is performed through the Registration Interface
   and the lifecycle management for NSFs (VNFs) is performed through the
   Ve-Vnfm interface between the DMS and VNFM, as shown in Figure 8.

9.  Security Considerations

   The same security considerations for the I2NSF framework [RFC8329]
   are applicable to this document.

   This document shares all the security issues of SDN that are
   specified in the "Security Considerations" section of [ITU-T.Y.3300].

   The role of the DMS is to provide an I2NSF system with the software
   packages or images for NSF execution.  The DMS must not access NSFs
   in activated status.  An inside attacker or a supply chain attacker
   at the DMS can seriously weaken the I2NSF system's security.  A
   malicious DMS is relevant to an insider attack, and a compromised DMS
   is relevant to a supply chain attack.  A malicious (or compromised)
   DMS could register an NSF of its choice in response to a capability
   request by the Security Controller.  As a result, a malicious DMS can
   attack the I2NSF system by providing malicious NSFs with arbitrary
   capabilities to include potentially controlling those NSFs in real
   time.  An unwitting DMS could be compromised and the infrastructure
   of the DMS could be coerced into distributing modified NSFs as well.

   To deal with these types of threats, an I2NSF system should not use
   NSFs from an untrusted DMS or without prior testing.  The practices
   by which these packages are downloaded and loaded into the system are
   out of scope for I2NSF.






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   I2NSF system operators should audit and monitor interactions with
   DMSs.  Additionally, the operators should monitor the running NSFs
   through the I2NSF NSF Monitoring Interface [nsf-monitoring-dm] as
   part of the I2NSF NSF-Facing Interface.  Note that the mechanics for
   monitoring the DMSs are out of scope for I2NSF.

10.  IANA Considerations

   This document does not require any IANA actions.

11.  References

11.1.  Normative References

   [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, July
              2017, <https://www.rfc-editor.org/rfc/rfc8192>.

   [RFC8329]  Lopez, D., Lopez, E., Dunbar, L., Strassner, J., and R.
              Kumar, "Framework for Interface to Network Security
              Functions", RFC 8329, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8329>.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010, <https://www.rfc-editor.org/rfc/rfc6020>.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              RFC 6241, June 2011,
              <https://www.rfc-editor.org/rfc/rfc6241>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, January 2017,
              <https://www.rfc-editor.org/rfc/rfc8040>.

   [RFC7665]  Halpern, J. and C. Pignataro, "Service Function Chaining
              (SFC) Architecture", RFC 7665, October 2015,
              <https://www.rfc-editor.org/rfc/rfc7665>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

   [RFC8300]  Quinn, P., Elzur, U., and C. Pignataro, "Network Service
              Header (NSH)", RFC 8300, January 2018,
              <https://www.rfc-editor.org/rfc/rfc8300>.



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   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, March 2014,
              <https://www.rfc-editor.org/rfc/rfc7149>.

   [RFC8612]  Mortensen, A., Reddy, T., and R. Moskowitz, "DDoS Open
              Threat Signaling (DOTS) Requirements", RFC 8612, May 2019,
              <https://www.rfc-editor.org/rfc/rfc8612>.

   [RFC8811]  Mortensen, A., Reddy, T., Andreasen, F., Teague, N., and
              R. Compton, "Distributed-Denial-of-Service Open Threat
              Signaling (DOTS) Architecture", RFC 8811, March 2020,
              <https://www.rfc-editor.org/rfc/rfc8811>.

   [consumer-facing-inf-dm]
              Jeong, J., Chung, C., Ahn, T., Kumar, R., and S. Hares,
              "I2NSF Consumer-Facing Interface YANG Data Model", Work in
              Progress, Internet-Draft, draft-ietf-i2nsf-consumer-
              facing-interface-dm-31, May 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-i2nsf-
              consumer-facing-interface-dm-31>.

   [nsf-monitoring-dm]
              Jeong, J., Lingga, P., Hares, S., Xia, L., and H.
              Birkholz, "I2NSF NSF Monitoring YANG Data Model", Work in
              Progress, Internet-Draft, draft-ietf-i2nsf-nsf-monitoring-
              data-model-20, June 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-i2nsf-
              nsf-monitoring-data-model-20>.

   [nsf-facing-inf-dm]
              Kim, J., Jeong, J., Park, J., Hares, S., and Q. Lin,
              "I2NSF Network Security Function-Facing Interface YANG
              Data Model", Work in Progress, Internet-Draft, draft-ietf-
              i2nsf-nsf-facing-interface-dm-29, June 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-i2nsf-
              nsf-facing-interface-dm-29>.

   [registration-inf-dm]
              Hyun, S., Jeong, J., Roh, T., Wi, S., and J. Park, "I2NSF
              Registration Interface YANG Data Model for NSF Capability
              Registration", Work in Progress, Internet-Draft, draft-
              ietf-i2nsf-registration-interface-dm-26, May 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-i2nsf-
              registration-interface-dm-26>.






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   [ITU-T.Y.3300]
              "Framework of Software-Defined Networking",
              Available: https://www.itu.int/rec/T-REC-
              Y.3300-201406-I/en, June 2014.

   [ONF-SDN-Architecture]
              "SDN Architecture (Issue 1.1)", Available: 
              https://opennetworking.org/wp-content/uploads/2014/10/TR-
              521_SDN_Architecture_issue_1.1.pdf, June 2016.

   [NFV-Terminology]
              "Network Functions Virtualisation (NFV); Terminology for
              Main Concepts in NFV", Available:
              https://www.etsi.org/deliver/etsi_gr/
              NFV/001_099/003/01.07.01_60/gr_NFV003v010701p.pdf, January
              2023.

   [ETSI-NFV] "Network Functions Virtualisation (NFV); Architectural
              Framework", Available:
              https://www.etsi.org/deliver/etsi_gs/
              nfv/001_099/002/01.02.01_60/gs_nfv002v010201p.pdf,
              December 2014.

   [AVANT-GUARD]
              Shin, S., Yegneswaran, V., Porras, P., and G. Gu, "AVANT-
              GUARD: Scalable and Vigilant Switch Flow Management in
              Software-Defined Networks", ACM CCS, November 2013.

11.2.  Informative References

   [SPT]      Lingga, P., Jeong, J., Yang, J., and J. Kim, "SPT:
              Security Policy Translator for Network Security Functions
              in Cloud-Based Security Services", IEEE Transactions on
              Dependable and Secure Computing, Volume 21, Issue 6,
              DOI https://doi.org/10.1109/TDSC.2024.3371788, November
              2024, <https://doi.org/https://doi.org/10.1109/
              TDSC.2024.3371788>.

   [tls-esni] Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
              Encrypted Client Hello", Work in Progress, Internet-Draft,
              draft-ietf-tls-esni-23, February 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              esni-23>.








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   [ITU-T.X.800]
              "Security Architecture for Open Systems Interconnection
              for CCITT Applications",
              Available: https://www.itu.int/rec/T-REC-
              X.800-199103-I/en, March 1991.

   [opsawg-firewalls]
              Baker, F. and P. Hoffman, "On Firewalls in Internet
              Security", Work in Progress, Internet-Draft, draft-ietf-
              opsawg-firewalls-01, October 2012,
              <https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
              firewalls-01>.

   [ETSI-NFV-MANO]
              "Network Functions Virtualisation (NFV) Release 4;
              Management and Orchestration; Architectural Framework
              Specification", Available:
              https://www.etsi.org/deliver/etsi_gs/
              NFV/001_099/006/04.04.01_60/gs_NFV006v040401p.pdf,
              December 2022.

   [VNF-ONBOARDING]
              "Welcome to Open Source MANO's VNF Onboarding guide!",
              Available: https://osm.etsi.org/docs/vnf-onboarding-
              guidelines/, 2019.

Appendix A.  Acknowledgments

   This document is made by the group effort of I2NSF working group.
   Many people actively contributed to this document, such as Linda
   Dunbar, Yoav Nir, Roman Danyliw, and Patrick Lingga.  The authors
   sincerely appreciate their contributions.

   This work was supported by Institute of Information & Communications
   Technology Planning & Evaluation (IITP) grant funded by the Korea
   Ministry of Science and ICT (MSIT)(No.  R-20160222-002755, Cloud
   based Security Intelligence Technology Development for the Customized
   Security Service Provisioning).

   This work was supported in part by Institute of Information &
   Communications Technology Planning & Evaluation (IITP) grant funded
   by the Korea Ministry of Science and ICT (MSIT) (No.  RS-
   2024-00398199, Standard Development of SDV Software Framework for
   Intelligent Convergence Services).







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   This work has been partially supported by the European Commission
   under Horizon 2020 grant agreement no. 700199 "Securing against
   intruders and other threats through a NFV-enabled environment
   (SHIELD)".  This support does not imply endorsement.

Appendix B.  Contributors

   The following are coauthors of this document:

   Jinyong Tim Kim
   Department of Electronic, Electrical and Computer Engineering
   Sungkyunkwan University
   2066 Seobu-ro, Jangan-gu
   Suwon
   Gyeonggi-do
   16419
   Republic of Korea
   Phone: +82 31 299 4106
   Email: timkim@skku.edu


   Hyoungshick Kim
   Department of Computer Science and Engineering
   Sungkyunkwan University
   2066 Seobu-ro, Jangan-gu
   Suwon
   Gyeonggi-do
   16419
   Republic of Korea
   Phone: +82 31 299 4324
   Email: hyoung@skku.edu


   Jung-Soo Park
   Standards & Open Source Research Division
   Electronics and Telecommunications Research Institute
   218 Gajeong-ro, Yuseong-gu,
   Daejeon
   34129
   Republic of Korea
   Phone: +82 42 860 6514
   Email: pjs@etri.re.kr


   Hyunsik Yang
   School of Electronic Engineering
   Soongsil University
   369, Sangdo-ro, Dongjak-gu



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   Seoul
   06978
   Republic of Korea
   Email: yangun@dcn.ssu.ac.kr


   Younghan Kim
   School of Electronic Engineering
   Soongsil University
   369, Sangdo-ro, Dongjak-gu
   Seoul
   06978
   Republic of Korea
   Email: younghak@ssu.ac.kr


   Sehui Lee
   KT
   70 Yuseong-ro, Yuseong-gu
   Daejeon
   34047
   Republic of Korea
   Phone: +82 42 870 8162
   Email: sehuilee@kt.com


   Mohamed Boucadair
   Orange
   France
   Email: mohamed.boucadair@orange.com


Authors' Addresses

   Jaehoon Paul Jeong
   Department of Computer Science and Engineering
   Sungkyunkwan University
   2066 Seobu-ro, Jangan-gu
   Suwon
   Gyeonggi-do
   16419
   Republic of Korea
   Phone: +82 31 299 4957
   Email: pauljeong@skku.edu
   URI:   http://iotlab.skku.edu/people-jaehoon-jeong.php






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   Sangwon Hyun
   Department of Computer Engineering
   Myongji University
   116 Myongji-ro, Cheoin-gu
   Yongin
   17058
   Republic of Korea
   Phone: +82 31 330 6782
   Email: shyun@mju.ac.kr


   Tae-Jin Ahn
   KT
   70 Yuseong-ro, Yuseong-gu
   Daejeon
   34047
   Republic of Korea
   Phone: +82 42 870 8409
   Email: taejin.ahn@kt.com


   Susan Hares
   Huawei
   7453 Hickory Hill
   Saline, MI 48176
   United States of America
   Phone: +1-734-604-0332
   Email: shares@ndzh.com


   Diego R. Lopez
   Telefonica I+D
   Jose Manuel Lara, 9
   41013 Seville
   Spain
   Phone: +34 682 051 091
   Email: diego.r.lopez@telefonica.com














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