Diameter Network Address and Port Translation Control Application
draft-ietf-dime-nat-control-02

Abstract

This document describes the framework, messages, and procedures for the Diameter Network Address and Port Translation Control Application (DNCA), allowing for per-endpoint control of large scale NAT/NAPT devices, which are put in place to cope with IPv4-address space completion. The DNCA allows external devices to configure and manage a NAT device - expanding the existing Diameter-based AAA and policy control capabilities with a NAT/NAPT control component. These external devices can be network elements in the data plane such as a Network Access Server (NAS), or can be more centralized control plane devices such as AAA-servers. DNCA establishes a context to commonly identify and manage endpoints on a gateway or server, and a large scale NAPT/NAT device. This includes, for example, the control of the total number of NAT-bindings allowed or the allocation of a specific NAT-binding for a particular endpoint. In addition, it allows large scale NAT devices to provide information relevant to accounting purposes.

Status of this Memo

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Table of Contents

1.  Introduction
2.  Conventions
3.  Deployment Framework
    3.1.  Deployment Scenario
    3.2.  Diameter NAPT Control Application Overview
    3.3.  Deployment Scenarios For The Diameter NAPT Control Application
4.  Diameter NAT Control Application Session Establishment and Management
    4.1.  Parties Involved
    4.2.  Session Establishment
    4.3.  Session Re-Authorization
    4.4.  Session And Binding Query
    4.5.  Session Termination
    4.6.  DNCA Manager/Agent Failures
5.  Use Of The Diameter Base Protocol
    5.1.  Securing Diameter Messages
    5.2.  Accounting Functionality
    5.3.  Use Of Sessions
    5.4.  Routing Considerations
    5.5.  Advertising Application Support
6.  Diameter NAT Control Application Commands
    6.1.  NAT-Control Request (NCR) Command
    6.2.  NAT-Control Answer (NCA) Command
7.  Diameter NAT Control Application AVPs
    7.1.  Reused Base Protocol AVPs
    7.2.  Additional Result-Code AVP Values
        7.2.1.  Success
        7.2.2.  Transient Failures
        7.2.3.  Permanent Failures
    7.3.  Reused NASREQ Diameter Application AVPs
    7.4.  Reused from RFC 4675
    7.5.  Reused from Diameter QoS Application
    7.6.  Reused From ETSI ES 283 034, e4 Diameter Application
    7.7.  Diameter NAT Control Application Defined AVPs
        7.7.1.  NC-Request-Type AVP
        7.7.2.  NAT-Control-Install AVP
        7.7.3.  NAT-Control-Remove AVP
        7.7.4.  NAT-Control-Definition AVP
        7.7.5.  NAT-Internal-Address AVP
        7.7.6.  NAT-External-Address AVP
        7.7.7.  Max-NAT-Bindings
        7.7.8.  NAT-Control-Binding-Rule AVP
        7.7.9.  Duplicate-Session-Id AVP
8.  Accounting Commands
    8.1.  NAT Control Accounting Messages
    8.2.  NAT Control Accounting AVPs
        8.2.1.  NAT-Control-Record
        8.2.2.  NAT-Control-Binding-Status
        8.2.3.  Current-NAT-Bindings
9.  AVP Occurrence Table
    9.1.  DNCA AVP Table for NAT control initial and update requests
    9.2.  DNCA AVP Table for Session Query request
    9.3.  DNCA AVP Table for NAT Control Terminate requests
    9.4.  DNCA AVP Table For Accounting Message
10.  IANA Considerations
    10.1.  Command Codes
    10.2.  AVP Codes
    10.3.  AVP Values
        10.3.1.  Result-Code AVP Values
    10.4.  Application IDs
11.  Security Considerations
12.  Acknowledgements
13.  Change History (to be removed prior to publication as an RFC)
14.  References
    14.1.  Normative References
    14.2.  Informative References
§  Authors' Addresses

1.  Introduction

Internet service providers have started to deploy Network Address Translators (NATs) and Network Address and Port Translators (NAPTs) at the edge of their networks to deal with the depletion of available public IPv4 addresses. This document defines a Diameter application for providers deploying such NATs and NAPT devices. The use of a Diameter application allows for simple integration into the existing AAA environment of a provider.

The Diameter NAPT Control Application (DNCA) offers the following capabilities:

1. Limit/Define the number of NAPT/NAT-bindings made available to an individual subscriber or end point.
2. Support the allocation of specific NAPT/NAT-bindings. Two types of specific bindings can be distinguished:
   • Allocation of a pre-defined NAT-binding. Both the internal as well as the external IP-address/port pair are specified within the request. Some deployment cases, such as access to a web-server within a user’s home network with IP-address and port, benefit from statically configured bindings.
   • Allocation of an external IP-address for a given internal IP-address. The allocated external IP-address will be reported back to the requestor. In some deployment scenarios, the application requires immediate knowledge of the allocated binding for a given internal IP-address but does not control the allocation of the external IP-address (e.g. SIP-proxy server deployments).
3. Define the external address-pool(s) to be used for allocating an external IP-address. External address-pools can either be pre- assigned at the NAPT/NAT, 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 will contain a description of the IP- address pool(s) to be used (e.g. list of IP-subnets).
4. Accounting/Reporting: Report established bindings for a particular user. The collected information is used by accounting systems, for statistical purposes, etc.
5. Query functionality to retrieve details about bindings on demand. This feature complements the previously mentioned accounting functionality mentioned above (see item 4). The query functionality complements alternative information query mechanisms such as SNMP-based mechanisms, if available.
6. Common identification of a subscriber or endpoint on multiple network devices such as the NAPT/NAT device, the AAA server, or the Network Access Server (NAS). Endpoint identification is facilitated through a Global Endpoint ID. Endpoints are identified through a single or a set of classifiers such as IP address, VLAN identifier, or interface identifier which uniquely identify the traffic associated with a particular global endpoint

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

2.  Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

Abbreviations are used in this document:

AAA: Authentication, Authorization, Accounting

DNCA: Diameter NAT Control Application

NAPT: Network Address and Port Translation

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

NAS: Network Access Server

3.  Deployment Framework

3.1.  Deployment Scenario

Figure 1 (Typical network deployment for internet access) shows a typical network deployment for internet access. A user’s IPv4-host gains access to the internet though a Network Access Server (NAS) which facilitates the authentication of the endpoint and configures the user’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.

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

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

Figure 2 (Access network deployment with LSN) depicts the deployment scenario when a service provider introduces a NAT device to increase the efficiency of the global IPv4 address pool utilization. The objective is to provide the customer with connectivity to the public IPv4 Internet. The NAT device performs network address (and optionally protocol) translation, depending on whether the access network uses private IPv4 addresses or public IPv6 addresses, to public IPv4 addresses. If the NAT device would be put in place without any endpoint awareness, the service offerings of the service provider would be hampered. Provisioning static NAT-bindings for particular endpoints, using different public IP-address pools for different set of endpoints (e.g. residential or business customers), as well as reporting on the allocated bindings on a per-endpoint basis would be burdensome for a service provider if the NAT device would not be aware of endpoints and allow for per-endpoint control and management which easily integrates with the already existing per-endpoint management infrastructure of the service provider.

                +---------+
                |         |
                |   AAA   |
                |         |
                +---------+
                     |
                     |
                     |
                     |
  +--------+    +---------+    +---------+    +----------+
  |  IPv4  |    |         |    |         |    |  IPv4    |
  |  Host  |----|   NAS   |----|   NAT   |----| Internet |
  |        |    |         |    |         |    |          |
  +--------+    +---------+    +---------+    +----------+
  <-------- Private IPv4 -----------><--- Public IPv4 --->
  <-------- Public  IPv6 -----------><--- Public IPv4 --->

3.2.  Diameter NAPT Control Application Overview

The Diameter NAT Control Application runs between a Diameter NAT Control Application Agent on the NAT and the Diameter NAT Control Application Manager. DNCA allows for per-endpoint control and management of a NAT. Being 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 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, to provide per endpoint reporting on the allocated NAT-bindings, as well as to provide for unique identification of an endpoint on both NAT, AAA-server and NAS, thus simplifying the correlation of accounting data streams.

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

3.3.  Deployment Scenarios For The Diameter NAPT Control Application

Deployment dependent, the role of the Diameter NAT Control Manager can be fulfilled by either the NAS or by an external server such as an AAA-server. The two deployment scenarios are outlined in Figure 3 (LSN Control deployment: Integrated deployment) (“integrated deployment”) and Figure 4 (LSN Control deployment: Autonomous deployment) (“autonomous deployment”).

Within the figures (M) denotes the network element which takes on the DNCA manager role. Similarly, (A) identifies the network element which performs the DNCA agent role.

The integrated deployment approach hides the existence of the NAT device from external servers such as the AAA-server as much as possible. It is suited for environments where minimal changes to the existing AAA deployment are desired. The NAS, taking the role of the DNCA manager, is in charge of initiating and managing the session to the NAT device, exchanging NAT specific configuration information as well as handling reporting and accounting information. The NAS receives reporting and accounting information from NAT device. This way the NAS can provide for a single accounting record for the user, offloading external accounting systems from correlating accounting information received from multiple sources.

An example network attachment for an integrated NAT deployment could be described as follows: An endpoint connects to the network, with the NAS being the point of attachment. After successful authentication, 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. NAS will initiate a DNCA session to the NAT and send the relevant authorization and configuration information for the particular endpoint to the NAT device. This could comprise e.g. 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 or accounting requirements. The NAT device will send its per-endpoint accounting information to the NAS which aggregates the accounting information received form the NAT with its local accounting information for the endpoint into a single accounting stream towards the AAA-server.

                +---------+
                |         |
                |   AAA   |
                |         |
                +---------+
                     |
                     |
                     |
  +--------+    +---------+    +---------+    +----------+
  |  IPv4  |    |   (M)   |    |   (A)   |    |  IPv4    |
  |  Host  |----|   NAS   |----|   NAT   |----| Internet |
  |        |    |         |    |         |    |          |
  +--------+    +---------+    +---------+    +----------+
  <-------- Public  IPv6 ----------><--- Public IPv4 ---->
  <-------- Private IPv4 ----------><--- Public IPv4 ---->

The autonomous deployment approach decouples user management on NAS and NAT device. The AAA system performing the role of the DNCA manager manages the connection to the NAT device, controls the per-endpoint configuration, and also receives accounting and reporting information from the NAT device. Different from the integrated deployment scenario, the autonomous deployment scenario does not “hide” the existence of the NAT device from the AAA infrastructure. Here two accounting streams are received by the AAA-server for one particular endpoint, one from the NAS, and one from the NAT device.

                  +---------+
                  |   (M)   |
                  |   AAA   |
                  |         |
                  +---------+
                       |
                       |
                       |
    +--------+    +---------+    +---------+    +----------+
    |  IPv4  |    |         |    |   (A)   |    |  IPv4    |
    |  Host  |----|   NAS   |----|   NAT   |----| Internet |
    |        |    |         |    |         |    |          |
    +--------+    +---------+    +---------+    +----------+
    <-------- Public  IPv6 ----------><---- Public IPv4 --->
    <-------- Private IPv4 ----------><---- Public IPv4 --->

4.  Diameter NAT Control Application Session Establishment and Management

Note that this section forward references some of the commands and AVPs defined for the DNCA. Please refer to Section 6 (Diameter NAT Control Application Commands) and Section 7 (Diameter NAT Control Application AVPs) for details.

4.1.  Parties Involved

Authorization and control models supported by this application include the following parties:

• Diameter NAT Control Application (DNCA) agent: The DNCA agent is part of the Large scale NAT (NAT) device
• Diameter NAT Control Application (DNCA) manager

The NAT control requesting entity is always the DNCA manager. Sessions will always be initiated, updated, or terminated by the DNCA manager. This mode of operation is sometimes also referred to as "push mode".

DNCA manager can be NAS or AAA Server. DNCA manager will initiate a session with DNCA agent when it learns about the subscriber. DNCA manager may learn about a subscriber when it receives authentication, authorization or accounting request for that subscriber or by some other means such as on the box configuration to identify subscriber w.r.t IP packets.

4.2.  Session Establishment

The DNCA manager establishes a session to the DNCA agent to control the behavior of the NAT device. During session establishment, the DNCA manager will pass along configuration information to the DNCA agent. Session configuration information could for example comprise the maximum number of bindings allowed for the endpoint associated with this session, a set of pre-defined NAT-bindings to be established for this endpoint, or a description of the address pool, external addresses should be allocated from.

The DNCA manager initiates the Diameter NAT Control session to the DNCA agent. The DNCA manager generates a NAT-Control Request (NCR) message to the DNCA agent with NC-Request-Type AVP set to INITIAL_REQUEST. On receipt of the NCR the DNCA agent will setup a new session for the endpoint associated with the endpoint classifier(s) contained in the NCR. The DNCA agent notifies the DNCA manager about successful session setup using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 5 (Initial NAT Control request and session establishment ) shows the protocol interaction between the DNCA manager and the DNCA agent.

The initial NAT-Control-Request can contain configuration information for the session which specifies the behavior of the NAT for the session. Configuration information which can be included comprises:

• A list of NAT-bindings which should be pre-allocated for the session (e.g. in case a subscriber requires a fixed external IP- address/port pair for one of his applications).
• The maximum number of NAT bindings allowed for an endpoint.
• A description of the external address pool(s) to be used for the session.
• A reference to a predefined binding rule on DNCA agent that will be applied to the session. Such a predefined binding rule on DNCA agent may contain, for example, the name of the IP-address pool that external IP-addresses should be allocated from, maximum number of bindings permitted for the endpoint etc.

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

• If a DNCA agent receives a NCR from a DNCA manager with NC- Request-Type AVP set to INITIAL_REQUEST that identifies an already existing session (i.e. DNCA manager and endpoint identifier match an already existing session), the DNCA agent will return NCA with Result-Code set to SESSION_EXISTS, and provides Session-Id of the existing session in Duplicate-Session-Id AVP.
• If a DNCA agent receives an NCR from a DNCA manager with NC- Request-Type AVP set to INITIAL_REQUEST that matches more than one of the already existing sessions (i.e. DNCA manager and endpoint identifier match already existing sessions), the DNCA agent will return a NCA with Result-Code set to Insufficient-Classifiers. In case a DNCA manager receives a NCA that reports Insufficient-Classifiers, it may choose to retry establishing a new session using additional/more specific classifiers.
• If the NCR contains a binding rule not defined on the NAT, the DNCA agent will return a NCA with Result-Code AVP set to UNKNOWN_BINDING_RULE.
• In case the DNCA agent is unable to establish all of the bindings requested in the NCR, it will return a NCA with Result-Code set to BINDING_FAILURE. The DNCA agent (i.e. NAT) treats a NCR as an atomic operation; hence none of the requested bindings will be established by NAT. Either all requested actions within a NCR are completed successfully, or the entire request fails.
• If DNCA agent does not have sufficient resources to process a request, it will return NCA with Result-Code set to RESOURCE_FAILURE.
• In case Max-NAT-Binding and Nat-Control-Definition are included in the NCR along with a reference to a binding rule (i.e. a predefined template on NAT) and the values in Max-NAT-Binding and NAT-Control-Definition contradict those specified in the pre- defined binding rule, Max-NAT-Binding and NAT-Control-Definition override the values specified in the binding rule.

         DNCA Manager                             DNCA Agent
            |                                           |
            |                                           |
            |                                           |
         Trigger                                        |
            |                                           |
            |                   NCR                     |
            |------------------------------------------>|
            | (INITIAL_REQUEST, endpoint classifier,    |
            |     session id, NAT control config data)  |
            |                                           |
            |                                           |
            |                                  Create session state
            |                                           |
            |                                           |
            |                     NCA                   |
            |<------------------------------------------|
            |                 (result code)             |
            |                                           |
            |                                           |

4.3.  Session Re-Authorization

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

The DNCA manager generates a NAT-Control Request (NCR) message to the DNCA agent with NC-Request-Type AVP set to UPDATE_REQUEST upon receiving a trigger signal. In case the session is updated successfully, the DNCA agent notifies the DNCA manager about successful session update using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 6 (NAT Control request for session update ) shows the protocol interaction between the DNCA manager and the DNCA agent.

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

• If DNCA agent receives a NCR update/query request for non-existent session it will set error code in answer, to DIAMETER_UNKNOWN_SESSION_ID.
• If the NCR contains a binding rule not defined on the NAT, the DNCA agent will return a NCA with Result-Code AVP set to UNKNOWN_BINDING_RULE.
• If the DNCA agent cannot establish the requested binding because the maximum number of allowed bindings has been reached for the Endpoint Classifier, it will return NCA with Result-Code AVP set to MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT.
• In case the DNCA agent cannot establish some or all of the bindings requested in a NCR, but has not yet reached the maximum number of allowed bindings for the subscriber, it will return a NCA with Result-Code set to BINDING_FAILURE. The DNCA agent (i.e. NAT) treats a NCR as an atomic operation; hence none of the requested bindings will be established by NAT. Either all requested actions within a NCR are completed successfully, or the entire request fails.
• If DNCA agent does not have sufficient resources to process a request, it will return a NCA with Result-Code set to RESOURCE_FAILURE.
• If a NCR redefines the maximum number of NAT bindings allowed for the endpoint, the new value will override any previously defined limit on NAT-bindings. It depends on the implementation of the NAT how NAT would cope with a case where the new value is lower than the actual number of allocated bindings. Typically the NAT would refrain from enforcing the new limit immediately (i.e. actively remove bindings) but rather disallow the establishment of new bindings until the current number of bindings is lower than the newly established maximum number of allowed bindings.
• If a NCR specifies a new binding rule, predefined on the DNCA agent, the binding rule will override any previously defined rules for the session.
• In case Max-NAT-Binding and Nat-Control-Definition AVPs are included in the NCR along with a reference to a binding rule (i.e. a predefined template on NAT) and the values in Max-NAT-Binding and Nat-Control-Definition AVPs contradict those specified in the pre-defined binding rule, Max-NAT-Binding and NAT-Control-Definition AVPs override the values specified in the binding rule.

         DNCA Manager                             DNCA Agent
            |                                           |
            |                                           |
            |                                           |
     Change of session                                  |
        attributes                                      |
            |                                           |
            |                   NCR                     |
            |------------------------------------------>|
            |       (UPDATE_REQUEST session id,         |
            |         NAT control config data)          |
            |                                           |
            |                                           |
            |                                  Update session state
            |                                           |
            |                                           |
            |                     NCA                   |
            |<------------------------------------------|
            |                 (result code)             |
            |                                           |
            |                                           |

4.4.  Session And Binding Query

Session query can be used by the DNCA manager to either retrieve information on the current bindings for a particular session at the NAT or discover the session identifier for a particular external IP-address/port pair.

The DNCA manager initiates a session query by sending a NAT-Control Request (NCR) message to the DNCA agent with NC-Request-Type AVP set to QUERY_REQUEST. Figure 7 (Session Query) shows the protocol interaction between the DNCA manager and the DNCA agent.

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 manager retrieve the current set of bindings for a specific session. The second type of query request is used in to retrieve the session identifiers, along with the associated bindings, matching a criteria. This enables the DNCA manager to find out which sessions utilize a specific external IP address.

1. Request a list of currently allocated NAT-bindings for a particular session: The DNCA agent will, on receipt of the NCR, lookup the session information for the session id contained in the NCR, and will report all currently active NAT-bindings for the session using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. In this case the NCR MUST NOT contain a NAT-Control-Definition AVP. Each NAT-Binding will be reported in a NAT-Control-Definition AVP. In case the session id is unknown to the DNCA agent a DIAMETER_UNKNOWN_SESSION_ID error is returned.
2. Retrieve session ids and internal IP-address/port pairs for one or multiple external IP-address/port pairs: If the DNCA manager wishes to retrieve the session id(s) for one or multiple external IP-address/port pairs, it MUST include the external IP-address/port pair(s) as part of the NAT-Control-Definition AVP of the NCR. The session id used within the NCR is not meaningful for this type of a query. The DNCA agent will report the NAT-bindings and associated session ids corresponding to the external IP-address/port pairs in a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS and the same session id as the one used in the NCR. 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.

         DNCA Manager                             DNCA Agent
            |                                           |
            |                                           |
            |                                           |
  DNCA Session Established                              |
            |                                           |
            |                   NCR                     |
            |------------------------------------------>|
            |              (QUERY_REQUEST)              |
            |                                           |
            |                                           |
            |                                           |
            |                          Look up corresponding session
            |                            and associated NAT Bindings
            |                                           |
            |                     NCA                   |
            |<------------------------------------------|
            |                 (result code)             |
            |                                           |
            |                                           |

4.5.  Session Termination

The DNCA manager generates a NAT-Control Request (NCR) message to the DNCA agent with NC-Request-Type AVP set to TERMINATE_REQUEST upon receiving a trigger signal. The DNCA agent sends accounting stop record reporting all the bindings and notifies the DNCA manager about successful session termination using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 8 (Terminate NAT Control session) shows the protocol interaction between the DNCA manager and the DNCA agent.

If a DNCA agent receives a NCR from a DNCA manager with NC-Request-Type AVP set to TERMINATE_REQUEST and fails to find a matching session, the DNCA agent returns DIAMETER_UNKNOWN_SESSION_ID error.

         DNCA Manager                             DNCA Agent
            |                                            |
            |                                            |
         Trigger                                         |
            |                                            |
            |                   NCR                      |
            |------------------------------------------->|
            |       (TERMINATE_REQUEST, session id)      |
            |                                            |
            |                                            |
            |                                  Remove NAT bindings
            |                                       of session
            |                                            |
            |                                            |
            |           Send accounting stop             |
            |<-------------------------------------------|
            |           for all session bindings         |
            |                                            |
            |                                  Terminate Session /
            |                                 Remove session state
            |                                            |
            |                                            |
            |                                            |
            |                     NCA                    |
            |<-------------------------------------------|
            |                 (result code)              |
            |                                            |

4.6.  DNCA Manager/Agent Failures

This document does not cover details in case DNCA manager and DNCA agent go out of sync, which could happen for example due to DNCA manager or DNCA agent restart, (temporary) loss of network connectivity etc. DNCA application will rely on DNCA Manager and DNCA Agent to have builtin redundancy support to recover state in case of failure.

Example failure cases include the following:

• The DNCA manager loses session state (e.g. due to a restart). In this case,
  • the DNCA agent may receive a NCR with NC-Request-Type AVP set to INITIAL_REQUEST that matches an existing session of DNCA agent. The DNCA agent will return an error that contains Duplicate-Session-Id AVP to report Session-Id of existing session. The DNCA manager may then send an explicit TERMINATE_REQUEST for the older session that was lost.
  • the DNCA manager may receive accounting records for a session that does not exist. The DNCA manager will send an accounting answer with error-code set to DIAMETER_UNKNOWN_SESSION_ID. On receipt of which the DNCA agent clears the session and removes the associated session state.
• The DNCA agent loses session state. In such a case, the DNCA agent could receive a NCR with NC-Request-Type AVP set to UPDATE_REQUEST for a non-existent session. The DNCA agent will return NCA with error code set to DIAMETER_UNKNOWN_SESSION_ID. State recovery procedures of the DNCA agent will be covered in a future version of this document.
• The DNCA manager is unreachable (as e.g. detected by Diameter watchdog) or down and accounting requests from the DNCA agent fail to get a response. The mechanism to ensure that a DNCA manager no longer has associated state for a session being cleared at the DNCA agent is beyond the scope of this document.
• The DNCA agent is unreachable or down and NCR requests fail 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 terminate the access session to the endpoint.

5.  Use Of The Diameter Base Protocol

The Diameter Base Protocol defined by [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) shall apply, with the clarifications listed in the present specification.

5.1.  Securing Diameter Messages

For secure transport of Diameter messages, IPSec MAY be used.

The DNCA agent MAY verify the identity of the DNCA Manager during the Capabilities Exchange Request procedure.

The DNCA agent MAY verify if the DNCA Manager that issues a NCR command is allowed to do so, based on:

• The Identity of the DNCA Manager
• The Type of NCR Command
• The content of the NCR Command
• Any combination of the above

5.2.  Accounting Functionality

Accounting functionality (Accounting Session State Machine, related command codes and AVPs) is defined in Section 8 (Accounting Commands) below.

5.3.  Use Of Sessions

Each DNCA session MUST have a globally unique Session-Id as defined in [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.), which MUST NOT be changed during the lifetime of a DNCA session. The Diameter Session-Id serves as the global endpoint identifier. The DNCA agent and DNCA manager maintain state associated with the Session-Id. This globally unique Session-Id is used for updating, accounting for and terminating the session. DNCA session MUST NOT have more than one outstanding request at any given instant. The DNCA agent sends an Abort-Session-Request as defined in [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) if it is unable to maintain sessions due to resource limitation.

5.4.  Routing Considerations

It is assumed that the DNCA manager knows the DiameterIdentity of the DNCA agent for a given endpoint. Both the Destination-Realm and Destination-Host AVPs are present in the Request from the DNCA manager to the DNCA agent.

5.5.  Advertising Application Support

Diameter applications conforming to this specification MUST advertise support by including the value of TBD in:

• Auth-Application-Id and Acct-Application-Id of Capabilities-Exchange-Request (CER)
• Auth-Application-Id of NC-request (NCR), NC-Answer (NCA), Abort-Session-Request(ASR), Abort-Session-Answer (AAA) messages
• Acct-Application-Id in Accounting-Request (ACR) and Accounting-Answer (AAA) messages.

6.  Diameter NAT Control Application Commands

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

6.1.  NAT-Control Request (NCR) Command

The NAT-Control Request (NCR) command, indicated by the command field set to TBD and the "R" bit set in the Command Flags field, is sent from the DNCA manager to the DNCA agent in order to install NAT bindings.

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

Message Format:

   < NC-Request > ::= < Diameter Header: TBD, REQ, PXY>

                    < Session-Id >
                    { Auth-Application-Id }
                    { Origin-Host }
                    { Origin-Realm }
                    { Destination-Realm }
                    { Destination-Host }
                    { NC-Request-Type }
                    [ Origin-State-Id ]
                    [ Auth-Session-State ]
                  * [ NAT-Control-Remove ]
                  * [ NAT-Control-Install ]
                    [ 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 ]

6.2.  NAT-Control Answer (NCA) Command

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

Message Format:

   <NC-Answer> ::= < Diameter Header: TBD, PXY >
                   < Session-Id >
                   { Origin-Host }
                   { Origin-Realm }
                   { NC-Request-Type }
                   [ Result-Code ]
                 * [ 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 ]
                 * [ AVP ]

7.  Diameter NAT Control Application AVPs

7.1.  Reused Base Protocol AVPs

AVPs reused from Diameter Base Protocol [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) are listed below.

                                                +-------------------+
                                                |  AVP Flag rules   |
+-----------------------------------------------|-----+---+---------+
|                           AVP                 |     |   |   May   |
| Attribute Name            Code     Data Type  |MUST |MAY| encrypt |
+-----------------------------------------------+-----+---+---------+
|Acct-Interim-Interval      85       Unsigned32 | M   | P |    Y    |
|Auth-Application-Id        258      Unsigned32 | M   | P |    N    |
|Auth-Session-State         277      Enumerated | 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    |
+-----------------------------------------------+-----+---+---------+
|M - Mandatory bit. An AVP with "M" bit set and its value MUST be   |
|    supported and recognized by a Diameter entity in order the     |
|    message, which carries this AVP, to be accepted.               |
|P - Indicates the need for encryption for end-to-end security.     |
+-------------------------------------------------------------------+

The Auth-Application-Id AVP (AVP Code 258) is assigned by IANA to Diameter applications. The value of the Auth-Application-Id for the Diameter NAT Control Application is TBD.

7.2.  Additional Result-Code AVP Values

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

7.2.1.  Success

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

7.2.2.  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.

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

RESOURCE_FAILURE (TBD)

The DNCA agent indicates that the binding could not be installed or a new session could not be created due to resource shortage.

7.2.3.  Permanent Failures

Result-Code AVP values that 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_RULE_NAME (TBD)

The DNCA agent indicates that the binding could not be installed or a new session could not be created due to resource shortage.

BINDING_FAILURE (TBD)

The DNCA indicates that the requested binding(s) could not be installed.

MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT (TBD)

The DNCA agent denies the request because the maximum number of allowed bindings has been reached for the specified Endpoint Classifier.

SESSION_EXISTS (TBD)

The DNCA agent denies request to initialize a new session, if it already has a DNCA session that uses the same set of classifiers as indicated by DNCA manager in the new session init request.

INSUFFICIENT_CLASSIFIERS (TBD)

The DNCA agent defines request to initialize a new session, if the classifiers in the request match more than one of the existing sessions on DNCA agent.

7.3.  Reused NASREQ Diameter Application AVPs

The following AVPs are reused from Diameter Network Access Server Application [RFC4005] (Calhoun, P., Zorn, G., Spence, D., and D. Mitton, “Diameter Network Access Server Application,” August 2005.).

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

7.4.  Reused from RFC 4675

The following AVPs are reused from "RADIUS Attributes for Virtual LAN and Priority Support" specification [RFC4675] (Congdon, P., Sanchez, M., and B. Aboba, “RADIUS Attributes for Virtual LAN and Priority Support,” September 2006.).

                                       +---------------------+
                                       |    AVP Flag rules   |
+------------------+------+------------|----+-----+----+-----|----+
|                  | AVP  |            |    |     |SHLD| MUST|    |
| Attribute Name   | Code |  Value Type|MUST| MAY | NOT|  NOT|Encr|
|------------------|------|------------|----+-----+----+-----|----|
| Egress-VLANID    |  56  | OctetString| M  |  P  |    |  V  | Y  |
+------------------+------+------------|----+-----+----+-----|----+

7.5.  Reused from Diameter QoS Application

The following AVPs are reused from the Diameter QoS Application [I‑D.ietf‑dime‑diameter‑qos] (Sun, D., McCann, P., Tschofenig, H., ZOU), T., Doria, A., and G. Zorn, “Diameter Quality of Service Application,” February 2010.).

                                                +-------------------+
                                                |  AVP Flag rules   |
+-----------------------------------------------|-----+---+---------+
|                           AVP                 |     |   |   May   |
| Attribute Name            Code     Data Type  |MUST |MAY| encrypt |
+-----------------------------------------------+-----+---+---------+
|Port                       TBD     Integer32   |  M  | P |    Y    |
|IP-Address-Mask            TBD     Grouped     |  M  | P |    Y    |
|Protocol                   TBD     Enumerated  |  M  | P |    Y    |
|Direction                  TBD     Enumerated  |  M  | P |    Y    |
+-----------------------------------------------+-----+---+---------+
|M - Mandatory bit. An AVP with "M" bit set and its value MUST be   |
|    supported and recognized by a Diameter entity in order the     |
|    message, which carries this AVP, to be accepted.               |
|P - Indicates the need for encryption for end-to-end security.     |
+-------------------------------------------------------------------+

7.6.  Reused From ETSI ES 283 034, e4 Diameter Application

The following AVPs are reused from the Diameter e4 Application [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.).

                                                +-------------------+
                                                |  AVP Flag rules   |
+-----------------------------------------------|-----+---+---------+
|                           AVP                 |     |   |   May   |
| Attribute Name            Code     Data Type  |MUST |MAY| encrypt |
+-----------------------------------------------+-----+---+---------+
|Address-Realm              301     OctetString | M,V |   |    Y    |
|Logical-Access-Id          302     OctetString |   V | M |    Y    |
|Physical-Access-ID         313     UTF8String  |   V | M |    Y    |
+-----------------------------------------------+-----+---+---------+
|M - Mandatory bit. An AVP with "M" bit set and its value MUST be   |
|    supported and recognized by a Diameter entity in order the     |
|    message, which carries this AVP, to be accepted.               |
|P - Indicates the need for encryption for end-to-end security.     |
|V - Indicates whether the optional Vendor-ID field is present      |
|    in the AVP header. Vendor-Id header of all AVPs in             |
|    this table will be set to ETSI (13019)                         |
+-------------------------------------------------------------------+

7.7.  Diameter NAT Control Application Defined AVPs

The following table describes the new Diameter AVPs used in the present document, their AVP Code values, types, possible flag values and whether the AVP may or not be encrypted.

                                                +-------------------+
                                                |  AVP Flag rules   |
+-----------------------------------------------|-----+---+---------+
|                       AVP  Section            |     |   |   May   |
| Attribute Name        Code Defined Data Type  |MUST |MAY| encrypt |
+-----------------------------------------------+-----+---+---------+
|NC-Request-Type        TBD  7.7.1   Enumerated | M   | P |    Y    |
|NAT-Control-Install    TBD  7.7.2   Grouped    | M   | P |    Y    |
|NAT-Control-Remove     TBD  7.7.3   Grouped    | M   | P |    Y    |
|NAT-Control-Definition TBD  7.7.4   Grouped    | M   | P |    Y    |
|NAT-Internal-Address   TBD  7.7.5   Grouped    | M   | P |    Y    |
|NAT-External-Address   TBD  7.7.6   Grouped    | M   | P |    Y    |
|Max-NAT-Bindings       TBD  7.7.7   Unsigned32 | M   | P |    Y    |
|NAT-Control-           TBD  7.7.8   OctetString| M   | P |    Y    |
| Binding-Rule                                  |     |   |         |
|Duplicate-             TBD  7.7.9   UTF8String | M   | P |    Y    |
| Session-ID                                    |     |   |         |
|NAT-Control-Record     TBD  8.2.1   Grouped    | M   | P |    Y    |
|NAT-Control-           TBD  8.2.2   Enumerated | M   | P |    Y    |
| Binding-Status                                |     |   |         |
|Current-NAT-Bindings   TBD  8.2.3   Unsigned32 | M   | P |    Y    |
+-----------------------------------------------+-----+---+---------+
|M - Mandatory bit. An AVP with "M" bit set and its value MUST be   |
|    supported and recognized by a Diameter entity in order the     |
|    message, which carries this AVP, to be accepted.               |
|P - Indicates the need for encryption for end-to-end security.     |
|V - Vendor specific bit that indicates whether the optional        |
|    Vendor-ID field is present in the AVP header                   |
+-------------------------------------------------------------------+

7.7.1.  NC-Request-Type AVP

The NC-Request-Type AVP (AVP Code TBD) 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 used to install binding at the DNCA agent on a successful access session setup.

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.

TERMINATION_REQUEST (3)

Termination Request is used to deactivate and remove all bindings previously activated on a given access session.

QUERY_REQUEST (4)

Query Request is used to query the DNCA agent about the currently installed bindings for an endpoint classifier.

7.7.2.  NAT-Control-Install AVP

The NAT-Control AVP (AVP code TBD) is of type Grouped, and it is used to activate or install NAT bindings. It also contains Max-NAT- Bindings that defines maximum number of NAT bindings to be allowed for a subscriber and NAT-Control-Binding-Rule that references predefined policy template on DNCA agent that may contain static bindings, maximum number of bindings to be allowed, address pool from which external binding address should be allocated.

AVP format:

  NAT-Control-Install ::= < AVP Header: TBD >
                           * [ NAT-Control-Definition ]
                             [ NAT-Control-Binding-Rule ]
                             [ Max-NAT-Bindings]
                           * [ AVP ]

7.7.3.  NAT-Control-Remove AVP

The NAT-Control-Remove AVP (AVP code TBD) is of type Grouped, and it is used to deactivate or remove NAT bindings.

AVP format:

  NAT-Control-Remove ::= < AVP Header: TBD >
                          * [ NAT-Control-Definition ]
                            [ NAT-Control-Binding-Rule ]
                          * [ AVP ]

7.7.4.  NAT-Control-Definition AVP

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

The NAT-Control-Definition AVP uniquely identifies the binding between the DNCA agent and the DNCA manager.

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

The Protocol AVP describes the transport protocol for which the binding is created. Exactly zero or one Protocol AVP may be contained within NAT-Control-Definition AVP. If the Protocol AVP is omitted and if both internal and external address are specified then the binding reserves the addresses for all transport protocols.

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

AVP format:

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

7.7.5.  NAT-Internal-Address AVP

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

AVP format:

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

7.7.6.  NAT-External-Address AVP

The NAT-External-Address AVP (AVP code TBD) is of type Grouped, and it describes the external IP address and port for a binding. IP-Address-Mask AVP can only be specified when Framed-IP-Address AVP is present.

AVP format:

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

7.7.7.  Max-NAT-Bindings

The Max-NAT-Bindings AVP (AVP code TBD) is of type Unsigned32, and it indicates the maximum number of NAT bindings allowed.

7.7.8.  NAT-Control-Binding-Rule AVP

The NAT-Control-Binding-Rule AVP (AVP code TBD) is of type is of type OctetString, and it defines a name for a policy template that will be predefined at NAT. Details on the contents and structure of the template as well as how it would be configured are outside the scope of this document. The policy to which this AVP refers to may contain NAT Bindings, address pool for external address allocation of NAT binding, maximum allowed NAT bindings etc.

7.7.9.  Duplicate-Session-Id AVP

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

8.  Accounting Commands

The Diameter NAT Control Application reuses session based accounting as defined in Diameter Base Protocol [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) to report the bindings used per endpoint. This reporting is achieved by sending Diameter Accounting Requests (ACR) [Start, Interim and Stop] from the DNCA agent to DNCA manager.

The DNCA agent sends an ACR Start on receiving an NCR with NC-Request-Type AVP set to INITIAL_REQUEST received for a session, or on creation of the first binding for a session requested in an earlier NCR. The 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, or periodically as specified in Acct-Interim-Interval by DNCA Manager or when it creates/tears down bindings. An ACR Stop is sent by the DNCA agent on receiving an NCR with NC-Request-Type AVP set to TERMINATION_REQUEST.

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

The DNCA agent may trigger an interim accounting record when maximum number of bindings, if received in NCR, is reached.

8.1.  NAT Control Accounting Messages

The ACR and ACA messages are reused as defined in Diameter Base Protocol [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) for exchanging endpoint NAT binding details between the DNCA agent and the CDF. DNCA Application ID is used in the accounting commands. ACR will contain one or more optional NAT-Control-Record AVP to report the bindings. The DNCA agent indicates the number of the currently allocated NAT bindings to the DNCA manager using the Current-NAT-Bindings AVP. This number needs to match the number of bindings identified as active within the NAT-Control-Record AVP.

8.2.  NAT Control Accounting AVPs

In addition to AVPs for ACR specified in [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.), the DNCA agent must add the NAT-Control-Record AVP.

8.2.1.  NAT-Control-Record

The NAT-Control-Record AVP (AVP code TBD) is of type Grouped, and it describes a binding and its status. Event-Timestamp indicates the time at which binding was created if NAT-Control-Binding-Status is set to Created, or time at which the binding was removed if NAT-Control-Binding-Status is set to removed. If the NAT-Control-Binding-Status is active Event-Timestamp need not be present, if present it indicates that binding is active at the mentioned time.

  NAT-Control-Record ::= < AVP Header: TBD >
                         { NAT-Control-Definition }
                         { NAT-Control-Binding-Status }
                         [ Event-Timestamp ]

8.2.2.  NAT-Control-Binding-Status

The NAT-Control-Binding-Status AVP (AVP code TBD) is of type enumerated and it describes whether the binding being reported was created or removed or simply indicates that it is active.

The following values are defined:

Created (1)

Indicates that NAT binding is created.

Active (2)

Indicates that NAT binding is active.

Removed (3)

Indicates that the NAT binding was removed.

8.2.3.  Current-NAT-Bindings

The Current-NAT-Bindings AVP (AVP code TBD) is of type Unsigned32, and it indicates number of NAT bindings active on NAT.

9.  AVP Occurrence Table

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

The table uses the following symbols:

0

The AVP MUST NOT be present in the message.

0+

Zero or more instances of the AVP MAY be present in the message.

0-1

Zero or one instance of the AVP MAY 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.

9.1.  DNCA AVP Table for NAT control initial and update requests

The following table presents which NAT control application specific AVPs are to be present in NCR/NCA with 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       |
|NAT-Control-Record                      0      0       |
|Current-NAT-Bindings                    0      0       |
|Duplicate-Session-Id                    0      0-1     |
+-------------------------------------------------------+

9.2.  DNCA AVP Table for Session Query request

The following table presents which NAT control application specific AVPs are to be present in NCR/NCA with 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-Control-Record                      0      0       |
|Current-NAT-Bindings                    0      1       |
|Duplicate-Session-Id                    0      0       |
+-------------------------------------------------------+

9.3.  DNCA AVP Table for NAT Control Terminate requests

The following table presents which NAT control application specific AVPs are to be present in NCR/NCA with NC-Request-Type set to TERMINATION_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-Control-Record                      0      0       |
|Current-NAT-Bindings                    0      0       |
|Duplicate-Session-Id                    0      0       |
+-------------------------------------------------------+

9.4.  DNCA AVP Table For Accounting Message

Following table presents which NAT control application specific AVPs May or May Not be present in ACR/ACA messages.

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

10.  IANA Considerations

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

10.1.  Command Codes

IANA is requested to allocate command code values for the following.

Registry:

10.2.  AVP Codes

IANA is requested to allocate AVP codes for the following AVPs that are defined in this document.

Registry:

10.3.  AVP Values

10.3.1.  Result-Code AVP Values

Section 7.2 (Additional Result-Code AVP Values) defines several new values for the Result-Code AVP for transient failures and permanent failures. IANA is requested to allocate the corresponding values from the ranges for transient (4xxx) and permantent (5xxx) failures.

10.4.  Application IDs

IANA is requested to allocate the following application ID using the next value from the 7-16777215 range.

Registry:

11.  Security Considerations

Similar to what the Diameter QoS application (see [I‑D.ietf‑dime‑diameter‑qos] (Sun, D., McCann, P., Tschofenig, H., ZOU), T., Doria, A., and G. Zorn, “Diameter Quality of Service Application,” February 2010.)) does for authorization of QoS reservations, this document describes procedures for authorizing network address translation related attributes and parameters by an entity which is non-local to the device performing network address translation. The security considerations for the Diameter QoS application (see [I‑D.ietf‑dime‑diameter‑qos] (Sun, D., McCann, P., Tschofenig, H., ZOU), T., Doria, A., and G. Zorn, “Diameter Quality of Service Application,” February 2010.) section 11) apply in a similar way to the DNCA. Securing the information exchange between the authorizing entity (the DNCA manager) as well as the NAT device requires bilateral authentication of the involved parties, authorization of the involved parties to perform the required procedures and functions, as well as procedures to ensure integrity and confidentiality of the information exchange. DNCA makes use of the capabilities offered by Diameter as well as the underlying transport protocols to deliver on these requirements (see Section 5.1 (Securing Diameter Messages ) ).

It is assumed that the DNCA agent and DNCA manager are in the same domain and have a mutual trust set up. Authorization between the DNCA agent and DNCA manager is beyond the scope of this document.

12.  Acknowledgements

The authors would like to thank Jouni Korhonen, Avi Lior, Chris Metz, Hannes Tschofenig, Greg Weber, and Glen Zorn for their input on this document.

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

Changes from -00 to -01

a.

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

b.

added support for transport specific binding (UDP/TCP)

c.

added support for twice-NAT

d.

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

Changes from -01 to -02

a.

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

b.

added Redirect-* AVPs in NCA command

c.

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

d.

Editorial changes (shorted intro section

e.

added support for bindings providing AFT (NAT64)

14.  References

14.1. Normative References

14.2. Informative References

Authors' Addresses