Diameter Network Address and Port Translation Control Application
draft-ietf-dime-nat-control-05

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

Status of this Memo

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

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

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This Internet-Draft will expire on April 25, 2011.

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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 DNCA
4.  DNCA 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 and 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.  DNCA Commands
    6.1.  NAT-Control Request (NCR) Command
    6.2.  NAT-Control Answer (NCA) Command
7.  NAT Control Application Session State Machine
8.  DNCA AVPs
    8.1.  Reused Base Protocol AVPs
    8.2.  Additional Result-Code AVP Values
        8.2.1.  Success
        8.2.2.  Transient Failures
        8.2.3.  Permanent Failures
    8.3.  Reused NASREQ Diameter Application AVPs
    8.4.  Reused from RFC 4675
    8.5.  Reused from Diameter QoS Application
    8.6.  Reused from ETSI ES 283 034, e4 Diameter Application
    8.7.  DNCA Defined AVPs
        8.7.1.  NC-Request-Type AVP
        8.7.2.  NAT-Control-Install AVP
        8.7.3.  NAT-Control-Remove AVP
        8.7.4.  NAT-Control-Definition AVP
        8.7.5.  NAT-Internal-Address AVP
        8.7.6.  NAT-External-Address AVP
        8.7.7.  Max-NAT-Bindings
        8.7.8.  NAT-Control-Binding-Rule AVP
        8.7.9.  Duplicate-Session-Id AVP
9.  Accounting Commands
    9.1.  NAT Control Accounting Messages
    9.2.  NAT Control Accounting AVPs
        9.2.1.  NAT-Control-Record
        9.2.2.  NAT-Control-Binding-Status
        9.2.3.  Current-NAT-Bindings
10.  AVP Occurrence Table
    10.1.  DNCA AVP Table for NAT Control Initial and Update Requests
    10.2.  DNCA AVP Table for Session Query request
    10.3.  DNCA AVP Table for Accounting Message
11.  IANA Considerations
    11.1.  Command Codes
    11.2.  AVP Codes
    11.3.  AVP Values
        11.3.1.  Result-Code AVP Values
    11.4.  Application IDs
12.  Security Considerations
13.  Acknowledgements
14.  Change History (to be removed prior to publication as an RFC)
15.  References
    15.1.  Normative References
    15.2.  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 NAT and NAPT devices. The use of a Diameter application allows for simple integration into the existing 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 subscriber or end point.
2. Supports the allocation of specific NAPT/NAT bindings. Two types of specific bindings can be distinguished:
   • Allocation of a pre-defined NAT binding: Both the internal and external IP address and port pair are specified within the request. In some deployment cases, such as access to a web-server within a user’s home network with IP address and port, benefit from statically configured bindings.
   • Allocation of an external IP address for a given internal IP address: The allocated external IP address is reported back to the requestor. In some deployment scenarios, the application requires immediate knowledge of the allocated binding for a given internal IP address but does not control the allocation of the external IP address; for example, SIP-proxy server deployments.
3. Defines the external address pool(s) to be used for allocating an external IP address: External address pools can either be pre-assigned at the NAPT/NAT, 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, list of IP-subnets. Such External address pools can be used to select external IP address in NAPT/NAT bindings for multiple subscribers.
4. Generates reports and accounting records: Reports established bindings for a particular user. 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). The query functionality complements alternative information query mechanisms, such as SNMP-based mechanism, if available.
6. Identifies a subscriber or endpoint on multiple network devices (NAPT or 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 DNCA 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 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 used in this document:

AAA: Authentication, Authorization, Accounting

DNCA: Diameter Network address and port translation 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

NCR:NAT Control Request

NCA:NAT Control Answer

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 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 port (and optionally address family) 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 could be hampered. Provisioning static NAT bindings for particular endpoints, using different public IP address pools for different set of endpoints; for example, residential or business customers, and reporting allocated bindings on a per endpoint basis is burdensome for a service provider if the NAT device is not aware of endpoints and allows per endpoint control and management, which easily integrates with the already existing per endpoint management infrastructure of the service provider.

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

3.2.  Diameter NAPT Control Application Overview

The DNCA runs between a DNCA Agent on the NAT and the DNCA Manager. DNCA allows per endpoint control and management of NAT. 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.
• Provides per endpoint reporting of the allocated NAT bindings.
• Provides unique identification of an endpoint on NAT device, AAA-server and NAS, to simplify correlation of accounting data streams.

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

3.3.  Deployment Scenarios For DNCA

The role of the Diameter NAT Control Manager can be fulfilled by either the NAS or by an external server, such as 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. As DNCA Manager the NAS, initiates and manages session with the NAT device, exchanges NAT specific configuration information and handles reporting and accounting information. The NAS receives reporting and accounting information from NAT device. With this information, the NAS provides a single accounting record for the user. This reduces the usage of an external accounting system for correlating the information received from multiple sources.

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, 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. 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 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 or accounting requirements. The NAT device sends its per endpoint accounting information to the NAS, which aggregates the accounting information received form the NAT device with its local accounting information for the endpoint into a single accounting stream towards the AAA-server.

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

4.  DNCA 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 (DNCA Commands) and Section 8 (DNCA AVPs) for details.

4.1.  Parties Involved

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

• DNCA agent: The DNCA agent is part of the NAT device
• DNCA Manager

The NAT control requesting entity is always the DNCA Manager. The DNCA Manager always initiates, updates, or terminates the sessions. This mode of operation is sometimes also referred to as "push mode".

The DNCA Manager can be NAS or AAA-server. The DNCA Manager initiates a session with the DNCA agent when it learns about the subscriber. The 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 a subscriber with respect to his IP packets.

4.2.  Session Establishment

The DNCA Manager establishes a session with the DNCA agent to control the behavior of the NAT device. During session establishment, the DNCA Manager passes along configuration information to the DNCA agent. The session configuration information comprises the maximum number of bindings allowed for the endpoint associated with this session, a set of pre-defined NAT bindings to be established for this endpoint, or a description of the address pool, external addresses to 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 NCR the DNCA Agent sets up 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 may contain configuration information for the session, which specifies the behavior of the NAT device for the session. The configuration information, which may be included, comprises:

• A list of NAT bindings, which should be pre-allocated for the session; for example, in case a subscriber requires a fixed external IP- address/port pair for one of the 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 the DNCA Agent, which is applied to the session. Such a predefined binding rule on the 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; that is, DNCA Manager and endpoint identifier match an already existing session, the DNCA Agent returns NCA with Result-Code set to SESSION_EXISTS, and provides the 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; that is, DNCA Manager and endpoint identifier match already existing sessions, the DNCA Agent returns a NCA with Result-Code set to Insufficient-Classifiers. In case a DNCA Manager receives NCA that reports Insufficient-Classifiers, it may choose to retry establishing a new session using additional or more specific classifiers.
• If the NCR contains a binding rule not defined on the NAT device, the DNCA Agent returns 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, that is NAT device, treats a NCR as an atomic operation; hence none of the requested bindings will be established by the NAT device. Either all requested actions within a NCR are completed successfully, or the entire request fails.
• If DNCA Agent does not have sufficient resources to process a request, it returns 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; that is, a predefined template on NAT device, 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 NC 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 perfborm the tasks requested within the NCR. These include the following:

• If DNCA Agent receives a NCR update or query request for a non-existent session, it sets Result-Code in the answer to DIAMETER_UNKNOWN_SESSION_ID.
• If the NCR contains a binding rule not defined on the NAT device, the DNCA Agent returns 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 returns NCA with Result-Code AVP set to MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT.
• If 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 returns a NCA with Result-Code set to BINDING_FAILURE. The DNCA Agent (i.e., NAT device) treats a NCR as an atomic operation. Hence none of the requested bindings will be established by NAT device. Either all requested actions within a NCR are either successful or failed completely..
• If DNCA Agent does not have sufficient resources to process a request, it returns 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 device on how the NAT device copes with a case where the new value is lower than the actual number of allocated bindings. Typically the NAT device refrains from enforcing the new limit immediately; that is, 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 overrides any previously defined rules for the session.
• If Max-NAT-Binding and NAT-Control-Definition AVPs are included in the NCR along with a reference to a binding rule (a predefined template on NAT device) 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 device or discover the session identifier for a particular external IP address/port pair.

The DNCA Manager initiates a session query by sending a 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 to retrieve the session identifiers, along with the associated bindings, matching a criteria. This enables the DNCA Manager to find the sessions, which utilize a specific external IP address.

1. Request a list of currently allocated NAT bindings for a particular session: The DNCA Agent on receiving NCR, looks up session information for the session ID contained in the NCR, and reports all currently active NAT bindings for the session using NCA message with Result-Code set to DIAMETER_SUCCESS. In this case the NCR MUST NOT contain a NAT-Control-Definition AVP. Each NAT binding is reported in a NAT-Control-Definition AVP. In case the session ID is unknown, the DNCA Agent returns NCA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.
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 reports the NAT bindings and associated session IDs corresponding to the external IP address/port pairs in a NCA message with Result-Code set to DIAMETER_SUCCESS with the same session ID, which is used in 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 Session Terminate Request (STR) message to the DNCA Agent upon receiving a trigger signal. The source of the trigger signal is outside the scope of this document. The DNCA Agent sends accounting stop record reporting all the bindings and notifies the DNCA Manager about successful session termination using a Session Terminate Answer (STA) 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 STR from a DNCA Manager and fails to find a matching session, the DNCA Agent returns STA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.

         DNCA Manager                             DNCA Agent
            |                                            |
            |                                            |
         Trigger                                         |
            |                                            |
            |                   STR                      |
            |------------------------------------------->|
            |               (session id)                 |
            |                                            |
            |                                            |
            |                                  Remove NAT bindings
            |                                       of session
            |                                            |
            |                                            |
            |           Send accounting stop             |
            |<-------------------------------------------|
            |           for all session bindings         |
            |                                            |
            |                                  Terminate Session /
            |                                 Remove session state
            |                                            |
            |                                            |
            |                                            |
            |                  STA                       |
            |<-------------------------------------------|
            |             (Result-Code)                  |
            |                                            |

4.6.  DNCA Manager and Agent Failures

This document does not cover details in case DNCA Manager and DNCA Agent are out of sync. This happens when the DNCA Manager or DNCA Agent restart, (temporary) loss of network connectivity etc. The DNCA relies 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 returns an error that contains Duplicate-Session-Id AVP to report the Session-ID of existing session. The DNCA Manager may send an explicit Sesstion Terminate Request(STR) for the older session, which was lost.
  • The DNCA Manager may receive accounting records for a session that does not exist. The DNCA Manager sends an accounting answer with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID. On receiving this, 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 may receive a NCR with NC-Request-Type AVP set to UPDATE_REQUEST for a non-existent session. The DNCA Agent returns NCA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.
• The DNCA Manager is unreachable, for example detected by Diameter watchdog, or down and accounting request from the DNCA Agent fails to get a response. The mechanism to ensure that a DNCA Manager no longer has associated state for a session being cleared by a 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 can 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.) applies 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 and it is 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 9 (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, and terminating the session. The 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 (ASA) messages
• Acct-Application-Id in Accounting-Request (ACR) and Accounting-Answer (ACA) messages.

6.  DNCA Commands

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

6.1.  NAT-Control Request (NCR) Command

The NAT-Control Request (NCR) command, indicated by the command field set to TBD 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 ]
                  * [ 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.  NAT Control Application Session State Machine

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

In the state table, the event 'Failure to send NCR' means that the DNCA Manager is unable to send command NCR to the desired destination. This could be due to the peer being down, or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of NCA.

In the state table "FAILED NCA" means that the DNCA Agent was not able to honor corresponding NCR. This can happen due to any of the transient and permanent error at DNCA Agent indicated by the following error Result-Code values - RESOURCE_FAILURE, UNKNOWN_BINDING_RULE_NAME, BINDING_FAILURE, MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT, SESSION_EXISTS, INSUFFICIENT_CLASSIFIERS

The following state machine is observed by a DNCA Manager:

                           MANAGER
   State     Event                          Action     New State
   -------------------------------------------------------------
   Idle      New Host 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                 Sent STR   Discon
             received
             but Agent unable to provide
             service

   Pending   Error processing successful    Sent STR   Discon
             NCA

   Pending   Failed                         Cleanup    Idle
             NCA received

   Open      NAT control                    Send       Open
             update required                NCR Update
                                            Request

   Open      Successful                                Open
             NCA received

   Open      Failed                         Cleanup    Idle
             NCA received.


   Open      Access Session end detected    Send STR   Discon


   Open      ASR Received,                  Send ASA   Discon
             client will comply with        with
             request to end the session     Result-Code
                                            = SUCCESS,
                                            Send STR.

   Open      ASR Received,                  Send ASA   Open
             client will not comply with    with
             request to end the session     Result-Code
                                            != SUCCESS

   Discon    ASR Received                   Send ASA   Idle

   Discon    STA Received                   Discon.    Idle
                                            user/device

The following state machine is observed by a DNCA Agent:

                          AGENT
   State     Event                          Action     New State
   -------------------------------------------------------------
   Idle      NCR request                    Send       Open
             received, and                  successful
             able to provide requested      NCA
             NAT control service

   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            Cleanup

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

   Discon    Failure to send ASR            Wait,      Discon
                                            resend ASR

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

   Not       ASA Received                   None       No Change.
   Discon

   Any       STR Received                   Send STA,  Idle
                                            Cleanup.

8.  DNCA AVPs

8.1.  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    |
|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.

8.2.  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.

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.

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.

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_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 initializationrequest.

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.

8.3.  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          |      |            |    |     |    |     |    |
+------------------+------+------------|----+-----+----+-----|----+

8.4.  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  |
+------------------+------+------------|----+-----+----+-----|----+

8.5.  Reused from Diameter QoS Application

The following AVPs are reused from the Traffic Classification and Quality of Service (QoS) Attributes for Diameter [RFC5777] (Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M., and A. Lior, “Traffic Classification and Quality of Service (QoS) Attributes for Diameter,” 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.     |
+-------------------------------------------------------------------+

8.6.  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).                        |
+-------------------------------------------------------------------+

8.7.  DNCA Defined AVPs

The following table describes the new Diameter AVPs used in this document.

                                                +-------------------+
                                                |  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.                  |
+-------------------------------------------------------------------+

8.7.1.  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.

QUERY_REQUEST (4)

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

8.7.2.  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 ]

8.7.3.  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 ]

8.7.4.  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 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 address are specified then the binding reserves the 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, 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 ]

8.7.5.  NAT-Internal-Address AVP

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

AVP format:

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

8.7.6.  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. External IP address specified in this attribute can be reused for multiple subscribers by specifying the same address in the respective NAT-External-Address AVPs.

AVP format:

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

8.7.7.  Max-NAT-Bindings

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

8.7.8.  NAT-Control-Binding-Rule AVP

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

8.7.9.  Duplicate-Session-Id AVP

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

9.  Accounting Commands

The DNCA 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 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 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 a NCR with NC-Request-Type AVP set to UPDATE_REQUEST, or periodically as specified in Acct-Interim-Interval by the DNCA Manager, or when it creates or tears down bindings. An ACR Stop is sent by the DNCA Agent on receiving STR.

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

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

9.1.  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 DNCA Manager. The DNCA Application ID is used in the accounting commands. ACR contains one or more optional NAT-Control-Record AVP to report the bindings. The DNCA Agent indicates the number of 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.

9.2.  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.

9.2.1.  NAT-Control-Record

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

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

9.2.2.  NAT-Control-Binding-Status

The NAT-Control-Binding-Status AVP (AVP code TBD) 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 TBD) is of type Unsigned32. It indicates number of NAT bindings active on NAT device.

10.  AVP Occurrence Table

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

The table uses the following symbols:

0

The AVP MUST NOT be present in the message.

0+

Zero or more instances of the AVP 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.

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

The following table lists the DNCA specific AVPs that have to be present in NCR and 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     |
+-------------------------------------------------------+

10.2.  DNCA AVP Table for Session Query request

The following table lists the DNCA specific AVPs that have to be present in NCR and 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       |
+-------------------------------------------------------+

10.3.  DNCA AVP Table for Accounting Message

The following table lists the DNCA specific AVPs, which may or may not be present in ACR and 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       |
+-------------------------------------------------------+

11.  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.

11.1.  Command Codes

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

Registry:

11.2.  AVP Codes

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

Registry:

11.3.  AVP Values

11.3.1.  Result-Code AVP Values

Section 8.2 (Additional Result-Code AVP Values) defines several new values for the Result-Code AVP for transient and permanent failures. IANA is requested to allocate the corresponding values from the ranges for transient (4xxx) and permantent (5xxx) failures.

11.4.  Application IDs

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

Registry:

12.  Security Considerations

Similar to the impact of 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.)) on authorization of QoS reservations, this document describes procedures for authorizing NAT related attributes and parameters by an entity, which is non-local to the device performing NAT. 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) and the NAT device requires bilateral authentication of the involved parties, authorization of the involved parties to perform the required procedures and functions, and procedures to ensure integrity and confidentiality of the information exchange. The DNCA makes use of the capabilities offered by Diameter and the underlying transport protocols to deliver 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.

13.  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.

14.  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

e.

added support for bindings providing AFT (NAT64)

Changes from -02 to -03

a.

Editorial changes

Changes from -03 to -04

a.

Editorial changes suggested in WG Lastcall review

b.

Removed NCR Request type terminate and replaced with STR

c.

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

d.

Clarified reuse of External address and address pools among multiple subscribers

Changes from -04 to -05

a.

Removed references to Large Scale NAT as per review comments

15.  References

15.1. Normative References

15.2. Informative References

Authors' Addresses