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rfc:rfc6736

Internet Engineering Task Force (IETF) F. Brockners Request for Comments: 6736 S. Bhandari Category: Standards Track Cisco ISSN: 2070-1721 V. Singh

                                                            V. Fajardo
                                                Telcordia Technologies
                                                          October 2012
 Diameter Network Address and Port Translation Control Application

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 Authentication, Authorization,
 and Accounting (AAA) and policy control capabilities with a Network
 Address Translator and Network Address and Port Translator 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 is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6736.

Brockners, et al. Standards Track [Page 1] RFC 6736 Diameter NAT Control Application October 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.

Table of Contents

 1. Introduction ....................................................4
 2. Conventions .....................................................6
 3. Deployment Framework ............................................7
    3.1. Deployment Scenario ........................................7
    3.2. Diameter NAPT Control Application Overview .................9
    3.3. Deployment Scenarios for DNCA .............................10
 4. DNCA Session Establishment and Management ......................12
    4.1. Session Establishment .....................................13
    4.2. Session Update ............................................16
    4.3. Session and Binding Query .................................18
    4.4. Session Termination .......................................20
    4.5. Session Abort .............................................21
    4.6. Failure Cases of the DNCA Diameter Peers ..................22
 5. Use of the Diameter Base Protocol ..............................23
    5.1. Securing Diameter Messages ................................23
    5.2. Accounting Functionality ..................................24
    5.3. Use of Sessions ...........................................24
    5.4. Routing Considerations ....................................24
    5.5. Advertising Application Support ...........................24
 6. DNCA Commands ..................................................25
    6.1. NAT-Control-Request (NCR) Command .........................25
    6.2. NAT-Control-Answer (NCA) Command ..........................26
 7. NAT Control Application Session State Machine ..................26
 8. DNCA AVPs ......................................................29
    8.1. Reused Base Protocol AVPs .................................29
    8.2. Additional Result-Code AVP Values .........................30
         8.2.1. Success ............................................30
         8.2.2. Transient Failures .................................30
         8.2.3. Permanent Failures .................................31

Brockners, et al. Standards Track [Page 2] RFC 6736 Diameter NAT Control Application October 2012

    8.3. Reused NASREQ Diameter Application AVPs ...................32
    8.4. Reused AVPs from RFC 4675 .................................33
    8.5. Reused AVPs from Diameter QoS Application .................33
    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 ............................36
         8.7.3. NAT-Control-Remove AVP .............................37
         8.7.4. NAT-Control-Definition AVP .........................37
         8.7.5. NAT-Internal-Address AVP ...........................38
         8.7.6. NAT-External-Address AVP ...........................38
         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 .......................39
 9. Accounting Commands ............................................40
    9.1. NAT Control Accounting Messages ...........................40
    9.2. NAT Control Accounting AVPs ...............................40
         9.2.1. NAT-Control-Record .................................41
         9.2.2. NAT-Control-Binding-Status .........................41
         9.2.3. Current-NAT-Bindings ...............................41
 10. AVP Occurrence Tables .........................................41
    10.1. DNCA AVP Table for NAT Control Initial and Update
          Requests .................................................42
    10.2. DNCA AVP Table for Session Query Requests ................43
    10.3. DNCA AVP Table for Accounting Messages ...................43
 11. IANA Considerations ...........................................44
    11.1. Application Identifier ...................................44
    11.2. Command Codes ............................................44
    11.3. AVP Codes ................................................44
    11.4. Result-Code AVP Values ...................................44
    11.5. NC-Request-Type AVP ......................................44
    11.6. NAT-External-Port-Style AVP ..............................45
    11.7. NAT-Control-Binding-Status AVP ...........................45
 12. Security Considerations .......................................45
 13. Examples ......................................................47
    13.1. DNCA Session Establishment Example .......................47
    13.2. DNCA Session Update with Port Style Example ..............50
    13.3. DNCA Session Query Example ...............................51
    13.4. DNCA Session Termination Example .........................53
 14. Acknowledgements ..............................................55
 15. References ....................................................55
    15.1. Normative References .....................................55
    15.2. Informative References ...................................56

Brockners, et al. Standards Track [Page 3] RFC 6736 Diameter NAT Control Application October 2012

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 (DoS)
     attacks.  If multiple endpoints share a single public IP address,
     these endpoints can share fate.  If one endpoint would (either
     intentionally, or due to misbehavior, misconfiguration, malware,
     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 [CGN-REQS].
 2.  Supports the allocation of specific NAPT/NAT-bindings.  Two types
     of specific bindings can be distinguished:
  • Allocation of a predefined NAT-binding: The internal and

external IP addresses as well as the 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.

Brockners, et al. Standards Track [Page 4] RFC 6736 Diameter NAT Control Application October 2012

  • Allocation of an external IP address for a given internal IP

address: The allocated external IP address is reported back to

        the requester.  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 be either 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
     classifier or a set of classifiers, such as IP address, Virtual
     Local Area Network (VLAN) identifier, or interface identifier
     that uniquely identify the traffic associated with a particular
     global endpoint.
 With the above capabilities, DNCA qualifies as a Middlebox
 Communications (MIDCOM) protocol [RFC3303], [RFC3304], [RFC5189] for
 middleboxes that perform NAT.  The MIDCOM protocol evaluation
 [RFC4097] evaluated Diameter as a candidate protocol for MIDCOM.
 DNCA provides the extensions to the Diameter base protocol [RFC6733]
 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

Brockners, et al. Standards Track [Page 5] RFC 6736 Diameter NAT Control Application October 2012

 MIDCOM protocol capabilities in that it allows the maintenance of the
 reference to an endpoint representing a user or subscriber in the
 control operation, 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, for example, Simple Network
 Management Protocol (SNMP) [RFC3411] and Network Configuration
 (NETCONF) [RFC6241], which can both be used for device configuration.
 Similarly, DNCA complements existing MIDCOM implementations, offering
 a MIDCOM protocol option for operators with an operational
 environment that is Diameter focused that desire the use of 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 (CLI), SNMP, NETCONF, or Port
 Control Protocol (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 3.2 to 8 cover DNCA specifics, with
 Section 3.2 describing session management, Section 5 the use of the
 Diameter base protocol, Section 6 new commands, Section 8 Attribute
 Value Pairs (AVPs) used, and Section 9 accounting aspects.
 Section 10 presents AVP occurrence tables.  IANA and security
 considerations are addressed in Sections 11 and 12, respectively.

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 and terminology 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.

Brockners, et al. Standards Track [Page 6] RFC 6736 Diameter NAT Control Application October 2012

    NAPT: Network Address and Port Translation, see also [RFC3022].
    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: 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 endpoints, 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 NAPT, 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 endpoint'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 an IPv4 host, associated with a
 subscriber, a user or a group of users.  An endpoint is represented

Brockners, et al. Standards Track [Page 7] RFC 6736 Diameter NAT Control Application October 2012

 by a single access-session on a NAS.  DNCA assumes a 1:1:1
 relationship between an endpoint, the access-session it represents,
 and the associated DNCA 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 [CGN-REQS].  This includes cases like the
 following:
 o  Provisioning static NAT-bindings for particular endpoints
 o  Using different public IP address pools for a 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

Brockners, et al. Standards Track [Page 8] RFC 6736 Diameter NAT Control Application October 2012

                 +---------+
                 |         |
                 |   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  Per-endpoint reporting of the allocated NAT-bindings.

Brockners, et al. Standards Track [Page 9] RFC 6736 Diameter NAT Control Application October 2012

 o  Unique identification of an endpoint on a 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 using either accounting mechanisms or 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 that they would not be unclear about to which NAT controller to
 send accounting information.  Operational considerations MAY require
 an operator to use alternate control mechanisms or protocols such as
 SNMP or manual configuration via a CLI to apply per-endpoint NAT-
 specific configuration, for example, static NAT-bindings.  For these
 cases, the NAT device MUST allow the operator to configure a policy
 on how configuration conflicts are resolved.  Such a policy could
 specify, for example, that manually configured NAT-bindings using the
 CLI 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
 reporting and accounting information from the NAT device.  With this

Brockners, et al. Standards Track [Page 10] RFC 6736 Diameter NAT Control Application October 2012

 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.  It illustrates
 two scenarios: one where an IPv4 host (with a private IPv4 address)
 accesses the IPv4 Internet and another where an IPv6 host accesses
 the IPv4 Internet.

Brockners, et al. Standards Track [Page 11] RFC 6736 Diameter NAT Control Application October 2012

 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 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.  It illustrates
 two scenarios: one where an IPv4 host (with a private IPv4 address)
 accesses the IPv4 Internet and another where an IPv6 host accesses
 the IPv4 Internet.

4. DNCA Session Establishment and Management

 Note that from this section on, there are references to some of the
 commands and AVPs defined for DNCA.  Please refer to Sections 6 and 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,
 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

Brockners, et al. Standards Track [Page 12] RFC 6736 Diameter NAT Control Application October 2012

 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 be due to, for example, 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 the 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 predefined NAT-
 bindings to be established for this endpoint, or a description of the
 address pool, from which external addresses are to be allocated.
 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 the NC-Request-Type AVP set to INITIAL_REQUEST to
 initiate a Diameter NAT control session.  On receipt of an 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 the 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.
 o  The maximum number of NAT-bindings allowed for an endpoint.

Brockners, et al. Standards Track [Page 13] RFC 6736 Diameter NAT Control Application October 2012

 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 from which external IP addresses
    should be allocated, 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 an NCR from
    a DNCA Diameter peer within a NAT controller with the NC-Request-
    Type AVP set to INITIAL_REQUEST that identifies an already
    existing session, that is, the endpoint identifier matches an
    already existing session, the DNCA Diameter peer within the NAT
    device MUST return an NCA with the 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 an NCR from
    a DNCA Diameter peer within a NAT controller with the NC-Request-
    Type AVP set to INITIAL_REQUEST that matches more than one of the
    already existing sessions, that is, the DNCA Diameter peer and
    endpoint identifier match already existing sessions, the DNCA
    Diameter peer within the NAT device MUST return an NCA with the
    Result-Code set to INSUFFICIENT-CLASSIFIERS.  In case a DNCA
    Diameter peer receives an 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 the 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 the Result-Code set to BINDING_FAILURE.  A DNCA Diameter peer
    within a NAT device MUST treat an NCR as an atomic operation;
    hence, none of the requested bindings will be established by the
    NAT device.  Either all requested actions within an NCR MUST be
    completed successfully or the entire request fails.

Brockners, et al. Standards Track [Page 14] RFC 6736 Diameter NAT Control Application October 2012

 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 the 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 the
    Result-Code set to RESOURCE_FAILURE.
 o  In the case where Max-NAT-Bindings, NAT-Control-Definition, and
    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
    that NAT-Control-Binding-Template references, Max-NAT-Bindings and
    NAT-Control-Definition MUST override the values specified in the
    template to which NAT-Control-Binding-Template refers.
 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 the Result-Code set to DIAMETER_SUCCESS.

Brockners, et al. Standards Track [Page 15] RFC 6736 Diameter NAT Control Application October 2012

4.2. Session Update

 A session update is performed if the NAT controller desires to change
 the behavior of the NAT device for an existing session.  A session
 update could be used, for example, to change the number of allowed
 bindings for a particular session or establish or remove a predefined
 binding.
 The DNCA Diameter peer within the NAT controller generates an NCR
 message to the DNCA Diameter peer within the NAT device with the 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 the 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 a DNCA Diameter peer within a NAT device receives an NCR update
    or query request for a non-existent session, it MUST set the
    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 the 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 the 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 the 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 an 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 the Result-Code AVP set to MAX_BINDINGS_SET_FAILURE.

Brockners, et al. Standards Track [Page 16] RFC 6736 Diameter NAT Control Application October 2012

 o  If the NAT device does not have sufficient resources to process a
    request, an NCA with the 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 the 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 the 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-Bindings, NAT-Control-Definition, and 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 that NAT-
    Control-Binding-Template references, Max-NAT-Bindings and NAT-
    Control-Definition MUST override the values specified in the
    template to which the NAT-Control-Binding-Template refers.
 Note: Already established bindings for the session SHOULD NOT be
 affected in case the tasks requested within the NCR cannot be
 completed.

Brockners, et al. Standards Track [Page 17] RFC 6736 Diameter NAT Control Application October 2012

 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 either to retrieve information on the
 current bindings for a particular session at the NAT device or to
 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 an 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

Brockners, et al. Standards Track [Page 18] RFC 6736 Diameter NAT Control Application October 2012

     session using an NCA message with the 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 the 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 an internal IP address or one or multiple external IP
     address/port pairs, it MUST include the internal IP address as
     part of the Framed-IP-Address AVP 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 known in advance by 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.

Brockners, et al. Standards Track [Page 19] RFC 6736 Diameter NAT Control Application October 2012

 NAT controller (DNCA Diameter peer)   NAT device (DNCA Diameter peer)
             |                                           |
             |                                           |
             |                                           |
   DNCA Session Established                              |
             |                                           |
             |                   NCR                     |
             |------------------------------------------>|
             |                                           |
             |                                           |
             |                                           |
             |                                           |
             |                          Look up corresponding session
             |                            and associated NAT-bindings
             |                                           |
             |                   NCA                     |
             |<------------------------------------------|
             |                                           |
             |                                           |
             |                                           |
                        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-Termination-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-Termination-
 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 an STR and fails
 to find a matching session, the DNCA Diameter peer MUST return an STA
 with the Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.

Brockners, et al. Standards Track [Page 20] RFC 6736 Diameter NAT Control Application October 2012

 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 a successful session abort using an Abort-Session-Answer
 (ASA) message with the 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 the 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 the
 Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.  If the DNCA Diameter

Brockners, et al. Standards Track [Page 21] RFC 6736 Diameter NAT Control Application October 2012

 peer within the NAT controller is unable to comply with the ASR for
 any other reason, an ASA with the 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 the 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 a Result-Code that contains a 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-Termination-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 the Result-Code set to

Brockners, et al. Standards Track [Page 22] RFC 6736 Diameter NAT Control Application October 2012

       DIAMETER_UNKNOWN_SESSION_ID in response.  On receiving the
       response, the DNCA Diameter peer SHOULD clear the session and
       remove associated session state.
 o  The NAT device and the DNCA Diameter peer within NAT device lose
    state.  In such a case, the DNCA Diameter peer MAY receive an NCR
    with the NC-Request-Type AVP set to UPDATE_REQUEST for a non-
    existent session.  The DNCA Diameter peer MUST return an NCA with
    the Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.  When a DNCA
    application within a NAT controller receives this NCA with the
    Result-Code set to DIAMETER_UNKNOWN_SESSION_ID, it MAY try to re-
    establish DNCA session or disconnect corresponding access session.
 o  The DNCA Diameter peer within the NAT controller is unreachable,
    for example, it is detected by Diameter device watchdog messages
    (as defined in Section 5.5 of [RFC6733]) 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 the 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 used for a NAT device to clean 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 that require periodic
    refresh, or time out otherwise, operating system watchdogs for
    applications, etc.

5. Use of the Diameter Base Protocol

 The Diameter base protocol [RFC6733] applies with the clarifications
 listed in the present specification.

5.1. Securing Diameter Messages

 For secure transport of Diameter messages, the recommendations in
 [RFC6733] apply.
 DNCA Diameter peers SHOULD verify their identity during the
 Capabilities Exchange Request procedure.

Brockners, et al. Standards Track [Page 23] RFC 6736 Diameter NAT Control Application October 2012

 A DNCA Diameter peer within the NAT device SHOULD verify that a DNCA
 Diameter peer that issues an 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 (the accounting session state machine,
 related Command Codes and AVPs) is defined in Section 9.

5.3. Use of Sessions

 Each DNCA session MUST have a globally unique Session-Id, as defined
 in [RFC6733], which MUST NOT be changed during the lifetime of the
 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 time.  A
 DNCA Diameter peer sends an Abort-Session-Request as defined in
 [RFC6733] 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 12 in the Auth-
 Application-Id of the Capabilities-Exchange-Request and Capabilities-
 Exchange-Answer commands [RFC6733].

Brockners, et al. Standards Track [Page 24] RFC 6736 Diameter NAT Control Application October 2012

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 330 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, and Calling-Station-ID AVPs serve as identifiers for
 the endpoint.
 Message format:
    < NC-Request > ::= < Diameter Header: 330, 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 ]

Brockners, et al. Standards Track [Page 25] RFC 6736 Diameter NAT Control Application October 2012

6.2. NAT-Control-Answer (NCA) Command

 The NAT-Control-Answer (NCA) command, indicated by the Command Code
 field set to 330 and the 'R' bit cleared in the Command Flags field,
 is sent by the DNCA Diameter peer within the NAT device in response
 to the NAT-Control-Request command.
 Message format:
    <NC-Answer> ::= < Diameter Header: 330, 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
 [RFC6733].  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 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

Brockners, et al. Standards Track [Page 26] RFC 6736 Diameter NAT Control Application October 2012

 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 or 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.
           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

Brockners, et al. Standards Track [Page 27] RFC 6736 Diameter NAT Control Application October 2012

    Open      NAT control                    Send        Open
              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

Brockners, et al. Standards Track [Page 28] RFC 6736 Diameter NAT Control Application October 2012

    Idle      NCR request                    Send       Idle
              received, and                  failed
              unable to provide requested    NCA
              NAT control service
    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 the Diameter base
 protocol [RFC6733]; their AVP Code values, types, and possible flag
 values and whether the AVP MAY be encrypted.  [RFC6733] specifies the
 AVP Flag rules for AVPs in Section 4.5.  The Diameter AVP rules are
 defined in [RFC6733], Section 4.

Brockners, et al. Standards Track [Page 29] RFC 6736 Diameter NAT Control Application October 2012

                                                 +---------+
                                                 |  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 from the Diameter Base Protocol
 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 12.  Please refer to [RFC6733]
 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.

Brockners, et al. Standards Track [Page 30] RFC 6736 Diameter NAT Control Application October 2012

 The following new values of the Result-Code AVP are defined:
    RESOURCE_FAILURE (4014)
       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 (5042)
       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,
       which refers to a predefined policy template in the NAT device,
       is unknown.
    BINDING_FAILURE (5043)
       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 (5044)
       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 that takes precedence over DNCA.
    MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT (5045)
       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.

Brockners, et al. Standards Track [Page 31] RFC 6736 Diameter NAT Control Application October 2012

    SESSION_EXISTS (5046)
       The DNCA Diameter peer within the NAT device denies a 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 (5047)
       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 [RFC6733] specifies the AVP Flag rules for AVPs in
 Section 4.5.  The Diameter AVP rules are defined in the [RFC6733],
 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
 [RFC6733] for the definition of the Diameter AVP Flag rules and the
 associated abbreviations used in the table.

Brockners, et al. Standards Track [Page 32] RFC 6736 Diameter NAT Control Application October 2012

8.4. Reused AVPs from RFC 4675

 The following table describes the AVPs reused from "RADIUS Attributes
 for Virtual LAN and Priority Support" [RFC4675]; their AVP Code
 values, types, and possible flag values; and whether the AVP MAY be
 encrypted.  [RFC6733] specifies the AVP Flag rules for AVPs in
 Section 4.5.  The Diameter AVP rules are defined in [RFC6733],
 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 [RFC4675].  Please refer to [RFC6733]
 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.  [RFC6733] specifies the AVP
 Flag rules for AVPs in Section 4.5.  The Diameter AVP rules are
 defined in [RFC6733], 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 [RFC6733] for the
 definition of the Diameter AVP Flag rules and the associated
 abbreviations used in the table.

Brockners, et al. Standards Track [Page 33] RFC 6736 Diameter NAT Control Application October 2012

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.
 [RFC6733] specifies the AVP Flag rules for AVPs in Section 4.5.  The
 Diameter AVP rules are defined in [RFC6733], Section 4.  The
 Vendor-ID field in these AVP header will be set to ETSI (13019).
                                                 +---------+
                                                 |  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 the Diameter e4 application.  Please refer
 to [RFC6733] for the definition of the Diameter AVP Flag rules and
 the associated abbreviations used in the table.

Brockners, et al. Standards Track [Page 34] RFC 6736 Diameter NAT Control Application October 2012

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.  [RFC6733] specifies the AVP Flag
 rules for AVPs in Section 4.5.  The Diameter AVP rules are defined in
 [RFC6733], Section 4.  The AVPs defined here MUST NOT have the 'V'
 bit in the AVP Flags field set.
                                                    +---------+
                                                    |  AVP    |
                                                    |  Flag   |
                                                    |  Rules  |
 +--------------------------------------------------|-----+---+------+
 |                       AVP                        |     |   |      |
 | Attribute Name        Code    Sect.   Data Type  |MUST |MAY| Encr |
 +--------------------------------------------------+-----+---+------+
 |NC-Request-Type        595     8.7.1   Enumerated | M   | P |  Y   |
 |NAT-Control-Install    596     8.7.2   Grouped    | M   | P |  Y   |
 |NAT-Control-Remove     597     8.7.3   Grouped    | M   | P |  Y   |
 |NAT-Control-Definition 598     8.7.4   Grouped    | M   | P |  Y   |
 |NAT-Internal-Address   599     8.7.5   Grouped    | M   | P |  Y   |
 |NAT-External-Address   600     8.7.6   Grouped    | M   | P |  Y   |
 |Max-NAT-Bindings       601     8.7.7   Unsigned32 | M   | P |  Y   |
 |NAT-Control-           602     8.7.8   OctetString| M   | P |  Y   |
 | Binding-Template                                 |     |   |      |
 |Duplicate-             603     8.7.9   UTF8String | M   | P |  Y   |
 | Session-Id                                       |     |   |      |
 |NAT-External-Port-     604     8.7.10  Enumerated | M   | P |  Y   |
 | Style                                            |     |   |      |
 |NAT-Control-Record     605     9.2.1   Grouped    | M   | P |  Y   |
 |NAT-Control-           606     9.2.2   Enumerated | M   | P |  Y   |
 | Binding-Status                                   |     |   |      |
 |Current-NAT-Bindings   607     9.2.3   Unsigned32 | M   | P |  Y   |
 +--------------------------------------------------+-----+---+------+
 Table 6: New Diameter AVPs.  Please refer to [RFC6733] for the
 definition of the Diameter AVP Flag rules and the associated
 abbreviations used in the table.

Brockners, et al. Standards Track [Page 35] RFC 6736 Diameter NAT Control Application October 2012

8.7.1. NC-Request-Type AVP

 The NC-Request-Type AVP (AVP Code 595) 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
       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-Install AVP (AVP code 596) 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, 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: 596 >
                            * [ NAT-Control-Definition ]
                              [ NAT-Control-Binding-Template ]
                              [ Max-NAT-Bindings ]
                              [ NAT-External-Port-Style ]
                            * [ AVP ]

Brockners, et al. Standards Track [Page 36] RFC 6736 Diameter NAT Control Application October 2012

8.7.3. NAT-Control-Remove AVP

 The NAT-Control-Remove AVP (AVP code 597) 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 or NAT-Control-Binding-Template
 AVP) SHOULD be present in the NAT-Control-Remove AVP.
 AVP format:
   NAT-Control-Remove ::= < AVP Header: 597 >
                           * [ NAT-Control-Definition ]
                             [ NAT-Control-Binding-Template ]
                           * [ AVP ]

8.7.4. NAT-Control-Definition AVP

 The NAT-Control-Definition AVP (AVP code 598) 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 predefined 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 addresses 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.

Brockners, et al. Standards Track [Page 37] RFC 6736 Diameter NAT Control Application October 2012

 AVP format:
   NAT-Control-Definition ::= < AVP Header: 598 >
                               { 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 599) 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.  The
 endpoint identifier Framed-IP-Address, Framed-IPv6-Prefix, and the
 internal address in this NAT-Internal-Address AVP to install NAT-
 bindings for the session MUST match.
 AVP format:
   NAT-Internal-Address ::= < AVP Header: 599 >
                             [ Framed-IP-Address ]
                             [ Framed-IPv6-Prefix ]
                             [ Port]
                           * [ AVP ]

8.7.6. NAT-External-Address AVP

 The NAT-External-Address AVP (AVP code 600) 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 an
 external port as per the NAT-External-Port-Style AVP.
 AVP format:
   NAT-External-Address ::= < AVP Header: 600 >
                             [ Framed-IP-Address ]
                             [ Port ]
                           * [ AVP ]

Brockners, et al. Standards Track [Page 38] RFC 6736 Diameter NAT Control Application October 2012

8.7.7. Max-NAT-Bindings

 The Max-NAT-Bindings AVP (AVP code 601) 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 602) 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 may contain NAT-
 bindings, an IP address pool for allocating the external IP address
 of a NAT-binding, and a maximum number of allowed NAT-bindings.  Such
 a 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 603) is of type UTF8String.
 It is used to report errors and contains the Session-Id of an
 existing session.

8.7.10. NAT-External-Port-Style AVP

 The NAT-External-Port-Style AVP (AVP Code 604) 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
       oddity 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.

Brockners, et al. Standards Track [Page 39] RFC 6736 Diameter NAT Control Application October 2012

9. Accounting Commands

 The DNCA reuses session-based accounting as defined in the Diameter
 base protocol [RFC6733] to report the bindings per endpoint.  This
 reporting is achieved by sending Diameter Accounting-Request (ACR)
 commands [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 an 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 an NCR with NC-
 Request-Type AVP set to UPDATE_REQUEST, 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
 an STR message.
 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.

9.1. NAT Control Accounting Messages

 The ACR and ACA messages are reused as defined in the Diameter base
 protocol [RFC6733] for exchanging endpoint NAT-binding details
 between the DNCA Diameter peers.  The DNCA Application ID is used in
 the accounting commands.  The 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 [RFC6733], the DNCA Diameter
 peer within the NAT device must add the NAT-Control-Record AVP.

Brockners, et al. Standards Track [Page 40] RFC 6736 Diameter NAT Control Application October 2012

9.2.1. NAT-Control-Record

 The NAT-Control-Record AVP (AVP code 605) 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: 605 >
                          { NAT-Control-Definition }
                          { NAT-Control-Binding-Status }
                          [ Event-Timestamp ]

9.2.2. NAT-Control-Binding-Status

 The NAT-Control-Binding-Status AVP (AVP code 606) 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.
    Removed (3)
       NAT-binding was removed.

9.2.3. Current-NAT-Bindings

 The Current-NAT-Bindings AVP (AVP code 607) is of type Unsigned32.
 It indicates the number of NAT-bindings active on the NAT device.

10. AVP Occurrence Tables

 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.

Brockners, et al. Standards Track [Page 41] RFC 6736 Diameter NAT Control Application October 2012

 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 the NC-Request-Type set to INITIAL_REQUEST or
 UPDATE_REQUEST.
                                     +-------------------+
                                     |  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 the NAT-Control-Install AVP nor the NAT-Control-Remove AVP
    is 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.

Brockners, et al. Standards Track [Page 42] RFC 6736 Diameter NAT Control Application October 2012

    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 Requests

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

 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       |
 +-------------------------------------------------------+

Brockners, et al. Standards Track [Page 43] RFC 6736 Diameter NAT Control Application October 2012

11. IANA Considerations

 This section contains either the namespaces that have 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 [RFC5226], 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 12, 'Diameter NAT Control
 Application', to the Application Identifier namespace defined in
 [RFC6733].  See Section 4 for more information.

11.2. Command Codes

 This specification uses the value 330 from the Command code namespace
 defined in [RFC6733] for the NAT-Control-Request (NCR) and 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 595-607 from the AVP Code
 namespace defined in [RFC6733].  See Section 8.7 for the assignment
 of the namespace in this specification.

11.4. Result-Code AVP Values

 This specification assigns the values 4014 and 5042-5047 from the
 Result-Code AVP value namespace defined in [RFC6733].  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].

Brockners, et al. Standards Track [Page 44] RFC 6736 Diameter NAT Control Application October 2012

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
 Diameter peers within a NAT controller and a NAT device as well as
 general considerations for a 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 DoS attack by
 setting the maximum number of bindings for a session on the NAT
 device to zero; provisioning bindings on a NAT device that includes
 IP addresses already in use in other parts of the network; or
 requesting session termination of the Diameter session and hampering
 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, a NAT-binding Predefined template on the
 NAT device could be configured differently than expected by the NAT
 controller.  If either of the two DNCA Diameter peers fail to provide
 the required credentials, the failure should be subject to logging.
 The corresponding logging infrastructure of the operator SHOULD be

Brockners, et al. Standards Track [Page 45] RFC 6736 Diameter NAT Control Application October 2012

 built in a way that it can mitigate potential DoS 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 request 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
 DoS.
 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 [RFC6733],
 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 mechanism 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.

Brockners, et al. Standards Track [Page 46] RFC 6736 Diameter NAT Control Application October 2012

 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 happen due to, e.g., 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
 Diameter protocol exchanges don't prevent such abuses of NAT-control.
 Prevention of misuse or misconfiguration 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 that
 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 does the following:
 a.  requests a maximum of 100 NAT-bindings for the endpoint.
 b.  defines a static binding for a TCP connection that 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.

Brockners, et al. Standards Track [Page 47] RFC 6736 Diameter NAT Control Application October 2012

 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.

Brockners, et al. Standards Track [Page 48] RFC 6736 Diameter NAT Control Application October 2012

 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: 330, 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.

Brockners, et al. Standards Track [Page 49] RFC 6736 Diameter NAT Control Application October 2012

    <NC-Answer> ::= < Diameter Header: 330, 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).

Brockners, et al. Standards Track [Page 50] RFC 6736 Diameter NAT Control Application October 2012

    < NC-Request > ::= < Diameter Header: 330, 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: 330, 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.

Brockners, et al. Standards Track [Page 51] RFC 6736 Diameter NAT Control Application October 2012

    <NC-Answer> ::= < Diameter Header: 330, 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;"
                     }

Brockners, et al. Standards Track [Page 52] RFC 6736 Diameter NAT Control Application October 2012

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
 case as a result of an access session (e.g., a PPP session)
 associated with an endpoint having 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 to tear down the associated
     DNCA session.

Brockners, et al. Standards Track [Page 53] RFC 6736 Diameter NAT Control Application October 2012

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

Brockners, et al. Standards Track [Page 54] RFC 6736 Diameter NAT Control Application October 2012

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

15.1. 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.
 [RFC4005]       Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
                 "Diameter Network Access Server Application",
                 RFC 4005, August 2005.

Brockners, et al. Standards Track [Page 55] RFC 6736 Diameter NAT Control Application October 2012

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

15.2. Informative References

 [CGN-REQS]      Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa,
                 A., and H. Ashida, "Common requirements for Carrier
                 Grade NATs (CGNs)", Work in Progress, September 2012.
 [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.

Brockners, et al. Standards Track [Page 56] RFC 6736 Diameter NAT Control Application October 2012

 [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.

Brockners, et al. Standards Track [Page 57] RFC 6736 Diameter NAT Control Application October 2012

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

Brockners, et al. Standards Track [Page 58]

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