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Versions: (draft-brockners-diameter-nat-control) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 RFC 6736

Internet Engineering Task Force                             F. Brockners
Internet-Draft                                               S. Bhandari
Intended status: Standards Track                                   Cisco
Expires: October 22, 2012                                       V. Singh

                                                              V. Fajardo
                                                  Telcordia Technologies
                                                          April 20, 2012


   Diameter Network Address and Port Translation Control Application
                     draft-ietf-dime-nat-control-16

Abstract

   This document describes the framework, messages, and procedures for
   the Diameter Network address and port translation Control
   Application.  This Diameter application allows per endpoint control
   of Network Address Translators and Network Address and Port
   Translators, which are added to networks to cope with IPv4-address
   space depletion.  This Diameter application allows external devices
   to configure and manage a Network Address Translator device -
   expanding the existing Diameter-based AAA and policy control
   capabilities with a Network Address Translators and Network Address
   and Port Translators control component.  These external devices can
   be network elements in the data plane such as a Network Access
   Server, or can be more centralized control plane devices such as AAA-
   servers.  This Diameter application establishes a context to commonly
   identify and manage endpoints on a gateway or server, and a Network
   Address Translator and Network Address and Port Translator device.
   This includes, for example, the control of the total number of
   Network Address Translator bindings allowed or the allocation of a
   specific Network Address Translator binding for a particular
   endpoint.  In addition, it allows Network Address Translator devices
   to provide information relevant to accounting purposes.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any



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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 22, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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
































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Deployment Framework . . . . . . . . . . . . . . . . . . . . .  8
     3.1.  Deployment Scenario  . . . . . . . . . . . . . . . . . . .  8
     3.2.  Diameter NAPT Control Application Overview . . . . . . . . 10
     3.3.  Deployment Scenarios For DNCA  . . . . . . . . . . . . . . 11
   4.  DNCA Session Establishment and Management  . . . . . . . . . . 13
     4.1.  Session Establishment  . . . . . . . . . . . . . . . . . . 14
     4.2.  Session Update . . . . . . . . . . . . . . . . . . . . . . 17
     4.3.  Session and Binding Query  . . . . . . . . . . . . . . . . 19
     4.4.  Session Termination  . . . . . . . . . . . . . . . . . . . 21
     4.5.  Session Abort  . . . . . . . . . . . . . . . . . . . . . . 22
     4.6.  Failure cases of the DNCA Diameter peers . . . . . . . . . 23
   5.  Use of the Diameter Base Protocol  . . . . . . . . . . . . . . 24
     5.1.  Securing Diameter Messages . . . . . . . . . . . . . . . . 24
     5.2.  Accounting Functionality . . . . . . . . . . . . . . . . . 25
     5.3.  Use of Sessions  . . . . . . . . . . . . . . . . . . . . . 25
     5.4.  Routing Considerations . . . . . . . . . . . . . . . . . . 25
     5.5.  Advertising Application Support  . . . . . . . . . . . . . 25
   6.  DNCA Commands  . . . . . . . . . . . . . . . . . . . . . . . . 26
     6.1.  NAT-Control Request (NCR) Command  . . . . . . . . . . . . 26
     6.2.  NAT-Control Answer (NCA) Command . . . . . . . . . . . . . 27
   7.  NAT Control Application Session State Machine  . . . . . . . . 27
   8.  DNCA AVPs  . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     8.1.  Reused Base Protocol AVPs  . . . . . . . . . . . . . . . . 30
     8.2.  Additional Result-Code AVP Values  . . . . . . . . . . . . 31
       8.2.1.  Success  . . . . . . . . . . . . . . . . . . . . . . . 31
       8.2.2.  Transient Failures . . . . . . . . . . . . . . . . . . 31
       8.2.3.  Permanent Failures . . . . . . . . . . . . . . . . . . 32
     8.3.  Reused NASREQ Diameter Application AVPs  . . . . . . . . . 33
     8.4.  Reused AVPs from RFC 4675  . . . . . . . . . . . . . . . . 33
     8.5.  Reused AVPs from Diameter QoS Application  . . . . . . . . 34
     8.6.  Reused AVPs from ETSI ES 283 034, e4 Diameter
           Application  . . . . . . . . . . . . . . . . . . . . . . . 34
     8.7.  DNCA Defined AVPs  . . . . . . . . . . . . . . . . . . . . 35
       8.7.1.  NC-Request-Type AVP  . . . . . . . . . . . . . . . . . 36
       8.7.2.  NAT-Control-Install AVP  . . . . . . . . . . . . . . . 37
       8.7.3.  NAT-Control-Remove AVP . . . . . . . . . . . . . . . . 37
       8.7.4.  NAT-Control-Definition AVP . . . . . . . . . . . . . . 38
       8.7.5.  NAT-Internal-Address AVP . . . . . . . . . . . . . . . 38
       8.7.6.  NAT-External-Address AVP . . . . . . . . . . . . . . . 39
       8.7.7.  Max-NAT-Bindings . . . . . . . . . . . . . . . . . . . 39
       8.7.8.  NAT-Control-Binding-Template AVP . . . . . . . . . . . 39
       8.7.9.  Duplicate-Session-Id AVP . . . . . . . . . . . . . . . 39
       8.7.10. NAT-External-Port-Style AVP  . . . . . . . . . . . . . 40
   9.  Accounting Commands  . . . . . . . . . . . . . . . . . . . . . 40



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     9.1.  NAT Control Accounting Messages  . . . . . . . . . . . . . 41
     9.2.  NAT Control Accounting AVPs  . . . . . . . . . . . . . . . 41
       9.2.1.  NAT-Control-Record . . . . . . . . . . . . . . . . . . 41
       9.2.2.  NAT-Control-Binding-Status . . . . . . . . . . . . . . 41
       9.2.3.  Current-NAT-Bindings . . . . . . . . . . . . . . . . . 42
   10. AVP Occurrence Table . . . . . . . . . . . . . . . . . . . . . 42
     10.1. DNCA AVP Table for NAT Control Initial and Update
           Requests . . . . . . . . . . . . . . . . . . . . . . . . . 42
     10.2. DNCA AVP Table for Session Query request . . . . . . . . . 43
     10.3. DNCA AVP Table for Accounting Message  . . . . . . . . . . 44
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 44
     11.1. Application Identifier . . . . . . . . . . . . . . . . . . 44
     11.2. Command Codes  . . . . . . . . . . . . . . . . . . . . . . 45
     11.3. AVP Codes  . . . . . . . . . . . . . . . . . . . . . . . . 45
     11.4. Result-Code AVP Values . . . . . . . . . . . . . . . . . . 45
     11.5. NC-Request-Type AVP  . . . . . . . . . . . . . . . . . . . 45
     11.6. NAT-External-Port-Style AVP  . . . . . . . . . . . . . . . 45
     11.7. NAT-Control-Binding-Status AVP . . . . . . . . . . . . . . 45
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 45
   13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
     13.1. DNCA Session Establishment Example . . . . . . . . . . . . 48
     13.2. DNCA Session Update with Port Style Example  . . . . . . . 51
     13.3. DNCA Session Query Example . . . . . . . . . . . . . . . . 52
     13.4. DNCA Session Termination Example . . . . . . . . . . . . . 53
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 56
   15. Change History (to be removed prior to publication as an
       RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 60
     16.2. Informative References . . . . . . . . . . . . . . . . . . 60
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 62




















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1.  Introduction

   Internet service providers deploy Network Address Translators (NATs)
   and Network Address and Port Translators (NAPTs) [RFC3022] in their
   networks.  A key motivation for doing so is the depletion of
   available public IPv4 addresses.  This document defines a Diameter
   application allowing providers to control the behavior of NAT and
   NAPT devices that implement IPv4-to-IPv4 network address and port
   translation [RFC2663] as well as stateful IPv6-to-IPv4 address family
   translation as defined in [RFC2663], [RFC6145], and [RFC6146].  The
   use of a Diameter application allows for simple integration into the
   existing Authentication, Authorization and Accounting (AAA)
   environment of a provider.

   The Diameter Network address and port translation Control Application
   (DNCA) offers the following capabilities:

   1.  Limits or defines the number of NAPT/NAT bindings made available
       to an individual endpoint.  The main motivation for restricting
       the number of bindings on a per endpoint basis is to protect the
       service of the service provider against denial of service
       attacks.  If multiple endpoints share a single public IP address,
       these endpoints can share fate.  If one endpoint would (either
       intentionally, or due to mis-behavior, mis-configuration, mal-
       ware, etc.) be able to consume all available bindings for a given
       single public IP address, service would be hampered (or might
       even become unavailable) for those other endpoints sharing the
       same public IP address.  The efficiency of a NAPT deployment
       depends on the maximum number of bindings an endpoint could use.
       Given that the typical number of bindings an endpoint uses
       depends on the type of endpoint (e.g. a personal computer of a
       broadband user is expected to use a higher number of bindings
       than a simple mobile phone) and a NAPT device is often shared by
       different types of endpoints, it is desirable to actively manage
       the maximum number of bindings.  This requirement is specified in
       REQ-3 of [I-D.ietf-behave-lsn-requirements]

   2.  Supports the allocation of specific NAPT/NAT bindings.  Two types
       of specific bindings can be distinguished:

       *  Allocation of a pre-defined NAT binding: Both the internal and
          external IP address and port pair are specified within the
          request.  Some deployment cases, such as access to a web-
          server within a user's home network with IP address and port,
          benefit from statically configured bindings.

       *  Allocation of an external IP address for a given internal IP
          address: The allocated external IP address is reported back to



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          the requestor.  In some deployment scenarios, the application
          requires immediate knowledge of the allocated binding for a
          given internal IP address but does not control the allocation
          of the external IP address; for example, SIP-proxy server
          deployments.

   3.  Defines the external address pool(s) to be used for allocating an
       external IP address: External address pools can either be pre-
       assigned at the NAPT/NAT device, or specified within a request.
       If pre-assigned address pools are used, a request needs to
       include a reference to identify the pool.  Otherwise, the request
       contains a description of the IP address pool(s) to be used; for
       example, a list of IP-subnets.  Such external address pools can
       be used to select the external IP address in NAPT/NAT bindings
       for multiple subscribers.

   4.  Generates reports and accounting records: Reports established
       bindings for a particular endpoint.  The collected information is
       used by accounting systems for statistical purposes.

   5.  Queries and retrieves details about bindings on demand: This
       feature complements the previously mentioned accounting
       functionality (see item 4).  This feature can be used by an
       entity to find NAT-bindings belonging to one or multiple
       endpoints on the NAT-device.  The entity is not required to
       create a DNCA control session to perform the query, but would
       obviously still need to create a Diameter session complying to
       the security requirements.

   6.  Identifies a subscriber or endpoint on multiple network devices
       (NAT/NAPT device, the AAA-server, or the Network Access Server
       (NAS)): Endpoint identification is facilitated through a Global
       Endpoint ID.  Endpoints are identified through a single or a set
       of classifiers, such as IP address, Virtual Local Area Network
       (VLAN) identifier, or interface identifier which uniquely
       identify the traffic associated with a particular global
       endpoint.

   With the above capabilities, DNCA qualifies as a MIDCOM protocol
   [RFC3303], [RFC3304], [RFC5189] for middle boxes which perform NAT.
   The MIDCOM protocol evaluation [RFC4097] evaluated Diameter as a
   candidate protocol for MIDCOM.  DNCA provides the extensions to the
   Diameter base protocol [RFC3588] following the MIDCOM protocol
   requirements, such as the support of NAT-specific rule transport,
   support for oddity of mapped ports, as well as support for
   consecutive range port numbers.  DNCA adds to the MIDCOM protocol
   capabilities in that it allows to maintain the reference to an
   endpoint representing a user or subscriber in the control operation,



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   enabling the control of the behavior of a NAT-device on a per
   endpoint basis.  Following the requirements of different operators
   and deployments, different management protocols are employed.
   Examples include e.g.  SNMP [RFC3411] and NETCONF [RFC6241] which can
   both be used for device configuration.  Similarly, DNCA is
   complementing existing MIDCOM implementations, offering a MIDCOM
   protocol option for operators with an operational environment that is
   Diameter-focused which desire to use Diameter to perform per endpoint
   NAT control.  Note that in case an operator uses multiple methods and
   protocols to configure a NAT-device, such as for example command line
   interface, SNMP, NETCONF, or PCP, along with DNCA specified in this
   document, the operator MUST ensure that the configurations performed
   using the different methods and protocols do not conflict in order to
   ensure a proper operation of the NAT service.

   This document is structured as follows: Section 2 lists terminology,
   while Section 3 provides an introduction to DNCA and its overall
   deployment framework.  Sections 4 to 8 cover DNCA specifics, with
   Section 4 describing session management, Section 5 the use of the
   Diameter base protocol, Section 6 new commands, Section 7 Attribute
   Value Pairs(AVPs) used, and Section 8 accounting aspects.  Section 9
   presents AVP occurrence tables.  IANA and security considerations are
   addressed in Sections 10 and 11.


2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Abbreviations used in this document:

      AAA: Authentication, Authorization, Accounting

      DNCA: Diameter Network address and port translation Control
      Application

      Endpoint: Managed entity of the DNCA.  An endpoint represents a
      network element or device, associated with a subscriber, a user or
      a group of users.  An endpoint is represented by a single access-
      session on a NAS.  DNCA assumes a 1:1 relationship between an
      endpoint, the access-session it represents, and the associated
      DNCA session.

      NAPT: Network Address and Port Translation, see also [RFC3022]





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      NAT: Network Address Translation (NAT and NAPT are used in this
      document interchangeably)

      NAT-binding or binding: Association of two IP address/port pairs
      (with one IP address typically being private and the other one
      public) to facilitate NAT

      NAT binding predefined template: Is a policy template or
      configuration that is predefined at the NAT-device.  It may
      contain NAT-bindings, IP-address pools for allocating the external
      IP-address of a NAT-binding, the maximum number of allowed NAT-
      bindings for end-points, etc.

      NAT-device: Network Address Translator or Network Address and Port
      Translator: An entity performing NAT or NAPT.

      NAT-controller: Entity controlling the behavior of a NAT-device.

      NAS: Network Access Server

      NCR: NAT Control Request

      NCA: NAT Control Answer

      NAT44: IPv4 to IPv4 network address and port translation, see
      [RFC2663]

      NAT64: IPv6 to IPv4 address family translation, see [RFC6145] and
      [RFC6146]

      PPP: Point-to-Point Protocol [RFC1661]


3.  Deployment Framework

3.1.  Deployment Scenario

   Figure 1 shows a typical network deployment for IPv4-Internet access.
   A user's IPv4 host (i.e. endpoint) gains access to the Internet
   though a NAS, which facilitates the authentication of the endpoint
   and configures the endpoints's connection according to the
   authorization and configuration data received from the AAA-server
   upon successful authentication.  Public IPv4 addresses are used
   throughout the network.  DNCA manages an endpoint that represents a
   network element or device or IPv4 host, associated with a subscriber,
   a user or a group of users.  An endpoint is represented by a single
   access-session on a NAS.  DNCA assumes a 1:1 relationship between an
   endpoint, the access-session it represents, and the associated DNCA



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   session.

                         +---------+
                         |         |
                         |   AAA   |
                         |         |
                         +---------+
                              |
                              |
                              |
                              |
    +---------+          +---------+             +----------+
    |  IPv4   |          |         |             |  IPv4    |
    |  Host   |----------|   NAS   |-------------| Internet |
    |         |          |         |             |          |
    +---------+          +---------+             +----------+

    <-------------------- Public IPv4 ---------------------->

         Figure 1: Typical network deployment for internet access

   Figure 2 depicts the deployment scenario where a service provider
   places a NAT between the host and the public Internet.  The objective
   is to provide the customer with connectivity to the public IPv4
   Internet.  The NAT-device performs network address and port (and
   optionally address family) translation, depending on whether the
   access network uses private IPv4 addresses or public IPv6 addresses,
   to public IPv4 addresses.  Note that there may be more than one NAS,
   NAT-device, or AAA-entity in a deployment, although the figures only
   depict one entity each for clarity.

   If the NAT-device would be put in place without any endpoint
   awareness, the service offerings of the service provider could be
   impacted as detailed in [I-D.ietf-behave-lsn-requirements].  This
   includes cases like:

   o  Provisioning static NAT bindings for particular endpoints

   o  Using different public IP address pools for different set of
      endpoints (for example, residential or business customers)

   o  Reporting allocated bindings on a per endpoint basis

   o  Integrate control of the NAT-device into the already existing per
      endpoint management infrastructure of the service provider






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                   +---------+
                   |         |
                   |   AAA   |
                   |         |
                   +---------+
                        |
                        |
                        |
                        |
     +--------+    +---------+    +--------+    +----------+
     |  IPv4  |----|         |----|  NAT-  |----| IPv4-    |
     |  Host  |    |   NAS   |    | device |    | Internet |
     |        |    |         |    |        |    |          |
     +--------+    +---------+    +--------+    +----------+

   For NAT44 deployments (IPv4 host):
        <----- Private IPv4 ----------><--- Public IPv4 --->

   For NAT64 deployments (IPv6 host):
        <----- Public  IPv6 ----------><--- Public IPv4 --->

               Figure 2: Access network deployment with NAT

   Figure 2 shows a typical deployment for IPv4-Internet access
   involving a NAT-device within the service provider network.  The
   figure describes two scenarios: One where an IPv4-host (with a
   private IPv4 address) accesses the IPv4-Internet, as well as one
   where an IPv6-host accesses the IPv4-Internet.

3.2.  Diameter NAPT Control Application Overview

   DNCA runs between two DNCA Diameter peers.  One DNCA Diameter peer
   resides within the NAT-device, the other DNCA Diameter peer resides
   within a NAT-controller (discussed in Section 3.3).  DNCA allows per
   endpoint control and management of NAT within the NAT-device.  Based
   on Diameter, DNCA integrates well with the suite of Diameter
   applications deployed for per endpoint authentication, authorization,
   accounting, and policy control in service provider networks.

   DNCA offers:

   o  Request and answer commands to control the allowed number of NAT
      bindings per endpoint to request the allocation of specific
      bindings for an endpoint, to define the address pool to be used
      for an endpoint.

   o  Provides per endpoint reporting of the allocated NAT bindings.




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   o  Provides unique identification of an endpoint on NAT-device, AAA-
      server and NAS, to simplify correlation of accounting data
      streams.

   DNCA allows controlling the behavior of a NAT-device on a per
   endpoint basis during initial session establishment and at later
   stages by providing an update procedure for already established
   sessions.  Using DNCA, per endpoint NAT binding information can be
   retrieved either using accounting mechanisms or through an explicit
   session query to the NAT.

3.3.  Deployment Scenarios For DNCA

   DNCA can be deployed in different ways.  DNCA supports deployments
   with "n" NAT-controllers and "m" NAT-devices, with n and m equal to
   or greater than 1.  From a DNCA perspective an operator should ensure
   that the session representing a particular endpoint is atomic.  Any
   deployment MUST ensure that for any given endpoint only a single DNCA
   NAT-controller and is active at any point in time.  This is to ensure
   that NAT-devices controlled by multiple NAT-controllers do not
   receive conflicting control requests for a particular endpoint, or
   would be unclear which NAT-controller to send accounting information
   to.  Operational considerations MAY require an operator to use
   alternate control mechanisms or protocols such as SNMP or manual
   configuration via a Command-Line-Interface to apply per-endpoint NAT-
   specific configuration, like for example static NAT-bindings.  For
   these cases, the NAT-device MUST allow the operator to configure a
   policy how configuration conflicts are resolved.  Such a policy could
   for example specify that manually configured NAT-bindings using the
   Command-Line-Interface always take precedence over those configured
   using DNCA.

   Two common deployment scenarios are outlined in Figure 3 ("integrated
   deployment") and Figure 4 ("autonomous deployment").  Per the note
   above, multiple instances of NAT-controllers and NAT-devices could be
   deployed.  The figures only show single instances for reasons of
   clarity.  The two shown scenarios differ in which entity fulfills the
   role of the NAT-controller.  Within the figures (C) denotes the
   network element performing the role of the NAT-controller.

   The integrated deployment approach hides the existence of the NAT-
   device from external servers, such as the AAA-server.  It is suited
   for environments where minimal changes to the existing AAA deployment
   are desired.  The NAS and the NAT-device are Diameter peers
   supporting the DNCA.  The Diameter peer within the NAS, performing
   the role of the NAT-controller, initiates and manages sessions with
   the NAT-device, exchanges NAT specific configuration information and
   handles reporting and accounting information.  The NAS receives



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   reporting and accounting information from the NAT-device.  With this
   information, the NAS can provide a single accounting record for the
   endpoint.  A system correlating the accounting information received
   from the NAS and NAT-device would not be needed.

   An example network attachment for an integrated NAT deployment can be
   described as follows: An endpoint connects to the network, with the
   NAS being the point of attachment.  After successful authentication,
   the NAS receives endpoint related authorization data from the AAA-
   server.  A portion of the authorization data applies to per endpoint
   configuration on the NAS itself, another portion describes
   authorization and configuration information for NAT control aimed at
   the NAT-device.  The NAS initiates a DNCA session to the NAT-device
   and sends relevant authorization and configuration information for
   the particular endpoint to the NAT-device.  This can comprise NAT-
   bindings, which have to be pre-established for the endpoint, or
   management related configuration, such as the maximum number of NAT-
   bindings allowed for the endpoint.  The NAT-device sends its per
   endpoint accounting information to the NAS, which aggregates the
   accounting information received from the NAT-device with its local
   accounting information for the endpoint into a single accounting
   stream towards the AAA-server.

                   +---------+
                   |         |
                   |   AAA   |
                   |         |
                   +---------+
                        |
                        |
                        |
     +--------+    +---------+    +--------+    +----------+
     |        |    |   (C)   |    |        |    |          |
     |  Host  |----|   NAS   |----|  NAT-  |----| IPv4-    |
     |        |    |         |    | device |    | Internet |
     +--------+    +---------+    +--------+    +----------+

   For NAT44 deployments (IPv4 host):
        <----- Private IPv4 ----------><--- Public IPv4 --->

   For NAT64 deployments (IPv6 host):
        <----- Public  IPv6 ----------><--- Public IPv4 --->

          Figure 3: NAT control deployment: Integrated deployment

   Figure 3 shows examples of integrated deployments.  The figure
   describes two scenarios: One where an IPv4-host (with a private IPv4
   address) accesses the IPv4-Internet, as well as one where an IPv6-



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   host accesses the IPv4-Internet.

   The autonomous deployment approach decouples endpoint management on
   the NAS and NAT-device.  In the autonomous deployment approach, the
   AAA-system and the NAT-device are the Diameter peers running the
   DNCA.  The AAA-system also serves as NAT-controller.  It manages the
   connection to the NAT-device, controls the per endpoint
   configuration, and also receives accounting and reporting information
   from the NAT-device.  Different from the integrated deployment
   scenario, the autonomous deployment scenario does not "hide" the
   existence of the NAT-device from the AAA infrastructure.  Here two
   accounting streams are received by the AAA-server for one particular
   endpoint, one from the NAS, and one from the NAT-device.

                   +---------+
                   |   (C)   |
                   |   AAA   |---------
                   |         |         |
                   +---------+         |
                        |              |
                        |              |
                        |              |
     +--------+    +---------+    +---------+    +----------+
     |  IPv4/ |    |         |    |         |    |  IPv4    |
     |  IPv6  |----|   NAS   |----|  NAT-   |----| Internet |
     |  Host  |    |         |    | device  |    |          |
     +--------+    +---------+    +---------+    +----------+

   For NAT44 deployments (IPv4 host):
        <----- Private IPv4 ----------><--- Public IPv4 --->

   For NAT64 deployments (IPv6 host):
        <----- Public  IPv6 ----------><--- Public IPv4 --->

          Figure 4: NAT control deployment: Autonomous deployment

   Figure 4 shows examples of autonomous deployments.  The figure
   describes two scenarios: One where an IPv4-host (with a private IPv4
   address) accesses the IPv4-Internet, as well as one where an IPv6-
   host accesses the IPv4-Internet.


4.  DNCA Session Establishment and Management

   Note that this section forward references some of the commands and
   AVPs defined for DNCA.  Please refer to Section 6 and Section 8 for
   details.  DNCA runs between a Diameter peer residing in a NAT-
   controller and a Diameter peer residing in a NAT-device.  Note that,



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   per what was already mentioned above, each DNCA session between
   Diameter peers in a NAT-controller and a NAT-device represents a
   single endpoint, with an endpoint being either a network element, a
   device or an IPv4 host associated with a subscriber, a user, or a
   group of users.  The Diameter peer within the NAT-controller is
   always the control requesting entity: It initiates, updates, or
   terminates the sessions.  Sessions are initiated when the NAT-
   controller learns about a new endpoint (i.e., host) that requires a
   NAT service.  This could for example be due to the entity hosting the
   NAT-controller receiving authentication, authorization, or accounting
   requests for or from the endpoint.  Alternate methods that could
   trigger session setup include local configuration, receipt of a
   packet from a formerly unknown IP-address, etc.

4.1.  Session Establishment

   The DNCA Diameter peer within the NAT-controller establishes a
   session with the DNCA Diameter peer within the NAT-device to control
   the behavior of the NAT function within the NAT-device.  During
   session establishment, the DNCA Diameter peer within the NAT-
   controller passes along configuration information to DNCA Diameter
   peer within the NAT-device.  The session configuration information
   comprises the maximum number of bindings allowed for the endpoint
   associated with this session, a set of pre-defined NAT bindings to be
   established for this endpoint, or a description of the address pool,
   that external addresses are to be allocated from.

   The DNCA Diameter peer within the NAT-controller generates a NAT-
   Control Request (NCR) message to the DNCA Diameter peer within the
   NAT-device with NC-Request-Type AVP set to INITIAL_REQUEST to
   initiate a Diameter NAT control session.  On receipt of a NCR the
   DNCA Diameter peer within the NAT-device sets up a new session for
   the endpoint associated with the endpoint classifier(s) contained in
   the NCR.  The DNCA Diameter peer within the NAT-device notifies its
   DNCA Diameter peer within the NAT-controller about successful session
   setup using a NAT-Control Answer (NCA) message with Result-Code set
   to DIAMETER_SUCCESS.  Figure 5 shows the initial protocol interaction
   between the two DNCA Diameter peers.

   The initial NAT-Control-Request MAY contain configuration information
   for the session, which specifies the behavior of the NAT-device for
   the session.  The configuration information that MAY be included,
   comprises:

   o  A list of NAT bindings, which should be pre-allocated for the
      session; for example, in case an endpoint requires a fixed
      external IP-address/port pair for an application.




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   o  The maximum number of NAT-bindings allowed for an endpoint.

   o  A description of the external IP-address pool(s) to be used for
      the session.

   o  A reference to a NAT Binding Predefined template on the NAT-
      device, which is applied to the session.  Such a NAT Binding
      Predefined template on the NAT-device may contain, for example,
      the name of the IP-address pool that external IP-addresses should
      be allocated from, the maximum number of bindings permitted for
      the endpoint, etc.

   In certain cases, the NAT-device may not be able to perform the tasks
   requested within the NCR.  These include the following:

   o  If a DNCA Diameter peer within the NAT-device receives a NCR from
      a DNCA Diameter peer within a NAT-controller with NC-Request-Type
      AVP set to INITIAL_REQUEST that identifies an already existing
      session; that is endpoint identifier match an already existing
      session, the DNCA Diameter peer within the NAT-device MUST return
      an NCA with Result-Code set to SESSION_EXISTS, and provide the
      Session-Id of the existing session in the Duplicate-Session-Id
      AVP.

   o  If a DNCA Diameter peer within the NAT-device receives a NCR from
      a DNCA Diameter peer within a NAT-controller with NC-Request-Type
      AVP set to INITIAL_REQUEST that matches more than one of the
      already existing sessions; that is, DNCA Diameter peer and
      endpoint identifier match already existing sessions, the DNCA
      Diameter peer within the NAT-device MUST return an NCA with
      Result-Code set to INSUFFICIENT-CLASSIFIERS.  In case a DNCA
      Diameter peer receives a NCA that reports Insufficient-
      Classifiers, it MAY choose to retry establishing a new session
      using additional or more specific classifiers.

   o  If the NCR contains a NAT Binding predefined template not defined
      on the NAT-device, the DNCA Diameter peer within the NAT-device
      MUST return an NCA with Result-Code AVP set to
      UNKNOWN_BINDING_TEMPLATE_NAME.

   o  In case the NAT-device is unable to establish all of the bindings
      requested in the NCR, the DNCA Diameter peer MUST return an NCA
      with Result-Code set to BINDING_FAILURE.  A DNCA Diameter peer
      within a NAT-device MUST treat a NCR as an atomic operation; hence
      none of the requested bindings will be established by the NAT-
      device.  Either all requested actions within a NCR MUST be
      completed successfully, or the entire request fails.




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   o  If a NAT-device cannot conform to a request to set the maximum
      number of NAT bindings allowed for a session, the DNCA Diameter
      peer in the NAT-device MUST return an NCA with Result-Code AVP set
      to MAX_BINDINGS_SET_FAILURE.  Such a condition can for example
      occur if the operator specified the maximum number of NAT bindings
      through another mechanism, which per the operator's policy, takes
      precedence over DNCA.

   o  If a NAT-device does not have sufficient resources to process a
      request, the DNCA Diameter peer MUST return an NCA with Result-
      Code set to RESOURCE_FAILURE.

   o  In case Max-NAT-Bindings, NAT-Control-Definition as well as NAT-
      Control-Binding-Template are included in the NCR, and the values
      in Max-NAT-Bindings and NAT-Control-Definition contradict those
      specified in the pre-provisioned template on the NAT-device which
      NAT-Control-Binding-Template references, Max-NAT-Bindings and NAT-
      Control-Definition MUST override the values specified in the
      template that NAT-Control-Binding-Template refers to.


   NAT-controller (DNCA Diameter peer)   NAT-device (DNCA Diameter peer)
               |                                           |
               |                                           |
               |                                           |
            Trigger                                        |
               |                                           |
               |                   NCR                     |
               |------------------------------------------>|
               |                                           |
               |                                           |
               |                                           |
               |                                           |
               |                                 If Able to comply
               |                                 with Request then
               |                                 Create session state
               |                                           |
               |                                           |
               |                     NCA                   |
               |<------------------------------------------|
               |                                           |
               |                                           |

      Figure 5: Initial NAT control request and session establishment

   Note: The DNCA Diameter peer within the NAT-device creates session
   state only if it is able to comply with the NCR.  On success it will
   reply with an NCA with Result-Code set to DIAMETER_SUCCESS.



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4.2.  Session Update

   Session update is performed if the NAT-controller desires to change
   the behavior of the NAT-device for an existing session.  Session
   update could be used, for example, to change the number of allowed
   bindings for a particular session, or establish or remove a pre-
   defined binding.

   The DNCA Diameter peer within the NAT-controller generates a NCR
   message to the DNCA Diameter peer within the NAT-device with NC-
   Request-Type AVP set to UPDATE_REQUEST upon receiving a trigger
   signal.  If the session is updated successfully, the DNCA Diameter
   peer within the NAT-device notifies the DNCA Diameter peer within the
   NAT-controller about the successful session update using a NAT-
   Control Answer (NCA) message with Result-Code set to
   DIAMETER_SUCCESS.Figure 6 shows the protocol interaction between the
   two DNCA Diameter peers.

   In certain cases, the NAT-device may not be able to perform the tasks
   requested within the NCR.  These include the following:

   o  If DNCA Diameter peer within a NAT-device receives an NCR update
      or query request for a non-existent session, it MUST set Result-
      Code in the answer to DIAMETER_UNKNOWN_SESSION_ID.

   o  If the NCR contains a NAT Binding Predefined template not defined
      on the NAT-device, an NCA with Result-Code AVP set to
      UNKNOWN_BINDING_TEMPLATE_NAME MUST be returned.

   o  If the NAT-device cannot establish the requested binding because
      the maximum number of allowed bindings has been reached for the
      endpoint classifier, an NCA with Result-Code AVP set to
      MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT MUST be returned to the DNCA
      Diameter peer.

   o  If the NAT-device cannot establish some or all of the bindings
      requested in an NCR, but has not yet reached the maximum number of
      allowed bindings for the endpoint, an NCA with Result-Code set to
      BINDING_FAILURE MUST be returned.  As already noted, the DNCA
      Diameter peer in a NAT-device MUST treat an NCR as an atomic
      operation.  Hence none of the requested bindings will be
      established by the NAT-device in case of failure.  Actions
      requested within a NCR are either all successful or all fail.

   o  If the NAT-device cannot conform to a request to set the maximum
      number of bindings allowed for a session as specified by the Max-
      NAT-Bindings, the DNCA Diameter peer in the NAT-device MUST return
      an NCA with Result-Code AVP set to MAX_BINDINGS_SET_FAILURE.



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   o  If the NAT-device does not have sufficient resources to process a
      request, an NCA with Result-Code set to RESOURCE_FAILURE MUST be
      returned.

   o  If an NCR changes the maximum number of NAT-bindings allowed for
      the endpoint defined through an earlier NCR, the new value MUST
      override any previously defined limit on the maximum number of NAT
      bindings set through DNCA.  Note that prior to overwriting an
      existing value, the NAT-device MUST check whether the overwrite
      action conforms to the locally configured policy.  Deployment
      dependent, an existing value could have been set by a protocol or
      mechanism different from DNCA and with higher priority.  In which
      case, the NAT-device will refuse the change and the DNCA Diameter
      peer in the NAT-device MUST return an NCA with Result-Code AVP set
      to MAX_BINDINGS_SET_FAILURE.  It depends on the implementation of
      the NAT-device on how the NAT-device copes with a case where the
      new value is lower than the actual number of allocated bindings.
      The NAT-device SHOULD refrain from enforcing the new limit
      immediately (that is, actively remove bindings), but rather
      disallows the establishment of new bindings until the current
      number of bindings is lower than the newly established maximum
      number of allowed bindings.

   o  If an NCR specifies a new NAT Binding Predefined template on the
      NAT-device, the NAT Binding Predefined template overrides any
      previously defined rule for the session.  Existing NAT-bindings
      SHOULD NOT be impacted by the change of templates.

   o  In case Max-NAT-Binding, NAT-Control-Definition as well as NAT-
      Control-Binding-Template are included in the NCR, and the values
      in Max-NAT-Bindings and NAT-Control-Definition contradict those
      specified in the pre-provisioned template on the NAT-device which
      NAT-Control-Binding-Template references, Max-NAT-Bindings and NAT-
      Control-Definition MUST override the values specified in the
      template that the NAT-Control-Binding-Template refers to.

   Note: Already established bindings for the session SHOULD NOT be
   affected in case the tasks requested within the NCR cannot be
   completed.












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   NAT-controller (DNCA Diameter peer)   NAT-device (DNCA Diameter peer)
               |                                           |
               |                                           |
               |                                           |
        Change of session                                  |
           attributes                                      |
               |                                           |
               |                   NCR                     |
               |------------------------------------------>|
               |                                           |
               |                                           |
               |                                   If able to comply
               |                                   with the request:
               |                                  Update session state
               |                                           |
               |                                           |
               |                     NCA                   |
               |<------------------------------------------|
               |                                           |

             Figure 6: NAT control request for session update

4.3.  Session and Binding Query

   A Session and NAT-binding query MAY be used by the DNCA Diameter peer
   within the NAT-controller to either retrieve information on the
   current bindings for a particular session at the NAT-device or
   discover the session identifier for a particular external IP address/
   port pair.

   A DNCA Diameter peer within the NAT-controller starts a session query
   by sending an NCR message with NC-Request-Type AVP set to
   QUERY_REQUEST.  Figure 7 shows the protocol interaction between the
   DNCA Diameter peers.

   Two types of query requests exist.  The first type of query request
   uses the session ID as input parameter to the query.  It is to allow
   the DNCA Diameter peer within the NAT-controller to retrieve the
   current set of bindings for a specific session.  The second type of
   query request is used to retrieve the session identifiers, along with
   the associated bindings, matching a criteria.  This enables the DNCA
   Diameter peer within the NAT-controller to find those sessions, which
   utilize a specific external or internal IP-address.

   1.  Request a list of currently allocated NAT bindings for a
       particular session: On receiving a NCR, the NAT-device SHOULD
       look up the session information for the session ID contained in
       the NCR, and report all currently active NAT-bindings for the



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       session using an NCA message with Result-Code set to
       DIAMETER_SUCCESS.  In this case the NCR MUST NOT contain a NAT-
       Control-Definition AVP.  Each NAT-binding is reported in a NAT-
       Control-Definition AVP.  In case the session ID is unknown, the
       DNCA Diameter peer within the NAT-device MUST return an NCA
       message with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.

   2.  Retrieve session IDs and bindings for internal IP-address or one
       or multiple external IP-address/port pairs: If the DNCA Diameter
       peer within the NAT-controller wishes to retrieve the session
       ID(s) for internal IP-address or one or multiple external IP-
       address/port pairs, it MUST include the internal IP-address as
       part of Framed-IP-Address or external IP-address/port pair(s) as
       part of the NAT-External-Address AVP of the NCR.  The external
       IP-address/port pair(s) are pre-known to the controller via
       configuration, AAA interactions, or other means.  The session ID
       is not included in the NCR or the NCA for this type of a query.
       The DNCA Diameter peer within the NAT-device SHOULD report the
       NAT-bindings and associated session IDs corresponding to the
       internal IP-address or external IP-address/port pairs in an NCA
       message using one or multiple instances of the NAT-Control-
       Definition AVP.  The Result-Code is set to DIAMETER_SUCCESS.  In
       case an external IP-address/port pair has no associated existing
       NAT-binding, the NAT-Control-Definition AVP contained in the
       reply just contains the NAT-External-Address AVP.


   NAT-controller (DNCA Diameter peer)   NAT-device (DNCA Diameter peer)
               |                                           |
               |                                           |
               |                                           |
     DNCA Session Established                              |
               |                                           |
               |                   NCR                     |
               |------------------------------------------>|
               |                                           |
               |                                           |
               |                                           |
               |                                           |
               |                          Look up corresponding session
               |                            and associated NAT-bindings
               |                                           |
               |                   NCA                     |
               |<------------------------------------------|
               |                                           |
               |                                           |
               |                                           |




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                          Figure 7: Session query

4.4.  Session Termination

   Similar to session initiation, session tear down MUST be initiated by
   the DNCA Diameter peer within the NAT-controller.  The DNCA Diameter
   peer sends a Session Terminate Request (STR) message to its peer
   within the NAT-device upon receiving a trigger signal.  The source of
   the trigger signal is outside the scope of this document.  As part of
   STR message processing the DNCA Diameter peer within the NAT-device
   MAY send an accounting stop record reporting all bindings.  All the
   NAT-bindings belonging to the session MUST be removed and the session
   state MUST be cleaned up.  The DNCA Diameter peer within the NAT-
   device MUST notify its DNCA Diameter peer in the NAT-controller about
   successful session termination using a Session Terminate Answer (STA)
   message with Result-Code set to DIAMETER_SUCCESS.  Figure 8 shows the
   protocol interaction between the two DNCA Diameter peers.

   If a DNCA Diameter peer within a NAT-device receives a STR and fails
   to find a matching session, the DNCA Diameter peer MUST return a STA
   with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.






























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   NAT-controller (DNCA Diameter peer)   NAT-device (DNCA Diameter peer)
               |                                            |
               |                                            |
            Trigger                                         |
               |                                            |
               |                   STR                      |
               |------------------------------------------->|
               |                                            |
               |                                            |
               |                                            |
               |                                            |
               |                                            |
               |           Send accounting stop             |
               |<-------------------------------------------|
               |       reporting all session bindings       |
               |                                            |
               |                                            |
               |                                  Remove NAT-bindings
               |                                       of session
               |                                            |
               |                                  Terminate session /
               |                                 Remove session state
               |                                            |
               |                                            |
               |                                            |
               |                  STA                       |
               |<-------------------------------------------|
               |                                            |
               |                                            |

                  Figure 8: Terminate NAT control session

4.5.  Session Abort

   An Abort-Session-Request (ASR) message is sent from the DNCA Diameter
   peer within the NAT-device to the DNCA Diameter peer within the NAT-
   controller when it is unable to maintain a session due to resource
   limitations.  The DNCA Diameter peer within the NAT-controller MUST
   acknowledge successful session abort using a Abort Session Answer
   (ASA) message with Result-Code set to DIAMETER_SUCCESS.  Figure 9
   shows the protocol interaction between the DNCA Diameter peers.  The
   DNCA Diameter peers will start a session termination procedure as
   described in Section 4.4 following an ASA with Result-Code set to
   DIAMETER_SUCCESS.

   If the DNCA Diameter peer within a NAT-controller receives an ASR but
   fails to find a matching session, it MUST return an ASA with Result-
   Code set to DIAMETER_UNKNOWN_SESSION_ID.  If the DNCA Diameter peer



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   within the NAT-controller is unable to comply with the ASR for any
   other reason, an ASA with Result-Code set to
   DIAMETER_UNABLE_TO_COMPLY MUST be returned.

   NAT-controller (DNCA Diameter peer)   NAT-device (DNCA Diameter peer)
               |                                            |
               |                                            |
               |                                         Trigger
               |                                            |
               |                   ASR                      |
               |<-------------------------------------------|
               |                                            |
               |                                            |
               |                                            |
               |                  ASA                       |
               |------------------------------------------->|
               |                                            |
               |                                            |
               |                                            |
               |           On successful ASA                |
               |<------Session Termination Procedure------->|

                    Figure 9: Abort NAT control session

4.6.  Failure cases of the DNCA Diameter peers

   This document does not specify the behavior in case the NAT-device
   and NAT-controller, or their respective DNCA Diameter peers are out
   of sync or lose state.  This could happen for example if one of the
   entities restarts, in case of a (temporary) loss of network
   connectivity etc.  Example failure cases include the following:

   o  NAT-controller and the DNCA Diameter peer within the NAT-
      controller lose state (e.g., due to a restart).  In this case,

      *  the DNCA Diameter peer within the NAT-device MAY receive an NCR
         with NC-Request-Type AVP set to INITIAL_REQUEST that matches an
         existing session of the DNCA Diameter peer within the NAT-
         device.  The DNCA Diameter peer within the NAT-device MUST
         return Result-Code that contains Duplicate-Session-Id AVP to
         report the Session-ID of the existing session.  The DNCA
         Diameter peer within the NAT-controller MAY send an explicit
         Session Terminate Request (STR) for the older session, which
         was lost.

      *  a DNCA Diameter peer MAY receive accounting records for a
         session that does not exist.  The DNCA Diameter peer sends an
         accounting answer with Result-Code set to



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         DIAMETER_UNKNOWN_SESSION_ID in response.  On receiving the
         response, the DNCA Diameter peer SHOULD clear the session and
         remove associated session state.

   o  NAT-device and the DNCA Diameter peer within NAT-device lose
      state.  In such a case, the DNCA Diameter peer MAY receive a NCR
      with NC-Request-Type AVP set to UPDATE_REQUEST for a non-existent
      session.  The DNCA Diameter peer MUST return an NCA with Result-
      Code set to DIAMETER_UNKNOWN_SESSION_ID.  When DNCA application
      within NAT-controller receives this NCA within Result-Code set to
      DIAMETER_UNKNOWN_SESSION_ID, it MAY try to reestablish DNCA
      session or disconnect corresponding access session.

   o  The DNCA Diameter peer within the NAT-controller is unreachable,
      for example detected by Diameter device watchdog messages (as
      defined in Section 5.5 of [RFC3588]), or accounting requests from
      the DNCA Diameter peer fail to get a response, NAT-bindings and
      NAT-device state pertaining to that session MUST be cleaned up
      after a grace period that is configurable on the NAT-device.  The
      grace period can be configured as zero or higher, depending on
      operator preference.

   o  The DNCA Diameter peer within the NAT-device is unreachable or
      down and NCR fails to get a response.  Handling of this case
      depends on the actual service offering of the service provider.
      The service provider could for example choose to stop offering
      connectivity service.

   o  A discussion of the mechanisms how a NAT-device cleans up state in
      case the DNCA Diameter peer within the NAT-device crashes is
      outside the scope of this document.  Implementers of NAT-devices
      could choose from a variety of options such as coupling the state
      (e.g.  NAT bindings) to timers which require periodic refresh, or
      time out otherwise, operating system watchdogs for applications,
      etc.


5.  Use of the Diameter Base Protocol

   The Diameter Base Protocol defined by [RFC3588] applies with the
   clarifications listed in the present specification.

5.1.  Securing Diameter Messages

   For secure transport of Diameter messages, the recommendations in
   [RFC3588] apply.

   DNCA Diameter peers SHOULD verify their identity during the



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   Capabilities Exchange Request procedure.

   A DNCA Diameter peer within the NAT-device SHOULD verify that a DNCA
   Diameter peer that issues a NCR command is allowed to do so based on:

   o  The identity of the DNCA Diameter peer

   o  The type of NCR Command

   o  The content of the NCR Command

   o  Any combination of the above

5.2.  Accounting Functionality

   Accounting functionality (accounting session state machine, related
   command codes and AVPs) is defined in Section 9 below.

5.3.  Use of Sessions

   Each DNCA session MUST have a globally unique Session-ID as defined
   in [RFC3588], which MUST NOT be changed during the lifetime of a DNCA
   session.  The Diameter Session-ID serves as the global endpoint
   identifier.  The DNCA Diameter peers maintain state associated with
   the Session-ID.  This globally unique Session-ID is used for
   updating, accounting, and terminating the session.  A DNCA session
   MUST NOT have more than one outstanding request at any given instant.
   A DNCA Diameter peer sends an Abort-Session-Request as defined in
   [RFC3588] if it is unable to maintain sessions due to resource
   limitation.

5.4.  Routing Considerations

   It is assumed that the DNCA Diameter peer within a NAT-controller
   knows the DiameterIdentity of the Diameter peer within a NAT-device
   for a given endpoint.  Both the Destination-Realm and Destination-
   Host AVPs are present in the request from a DNCA Diameter peer within
   a NAT-controller to a DNCA Diameter peer within a NAT-device.

5.5.  Advertising Application Support

   Diameter nodes conforming to this specification MUST advertise
   support for DNCA by including the value of TBD.APP-ID in the Auth-
   Application-Id of the Capabilities-Exchange-Request and Capabilities-
   Exchange-Answer command[RFC3588].






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6.  DNCA Commands

   The following commands are used to establish, maintain and query NAT-
   bindings.

6.1.  NAT-Control Request (NCR) Command

   The NAT-Control Request (NCR) command, indicated by the command field
   set to TBD.COM-CODE and the "R" bit set in the Command Flags field,
   is sent from the DNCA Diameter peer within the NAT-controller to the
   DNCA Diameter peer within the NAT-device in order to install NAT-
   bindings.

   User-Name, Logical-Access-Id, Physical-Access-ID, Framed-IP-Address,
   Framed-IPv6-Prefix, Framed-Interface-Id, EGRESS-VLANID, NAS-Port-ID,
   Address-Realm, Calling-Station-ID AVPs serve as identifiers for the
   endpoint.

   Message format:
      < NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
                       { Auth-Application-Id }
                       { Origin-Host }
                       { Origin-Realm }
                       { Destination-Realm }
                       { Destination-Host }
                       { NC-Request-Type }
                       [ Session-Id ]
                       [ Origin-State-Id ]
                    *1 [ NAT-Control-Remove ]
                    *1 [ NAT-Control-Install ]
                       [ NAT-External-Address ]
                       [ User-Name ]
                       [ Logical-Access-Id ]
                       [ Physical-Access-ID ]
                       [ Framed-IP-Address ]
                       [ Framed-IPv6-Prefix ]
                       [ Framed-Interface-Id ]
                       [ EGRESS-VLANID]
                       [ NAS-Port-ID]
                       [ Address-Realm ]
                       [ Calling-Station-ID ]
                     * [ Proxy-Info ]
                     * [ Route-Record ]
                     * [ AVP ]







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6.2.  NAT-Control Answer (NCA) Command

   The NAT-Control-Answer (NCA) command, indicated by the Command-Code
   field set to TBD.COM-CODE and the "R" bit cleared in the Command
   Flags field, is sent by the DNCA Diameter peer within the NAT-device
   in response to NAT-Control-Request command.

   Message format:
      <NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
                      { Origin-Host }
                      { Origin-Realm }
                      { Result-Code }
                      [ Session-Id ]
                      [ NC-Request-Type ]
                    * [ NAT-Control-Definition ]
                      [ Current-NAT-Bindings ]
                      [ Origin-State-Id ]
                      [ Error-Message ]
                      [ Error-Reporting-Host ]
                    * [ Failed-AVP ]
                    * [ Proxy-Info ]
                      [ Duplicate-Session-ID ]
                    * [ Redirect-Host]
                      [ Redirect-Host-Usage ]
                      [ Redirect-Max-Cache-Time ]
                    * [ Proxy-Info ]
                    * [ Route-Record ]
                    * [ Failed-AVP ]
                    * [ AVP ]



7.  NAT Control Application Session State Machine

   This section contains a set of finite state machines, representing
   the life cycle of a DNCA session, which MUST be observed by all
   implementations of the DNCA Diameter application.  The DNCA Diameter
   peers are stateful and the state machine maintained is similar to the
   stateful Client and Server authorization state machine described in
   [RFC3588].  When a session is moved to the Idle state, any resources
   that were allocated for the particular session must be released.  Any
   event not listed in the state machines MUST be considered as an error
   condition, and an answer, if applicable, MUST be returned to the
   originator of the message.

   In the state table, the event 'Failure to send NCR' means that the
   DNCA Diameter peer within the NAT-controller is unable to send the
   NCR command to the desired destination.  This could be due to the



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   peer being down, or due to the peer sending back the transient
   failure or temporary protocol error notification DIAMETER_TOO_BUSY or
   DIAMETER_LOOP_DETECTED in the Result-Code AVP of an NCA.

   In the state table "FAILED NCA" means that the DNCA Diameter peer
   within the NAT-device was not able to honor the corresponding NCR.
   This can happen due to any transient and permanent error at the NAT-
   device or its associated DNCA Diameter peer within indicated by the
   following error Result-Code values: RESOURCE_FAILURE,
   UNKNOWN_BINDING_TEMPLATE_NAME, MAX_BINDINGS_SET_FAILURE,
   BINDING_FAILURE, MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT,
   SESSION_EXISTS, INSUFFICIENT_CLASSIFIERS.

   The following state machine is observed by a DNCA Diameter peer
   within a NAT-controller.  The state machine description uses the term
   "access session" to describe the connectivity service offered to the
   endpoint or host.  "Access session" should not be confused with the
   Diameter session ID.

             DNCA Diameter peer within a NAT-controller
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      New endpoint detected that     Send        Pending
                requires NAT Control           NCR
                                               Initial
                                               Request

      Idle      ASR Received                   Send ASA    Idle
                for unknown session            with
                                               Result-Code
                                               = UNKNOWN_
                                               SESSION_ID

      Pending   Successful NCA                 Setup       Open
                received                       complete

      Pending   Successful NCA                 Send STR    Discon
                received
                but peer unable to provide
                service

      Pending   Error processing successful    Send STR    Discon
                NCA

      Pending   Failed                         Clean up    Idle
                NCA received

      Open      NAT control                    Send        Open



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                update required                NCR Update
                                               Request
      Open      Successful                                 Open
                NCA received

      Open      Failed                         Clean up    Idle
                NCA received


      Open      Access session end detected    Send STR    Discon


      Open      ASR Received,                  Send ASA    Discon
                access session will be         with
                terminated                     Result-Code
                                               = SUCCESS,
                                               Send STR

      Open      ASR Received,                  Send ASA    Open
                access session will not        with
                be terminated                  Result-Code
                                               != SUCCESS

      Discon    ASR Received                   Send ASA    Idle

      Discon    STA Received                   Discon.     Idle
                                               endpoint

   The following state machine is observed by a DNCA Diameter peer
   within a NAT-device.

             DNCA Diameter peer within a NAT-device
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      NCR Query request              Send       Idle
                received, and                  successful
                able to provide requested      NCA
                NAT Binding report

      Idle      NCR received                   Send       Open
                and able to                    successful
                provide requested              NCA
                NAT control service

      Idle      NCR request                    Send       Idle
                received, and                  failed
                unable to provide requested    NCA
                NAT control service



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      Open      NCR  request                   Send       Open
                received, and                  successful
                able to provide requested      NCA
                NAT control service

      Open      NCR request                    Send       Idle
                received, and                  failed
                unable to provide requested    NCA,
                NAT control service            Clean up

      Open      Unable to continue             Send ASR   Discon
                providing requested
                NAT control service

      Open      Unplanned loss of session/     Clean up   Idle
                connection to DNCA Diameter
                peer in NAT controller
                detected (e.g. due to Diameter
                watchdog notification)

      Discon    Failure to send ASR            Wait,      Discon
                                               resend ASR

      Discon    ASR successfully sent and      Clean up   Idle
                ASA Received with Result-Code

      Not       ASA Received                   None       No change
      Discon

      Any       STR Received                   Send STA,  Idle
                                               Clean up


8.  DNCA AVPs

8.1.  Reused Base Protocol AVPs

   The following table describes the AVPs reused from Diameter Base
   Protocol [RFC3588]; their AVP Code values, types, and possible flag
   values; and whether the AVP MAY be encrypted.  The [RFC3588]
   specifies the AVP Flag rules for AVPs in section 4.5.  The Diameter
   AVP rules are defined in the [RFC3588], section 4.









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                                                   +---------+
                                                   |  AVP    |
                                                   |  Flag   |
                                                   |  rules  |
   +-----------------------------------------------|-----+---+---------+
   |                           AVP                 |     |   |         |
   | Attribute Name            Code     Data Type  |MUST |MAY|   Encr  |
   +-----------------------------------------------+-----+---+---------+
   |Acct-Interim-Interval      85       Unsigned32 | M   | P |    Y    |
   |Auth-Application-Id        258      Unsigned32 | M   | P |    N    |
   |Destination-Host           293      DiamIdent  | M   | P |    N    |
   |Destination-Realm          283      DiamIdent  | M   | P |    N    |
   |Error-Message              281      UTF8String | M   | P |    N    |
   |Error-Reporting-Host       294      DiamIdent  | M   | P |    N    |
   |Failed-AVP                 279      Grouped    | M   | P |    N    |
   |Origin-Host                264      DiamIdent  | M   | P |    N    |
   |Origin-Realm               296      DiamIdent  | M   | P |    N    |
   |Origin-State-Id            278      Unsigned32 | M   | P |    N    |
   |Proxy-Info                 284      Grouped    | M   | P |    N    |
   |Result-Code                268      Unsigned32 | M   | P |    N    |
   |Route-Record               282      DiamIdent  | M   |   |    N    |
   |Session-Id                 263      UTF8String | M   | P |    Y    |
   |User-Name                  1        UTF8String | M   | P |    Y    |
   +-----------------------------------------------+-----+---+---------+
   Table 1: DIAMETER AVPs used from Diameter base

   The Auth-Application-Id AVP (AVP Code 258) is assigned by IANA to
   Diameter applications.  The value of the Auth-Application-Id for the
   Diameter NAT Control Application is TBD.APP-ID.  Please refer to
   [RFC3588] for the definition of the Diameter AVP flag rules and the
   associated abbreviations used in the table.

8.2.  Additional Result-Code AVP Values

   This section defines new values for the Result-Code AVP that SHALL be
   supported by all Diameter implementations that conform to the present
   document.

8.2.1.  Success

   No new Result-Code AVP value is defined within this category.

8.2.2.  Transient Failures

   Result-Code AVP values that fall within the transient failures
   category are those used to inform a peer that the request could not
   be satisfied at the time that it was received.  The request may be
   able to be satisfied in the future.



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   The following new values of the Result-Code AVP are defined:

      RESOURCE_FAILURE (TBD.RCX)

         The DNCA Diameter peer within the NAT-device indicates that the
         binding could not be installed or a new session could not be
         created due to resource shortage.

8.2.3.  Permanent Failures

   The Result-Code AVP values, which fall within the permanent failures
   category are used to inform the peer that the request failed, and
   should not be attempted again.  The request may be able to be
   satisfied in the future.

   The following new values of the Result-Code AVP are defined:

      UNKNOWN_BINDING_TEMPLATE_NAME (TBD.RCX)

         The DNCA Diameter peer within the NAT-device indicates that the
         binding could not be installed or a new session could not be
         created because the specified NAT-Control-Binding-Template AVP,
         that refers to a predefined policy template in the NAT-device,
         is unknown.

      BINDING_FAILURE (TBD.RCX)

         The DNCA Diameter peer within the NAT-device indicates that the
         requested binding(s) could not be installed.  For example:
         Requested ports are already in use.

      MAX_BINDINGS_SET_FAILURE (TBD.RCX)

         The DNCA Diameter peer within the NAT-device indicates that it
         failed to conform to a request to configure the maximum number
         of bindings for a session.  For example: An operator defined
         the maximum number of bindings on the NAT-device using a method
         or protocol which takes precendence over DNCA.

      MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT (TBD.RCX)

         The DNCA Diameter peer within the NAT-device denies the request
         because the maximum number of allowed bindings has been reached
         for the specified endpoint classifier.

      SESSION_EXISTS (TBD.RCX)





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         The DNCA Diameter peer within the NAT-device denies request to
         initialize a new session, if it already has a DNCA session that
         uses the same set of classifiers as indicated by the DNCA
         Diameter peer within the NAT-controller in the new session
         initialization request.

      INSUFFICIENT_CLASSIFIERS (TBD.RCX)

         The DNCA Diameter peer within the NAT-device requests to
         initialize a new session, if the classifiers in the request
         match more than one of the existing sessions on the DNCA
         Diameter peer within the NAT-device.

8.3.  Reused NASREQ Diameter Application AVPs

   The following table describes the AVPs reused from the Diameter
   Network Access Server Application [RFC4005]; their AVP Code values,
   types, and possible flag values; and whether the AVP MAY be
   encrypted.  The [RFC3588] specifies the AVP Flag rules for AVPs in
   section 4.5.  The Diameter AVP rules are defined in the [RFC3588],
   section 4.
                                          +---------------------+
                                          |    AVP Flag rules   |
   +------------------+------+------------|----+-----+----+-----|----+
   |                  | AVP  |            |    |     |SHLD| MUST|    |
   | Attribute Name   | Code |  Value Type|MUST| MAY | NOT|  NOT|Encr|
   |------------------|------|------------|----+-----+----+-----|----|
   | NAS-Port         |   5  | Unsigned32 | M  |  P  |    |  V  | Y  |
   | NAS-Port-Id      |  87  | UTF8String | M  |  P  |    |  V  | Y  |
   | Calling-Station- |  31  | UTF8String | M  |  P  |    |  V  | Y  |
   |   Id             |      |            |    |     |    |     |    |
   | Framed-IP-Address|   8  | OctetString| M  |  P  |    |  V  | Y  |
   | Framed-Interface-|  96  | Unsigned64 | M  |  P  |    |  V  | Y  |
   |   Id             |      |            |    |     |    |     |    |
   | Framed-IPv6-     |  97  | OctetString| M  |  P  |    |  V  | Y  |
   |  Prefix          |      |            |    |     |    |     |    |
   +------------------+------+------------|----+-----+----+-----|----+
   Table 2: Reused NASREQ Diameter application AVPs.  Please refer to
   [RFC3588] for the definition of the Diameter AVP flag rules and the
   associated abbreviations used in the table.

8.4.  Reused AVPs from RFC 4675

   The following table describes the AVPs reused from "RADIUS Attributes
   for Virtual LAN and Priority Support" specification [RFC4675]; their
   AVP Code values, types, and possible flag values; and whether the AVP
   MAY be encrypted.  The [RFC3588] specifies the AVP Flag rules for
   AVPs in section 4.5.  The Diameter AVP rules are defined in the



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   [RFC3588], section 4.
                                          +---------------------+
                                          |    AVP Flag rules   |
   +------------------+------+------------|----+-----+----+-----|----+
   |                  | AVP  |            |    |     |SHLD| MUST|    |
   | Attribute Name   | Code |  Value Type|MUST| MAY | NOT|  NOT|Encr|
   |------------------|------|------------|----+-----+----+-----|----|
   | Egress-VLANID    |  56  | OctetString| M  |  P  |    |  V  | Y  |
   +------------------+------+------------|----+-----+----+-----|----+
   Table 3: Reused attributes from RFC 4675.  Please refer to [RFC3588]
   for the definition of the Diameter AVP flag rules and the associated
   abbreviations used in the table.

8.5.  Reused AVPs from Diameter QoS Application

   The following table describes the AVPs reused from the Traffic
   Classification and Quality of Service (QoS) Attributes for Diameter
   [RFC5777]; their AVP Code values, types, and possible flag values;
   and whether the AVP MAY be encrypted.  The [RFC3588] specifies the
   AVP Flag rules for AVPs in section 4.5.  The Diameter AVP rules are
   defined in the [RFC3588], section 4.
                                                   +---------+
                                                   |  AVP    |
                                                   |  Flag   |
                                                   |  rules  |
   +-----------------------------------------------|-----+---+---------+
   |                           AVP                 |     |   |         |
   | Attribute Name            Code     Data Type  |MUST |MAY|   Encr  |
   +-----------------------------------------------+-----+---+---------+
   |Port                       530     Integer32   |  M  | P |    Y    |
   |Protocol                   513     Enumerated  |  M  | P |    Y    |
   |Direction                  514     Enumerated  |  M  | P |    Y    |
   +-----------------------------------------------+-----+---+---------+

   Table 4: Reused QoS-attributes.  Please refer to [RFC3588] for the
   definition of the Diameter AVP flag rules and the associated
   abbreviations used in the table.

8.6.  Reused AVPs from ETSI ES 283 034, e4 Diameter Application

   The following table describes the AVPs reused from the Diameter e4
   Application [ETSIES283034]; their AVP Code values, types, and
   possible flag values; and whether the AVP MAY be encrypted.  The
   [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5.  The
   Diameter AVP rules are defined in the [RFC3588], section 4.  The
   Vendor-ID field in these AVP header will be set to ETSI (13019).





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                                                   +---------+
                                                   |  AVP    |
                                                   |  Flag   |
                                                   |  rules  |
   +-----------------------------------------------|-----+---+---------+
   |                           AVP                 |     |   |         |
   | Attribute Name            Code     Data Type  |MUST |MAY|   Encr  |
   +-----------------------------------------------+-----+---+---------+
   |Address-Realm              301     OctetString | M,V |   |    Y    |
   |Logical-Access-Id          302     OctetString |   V | M |    Y    |
   |Physical-Access-ID         313     UTF8String  |   V | M |    Y    |
   +-----------------------------------------------+-----+---+---------+

   Table 5: Reused AVPs from Diameter e4 application.  Please refer to
   [RFC3588] for the definition of the Diameter AVP flag rules and the
   associated abbreviations used in the table.

8.7.  DNCA Defined AVPs

   The following table describes the new Diameter AVPs defined in this
   document; their AVP Code values, types, and possible flag values; and
   whether the AVP MAY be encrypted.  The [RFC3588] specifies the AVP
   Flag rules for AVPs in section 4.5.  The Diameter AVP rules are
   defined in the [RFC3588], section 4.  The AVPs defined here MUST NOT
   have the V bit in the AVP Flag set.


























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                                                      +---------+
                                                      |  AVP    |
                                                      |  Flag   |
                                                      |  rules  |
   +--------------------------------------------------|-----+---+------+
   |                              AVP                 |     |   |      |
   | Attribute Name               Code     Data Type  |MUST |MAY| Encr |
   +--------------------------------------------------+-----+---+------+
   |NC-Request-Type        TBD.AX  8.7.1   Enumerated | M   | P |  Y   |
   |NAT-Control-Install    TBD.AX  8.7.2   Grouped    | M   | P |  Y   |
   |NAT-Control-Remove     TBD.AX  8.7.3   Grouped    | M   | P |  Y   |
   |NAT-Control-Definition TBD.AX  8.7.4   Grouped    | M   | P |  Y   |
   |NAT-Internal-Address   TBD.AX  8.7.5   Grouped    | M   | P |  Y   |
   |NAT-External-Address   TBD.AX  8.7.6   Grouped    | M   | P |  Y   |
   |Max-NAT-Bindings       TBD.AX  8.7.7   Unsigned32 | M   | P |  Y   |
   |NAT-Control-           TBD.AX  8.7.8   OctetString| M   | P |  Y   |
   | Binding-Template                                 |     |   |      |
   |Duplicate-             TBD.AX  8.7.9   UTF8String | M   | P |  Y   |
   | Session-ID                                       |     |   |      |
   |NAT-External-Port-     TBD.AX  8.7.10  Enumerated | M   | P |  Y   |
   | Style                                            |     |   |      |
   |NAT-Control-Record     TBD.AX  9.2.1   Grouped    | M   | P |  Y   |
   |NAT-Control-           TBD.AX  9.2.2   Enumerated | M   | P |  Y   |
   | Binding-Status                                   |     |   |      |
   |Current-NAT-Bindings   TBD.AX  9.2.3   Unsigned32 | M   | P |  Y   |
   +--------------------------------------------------+-----+---+------+

   Table 6: New Diameter AVPs.  Please refer to [RFC3588] for the
   definition of the Diameter AVP flag rules and the associated
   abbreviations used in the table.

8.7.1.  NC-Request-Type AVP

   The NC-Request-Type AVP (AVP Code TBD.AX) is of type Enumerated and
   contains the reason for sending the NAT-Control-Request command.  It
   shall be present in all NAT-Control-Request messages.

   The following values are defined:

      INITIAL_REQUEST (1)

         An Initial Request is to initiate a Diameter NAT control
         session between the DNCA Diameter peers.

      UPDATE_REQUEST (2)

         An Update Request is used to update bindings previously
         installed on a given access session, to add new binding on a



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         given access session, or to remove one or several binding(s)
         activated on a given access session.

      QUERY_REQUEST (3)

         Query Request is used to query a NAT-device about the currently
         installed bindings for an endpoint classifier.

8.7.2.  NAT-Control-Install AVP

   The NAT-Control AVP (AVP code TBD.AX) is of type Grouped, and it is
   used to activate or install NAT bindings.  It also contains Max-NAT-
   Bindings that defines the maximum number of NAT bindings allowed for
   an endpoint and the NAT-Control-Binding-Template that references a
   predefined template on the NAT-device that may contain static
   binding, a maximum number of bindings allowed, an IP-address pool
   from which external binding addresses should be allocated, etc.  If
   the NAT-External-Port-Style AVP is present, then the NAT-device MUST
   select the external ports for the NAT-Bindings as per the style
   specified.  The NAT-External-Port-Style is applicable for NAT-
   Bindings defined by the NAT-Control-Definition AVPs whose NAT-
   External-Address or Port AVPs within the NAT-External-Address are
   unspecified.

   AVP format:
     NAT-Control-Install ::= < AVP Header: TBD.AX >
                              * [ NAT-Control-Definition ]
                                [ NAT-Control-Binding-Template ]
                                [ Max-NAT-Bindings ]
                                [ NAT-External-Port-Style ]
                              * [ AVP ]

8.7.3.  NAT-Control-Remove AVP

   The NAT-Control-Remove AVP (AVP code TBD.AX) is of type Grouped, and
   it is used to deactivate or remove NAT-bindings.  At least one of the
   two AVPs (NAT-Control-Definition AVP, NAT-Control-Binding-Template
   AVP) SHOULD be present in the NAT-Control-Remove AVP.

   AVP format:
     NAT-Control-Remove ::= < AVP Header: TBD.AX >
                             * [ NAT-Control-Definition ]
                               [ NAT-Control-Binding-Template ]
                             * [ AVP ]







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8.7.4.  NAT-Control-Definition AVP

   The NAT-Control-Definition AVP (AVP code TBD.AX) is of type Grouped,
   and it describes a binding.

   The NAT-Control-Definition AVP uniquely identifies the binding
   between the DNCA Diameter peers.

   If both the NAT-Internal-Address and NAT-External-Address AVP(s) are
   supplied, it is a pre-defined binding.

   If the NAT-External-Address AVP is not specified then the NAT-device
   MUST select the external port as per the NAT-External-Port-Style AVP,
   if present in the NAT-Control-Definition AVP.

   The Protocol AVP describes the transport protocol for the binding.
   The NAT-Control-Definition AVP can contain either zero or one
   Protocol AVP.  If the Protocol AVP is omitted and if both internal
   and external IP-address are specified then the binding reserves the
   IP-addresses for all transport protocols.

   The Direction AVP is of type Enumerated.  It specifies the direction
   for the binding.  The values of the enumeration applicable in this
   context are: "IN","OUT".  If Direction AVP is OUT or absent, the NAT-
   Internal-Address refers to the IP-address of the endpoint that needs
   to be translated.  If Direction AVP is "IN", NAT-Internal-Address is
   the destination IP-address that has to be translated.

   AVP format:
     NAT-Control-Definition ::= < AVP Header: TBD.AX >
                                 { NAT-Internal-Address }
                                 [ Protocol ]
                                 [ Direction ]
                                 [ NAT-External-Address ]
                                 [ Session-Id ]
                               * [ AVP ]

8.7.5.  NAT-Internal-Address AVP

   The NAT-Internal-Address AVP (AVP code TBD.AX) is of type Grouped.
   It describes the internal IP-address and port for a binding.  Framed-
   IPV6-Prefix and Framed-IP-Address AVPs are mutually exclusive.

   AVP format:







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     NAT-Internal-Address ::= < AVP Header: TBD.AX >
                               [ Framed-IP-Address ]
                               [ Framed-IPv6-Prefix ]
                               [ Port]
                             * [ AVP ]

8.7.6.  NAT-External-Address AVP

   The NAT-External-Address AVP (AVP code TBD.AX) is of type Grouped,
   and it describes the external IP-address and port for a binding.  The
   external IP-address specified in this attribute can be reused for
   multiple endpoints by specifying the same address in the respective
   NAT-External-Address AVPs.  If the external IP-address is not
   specified and the NAT-External-Port-Style AVP is specified in the
   NAT-Control-Definition AVP then the NAT-device MUST select external
   port as per the NAT-External-Port-Style AVP.

   AVP format:
     NAT-External-Address ::= < AVP Header: TBD.AX >
                               [ Framed-IP-Address ]
                               [ Port ]
                             * [ AVP ]

8.7.7.  Max-NAT-Bindings

   The Max-NAT-Bindings AVP (AVP code TBD.AX) is of type Unsigned32.  It
   indicates the maximum number of NAT-bindings allowed for a particular
   endpoint.

8.7.8.  NAT-Control-Binding-Template AVP

   The NAT-Control-Binding-Template AVP (AVP code TBD.AX) is of type
   OctetString.  It defines a name for a policy template that is
   predefined at the NAT-device.  Details on the contents and structure
   of the template and configuration are outside the scope of this
   document.  The policy to which this AVP refers to may contain NAT-
   bindings, IP-address pool for allocating the external IP-address of a
   NAT-binding, and maximum number of allowed NAT-bindings.  Such policy
   template can be reused by specifying the same NAT-Control-Binding-
   Template AVP in the corresponding NAT-Control-Install AVPs of
   multiple endpoints.

8.7.9.  Duplicate-Session-Id AVP

   The Duplicate-Session-Id AVP (AVP Code TBD.AX) is of type UTF8String.
   It is used to report errors and contains the Session-Id of an
   existing session.




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8.7.10.  NAT-External-Port-Style AVP

   The NAT-External-Port-Style AVP (AVP Code TBD.AX) is of type
   Enumerated and contains the style to be followed while selecting the
   external port for a NAT-Binding relative to the internal port.

   The following values are defined:

      FOLLOW_INTERNAL_PORT_STYLE (1)

         External port numbers selected MUST follow the same sequence
         and oddity as the internal ports of the NAT-bindings.  The port
         odditity is required to support protocols like RTP and RTCP as
         defined in [RFC3550].  If for example the internal port in a
         requested NAT-binding is odd numbered then the external port
         allocated MUST also be odd numbered, and vice versa for an even
         numbered port.  In addition, the sequence of port numbering is
         maintained: If internal ports are consecutive, then the NAT-
         device MUST choose consecutive external ports for the NAT-
         bindings.


9.  Accounting Commands

   The DNCA reuses session based accounting as defined in the Diameter
   Base Protocol[RFC3588] to report the bindings per endpoint.  This
   reporting is achieved by sending Diameter Accounting Requests (ACR)
   [Start, Interim and Stop] from the DNCA Diameter peer within the NAT-
   device to its associated DNCA Diameter peer within the NAT-
   controller.

   The DNCA Diameter peer within the NAT-device sends an ACR Start on
   receiving a NCR with NC-Request-Type AVP set to INITIAL_REQUEST for a
   session or on creation of the first binding for a session requested
   in an earlier NCR.  DNCA may send ACR Interim updates, if required,
   either due to a change in bindings resulting from a NCR with NC-
   Request-Type AVP set to UPDATE_REQUEST, or periodically as specified
   in Acct-Interim-Interval by the DNCA Diameter peer within the NAT-
   controller, or when it creates or tears down bindings.  An ACR Stop
   is sent by the DNCA Diameter peer within the NAT-device on receiving
   STR.

   The function of correlating the multiple bindings used by an endpoint
   at any given time is relegated to the post processor.

   The DNCA Diameter peer within the NAT-device may trigger an interim
   accounting record when the maximum number of bindings, if received in
   an NCR, is reached.



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9.1.  NAT Control Accounting Messages

   The ACR and ACA messages are reused as defined in the Diameter Base
   Protocol [RFC3588] for exchanging endpoint NAT binding details
   between the DNCA Diameter peers.  The DNCA Application IDs is used in
   the accounting commands.  ACR contains one or more optional NAT-
   Control-Record AVPs to report the bindings.  The NAT-device indicates
   the number of allocated NAT bindings to the NAT-controller using the
   Current-NAT-Bindings AVP.  This number needs to match the number of
   bindings identified as active within the NAT-Control-Record AVP.

9.2.  NAT Control Accounting AVPs

   In addition to AVPs for ACR specified in [RFC3588], the DNCA Diameter
   peer within the NAT-device must add the NAT-Control-Record AVP.

9.2.1.  NAT-Control-Record

   The NAT-Control-Record AVP (AVP code TBD.AX) is of type Grouped.  It
   describes a binding and its status.  If NAT-Control-Binding-Status is
   set to Created, Event-Timestamp indicates the binding creation time.
   If NAT-Control-Binding-Status is set to Removed, Event-Timestamp
   indicates the binding removal time.  If NAT-Control-Binding-Status is
   active, Event-Timestamp need not be present; if a value is present,
   it indicates that binding is active at the given time.
     NAT-Control-Record ::= < AVP Header: TBD.AX >
                            { NAT-Control-Definition }
                            { NAT-Control-Binding-Status }
                            [ Event-Timestamp ]

9.2.2.  NAT-Control-Binding-Status

   The NAT-Control-Binding-Status AVP (AVP code TBD.AX) is of type
   enumerated.  It indicates the status of the binding - created,
   removed, or active.

   The following values are defined:

      Created (1)

         NAT binding is created.

      Active (2)

         NAT binding is active.






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      Removed (3)

         NAT binding was removed.

9.2.3.  Current-NAT-Bindings

   The Current-NAT-Bindings AVP (AVP code TBD.AX) is of type Unsigned32.
   It indicates the number of NAT bindings active on the NAT-device.


10.  AVP Occurrence Table

   The following sections present the AVPs defined in this document and
   specify the Diameter messages in which they can be present.  Note:
   AVPs that can only be present within a Grouped AVP are not
   represented in this table.

   The table uses the following symbols:



      0         The AVP MUST NOT be present in the message.

      0+        Zero or more instances of the AVP can be present in the
                message.

      0-1       Zero or one instance of the AVP can be present in the
                message.  It is considered an error if there is more
                than one instance of the AVP.

      1         One instance of the AVP MUST be present in the message.

      1+        At least one instance of the AVP MUST be present in the
                message.

10.1.  DNCA AVP Table for NAT Control Initial and Update Requests

   The following table lists DNCA specific AVPs that have to be present
   in NCRs and NCAs with NC-Request-Type set to INITIAL_REQUEST or
   UPDATE_REQUEST.











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                                       +-------------------+
                                       |  Command Code     |
   +-----------------------------------+-------------------+
   | Attribute Name                        NCR    NCA      |
   +-------------------------------------------------------+
   |NC-Request-Type                         1      1       |
   |NAT-Control-Install                     0-1    0       |
   |NAT-Control-Remove                      0-1    0       |
   |NAT-Control-Definition                  0      0       |
   |Current-NAT-Bindings                    0      0       |
   |Duplicate-Session-Id                    0      0-1     |
   +-------------------------------------------------------+

   Note that any combination of "NAT-Control-Install" and "NAT-Control-
   Remove" AVPs could be present in an update or initial requests.
   Consider the following examples:

      Neither "NAT-Control-Install AVP" nor "NAT-Control-Remove AVP" are
      present: This could for example be the case if the NAT-controller
      would only want to receive accounting information, but not control
      NAT-bindings.

      Only "NAT-Control-Install AVP" is present: This could for example
      be the case if a new NAT-binding is installed for an existing
      session.

      Only "NAT-Control-Remove AVP" is present: This could for example
      be the case if a new NAT-binding is removed from an existing
      session.

      Both, "NAT-Control-Install AVP" and "NAT-Control-Remove AVP" are
      present: This could for example be the case if a formerly created
      NAT-binding is removed and a new NAT-binding is established within
      the same request.

10.2.  DNCA AVP Table for Session Query request

   The following table lists DNCA specific AVPs that have to be present
   in NCRs and NCAs with NC-Request-Type set to QUERY_REQUEST.












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                                       +-------------------+
                                       |  Command Code     |
   +-----------------------------------+-------------------+
   | Attribute Name                        NCR    NCA      |
   +-------------------------------------------------------+
   |NC-Request-Type                         1      1       |
   |NAT-Control-Install                     0      0       |
   |NAT-Control-Remove                      0      0       |
   |NAT-Control-Definition                  0      0+      |
   |NAT-External-Address                    0+     0       |
   |Current-NAT-Bindings                    0      1       |
   |Duplicate-Session-Id                    0      0       |
   +-------------------------------------------------------+

10.3.  DNCA AVP Table for Accounting Message

   The following table lists DNCA specific AVPs, which may or may not be
   present in ACR and ACA messages.
                                       +-------------------+
                                       |  Command Code     |
   +-----------------------------------+-------------------+
   | Attribute Name                        ACR    ACA      |
   +-------------------------------------------------------+
   |NAT-Control-Record                      0+     0       |
   |Current-NAT-Bindings                    1      0       |
   +-------------------------------------------------------+


11.  IANA Considerations

   This section contains the namespaces that have either been created in
   this specification, or the values assigned to existing namespaces
   managed by IANA.

   In the subsections below, when we speak about review by a Designated
   Expert, please note that the designated expert will be assigned by
   the IESG.  Initially, such Expert discussions take place on the AAA
   WG mailing list.

11.1.  Application Identifier

   This specification assigns the value <TBD.APP-ID>, 'Diameter NAT
   Control Application', to the Application Identifier namespace defined
   in [RFC3588].  See Section 4 for more information.







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11.2.  Command Codes

   This specification uses the value <TBD.COM-CODE> from the Command
   code namespace defined in [RFC3588] for the NAT-Control-Request
   (NCR), NAT-Control-Answer (NCA) commands.  See Section 6.1 and
   Section 6.2 for more information on these commands.

11.3.  AVP Codes

   This specification assigns the values <TBD.AX> from the AVP code
   namespace defined in [RFC3588].  See Section 8.7 for the assignment
   of the namespace in this specification.

11.4.  Result-Code AVP Values

   This specification assigns the values <TBD.RCX> (4xxx, 5xxx, 5xxx,
   5xxx, 5xxx,5xxx) from the Result-Code AVP value namespace defined in
   [RFC3588].  See Section 8.2 for the assignment of the namespace in
   this specification.

11.5.  NC-Request-Type AVP

   As defined in Section 8.7.1, the NC-Request-Type AVP includes
   Enumerated type values 1 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [RFC5226].

11.6.  NAT-External-Port-Style AVP

   As defined in Section 8.7.10, the NAT-External-Port-Style AVP
   includes Enumerated type value 1.  IANA has created and is
   maintaining a namespace for this AVP.  All remaining values are
   available for assignment by a Designated Expert [RFC5226].

11.7.  NAT-Control-Binding-Status AVP

   As defined in Section 8.7.1, the NAT-Control-Binding-Status AVP
   includes Enumerated type values 1 - 3.  IANA has created and is
   maintaining a namespace for this AVP.  All remaining values are
   available for assignment by a Designated Expert [RFC5226].


12.  Security Considerations

   This document describes procedures for controlling NAT related
   attributes and parameters by an entity, which is non-local to the
   device performing NAT.  This section discusses security
   considerations for DNCA.  This includes the interactions between the



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   Diameter peers within a NAT-controller and a NAT-device as well as
   general considerations for NAT-control in a service provider network.

   Security between a NAT-controller and a NAT-device has a number of
   components: authentication, authorization, integrity, and
   confidentiality.

   Authentication refers to confirming the identity of an originator for
   all datagrams received from the originator.  Lack of authentication
   of Diameter messages between the Diameter peers can jeopardize the
   fundamental service of the peering network elements.  A consequence
   of not authenticating the message sender by the recipient would be
   that an attacker could spoof the identity of a "legitimate"
   authorizing entity in order to change the behavior of the receiver.
   An attacker could for example launch a denial of service attack by
   setting the maximum number of bindings for a session on the NAT-
   device to zero; provision bindings on a NAT-device which include IP-
   addresses already in use in other parts of the network; or request
   session termination of the Diameter session and hamper an endpoint's
   (i.e. a user's) connectivity.  Lack of authentication of a NAT-device
   to a NAT-controller could lead to situations where the NAT-device
   could provide a wrong view of the resources (i.e.  NAT-bindings).  In
   addition, NAT Binding Predefined template on the NAT-device could be
   configured differently than expected by the NAT-controller.  Failing
   of any of the two DNCA Diameter peers to provide the required
   credentials should be subject to logging.  The corresponding logging
   infrastructure of the operator SHOULD be built in a way that it can
   mitigate potential denial of service attacks resulting from large
   amounts of logging events.  This could include proper dimensioning of
   the logging infrastructure combined with policing the maximum amount
   of logging events accepted by the logging system to a threshold which
   the system is known to be able to handle.

   Authorization refers to whether a particular authorizing entity is
   authorized to signal a network element requests for one or more
   applications, adhering to a certain policy profile.  Failing the
   authorization process might indicate a resource theft attempt or
   failure due to administrative and/or credential deficiencies.  In
   either case, the network element should take the proper measures to
   log such attempts.

   Integrity is required to ensure that a Diameter message exchanged
   between the Diameter peers has not been maliciously altered by
   intermediate devices.  The result of a lack of data integrity
   enforcement in an untrusted environment could be that an impostor
   will alter the messages exchanged between the peers.  This could
   cause a change of behavior of the peers, including the potential of a
   denial of service.



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   Confidentiality protection of Diameter messages ensures that the
   signaling data is accessible only to the authorized entities.  When
   signaling messages between the DNCA Diameter peers traverse untrusted
   networks, lack of confidentiality will allow eavesdropping and
   traffic analysis.

   Diameter offers security mechanisms to deal with the functionality
   demanded above.  DNCA makes use of the capabilities offered by
   Diameter and the underlying transport protocols to deliver these
   requirements (see Section 5.1).  If the DNCA communication traverses
   untrusted networks, messages between DNCA Diameter peers SHOULD be
   secured using either IPsec or TLS.  Please refer to [RFC3588],
   section 13 for details.  DNCA Diameter peers SHOULD perform bilateral
   authentication, authorization as well as procedures to ensure
   integrity and confidentiality of the information exchange.  In
   addition the Session-Id chosen for a particular Diameter session
   SHOULD be chosen in a way that it is hard to guess in order to
   mitigate issues through potential message replay.

   DNCA Diameter peers SHOULD have a mutual trust setup.  This document
   does not specify a mechanisms for authorization between the DNCA
   Diameter peers.  The DNCA Diameter peers SHOULD be provided with
   sufficient information to make an authorization decision.  The
   information can come from various sources, for example the peering
   devices could store local authentication policy, listing the
   identities of authorized peers.

   Any mechanism or protocol providing control of a NAT-device, and DNCA
   is an example of such a control mechanism, could allow for misuse of
   the NAT-device given that it enables the definition of per-
   destination or per-source rules.  Misuse could include anti-
   competitive practices among providers, censorship, crime, etc.  NAT-
   control could be used as a tool for preventing or redirecting access
   to particular sites.  For instance, by controlling the NAT bindings,
   one could ensure that endpoints aren't able to receive particular
   flows, or that those flows are redirected to a relay that snoops or
   tampers with traffic instead of directly forwarding the traffic to
   the intended endpoint.  In addition one could set up a binding in a
   way that the source IP address used is one of a relay so that traffic
   coming back can be snooped on or interfered with.  The operator also
   needs to consider security threats resulting from unplanned
   termination of the DNCA session.  Unplanned session termination,
   which could e.g. happen due to an attacker taking down the NAT-
   controller, leads to the NAT-device cleaning up the state associated
   with this session after a grace period.  If the grace period is set
   to zero, the endpoint will experience an immediate loss of
   connectivity to services reachable through the NAT-device following
   the termination of the DNCA session.The protections on DNCA and its



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   Diameter protocol exchanges don't prevent such abuses of NAT-control.
   Prevention of mis-use or mis-configuration of a NAT-device by an
   authorized NAT-controller is beyond the scope of this protocol
   specification.  A service provider deploying DNCA needs to make sure
   that higher layer processes and procedures are put in place which
   allow them to detect and mitigate misuses.


13.  Examples

   This section shows example DNCA message content and exchange.

13.1.  DNCA Session Establishment Example

   Figure 15 depicts a typical call flow for DNCA session establishment.

   In this example, the NAT-controller:

   a.  requests a maximum of 100 NAT-bindings for the endpoint.

   b.  defines a static binding for a TCP connection which associates
       the internal IP-Address:Port 192.0.2.1:80 with the external IP-
       Address:Port 198.51.100.1:80 for the endpoint.

   c.  requests the use of a preconfigured template called "local-
       policy" while creating NAT-bindings for the endpoint.

























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   endpoint             NAT-Controller (within NAS)           NAT-device
      |                            |                               |
      |                            |                               |
      |      1. Trigger            |                               |
      |--------------------------->|                               |
      |       +-------------------------------------+              |
      |       |  2. Determine that NAT control      |              |
      |       |     is required for the endpoint   |              |
      |       +-------------------------------------+              |
      |                            |                               |
      |                            |                               |
      |                           ...................................
      |                           .|   3. Diameter Base CER/CEA    |.
      |                           .|<----------------------------->|.
      |                           ...................................
      |                            |                               |
      |                            |                               |
      |                            |         4.  NCR               |
      |                            |------------------------------>|
      |                            |                               |
      |                            |                     5. DNCA session
      |                            |                        established
      |                            |                               |
      |                            |         6.  NCA               |
      |                            |<------------------------------|
      |                            |                               |
      |                            |                               |
      |                  7. Data traffic                           |
      |----------------------------------------------------------->|
      |                            |                               |
      |                            |                               |
      |                            |                    8. NAT Bindings
      |                            |                     created as per
      |                            |                   directives in the
      |                            |                       DNCA session
      |                            |                               |


     Figure 15: Initial NAT control request and session establishment
                                  example

   Detailed description of the steps shown in Figure 15:

   1.  The NAT-controller (co-located with the NAS here) creates state
       for an endpoint based on a trigger.  This could for example be
       the successful establishment of a Point-to-Point Protocol (PPP)
       [RFC1661] access session.




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   2.  Based on the configuration of the DNCA Diameter peer within the
       NAT-controller, the NAT-controller determines that NAT-control is
       required and is to be enforced at a NAT-device.

   3.  If there is no Diameter session already established with the DNCA
       Diameter peer within NAT-device, a Diameter connection is
       established and Diameter Base CER/CEA are exchanged.

   4.  The NAT-Controller creates an NCR message (see below) and sends
       it to the NAT-device.  This example shows IPv4 to IPv4 address
       and port translation.  For IPv6 to IPv4 translation, the Framed-
       IP-Address AVP would be replaced by the Framed-IPv6-Address AVP
       with the value set to the IPv6 address of the endpoint.
     < NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
                      Session-Id =  "natC.example.com:33041;23432;"
                      Auth-Application-Id = <DNCA Application ID>
                      Origin-Host = "natC.example.com"
                      Origin-Realm = "example.com"
                      Destination-Realm = "example.com"
                      Destination-Host = "nat-device.example.com"
                      NC-Request-Type = INITIAL_REQUEST
                      User-Name = "subscriber_example1"
                      Framed-IP-Address = "192.0.2.1"
                      NAT-Control-Install = {
                           NAT-Control-Definition = {
                              Protocol = TCP
                              Direction = OUT
                              NAT-Internal-Address = {
                                   Framed-IP-Address = "192.0.2.1"
                                   Port = 80
                              }
                              NAT-External-Address = {
                                   Framed-IP-Address = "198.51.100.1"
                                   Port = 80
                              }
                           }
                           Max-NAT-Bindings = 100
                           NAT-Control-Binding-Template = "local-policy"
                     }

   5.  The NAT-device establishes a DNCA session as it is able to comply
       with the request.

   6.  The NAT-device sends an NCA to indicate the successful completion
       of the request.






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      <NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
                       Session-Id =  "natC.example.com:33041;23432;"
                       Origin-Host = "nat-device.example.com"
                       Origin-Realm = "example.com"
                       NC-Request-Type = INITIAL_REQUEST
                       Result-Code = DIAMETER_SUCCESS


   7.  The endpoint sends packets that reach the NAT-device.

   8.  The NAT-device performs NAT for traffic received from the
       endpoint with source address 192.0.2.1.  Traffic with source IP-
       address 192.0.2.1 and port 80 are translated to the external IP-
       address 198.51.100.1 and port 80.  Traffic with source IP-address
       192.0.2.1 and a source port different from 80 will be translated
       to IP-address 198.51.100.1 and a port chosen by the NAT-device.
       Note that this example assumes that the NAT-device follows
       typical binding allocation rules for endpoints, in that only a
       single external IP-address is used for all traffic received from
       a single IP-address of an endpoint.  The NAT-device will allow a
       maximum of 100 NAT-bindings be created for the endpoint.

13.2.  DNCA Session Update with Port Style Example

   This section gives an example for a DNCA session update: A new set of
   NAT-bindings is requested for an existing session.  The request
   contains a directive ( the "NAT-External-Port-Style" AVP set to
   FOLLOW_INTERNAL_PORT_STYLE) that directs the NAT-device to maintain
   port-sequence and port-oddity for the newly created NAT-bindings.  In
   the example shown, the internal ports are UDP port 1036 and 1037.
   The NAT-device follows the directive selects the external ports
   accordingly.  The NAT-device would for example create a mapping of
   192.0.2.1:1036 to 198.51.100.1:5056 and 192.0.2.1:1037 to
   198.51.100.1:5057, thereby maintaining port oddity (1036->5056,
   1037->5057) and sequence ( the consecutive internal ports 1036 and
   1037 map to the consecutive external ports 5056 and 5057).















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      < NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
                       Session-Id =  "natC.example.com:33041;23432;"
                       Auth-Application-Id = <DNCA Application ID>
                       Origin-Host = "natC.example.com"
                       Origin-Realm = "example.com"
                       Destination-Realm = "example.com"
                       Destination-Host = "nat-device.example.com"
                       NC-Request-Type = UPDATE_REQUEST
                       NAT-Control-Install = {
                           NAT-Control-Definition = {
                               Protocol = UDP
                               Direction = OUT
                               NAT-Internal-Address = {
                                    Framed-IP-Address = "192.0.2.1"
                                    Port = 1035
                               }
                           }
                           NAT-Control-Definition = {
                               Protocol = UDP
                               Direction = OUT
                               NAT-Internal-Address = {
                                    Framed-IP-Address = "192.0.2.1"
                                    Port = 1036
                               }
                           }
                           NAT-External-Port-
                                  Style = FOLLOW_INTERNAL_PORT_STYLE
                       }

13.3.  DNCA Session Query Example

   This section shows an example for DNCA session query for a subscriber
   whose internal IP-Address is 192.0.2.1.
      < NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
                       Auth-Application-Id = <DNCA Application ID>
                       Origin-Host = "natC.example.com"
                       Origin-Realm = "example.com"
                       Destination-Realm = "example.com"
                       Destination-Host = "nat-device.example.com"
                       NC-Request-Type = QUERY_REQUEST
                       Framed-IP-Address = "192.0.2.1"

   The NAT-device constructs an NCA to report all currently active NAT-
   bindings whose internal address is 192.0.2.1.







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      <NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
                    Origin-Host = "nat-device.example.com"
                    Origin-Realm = "example.com"
                    NC-Request-Type = QUERY_REQUEST
                    NAT-Control-Definition = {
                            Protocol = TCP
                            Direction = OUT
                            NAT-Internal-Address = {
                                Framed-IP-Address = "192.0.2.1"
                                Port = 80
                               }
                            NAT-External-Address = {
                                 Framed-IP-Address = "198.51.100.1"
                                 Port = 80
                               }
                            Session-Id = "natC.example.com:33041;23432;"
                    }
                    NAT-Control-Definition = {
                            Protocol = TCP
                            Direction = OUT
                            NAT-Internal-Address = {
                                Framed-IP-Address = "192.0.2.1"
                                Port = 1036
                               }
                            NAT-External-Address = {
                                 Framed-IP-Address = "198.51.100.1"
                                 Port = 5056
                               }
                            Session-Id = "natC.example.com:33041;23432;"
                    }
                    NAT-Control-Definition = {
                            Protocol = TCP
                            Direction = OUT
                            NAT-Internal-Address = {
                                Framed-IP-Address = "192.0.2.1"
                                Port = 1037
                               }
                            NAT-External-Address = {
                                 Framed-IP-Address = "198.51.100.1"
                                 Port = 5057
                               }
                            Session-Id = "natC.example.com:33041;23432;"
                    }

13.4.  DNCA Session Termination Example

   In this example the NAT-controller decides to terminate the
   previously established DNCA session.  This could for example be the



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   case as a result of an access session (e.g. a PPP session) associated
   with an endpoint been torn down.

       NAT-Controller                            NAT-device
             |                                       |
             |                                       |
    +--------------+                                 |
    |  1. Trigger  |                                 |
    +--------------+                                 |
             |                                       |
             |                                       |
             |             2.  STR                   |
             |-------------------------------------->|
             |                                       |
             |                             3. DNCA session
             |                                   lookup
             |             4.  ACR                   |
             |<--------------------------------------|
             |                                       |
             |             5.  ACA                   |
             |-------------------------------------->|
             |                                       |
             |                                       |
             |                             6. DNCA bindings
             |                            and session cleanup
             |                                       |
             |             7.  STA                   |
             |<--------------------------------------|
             |                                       |

            Figure 20:  NAT control session termination example

   The following steps describe the sequence of events for tearing down
   the DNCA session in the example above:

   1.  The NAT-controller receives a trigger that a DNCA session
       associated with a specific endpoint should be terminated.  An
       example event could be the termination of the PPP [RFC1661]
       access session to an endpoint in a NAS.  The NAS correspondingly
       triggers the NAT-controller request tear-down of the associated
       DNCA session.

   2.  The NAT-controller creates the required NCR message and sends it
       to the NAT-device:







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      < STR >     ::= < Diameter Header: 275, REQ, PXY>
                       Session-Id =  "natC.example.com:33041;23432;"
                       Auth-Application-Id = <DNCA Application ID>
                       Origin-Host = "natC.example.com"
                       Origin-Realm = "example.com"
                       Destination-Realm = "example.com"
                       Destination-Host = "nat-device.example.com"
                       Termination-Cause = DIAMETER_LOGOUT

   3.  The NAT-device looks up the DNCA session based on the Session-Id
       AVP and finds a previously established active session.

   4.  The NAT-device reports all NAT-bindings established for that
       subscriber using an ACR:
      < ACR >     ::= < Diameter Header: 271, REQ, PXY>
                       Session-Id =  "natC.example.com:33041;23432;"
                       Auth-Application-Id = <DNCA Application ID>
                       Origin-Host = "nat-device.example.com"
                       Origin-Realm = "example.com"
                       Destination-Realm = "example.com"
                       Destination-Host = "natC.example.com"
                       Accounting-Record-Type = STOP_RECORD
                       Accounting-Record-Number = 1
                       NAT-Control-Record = {
                           NAT-Control-Definition = {
                               Protocol = TCP
                               Direction = OUT
                               NAT-Internal-Address = {
                                   Framed-IP-Address = "192.0.2.1"
                                   Port = 5001
                                  }
                               NAT-External-Address = {
                                    Framed-IP-Address = "198.51.100.1"
                                    Port = 7777
                                  }
                              }
                             NAT-Control-Binding-Status = Removed
                          }


   5.  The NAT-controller receives and processes the ACR as per its
       configuration.  It responds with an ACA to the NAT-device.









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      <ACA>      ::= < Diameter Header: 271, PXY >
                       Session-Id =  "natC.example.com:33041;23432;"
                       Origin-Host = "natC.example.com"
                       Origin-Realm = "example.com"
                       Result-Code = DIAMETER_SUCCESS
                       Accounting-Record-Type = STOP_RECORD
                       Accounting-Record-Number = 1


   6.  On receipt of the ACA the NAT-device cleans up all NAT-bindings
       and associated session state for the endpoint.

   7.  NAT-device sends an STA.  On receipt of the STA the NAT-
       controller will clean up the corresponding session state.
      <STA>      ::= < Diameter Header: 275, PXY >
                       Session-Id =  "natC.example.com:33041;23432;"
                       Origin-Host = "nat-device.example.com"
                       Origin-Realm = "example.com"
                       Result-Code = DIAMETER_SUCCESS


14.  Acknowledgements

   The authors would like to thank Jari Arkko, Wesley Eddy, Stephen
   Farrell, Miguel A. Garcia, David Harrington, Jouni Korhonen, Matt
   Lepinski, Avi Lior, Chris Metz, Pallavi Mishra, Lionel Morand, Robert
   Sparks, Martin Stiemerling, Dave Thaler, Hannes Tschofenig, Sean
   Turner, Shashank Vikram, Greg Weber, and Glen Zorn for their input on
   this document.


15.  Change History (to be removed prior to publication as an RFC)

   Changes from -00 to -01

   a.  new values for Result-Code AVP used - instead of Experimental-
       Result AVP

   b.  added support for transport specific binding (UDP/TCP)

   c.  added support for twice-NAT

   d.  clarified the use of the two different types of query-requests

   Changes from -01 to -02






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   a.  Reference to pull mode removed, session initiation event
       clarified in section 4.1

   b.  added Redirect-* AVPs in NCA command

   c.  Removed reference to Called-Station-Id AVP in NCR command

   d.  Editorial changes

   e.  added support for bindings providing AFT (NAT64)

   Changes from -02 to -03

   a.  Editorial changes

   Changes from -03 to -04

   a.  Editorial changes suggested in WG last call review

   b.  Removed NCR Request type terminate and replaced with STR

   c.  All references to Auth-Session-State are removed and a new
       section to describe FSM for Manager and Agent has been added

   d.  Clarified reuse of External address and address pools among
       multiple subscribers

   Changes from -04 to -05

   a.  Removed references to Large Scale NAT as per review comments

   Changes from -05 to -06

   a.  Editorial changes

   Changes from -06 to -07

   a.  Added a note in section 4.3 stating the state of pre-existing
       bindings on update failure

   b.  Security considerations are made consistent between sections 5.1
       and 12

   c.  Editorial changes

   Changes from -07 to -08





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   a.  Added section 4.6 to describe session abort

   b.  Editorial changes

   c.  Nomenclature change: From DNCA Agent/Manager to DNCA Diameter
       peers identifying the location where they reside (NAT-controller
       or NAT-device)

   d.  IANA consideration Section format changes

   e.  Updated security section (included considerations directly,
       rather than referring to Diameter QoS similarities).

   Changes from -08 to -09

   a.  expanded on the need for an SP controlling the maximum number of
       bindings of an endpoint (see introduction section)

   b.  added a paragraph in the security section outlining general mis-
       uses of NAT-control (non specific to DNCA), with DNCA being an
       example of such a NAT-control protocol

   c.  editorial changes

   Changes from -09 to -10

   a.  Section 4 and security considerations updated with RFC 2119
       language

   b.  NAT-External-Port-Style AVP added to aid external port oddity
       requirement as per MIDCOM framework

   c.  NAT related RFCs added in normative reference

   d.  Section 13 added to provide example DNCA message exchange flows

   e.  Added a description to provide DNCA comparison with MIDCOM

   f.  n:1 deployment model for NAT-controllers and NAT-devices
       explicitly specified

   g.  editorial changes as per IESG DISCUSS comments

   Changes from -10 to -11

   a.  clarified DNCA session query to be done after Diameter session is
       established




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   b.  Section 4.4 Session Termination updated to specify resource
       cleanup at NAT-Device upon session termination

   c.  Removed Framed-IP-Netmask AVP from NAT-External-Address as
       external address is fully defined by Framed-IP-Address AVP

   d.  Updated Section 12 to highlight Session-Id to be chosen such that
       it is hard to guess

   e.  editorial changes as per IESG DISCUSS

   Changes from -11 to -12

   a.  endpoint replaces references to end point and user and defines
       what Endpoint means in this draft

   b.  editorial changes as per IESG DISCUSS

   Changes from -12 to -13

   a.  Section 4.3 session query updated to use NAT-External-Address for
       external IP-address based query

   Changes from -13 to -14

   a.  Added NAT-External-Address in NC-request for session query by
       external IP-address

   b.  Reordered all mandatory AVPs in NCR and NCA to appear before
       optional AVPs

   Changes from -14 to -15

   a.  As part of IESG discuss - clarified that multiple methods if used
       along with DNCA for NAT control should be configured to prevent
       conflict.

   b.  Clarified misuse of NAT-device by a Diameter authorized NAT-
       controller using DNCA is beyond the scope of this protocol
       specification.

   c.  Editorial updates.

   Changes from -15 to -16

   a.  Extended section covering case of a single NAT-device controlled
       by multiple NAT-ontrollers which use different protocols for
       configuring the NAT-device.



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   b.  Added NAT-device state cleanup in case of unexpected/unplanned
       termination of Diameter session or application either on NAT-
       controller or NAT-device.

   c.  Added MAX_BINDINGS_SET_FAILURE failure case (for those scenarios
       where the maximum number of bindings cannot be set by the
       controller)


16.  References

16.1.  Normative References

   [ETSIES283034]
              ETSI, "Telecommunications and Internet Converged Services
              and Protocols for Advanced Networks (TISPAN),Network
              Attachment Sub-System (NASS),e4 interface based on the
              Diameter protocol.", September 2008.

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

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC4005]  Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
              "Diameter Network Access Server Application", RFC 4005,
              August 2005.

   [RFC4675]  Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Attributes
              for Virtual LAN and Priority Support", RFC 4675,
              September 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5777]  Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,
              and A. Lior, "Traffic Classification and Quality of
              Service (QoS) Attributes for Diameter", RFC 5777,
              February 2010.

16.2.  Informative References

   [I-D.ietf-behave-lsn-requirements]
              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common requirements for Carrier Grade NATs
              (CGNs)", draft-ietf-behave-lsn-requirements-05 (work in



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              progress), November 2011.

   [RFC1661]  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
              RFC 1661, July 1994.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC3303]  Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and
              A. Rayhan, "Middlebox communication architecture and
              framework", RFC 3303, August 2002.

   [RFC3304]  Swale, R., Mart, P., Sijben, P., Brim, S., and M. Shore,
              "Middlebox Communications (midcom) Protocol Requirements",
              RFC 3304, August 2002.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4097]  Barnes, M., "Middlebox Communications (MIDCOM) Protocol
              Evaluation", RFC 4097, June 2005.

   [RFC5189]  Stiemerling, M., Quittek, J., and T. Taylor, "Middlebox
              Communication (MIDCOM) Protocol Semantics", RFC 5189,
              March 2008.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              RFC 6241, June 2011.




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Authors' Addresses

   Frank Brockners
   Cisco
   Hansaallee 249, 3rd Floor
   DUESSELDORF, NORDRHEIN-WESTFALEN  40549
   Germany

   Email: fbrockne@cisco.com


   Shwetha Bhandari
   Cisco
   Cessna Business Park, Sarjapura Marathalli Outer Ring Road
   Bangalore, KARNATAKA 560 087
   India

   Email: shwethab@cisco.com


   Vaneeta Singh
   18, Cambridge Road
   Bangalore 560008
   India

   Email: vaneeta.singh@gmail.com


   Victor Fajardo
   Telcordia Technologies
   1 Telcordia Drive #1S-222
   Piscataway, NJ 08854
   USA

   Email: vf0213@gmail.com
















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