SDNRG                                                     R. Marin-Lopez
Internet-Draft                                           G. Lopez-Millan
Intended status: Experimental                       University of Murcia
Expires: May 14, 2016                                  November 11, 2015

 Software-Defined Networking (SDN)-based AAA Infrastructures Management


   This document describes the management of Authentication,
   Authorization and Accounting (AAA) infraesctrutures by means of a
   Software-Defined Network (SDN) controller and raises the requirements
   to support this service.  It considers the management of AAA routing
   and the establishment of security associations between AAA entities.

Status of This Memo

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   This Internet-Draft will expire on May 14, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  AAA flow based routing  . . . . . . . . . . . . . . . . . . .   6
   6.  Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  AAA routing and security association establishment  . . .  10
     6.2.  AAA agents under different SDN controllers  . . . . . . .  12
   7.  Relationship with I2NSF . . . . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Software-Defined Networking (SDN) is an architecture that enables
   users to directly program, orchestrate, control and manage network
   resources through software.  SDN paradigm relocates the control of
   network resources to a dedicated network element, namely SDN
   controller.  The SDN controller manages and configures the
   distributed network resources and provides an abstracted view of the
   network resources to the SDN applications.  The SDN application can
   customize and automate the operations (including management) of the
   abstracted network resources in a programmable manner via this
   interface [RFC7149][ITU-T.Y.3300]

   Authentication, Authorization and Accounting (AAA) [RFC2903][RFC2904]
   infrastructures manage three basic security services to control the
   access to network resources: Authentication, in order to determine
   who the end user is; Authorization, in order to determine under what
   conditions an end user is granted access to the network resource; and
   Accounting, in order to account the resource usage of the end user.

   Following the terminology in [RFC6733], an AAA infrastructure is
   formed by AAA nodes.  An AAA protocol is used to exchange AAA
   information between them.  RADIUS [RFC2865], [RFC2866] and Diameter
   [RFC6733].  These AAA nodes can be classified as follows:

   o  AAA client.  It is a AAA node that implement the client part of a
      AAA protocol.

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   o  AAA server.  AAA node that handles authentication, authorization,
      and accounting requests for a particular realm.

   o  AAA agent.  AAA node that implements one of the following


      *  Relay Agents.  They are agents that accept requests and route
         messages (making use of a routing table) to other nodes based
         on information found in the DIAMETER messages.

      *  Proxy Agents.  Similarly to relays, proxy agents also route
         messages using a routing table.  However, they differ since
         they modify messages to implement policy enforcement.

      *  Redirect Agents.  Redirect agents do not relay Diameter
         messages, they return an answer with the information required
         by the agents to communicate directly, so they do not modify
         messages.  They are useful in scenarios where routing
         configuration needs to be centralized.

      *  Translation Agents.  A translation agent is a device that
         provides translation between two protocols (e.g.,
         RADIUS<->Diameter, TACACS+<->Diameter).

   As depicted in Figure 1, the AAA framework [RFC2903] defines a model
   consisting of the User desiring gain access to a specific network
   service; the AAA server in the User Home Organization (UHO) which has
   registered the User's identity and credentials; and the AAA server
   located in the Service Provider (SP) operating and controlling the
   access to the network service through a Service Equipment.  In non-
   federated environments, User Home Organization and Service Provider
   are the same organization.  In federated environments, they are two
   separate organizations.

   Between the AAA client and the AAA server in the UHO, the AAA
   infrastructure can deploy other intermediate AAA agents to forward
   the information between both entities.  RADIUS defines, apart from
   the RADIUS client and RADIUS server, the role of proxy RADIUS or
   forwarding RADIUS.  Proxy RADIUS receives authentication requests
   from a RADIUS client, forwards the request to a remote RADIUS server,
   receives authentication responses from the remote server and forwards
   the response to the client.  In Diameter, apart from the AAA client
   and the AAA server, it defines a set of these Diameter agents that
   corresponds with the agents described above.

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   It is important to note that the AAA node can act as AAA server in a
   realm but also can act as, for example, Relay/Proxy agent for those
   types of AAA requests that cannot be processed and need to be
   forwarded to the next AAA node.  It is also important to note that
   some kind of trust relationship is required to be established between
   these AAA nodes, in order to protect the AAA traffic

   Typically, Proxy RADIUS and Diameter agents (from now on AAA agents)
   hold and manage AAA routing information.  Moreover AAA
   infrastructures are manually configured, specially the AAA routing
   information.  For example, RADIUS implementations typically require
   the name or address of servers or clients be manually configured,
   besides passwords or cryptographic material to establish a security
   associations between AAA entities.  It makes difficult their
   management and generates a lack of flexibility, specially if the
   number of entities is high and the AAA infrastructure is complex.
   With the grow of SDN-based scenarios where network resources are
   deployed in an autonomous manner, a mechanism to manage AAA
   infrastructures according to the SDN paradigm becomes more relevant.
   Thus, the SDN-based service described in this document deals with AAA
   infrastructures in such as an autonomous manner.

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                     +------+      +-------------------------+
                     |      |      | User Home Organization  |
                     |      |      |  +-------------------+  |
                     |      |      |  |    AAA Server     |  |
                     |      |      |  |                   |  |
                     |      |      |  +-------------------+  |
                     |      |      |                         |
                     |      |      +-------------------------+
                     |      |
                     |      |
                     |      |
                     | User |      +-------------------------+
                     |      |      | Service Provider        |
                     |      |      |  +-------------------+  |
                     |      |      |  |    AAA Server     |  |
                     |      |      |  |                   |  |
                     |      |      |  +-------------------+  |
                     |      |      |                         |
                     |      |      |  +-------------------+  |
                     |      |      |  |    AAA Client     |  |
                     |      |      |  |-------------------|  |
                     |      |      |  |      Service      |  |
                     |      |      |  |     Equipment     |  |
                     |      |      |  +-------------------+  |
                     |      |      |                         |
                     +------+      +-------------------------+

                          Figure 1: AAA framework

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].
   When these words appear in lower case, they have their natural
   language meaning.

3.  Terminology

   This document uses the terminology described in [RFC7149], [RFC6733],
   [ITU-T.Y.3300], [ONF-SDN-Architecture], [ONF-OpenFlow],
   [ITU-T.X.1252], and [ITU-T.X.800].  In addition, the following terms
   are defined below:

   o  Software-Defined Networking: A set of techniques enabling 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].

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4.  Objectives

   o  Flow-based AAA traffic routing: SDN-based management allows to
      route AAA traffic (flow) between different AAA agents so that the
      authentication, authorization and accounting tasks can be
      preformed.  Thus, it can adapt quickly the routing information
      when a AAA route is not available to redirect the AAA traffic to
      other nodes.

   o  Bootstrapping security associations: SDN-based flow protection
      allows the centralized bootstrapping of credentials to protect the
      AAA traffic between two adjacent AAA nodes (hop-by-hop) or between
      two separate AAA nodes without intermediate AAA nodes in between

5.  AAA flow based routing

   As mentioned, the AAA infrastructure is formed by a set of AAA nodes.
   These nodes interconnect each other using the AAA protocol, such as
   RADIUS or Diameter.  When the User desires to access a service which
   requires authentication and authorization, she typically sends her
   identity to the Service Equipment.  The Service Equipment (e.g. an
   WiFi access point) deploys the AAA client to interact with the AAA
   infrastructure.  The User's identity contains the realm where she
   belongs to.  For example, an identity can be "".  The
   identifier is "alice" and the realm is "".  Based on this realm
   (realm-based routing), the AAA agents, for example, AAA relay or
   proxy, route the AAA information to the specific AAA server in the
   User Home Organization that has a register of "".  This
   AAA server will be in charge of authenticate and authorize the Users
   in the realm.  In order to achieve a correct routing of AAA
   information each AAA agent maintains a AAA routing table and another
   table with the adjacent AAA servers, which are considered as next
   "AAA hop".

   As an example of AAA routing table, Diameter defines a format where
   each table entry contains the following fields:

   Realm Name

      This is the field that MUST be used as a primary key in the
      routing table lookups.  Note that some implementations perform
      their lookups based on longest-match-from-the-right on the realm
      rather than requiring an exact match.

   Application Identifier

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      A Diameter Application (i.e.  NAS-REQ, EAP, etc.) is identified by
      an Application Id.  The Diameter message can have a different
      destination (route entry) based on the Application Id in the
      message header.  This field MUST be used as a secondary key field
      in routing table lookups.

   Local Action

      The Local Action field is used to identify how a message should be
      treated.  The following actions are supported:

      1.  LOCAL - Diameter messages that can be satisfied locally, and
          do not need to be routed to another Diameter entity.

      2.  RELAY - All Diameter messages that fall within this category
          MUST be routed to a next hop Diameter entity that is indicated
          by the identifier described below.  Routing is done without
          modifying any non-routing AVPs.

      3.  PROXY - All Diameter messages that fall within this category
          MUST be routed to a next Diameter entity that is indicated by
          the identifier described below.  The local server MAY apply
          its local policies to the message by including new AVPs to the
          message prior to routing.

      4.  REDIRECT - Diameter messages that fall within this category
          MUST have the identity of the home Diameter server(s)
          appended, and returned to the sender of the message.

   Additionally, Diameter specification defines the Peer Table, which is
   used for message forwarding, and referenced by the Routing Table.  A
   Peer Table entry contains the following fields:

   Host identity

      The name of the peer (i.e.  Diameter URI of the peer).


      This is the state of the peer entry.

   Static or Dynamic

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      Specifies whether a peer entry was statically configured or
      dynamically discovered.

   Expiration time

      Specifies the time at which dynamically discovered peer table
      entries are to be either refreshed, or expired.

   TLS/TCP and DTLS/SCTP Enabled

      Specifies whether TLS/TCP or DTLS/SCTP is to be used when
      communicating with the peer.

   Thus, the general idea presented in the document assumes that a SDN
   controller can manage and fill this routing information in the
   different AAA entities under its control.  In particular, a set of
   tasks (not exhaustive) that the SDN controller can perform over the
   AAA infrastructure is the following:

   o  The SDN controller can provide this AAA routing information to the
      AAA agents so having a dynamic AAA routing.  In general, the SDN
      controller can fill the AAA routing and peer table of any AAA
      agents and servers, but also the AAA client to indicate the next
      AAA hop.  This brings all the existing advantages right now for
      general IP routing with SDN paradigm to AAA routing.  That is, it
      provides flexibility, scalability, availability, and security.

   o  AAA entity and its adjacent ones typically keep a security
      association (hop-by-hop security).  For example, RADIUS has a
      simple and weak model based on shared secrets.  Extensions such as
      RADSec [RFC6614] has been proposed for running TLS between two
      RADIUS servers.  Diameter mandates the usage of TLS and optionally
      IPsec.  To avoid manual configuration of these security
      associations, the SDN controller can dynamically provide this
      cryptographic information to both interacting AAA servers.

   o  When forming AAA federations, security is usually provided hop-by-
      hop, which means that, between each pair of neighboring AAA
      entities, the AAA protocol provides message protection.
      Sometimes, for example in RADIUS, this protection is based on
      message authentication, but not message encryption.  So these
      intermediate AAA entities can see all the information in clear.
      To avoid this, end-to-end security MAY be required.  With a SDN-
      approach we foresee achieving the following.  When the SP's AAA
      server observes that the User belongs to a different realm that it

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      does not know (managed by the UHO's AAA server), it can inform the
      SDN controller.  The SDN controller can then enforce cryptographic
      material to both the UHO's AAA and SP's AAA server to establish a
      direct security association between them.  Thus, in a simple
      architecture, the SDN controller would act as the manager of the
      federation.  Nevertheless, more complex cases can be envisages
      such as each AAA server is managed by a different SDN-controller.

   o  The SDN controller can modulate the behaviour between a relay,
      proxy and translation agent.  For example, the SDN controller can
      enforce routing tables but not sending any particular policy to
      the agent, so that it behaves as a relay agent.  However, if a
      proxy is required the particular behaviour is enforced by the
      controller based on internal policies.  For certain routes the AAA
      agent can act as a Redirect Agent.  In fact, in relationship with
      Network Function Virtualization (NVF) and Network Security
      Function (NSF), we envisage that the SDN controller can order the
      instantiation of a particular AAA agent (VNF) when it is required
      and "places it" in the path of the chain of AAA agents where the
      AAA requests and responses have to travel.  For example, if the
      SDN controller realizes the request is a RADIUS message and it has
      to traverse a Diameter-based AAA infrastructure, it can
      instantiate a Translation Agent, so that the requests and
      responses are automatically translated from and to the different
      AAA protocols.  Once it is instantiated, the SDN controller can
      install a routing entry in the RADIUS proxy so that the AAA
      request goes through the Translation Agent.

   o  The SDN controller MAY also manage the User's credentials.  In
      other words, the SDN controller can store all the User information
      provided by the administrator.  When the AAA server is going to
      act as UHO's AAA server for a set of services and users, it will
      require this information to complete the authentication and
      authorization steps.  The SDN can proactively push this
      information to the AAA server.  Or, reactively, when the AAA
      server does not know how to authenticate and authorize a request
      it can ask for the advice of the SDN controller and the controller
      can enforce the behaviour and the user's 'information.

   o  The SDN controller can also select the AAA server in charge of
      (exclusively) Accounting.  This accounting information can be also
      route to the specific AAA server.

   NOTE: In general, the SDN controller MAY make use of NETCONF and YANG
   model for AAA entities to configure them.

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6.  Scenarios

   This section explains two main use cases as examples for the SDN-
   based AAA management: first, when a single SDN controller is used;
   second, when multiple SDN controllers take place in the

6.1.  AAA routing and security association establishment

   As depicted in Figure 2, the SDN controller represents the "AAA
   control plane" where the decisions of AAA routing are taken based on
   AAA policies provided by the administrator (1).  Once, the SDN
   controller interprets these policies (2), it sends the AAA routing
   information ("AAA data plane") to the AAA entities (e.g.  Relay,
   Proxies or Redirect) to carry out the forwarding of the AAA request.
   This information is used to fill the AAA routing table and peer table
   of AAA agent 1 and AAA agent 2 (3).  Associated to this routing
   information any security credential is also provided (4) by the SDN
   controller to establish hop-by-hop security (5).  In general, the SDN
   controller can fill all the required information to the different AAA
   agents that form the AAA routing path to the destination.

                        |             SDN Controller             |
                        |                                        |
                     (1)|  +--------------+ (2)+--------------+  |
                AAA ------>| AAA Routing/ |--->| South. Prot. |  |
               Policies |  | Key Distr.   |    |              |  |
                        |  +--------------+    +--------------+  |
                        |    AAA Control Plane     |     |       |
                        |                          |     |       |
                                                   |     |
                                                   | (3) |
                        |--------------------------+ (4) +---|
           AAA          V AAA Data Plane                     V    AAA
           request  +-------------+                +-----------+request
            ------->|    AAA      |===============>|   AAA     |------>
                    |  agent 1    |  hop-by-hop    |  agent 2  |
                    |             |    security    |           |
                    +-------------+      (5)       +-----------+

             Figure 2: Example of AAA agent-to-agent routing.

   Figure 3 represents the case where end-to-end security (5) is
   established.  In this case, the SDN controller enables credential and
   AAA routing information so that the AAA request goes directly between

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   the SP's AAA server and the UHO's AAA server without passing through
   any intermediate AAA entity.

                       |             SDN Controller             |
                       |                                        |
                    (1)|   +--------------+ (2)+--------------+ |
               AAA --------| AAA Routing/ |--->| South. Prot. | |
               Policies.   | Key Distr.   |    |              | |
                       |   +--------------+    +--------------+ |
                       |     AAA Control Plane    |          |  |
                       |                          |          |  |
                                                  |          |
                                       (3) (4)    |          |  (3)(4)
                             |--------------------+          + -----|
                             V  AAA Data Plane                      V
          AAA request  +----------------+                  +-----------+
                ------>|    SP's AAA    |                  | UHO's AAA |
                       |     server     |=================>|   Server  |
                       +----------------+       (5)        +-----------+

       Figure 3: Example of AAA server-to-server routing (end-to-end

   Finally, Figure 4 describes the case of pushing AAA routing
   information only when really required (reactive).  Let us assume that
   the administrator has provided general AAA policies (1).  When a
   initial AAA request arrives the first time to the AAA agent 1, it
   notifies about the request to the SDN Controller (2).  The SDN
   Controller looks for AAA routing information associated with the AAA
   policies and the information in the AAA request.  It decides that the
   AAA request has to be forwarded to AAA agent 2 (3).  The SDN
   controller installs then AAA routing information in the routing table
   and peer table in AAA agent 1 (4).  Moreover, it fills the routing
   and peer tables within AAA agent 2 (5).  It also sends credentials to
   both agents to establish a security association (6) in order to
   provide hop-by-hop or end-to-end security (7).

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                        |    (1)      SDN Controller             |
            AAA ----------------+                                |
          Policies      |       V                                |
                        |      +----------+ (3) +-------------+  |
                    ---------->| AAA      |<--->|South. Prot. |  |
                    |   |      | Policies |     |             |  |
                    |   |      +----------+     +-------------+  |
                    |   |                        |     |         |
                    |   |                        |     |         |
                (2) |   +------------------------| --- | --------+
                    |                            |     |
                    |                      (4)(6)|     |(5)(6)
                    |   |------------------------+     +--|
            AAA     |   V                                 V       AAA
         request +-------------+                   +-----------+request
         ------->|    AAA      |================= >|   AAA     |------>
                 |  agent 1    |    hop-to-hop/    |  agent 2  |
                 |             |      security     |           |
                 +-------------+     (7)           +-----------+

    Figure 4: Example of SDN controller pushing AAA routing information

   NOTE: It is worth noting that for the same AAA request some
   information can be enforced proactively and other can be retrieved
   reactively during the travel of the AAA request.

6.2.  AAA agents under different SDN controllers

   Another case (Figure 5) is when, for example, two organizations, ISP
   A and ISP B have their own SDN controller (A and B respectively),
   each one controlling a different set of AAA agents.  During the
   travel of a AAA request, it may need to pass from the AAA agent 1
   controlled by SDN Controller A to another AAA agent 2 which is under
   the control of a different SDN controller B.

   In this case, both SDN controllers may coordinate each other and
   determine whether the AAA request is allowed to traverse through both
   realms or not (1).  If they agree the conditions (2), the AAA
   policies that represents this agreement are enforced by the SDN
   controllers as AAA routing information and credentials into the AAA
   agents (3).  Then the AAA request can move forward (4).

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                   +-------------+                   +-------------+
        AAA        |     SDN     |<=================>|     SDN     |
        Policy. -->| Controller A|        (2)        |Controller B |
               (1) |             |                   |             |
                   +-------------+                   +-------------+
                          |                                 |
                          | (3)                         (3) |
             AAA          V                                 V     AAA
          request  +-------------+               +-------------+ request
            ------>| AAA agent 1 |<=============>| AAA agent 2 |------>
                   +-------------+      (4)      +-------------+

       Figure 5: Gateway-to-gateway multi controller flow in case 1

7.  Relationship with I2NSF

   According to [I-D.merged-i2nsf-framework-04] I2NSF needs to provide
   identity information, along with additional data that Authentication,
   Authorization, and Accounting (AAA) frameworks can use.  This enables
   those frameworks to perform AAA functions on the I2NSF traffic.  In
   this sense, we assume that each AAA entity is, in the end, a NSF that
   may need to be configured with AAA-related information and where the
   administrator can obtain some valuable information such as, number
   authentications executed, number of active users accessing the
   service, accounting records, etc.

   We envisage that SDN controller MAY also instantiate a vNSF acting as
   one of the AAA agents (relay, proxy, redirect, translation, server,
   etc...) when necessary.  Even more, an administrator MAY instantiate
   a AAA server that works as UHO's AAA server.  For that, apart from
   create the vNSF, it needs to register the users that the AAA server

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               |             Security Application          | App.
               |       (e.g.Identity and AAA Management)   | Layer
               |             Application Support           | SDN/
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Security
               |AAA Control Plane(routing,key distribution.| Controller
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ AAA server
               |               AAA Data Plane              |(NSF)
        ---->  |         Policy and Event Repository (PER) | --->
               |             AAA routing table  (AAA-RT)   |

      Figure 6: High-level Architecture for SDN-based AAA management

   Figure 6 describes the mapping with our use cases.  In the right side
   of the figure each entity follows the same terminology than

8.  Security Considerations


9.  Acknowledgements


10.  References

10.1.  Normative References

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

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,

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   [RFC2866]  Rigney, C., "RADIUS Accounting", RFC 2866,
              DOI 10.17487/RFC2866, June 2000,

   [RFC2903]  de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and
              D. Spence, "Generic AAA Architecture", RFC 2903,
              DOI 10.17487/RFC2903, August 2000,

   [RFC2904]  Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
              Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
              D. Spence, "AAA Authorization Framework", RFC 2904,
              DOI 10.17487/RFC2904, August 2000,

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,

10.2.  Informative References

              Lopez, E., Lopez, D., Zhuang, X., Dunbar, L., Parrott, J.,
              Krishnan, R., and SR. Durbha, "Framework for Interface to
              Network Security Functions", draft-merged-i2nsf-framework-
              04.txt (work in progress), October 2015.

              "Baseline Identity Management Terms and Definitions",
              April 2010.

              "Security Architecture for Open Systems Interconnection
              for CCITT Applications", March 1991.

              "Recommendation ITU-T Y.3300", June 2014.

              ONF, "OpenFlow Switch Specification (Version 1.4.0)",
              October 2013.

Marin-Lopez  & Lopez-MillaExpires May 14, 2016                 [Page 15]

Internet-Draft             SDN AAA Management              November 2015

              "SDN Architecture", June 2014.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,

Authors' Addresses

   Rafa Marin-Lopez
   University of Murcia
   Campus de Espinardo S/N, Faculty of Computer Science
   Murcia  30100

   Phone: +34 868 88 85 01

   Gabriel Lopez-Millan
   University of Murcia
   Campus de Espinardo S/N, Faculty of Computer Science
   Murcia  30100

   Phone: +34 868 88 85 04

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