Internet Engineering Task Force F. Brockners Internet-Draft S. Bhandari Intended status: Standards Track Cisco Expires: January 1, 2012 V. Singh V. Fajardo Telcordia Technologies June 30, 2011 Diameter Network Address and Port Translation Control Application draft-ietf-dime-nat-control-08 Abstract This document describes the framework, messages, and procedures for the Diameter Network address and port translation Control Application. This Diameter application allows per endpoint control of Network Address Translators and Network Address and Port Translators, which are added to networks to cope with IPv4-address space 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any Brockners, et al. Expires January 1, 2012 [Page 1] Internet-Draft Diameter NAT Control Application June 2011 time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 1, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Brockners, et al. Expires January 1, 2012 [Page 2] Internet-Draft Diameter NAT Control Application June 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Deployment Framework . . . . . . . . . . . . . . . . . . . . . 7 3.1. Deployment Scenario . . . . . . . . . . . . . . . . . . . 7 3.2. Diameter NAPT Control Application Overview . . . . . . . . 8 3.3. Deployment Scenarios For DNCA . . . . . . . . . . . . . . 9 4. DNCA Session Establishment and Management . . . . . . . . . . 11 4.1. Session Establishment . . . . . . . . . . . . . . . . . . 11 4.2. Session Re-Authorization . . . . . . . . . . . . . . . . . 14 4.3. Session and Binding Query . . . . . . . . . . . . . . . . 16 4.4. Session Termination . . . . . . . . . . . . . . . . . . . 18 4.5. Session Abort . . . . . . . . . . . . . . . . . . . . . . 19 4.6. Failure cases of the DNCA Diameter peers . . . . . . . . . 20 5. Use Of The Diameter Base Protocol . . . . . . . . . . . . . . 21 5.1. Securing Diameter Messages . . . . . . . . . . . . . . . . 21 5.2. Accounting Functionality . . . . . . . . . . . . . . . . . 22 5.3. Use Of Sessions . . . . . . . . . . . . . . . . . . . . . 22 5.4. Routing Considerations . . . . . . . . . . . . . . . . . . 22 5.5. Advertising Application Support . . . . . . . . . . . . . 22 6. DNCA Commands . . . . . . . . . . . . . . . . . . . . . . . . 22 6.1. NAT-Control Request (NCR) Command . . . . . . . . . . . . 22 6.2. NAT-Control Answer (NCA) Command . . . . . . . . . . . . . 23 7. NAT Control Application Session State Machine . . . . . . . . 24 8. DNCA AVPs . . . . . . . . . . . . . . . . . . . . . . . . . . 27 8.1. Reused Base Protocol AVPs . . . . . . . . . . . . . . . . 27 8.2. Additional Result-Code AVP Values . . . . . . . . . . . . 28 8.2.1. Success . . . . . . . . . . . . . . . . . . . . . . . 28 8.2.2. Transient Failures . . . . . . . . . . . . . . . . . . 28 8.2.3. Permanent Failures . . . . . . . . . . . . . . . . . . 29 8.3. Reused NASREQ Diameter Application AVPs . . . . . . . . . 30 8.4. Reused AVPs from RFC 4675 . . . . . . . . . . . . . . . . 30 8.5. Reused AVPs from Diameter QoS Application . . . . . . . . 31 8.6. Reused AVPs from ETSI ES 283 034, e4 Diameter Application . . . . . . . . . . . . . . . . . . . . . . . 31 8.7. DNCA Defined AVPs . . . . . . . . . . . . . . . . . . . . 32 8.7.1. NC-Request-Type AVP . . . . . . . . . . . . . . . . . 32 8.7.2. NAT-Control-Install AVP . . . . . . . . . . . . . . . 33 8.7.3. NAT-Control-Remove AVP . . . . . . . . . . . . . . . . 33 8.7.4. NAT-Control-Definition AVP . . . . . . . . . . . . . . 33 8.7.5. NAT-Internal-Address AVP . . . . . . . . . . . . . . . 34 8.7.6. NAT-External-Address AVP . . . . . . . . . . . . . . . 34 8.7.7. Max-NAT-Bindings . . . . . . . . . . . . . . . . . . . 35 8.7.8. NAT-Control-Binding-Rule AVP . . . . . . . . . . . . . 35 8.7.9. Duplicate-Session-Id AVP . . . . . . . . . . . . . . . 35 9. Accounting Commands . . . . . . . . . . . . . . . . . . . . . 35 9.1. NAT Control Accounting Messages . . . . . . . . . . . . . 36 Brockners, et al. Expires January 1, 2012 [Page 3] Internet-Draft Diameter NAT Control Application June 2011 9.2. NAT Control Accounting AVPs . . . . . . . . . . . . . . . 36 9.2.1. NAT-Control-Record . . . . . . . . . . . . . . . . . . 36 9.2.2. NAT-Control-Binding-Status . . . . . . . . . . . . . . 36 9.2.3. Current-NAT-Bindings . . . . . . . . . . . . . . . . . 37 10. AVP Occurrence Table . . . . . . . . . . . . . . . . . . . . . 37 10.1. DNCA AVP Table for NAT Control Initial and Update Requests . . . . . . . . . . . . . . . . . . . . . . . . . 37 10.2. DNCA AVP Table for Session Query request . . . . . . . . . 38 10.3. DNCA AVP Table for Accounting Message . . . . . . . . . . 38 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 11.1. Application Identifier . . . . . . . . . . . . . . . . . . 39 11.2. Command Codes . . . . . . . . . . . . . . . . . . . . . . 39 11.3. AVP Codes . . . . . . . . . . . . . . . . . . . . . . . . 39 11.4. Result-Code AVP Values . . . . . . . . . . . . . . . . . . 39 11.5. NC-Request-Type AVP . . . . . . . . . . . . . . . . . . . 39 11.6. NAT-Control-Binding-Status AVP . . . . . . . . . . . . . . 39 12. Security Considerations . . . . . . . . . . . . . . . . . . . 40 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 41 14. Change History (to be removed prior to publication as an RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 15. Normative References . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43 Brockners, et al. Expires January 1, 2012 [Page 4] Internet-Draft Diameter NAT Control Application June 2011 1. Introduction Internet service providers have started to deploy Network Address Translators (NATs) and Network Address and Port Translators (NAPTs) in their networks to deal with the depletion of available public IPv4 addresses. This document defines a Diameter application allowing providers to control the behavior of these NAT and NAPT devices. The use of a Diameter application allows for simple integration into the existing Authentication, Authorization and Accounting (AAA) environment of a provider. The Diameter Network address and port translation Control Application (DNCA) offers the following capabilities: 1. Limits or defines the number of NAPT/NAT bindings made available to an individual 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. 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 device, or specified within a request. If pre-assigned address pools are used, a request needs to include a reference to identify the pool. Otherwise, the request contains a description of the IP address pool(s) to be used; for example, a list of IP-subnets. Such external address pools can be used to select the external IP address in NAPT/NAT bindings for multiple subscribers. 4. Generates reports and accounting records: Reports established bindings for a particular user. The collected information is used by accounting systems for statistical purposes. Brockners, et al. Expires January 1, 2012 [Page 5] Internet-Draft Diameter NAT Control Application June 2011 5. Queries and retrieves details about bindings on demand: This feature complements the previously mentioned accounting functionality (see item 4). 6. Identifies a subscriber or endpoint on multiple network devices (NAT/NAPT device, the AAA-server, or the Network Access Server (NAS)): Endpoint identification is facilitated through a Global Endpoint ID. Endpoints are identified through a single or a set of classifiers, such as IP address, Virtual Local Area Network (VLAN) identifier, or interface identifier which uniquely identify the traffic associated with a particular global endpoint. This document is structured as follows: Section 2 lists terminology, while Section 3 provides an introduction to DNCA and its overall deployment framework. Sections 4 to 8 cover DNCA specifics, with Section 4 describing session management, Section 5 the use of the Diameter base protocol, Section 6 new commands, Section 7 AVPs used, and Section 8 accounting aspects. Section 9 presents an AVP occurence 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]. 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 NAT-device: Network Address Translator or Network Address and Port Translator: An entity performing NAT or NAPT Brockners, et al. Expires January 1, 2012 [Page 6] Internet-Draft Diameter NAT Control Application June 2011 NAT-controller: Entity controlling the behavior of a NAT-device NAS: Network Access Server NCR: NAT Control Request NCA: NAT Control Answer 3. Deployment Framework 3.1. Deployment Scenario Figure 1 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 1: Typical network deployment for internet access Figure 2 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 Brockners, et al. Expires January 1, 2012 [Page 7] Internet-Draft Diameter NAT Control Application June 2011 impacted. This includes cases like: o Provisioning static NAT bindings for particular endpoints o Using different public IP address pools for different set of endpoints (for example, residential or business customers) o Reporting allocated bindings on a per endpoint basis o Integrate control of the NAT-device into the already existing per endpoint management infrastructure of the service provider +---------+ | | | AAA | | | +---------+ | | | | +--------+ +---------+ +--------+ +----------+ | IPv4/ | | | | | | IPv4 | | IPv6 |----| NAS |----| NAT- |----| Internet | | Host | | | | device | | | +--------+ +---------+ +--------+ +----------+ <-------- Private IPv4 ----------><--- Public IPv4 ---> <-------- Public IPv6 ----------><--- Public IPv4 ---> Figure 2: Access network deployment with NAT 3.2. Diameter NAPT Control Application Overview DNCA runs between two DNCA Diameter peers. One DNCA Diameter peer resides within the NAT-device, the other DNCA Diameter peer resides within the NAT-Controller. DNCA allows per endpoint control and management of NAT within the NAT-device. Based on Diameter, DNCA integrates well with the suite of Diameter applications deployed for per endpoint authentication, authorization, accounting, and policy control in service provider networks. DNCA offers: o Request and answer commands to control the allowed number of NAT bindings per endpoint , to request the allocation of specific bindings for an endpoint, to define the address pool to be used for an endpoint. Brockners, et al. Expires January 1, 2012 [Page 8] Internet-Draft Diameter NAT Control Application June 2011 o Provides per endpoint reporting of the allocated NAT bindings. o Provides unique identification of an endpoint on NAT-device, AAA- server and NAS, to simplify correlation of accounting data streams. DNCA allows controlling the behavior of a NAT-device on a per endpoint basis during initial session establishment and at later stages by providing an update procedure for already established sessions. Using DNCA, per endpoint NAT binding information can be retrieved either using accounting mechanisms or through an explicit session query to the NAT. 3.3. Deployment Scenarios For DNCA DNCA can be deployed in different ways. Two common deployment scenarios are outlined in Figure 3 ("integrated deployment") and Figure 4 ("autonomous deployment"). The two scenarios differ in which entity fulfills the role of the NAT-controller. Within the figures (C) denotes the network element performing the role of the NAT-controller. The integrated deployment approach hides the existence of the NAT- device from external servers, such as the AAA-server. It is suited for environments where minimal changes to the existing AAA deployment are desired. The NAS and the NAT-device are Diameter peers supporting the DNCA. The Diameter peer within the NAS, performing the role of the NAT-controller, initiates and manages sessions with the NAT-device, exchanges NAT specific configuration information and handles reporting and accounting information. The NAS receives reporting and accounting information from NAT-device. With this information, the NAS can provide a single accounting record for the endpoint. A system correlating the accounting information received from NAS and NAT-device would not be needed. An example network attachment for an integrated NAT deployment can be described as follows: An endpoint connects to the network, with the NAS being the point of attachment. After successful authentication, the NAS receives endpoint related authorization data from the AAA- server. A portion of the authorization data applies to per endpoint configuration on the NAS itself, another portion describes authorization and configuration information for NAT control aimed at the NAT-device. The NAS initiates a DNCA session to the NAT-device and sends relevant authorization and configuration information for the particular endpoint to the NAT-device. This can comprise NAT- bindings, which have to be pre-established for the endpoint, or management related configuration, such as the maximum number of NAT- bindings allowed for the endpoint. The NAT-device sends its per Brockners, et al. Expires January 1, 2012 [Page 9] Internet-Draft Diameter NAT Control Application June 2011 endpoint accounting information to the NAS, which aggregates the accounting information received from the NAT-device with its local accounting information for the endpoint into a single accounting stream towards the AAA-server. +---------+ | | | AAA | | | +---------+ | | | +--------+ +---------+ +--------+ +----------+ | IPv4/ | | (C) | | | | IPv4 | | IPv6 |----| NAS |----| NAT- |----| Internet | | Host | | | | device | | | +--------+ +---------+ +--------+ +----------+ <-------- Public IPv6 ----------><--- Public IPv4 ---> <-------- Private IPv4 ----------><--- Public IPv4 ---> Figure 3: NAT control deployment: Integrated deployment The autonomous deployment approach decouples user management on NAS and NAT-device. In the autonomous deployment approach, the AAA- system and the NAT-device are the Diameter peers running the DNCA. The AAA-system also serves as NAT-controller. It manages the connection to the NAT-device, controls the per endpoint configuration, and also receives accounting and reporting information from the NAT-device. Different from the integrated deployment scenario, the autonomous deployment scenario does not "hide" the existence of the NAT-device from the AAA infrastructure. Here two accounting streams are received by the AAA-server for one particular endpoint, one from the NAS, and one from the NAT-device. Brockners, et al. Expires January 1, 2012 [Page 10] Internet-Draft Diameter NAT Control Application June 2011 +---------+ | (C) | | AAA |--------- | | | +---------+ | | | | | | | +--------+ +---------+ +---------+ +----------+ | IPv4/ | | | | | | IPv4 | | IPv6 |----| NAS |----| NAT- |----| Internet | | Host | | | | device | | | +--------+ +---------+ +---------+ +----------+ <-------- Public IPv6 ----------><---- Public IPv4 ---> <-------- Private IPv4 ----------><---- Public IPv4 ---> Figure 4: NAT control deployment: Autonomous deployment 4. DNCA Session Establishment and Management Note that this section forward references some of the commands and AVPs defined for DNCA. Please refer to Section 6 and Section 8 for details. DNCA runs between a Diameter peer residing in a NAT- controller and a Diameter peer residing in a NAT-device. The Diameter peer within the NAT-controller is always the control requesting entity: It initiates, updates, or terminates the sessions. Sessions are initiated when the NAT-controller learns about a new endpoint (i.e., host) that requires a NAT service. This could for example be due to the entity hosting the NAT-controller receiving authentication, authorization, or accounting requests for or from the endpoint. Alternate methods that could trigger session set up include local configuration, receipt of a packet from a formerly unknown IP-address, etc. 4.1. Session Establishment The DNCA Diameter peer within the NAT-controller establishes a session with the DNCA Diameter peer within the NAT-device to control the behavior of the NAT function within the NAT-device. During session establishment, the DNCA Diameter peer within the NAT- controller passes along configuration information to DNCA Diameter peer within the NAT-device. The session configuration information comprises the maximum number of bindings allowed for the endpoint associated with this session, a set of pre-defined NAT bindings to be established for this endpoint, or a description of the address pool, that external addresses are to be allocated from. Brockners, et al. Expires January 1, 2012 [Page 11] Internet-Draft Diameter NAT Control Application June 2011 The DNCA Diameter peer within the NAT-controller generates a NAT- Control Request (NCR) message to the DNCA Diameter peer within the NAT-device with NC-Request-Type AVP set to INITIAL_REQUEST to initiate a Diameter NAT control session. On receipt of a NCR the DNCA Diameter peer within the NAT-device sets up a new session for the endpoint associated with the endpoint classifier(s) contained in the NCR. The DNCA Diameter peer within the NAT-device notifies its DNCA Diameter peer within the NAT-controller about successful session setup using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 5 shows the initial protocol interaction between the two DNCA Diameter peers. The initial NAT-Control-Request may contain configuration information for the session, which specifies the behavior of the NAT-device for the session. The configuration information which may be included, comprises: o A list of NAT bindings, which should be pre-allocated for the session; for example, in case a user requires a fixed external IP- address/port pair for one of his applications. o The maximum number of NAT-bindings allowed for an endpoint. o A description of the external IP-address pool(s) to be used for the session. o A reference to a predefined binding rule on the NAT-device, which is applied to the session. Such a predefined binding rule on the NAT-device may contain, for example, the name of the IP-address pool that external IP-addresses should be allocated from, the maximum number of bindings permitted for the endpoint, etc. In certain cases, the NAT-device may not be able to perform the tasks requested within the NCR. These include the following: o If a DNCA Diameter peer within the NAT-device receives a NCR from a DNCA Diameter peer within a NAT-controller with NC- Request-Type AVP set to INITIAL_REQUEST that identifies an already existing session; that is, DNCA Diameter peer and endpoint identifier match an already existing session, the DNCA Diameter peer within the NAT-device returns NCA with Result-Code set to SESSION_EXISTS, and provides the Session-Id of the existing session in the Duplicate- Session-Id AVP. o If a DNCA Diameter peer within the NAT-device receives a NCR from a DNCA Diameter peer within a NAT-controller with NC- Request-Type AVP set to INITIAL_REQUEST that matches more than one of the already existing sessions; that is, DNCA Diameter peer and Brockners, et al. Expires January 1, 2012 [Page 12] Internet-Draft Diameter NAT Control Application June 2011 endpoint identifier match already existing sessions, the DNCA Diameter peer within the NAT-device returns a NCA with Result-Code set to INSUFFICIENT-CLASSIFIERS. In case a DNCA Diameter peer receives a NCA that reports Insufficient-Classifiers, it may choose to retry establishing a new session using additional or more specific classifiers. o If the NCR contains a binding rule not defined on the NAT-device, the DNCA Diameter peer within the NAT-device returns NCA with Result-Code AVP set to UNKNOWN_BINDING_RULE. o In case the NAT-device is unable to establish all of the bindings requested in the NCR, the DNCA Diameter peer will return a NCA with Result-Code set to BINDING_FAILURE. A DNCA Diameter peer within a 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. o If a NAT-device does not have sufficient resources to process a request, the DNCA Diameter peer returns a NCA with Result-Code set to RESOURCE_FAILURE. o 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. Brockners, et al. Expires January 1, 2012 [Page 13] Internet-Draft Diameter NAT Control Application June 2011 NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer) | | | | | | Trigger | | | | NCR | |------------------------------------------>| | (INITIAL_REQUEST, endpoint classifier, | | session id, NAT control config data) | | | | | | | | | | If Able to comply | with Request then | Create session state | | | | | NCA | |<------------------------------------------| | (result code) | | | | | Figure 5: Initial NAT control request and session establishment Note: The DNCA Diameter peer within the NAT-device creates session state only if it is able to comply with the NCR. On success it will reply with a NCA with Result-Code set to DIAMETER_SUCCESS. 4.2. Session Re-Authorization Session re-authorization is performed if the NAT-controller desires to change the behavior of the NAT-device for an existing session. 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 Diameter peer within the NAT-controller generates a NCR message to DNCA Diameter peer within NAT-device with NC-Request-Type AVP set to UPDATE_REQUEST upon receiving a trigger signal. If the session is updated successfully, the DNCA Diameter peer within the NAT-device notifies the DNCA Diameter peer within the NAT-controller about the successful session update using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 6 shows the protocol interaction between the two DNCA Diameter peers. Brockners, et al. Expires January 1, 2012 [Page 14] Internet-Draft Diameter NAT Control Application June 2011 In certain cases, the NAT-device may not be able to perform the tasks requested within the NCR. These include the following: o If DNCA Diameter peer within a NAT-device receives a NCR update or query request for a non-existent session, it sets Result-Code in the answer to DIAMETER_UNKNOWN_SESSION_ID. o If the NCR contains a binding rule not defined on the NAT-device, a NCA with Result-Code AVP set to UNKNOWN_BINDING_RULE is returned. o If the NAT-device cannot establish the requested binding because the maximum number of allowed bindings has been reached for the endpoint classifier, a NCA with Result-Code AVP set to MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT by the DNCA Diameter peer. o If the NAT-device 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 endpoint, a NCA with Result-Code set to BINDING_FAILURE is returned. As already noted, the DNCA Diameter peer in a NAT-device treats a NCR as an atomic operation. Hence none of the requested bindings will be established by the NAT- device in case of failure. Actions requested within a NCR are either all successful or all fail. o If the NAT-device does not have sufficient resources to process a request, a NCA with Result-Code set to RESOURCE_FAILURE is returned. o 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. o If a NCR specifies a new binding rule, predefined on the NAT- device, the binding rule overrides any previously defined rule for the session. o 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 the NAT-device) and the values in Max-NAT-Binding and NAT-Control-Definition AVPs contradict those specified in the pre- Brockners, et al. Expires January 1, 2012 [Page 15] Internet-Draft Diameter NAT Control Application June 2011 defined binding rule, Max-NAT-Binding and NAT-Control-Definition AVPs override the values specified in the binding rule. Note: Already established bindings for the session will not be affected in case the tasks requested within the NCR cannot be completed. NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer) | | | | | | Change of session | attributes | | | | NCR | |------------------------------------------>| | (UPDATE_REQUEST session id, | | NAT control config data) | | | | | | If able to comply | with the request: | Update session state | | | | | NCA | |<------------------------------------------| | (result code) | | | | | Figure 6: NAT control request for session update 4.3. Session and Binding Query Session query can be used by the DNCA Diameter peer within the NAT- controller to either retrieve information on the current bindings for a particular session at the NAT-device or discover the session identifier for a particular external IP address/port pair. A DNCA Diameter peer within the NAT-controller starts a session query by sending a NCR message with NC-Request-Type AVP set to QUERY_REQUEST. Figure 7 shows the protocol interaction between the DNCA Diameter peers. Two types of query requests exist. The first type of query request uses the session ID as input parameter to the query. It is to allow the DNCA Diameter peer within the NAT-controller to retrieve the Brockners, et al. Expires January 1, 2012 [Page 16] Internet-Draft Diameter NAT Control Application June 2011 current set of bindings for a specific session. The second type of query request is used to retrieve the session identifiers, along with the associated bindings, matching a criteria. This enables the DNCA Diameter peer within the NAT-controller to find those sessions, which utilize a specific external IP-address. 1. Request a list of currently allocated NAT bindings for a particular session: On receiving a NCR, the NAT-device looks up the session information for the session ID contained in the NCR, and reports all currently active NAT-bindings for the session using a NCA message with Result-Code set to DIAMETER_SUCCESS. In this case the NCR MUST NOT contain a NAT-Control-Definition AVP. Each NAT-binding is reported in a NAT-Control-Definition AVP. In case the session ID is unknown, the DNCA Diameter peer within the NAT-device 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 Diameter peer within the NAT-controller 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 is not included in the NCR or the NCA for this type of a query. The DNCA Diameter peer within the NAT-device 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 was 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. Brockners, et al. Expires January 1, 2012 [Page 17] Internet-Draft Diameter NAT Control Application June 2011 NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer) | | | | | | DNCA Session Established | | | | NCR | |------------------------------------------>| | (QUERY_REQUEST) | | | | | | | | Look up corresponding session | and associated NAT-bindings | | | NCA | |<------------------------------------------| | (Result-Code) | | | | | Figure 7: Session query 4.4. Session Termination Similar to session initiation, session tear down is always initiated by the DNCA Diameter peer within the NAT-controller. The DNCA Diameter peer sends a Session Terminate Request (STR) message to its peer within the NAT-device upon receiving a trigger signal. The source of the trigger signal is outside the scope of this document. In response, the DNCA Diameter peer within the NAT-device sends an accounting stop record reporting all bindings and notifies its DNCA Diameter peer about successful session termination using a Session Terminate Answer (STA) message with Result-Code set to DIAMETER_SUCCESS. Figure 8 shows the protocol interaction between the two DNCA Diameter peers. If a DNCA Diameter peer within a NAT-device receives a STR and fails to find a matching session, the DNCA Diameter peer returns a STA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID. Brockners, et al. Expires January 1, 2012 [Page 18] Internet-Draft Diameter NAT Control Application June 2011 NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer) | | | | Trigger | | | | STR | |------------------------------------------->| | (session id) | | | | | | Remove NAT-bindings | of session | | | | | Send accounting stop | |<-------------------------------------------| | reporting all session bindings | | | | Terminate session / | Remove session state | | | | | | | STA | |<-------------------------------------------| | (Result-Code) | | | Figure 8: Terminate NAT control session 4.5. Session Abort An Abort-Session-Request (ASR) message is sent from the DNCA Diameter peer within the NAT-device to the DNCA Diameter peer within the NAT- controller when it is unable to maintain a session due to resource limitations. The DNCA Diameter peer within the NAT-controller acknowledges successful session abort using a Abort Session Answer (ASA) message with Result-Code set to DIAMETER_SUCCESS. Figure 9 shows the protocol interaction between the DNCA Diameter peers. The DNCA Diameter peers will start a session termination procedure as described in Section 4.4 following an ASA with Result-Code set to DIAMETER_SUCCESS. If the DNCA Diameter peer within a NAT-controller receives an ASR but fails to find a matching session, it returns an ASA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID. If the DNCA Diameter peer within the NAT-controller is unable to comply with the ASR for any other reason, an ASA with Result-Code set to DIAMETER_UNABLE_TO_COMPLY is Brockners, et al. Expires January 1, 2012 [Page 19] Internet-Draft Diameter NAT Control Application June 2011 returned. NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer) | | | | | Trigger | | | ASR | |<-------------------------------------------| | (session id) | | | | | | ASA | |------------------------------------------->| | (Result-Code) | | | | | | On successful ASA | |<------Session Termination Procedure------->| Figure 9: Abort NAT control session 4.6. Failure cases of the DNCA Diameter peers This document does not specify the behavior in case NAT-device and NAT-controller, or their respective DNCA Diameter peers are out of sync. This could happen for example if one of the entities restarts, in case of a (temporary) loss of network connectivity etc. The peering entities MUST have built-in redundancy support to recover state in case of failure. Example failure cases include the following: o NAT-controller and the DNCA Diameter peer within the NAT- controller lose state (e.g. due to a restart). In this case, * the DNCA Diameter peer within the NAT-device may receive a NCR with NC-Request-Type AVP set to INITIAL_REQUEST that matches an existing session of the DNCA Diameter peer within the NAT- device. The DNCA Diameter peer within the NAT-device returns a Result-Code that contains Duplicate-Session-Id AVP to report the Session-ID of the existing session. The DNCA Diameter peer within the NAT-controller may send an explicit Session Terminate Request (STR) for the older session, which was lost. * a DNCA Diameter peer may receive accounting records for a session that does not exist. The DNCA Diameter peer sends an accounting answer with Result-Code set to Brockners, et al. Expires January 1, 2012 [Page 20] Internet-Draft Diameter NAT Control Application June 2011 DIAMETER_UNKNOWN_SESSION_ID in response. On receiving the response, the DNCA Diameter peer clears the session and removes the associated session state. o NAT-device and the DNCA Diameter peer within NAT-device lose state. In such a case, the DNCA Diameter peer may receive a NCR with NC-Request-Type AVP set to UPDATE_REQUEST for a non-existent session. The DNCA Diameter peer returns NCA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID. o The DNCA Diameter peer within the NAT-controller is unreachable, for example detected by Diameter watchdog, or down and accounting requests from the DNCA Diameter peer fail to get a response. The mechanism to ensure that a DNCA Diameter peer within the NAT- controller no longer has associated state for a session which was cleared or removed by the DNCA Diameter peer within the NAT-device is beyond the scope of this document. o The DNCA Diameter peer within the NAT-device 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 stop offering connectivity service. 5. Use Of The Diameter Base Protocol The Diameter Base Protocol defined by [RFC3588] applies with the clarifications listed in the present specification. 5.1. Securing Diameter Messages For secure transport of Diameter messages recommendations in [RFC3588] apply. DNCA Diameter peers MAY verify their identity during the Capabilities Exchange Request procedure. A DNCA Diameter peer within the NAT-device MAY verify that a DNCA Diameter peer that issues a NCR command is allowed to do so based on: o The identity of the DNCA Diameter peer o The type of NCR Command o The content of the NCR Command Brockners, et al. Expires January 1, 2012 [Page 21] Internet-Draft Diameter NAT Control Application June 2011 o Any combination of the above 5.2. Accounting Functionality Accounting functionality (accounting session state machine, related command codes and AVPs) is defined in Section 9 below. 5.3. Use Of Sessions Each DNCA session MUST have a globally unique Session-ID as defined in [RFC3588], which MUST NOT be changed during the lifetime of a DNCA session. The Diameter Session-ID serves as the global endpoint identifier. The DNCA Diameter peers maintain state associated with the Session-ID. This globally unique Session-ID is used for updating, accounting, and terminating the session. DNCA session MUST NOT have more than one outstanding request at any given instant. A DNCA Diameter peer sends an Abort-Session-Request as defined in [RFC3588] if it is unable to maintain sessions due to resource limitation. 5.4. Routing Considerations It is assumed that the DNCA Diameter peer within a NAT-controller knows the DiameterIdentity of the Diameter peer within a NAT-device for a given endpoint. Both the Destination-Realm and Destination- Host AVPs are present in the request from a DNCA Diameter peer within a NAT-controller to a DNCA Diameter peer within a NAT-device. 5.5. Advertising Application Support Diameter nodes conforming to this specification MUST advertise support for DNCA by including the value of TBD in the Auth- Application-Id of the Capabilities-Exchange-Request and Capabilities- Exchange-Answer command[RFC3588]. 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 Diameter peer within the NAT-controller to the DNCA Diameter peer within the NAT-device in order to install NAT-bindings. Brockners, et al. Expires January 1, 2012 [Page 22] Internet-Draft Diameter NAT Control Application June 2011 User-Name, Logical-Access-Id, Physical-Access-ID, Framed-IP-Address, Framed-IPv6-Prefix , Framed-Interface-Id, EGRESS-VLANID, NAS-Port-ID, Address-Realm, Calling-Station-ID AVPs serve as identifiers for the endpoint. Message format: < NC-Request > ::= < Diameter Header: TBD, REQ, PXY> [ Session-Id ] { Auth-Application-Id } { Origin-Host } { Origin-Realm } { Destination-Realm } { Destination-Host } { NC-Request-Type } [ Origin-State-Id ] *1 [ NAT-Control-Remove ] *1 [ 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 Diameter peer within the NAT-device in response to NAT-Control-Request command. Message format: Brockners, et al. Expires January 1, 2012 [Page 23] Internet-Draft Diameter NAT Control Application June 2011 ::= < Diameter Header: TBD, PXY > [ Session-Id ] { Origin-Host } { Origin-Realm } { Result-Code } [ NC-Request-Type ] * [ NAT-Control-Definition ] [ Current-NAT-Bindings ] [ Origin-State-Id ] [ Error-Message ] [ Error-Reporting-Host ] * [ Failed-AVP ] * [ Proxy-Info ] [ Duplicate-Session-ID ] * [ Redirect-Host] [ Redirect-Host-Usage ] [ Redirect-Max-Cache-Time ] * [ Proxy-Info ] * [ Route-Record ] * [ Failed-AVP ] * [ AVP ] 7. NAT Control Application Session State Machine This section contains a set of finite state machines, representing the life cycle of DNCA session, which MUST be observed by all implementations of the DNCA Diameter application. The DNCA Diameter peers are stateful and the state machine maintained is similar to the stateful Client and Server authorization state machine described in [RFC3588]. When a session is moved to the Idle state, any resources that were allocated for the particular session must be released. Any event not listed in the state machines MUST be considered as an error condition, and an answer, if applicable, MUST be returned to the originator of the message. In the state table, the event 'Failure to send NCR' means that the DNCA Diameter peer within the NAT-controller is unable to send the NCR command to the desired destination. This could be due to the peer being down, or due to the peer sending back the transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of NCA. In the state table "FAILED NCA" means that the DNCA Diameter peer within the NAT-device was not able to honor the corresponding NCR. This can happen due to any transient and permanent error at the NAT- device or its associated DNCA Diameter peer within indicated by the Brockners, et al. Expires January 1, 2012 [Page 24] Internet-Draft Diameter NAT Control Application June 2011 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 Diameter peer within a NAT-controller. The state machine description uses the term "access session" to describe the connectivity service offered to the endpoint or host. "Access session" should not be confused with the Diameter session ID. DNCA Diameter peer within a NAT-controller State Event Action New State ------------------------------------------------------------- Idle New endpoint detected that Send Pending requires NAT Control NCR Initial Request Idle ASR Received Send ASA Idle for unknown session with Result-Code = UNKNOWN_ SESSION_ID Pending Successful NCA Setup Open received complete Pending Successful NCA Sent STR Discon received but peer 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. Brockners, et al. Expires January 1, 2012 [Page 25] Internet-Draft Diameter NAT Control Application June 2011 Open Access session end detected Send STR Discon Open ASR Received, Send ASA Discon access session will be with terminated Result-Code = SUCCESS, Send STR. Open ASR Received, Send ASA Open access session will not with be terminated Result-Code != SUCCESS Discon ASR Received Send ASA Idle Discon STA Received Discon. Idle user/device The following state machine is observed by a DNCA Diameter peer within a NAT-device. Brockners, et al. Expires January 1, 2012 [Page 26] Internet-Draft Diameter NAT Control Application June 2011 DNCA Diameter peer within a NAT-device 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] are listed below. Brockners, et al. Expires January 1, 2012 [Page 27] Internet-Draft Diameter NAT Control Application June 2011 +-------------------+ | 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. | +-------------------------------------------------------------------+ Figure 10: DIAMETER AVPs used from Diameter base The Auth-Application-Id AVP (AVP Code 258) is assigned by IANA to Diameter applications. The value of the Auth-Application-Id for the Diameter NAT Control Application is TBD. 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 Brockners, et al. Expires January 1, 2012 [Page 28] Internet-Draft Diameter NAT Control Application June 2011 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 Diameter peer within the NAT-device indicates that the binding could not be installed or a new session could not be created due to resource shortage. 8.2.3. Permanent Failures The Result-Code AVP values, which fall within the permanent failures category are used to inform the peer that the request failed, and should not be attempted again. The request may be able to be satisfied in the future. The following new values of the Result-Code AVP are defined: UNKNOWN_BINDING_RULE_NAME (TBD) The DNCA Diameter peer within the NAT-device indicates that the binding could not be installed or a new session could not be created because the specified NAT-Control-Binding-Rule AVP, that refers to a predefined policy template in the NAT-device, is unknown. BINDING_FAILURE (TBD) DNCA indicates that the requested binding(s) could not be installed. For example: Requested ports are already in use. MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT (TBD) The DNCA Diameter peer within the NAT-device denies the request because the maximum number of allowed bindings has been reached for the specified endpoint classifier. SESSION_EXISTS (TBD) The DNCA Diameter peer within the NAT-device denies request to initialize a new session, if it already has a DNCA session that uses the same set of classifiers as indicated by the DNCA Diameter peer within the NAT-controller in the new session initialization request. Brockners, et al. Expires January 1, 2012 [Page 29] Internet-Draft Diameter NAT Control Application June 2011 INSUFFICIENT_CLASSIFIERS (TBD) The DNCA Diameter peer within the NAT-device requests to initialize a new session, if the classifiers in the request match more than one of the existing sessions on the DNCA Diameter peer within the NAT-device. 8.3. Reused NASREQ Diameter Application AVPs The following AVPs are reused from Diameter Network Access Server Application [RFC4005]. +---------------------+ | 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 | | | | | | | | +------------------+------+------------|----+-----+----+-----|----+ Figure 11: Reused NASREQ Diameter application AVPs 8.4. Reused AVPs from RFC 4675 The following AVPs are reused from "RADIUS Attributes for Virtual LAN and Priority Support" specification [RFC4675]. +---------------------+ | AVP Flag rules | +------------------+------+------------|----+-----+----+-----|----+ | | AVP | | | |SHLD| MUST| | | Attribute Name | Code | Value Type|MUST| MAY | NOT| NOT|Encr| |------------------|------|------------|----+-----+----+-----|----| | Egress-VLANID | 56 | OctetString| M | P | | V | Y | +------------------+------+------------|----+-----+----+-----|----+ Figure 12: Reused attributes from RFC 4675 Brockners, et al. Expires January 1, 2012 [Page 30] Internet-Draft Diameter NAT Control Application June 2011 8.5. Reused AVPs from Diameter QoS Application The following AVPs are reused from the Traffic Classification and Quality of Service (QoS) Attributes for Diameter [RFC5777]. +-------------------+ | 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. | +-------------------------------------------------------------------+ Figure 13: Reused QoS-attributes 8.6. Reused AVPs from ETSI ES 283 034, e4 Diameter Application The following AVPs are reused from the Diameter e4 Application [ETSIES283034]. +-------------------+ | 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). | +-------------------------------------------------------------------+ Figure 14: Reused AVPs from Diameter e4 application Brockners, et al. Expires January 1, 2012 [Page 31] Internet-Draft Diameter NAT Control Application June 2011 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 8.7.1 Enumerated | M | P | Y | |NAT-Control-Install TBD 8.7.2 Grouped | M | P | Y | |NAT-Control-Remove TBD 8.7.3 Grouped | M | P | Y | |NAT-Control-Definition TBD 8.7.4 Grouped | M | P | Y | |NAT-Internal-Address TBD 8.7.5 Grouped | M | P | Y | |NAT-External-Address TBD 8.7.6 Grouped | M | P | Y | |Max-NAT-Bindings TBD 8.7.7 Unsigned32 | M | P | Y | |NAT-Control- TBD 8.7.8 OctetString| M | P | Y | | Binding-Rule | | | | |Duplicate- TBD 8.7.9 UTF8String | M | P | Y | | Session-ID | | | | |NAT-Control-Record TBD 9.2.1 Grouped | M | P | Y | |NAT-Control- TBD 9.2.2 Enumerated | M | P | Y | | Binding-Status | | | | |Current-NAT-Bindings TBD 9.2.3 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. | +-------------------------------------------------------------------+ Figure 15: New Diameter AVPs 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 to initiate a Diameter NAT control session between the DNCA Diameter peers. UPDATE_REQUEST (2) Brockners, et al. Expires January 1, 2012 [Page 32] Internet-Draft Diameter NAT Control Application June 2011 An Update Request is used to update bindings previously installed on a given access session, to add new binding on a given access session, or to remove one or several binding(s) activated on a given access session. QUERY_REQUEST (3) Query Request is used to query a NAT-device about the currently installed bindings for an endpoint classifier. 8.7.2. NAT-Control-Install AVP The NAT-Control 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 the maximum number of NAT bindings to be allowed for a subscriber and the NAT-Control-Binding-Rule that references a predefined policy template on the NAT-device that may contain static binding, a maximum number of bindings allowed, an IP- address pool from which external binding addresses should be allocated. 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 Diameter peers. If both the NAT-Internal-Address and NAT-External-Address AVP(s) are Brockners, et al. Expires January 1, 2012 [Page 33] Internet-Draft Diameter NAT Control Application June 2011 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 IP-address are specified then the binding reserves the IP-addresses for all transport protocols. The Direction AVP is of type Enumerated. It specifies the direction for the binding. The values of the enumeration applicable in this context are: "IN","OUT". If Direction AVP is OUT or absent, the NAT- Internal-Address refers to the IP-address of the endpoint that needs to be translated. If Direction AVP is "IN", NAT-Internal-Address is the destination IP-address that has to be translated. AVP format: NAT-Control-Definition ::= < AVP Header: TBD > { 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 the Framed-IP-Address AVP is present. The external IP-address specified in this attribute can be reused for multiple endpoints by specifying the same address in the respective NAT-External-Address AVPs. AVP format: Brockners, et al. Expires January 1, 2012 [Page 34] Internet-Draft Diameter NAT Control Application June 2011 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 for a particular endpoint. 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 is predefined at the NAT-device. Details on the contents and structure of the template and configuration are outside the scope of this document. The policy to which this AVP refers to may contain NAT- bindings, IP-address pool for allocating the external IP-address of a NAT-binding, and maximum number of allowed NAT-bindings. Such policy template can be reused by specifying the same NAT-Control-Binding- Rule AVP in the corresponding NAT-Control-Install AVPs of multiple endpoints. 8.7.9. Duplicate-Session-Id AVP The Duplicate-Session-Id AVP (AVP Code TBD) is of type UTF8String. It is used to report errors and contains the Session-Id of an existing session. 9. Accounting Commands The DNCA reuses session based accounting as defined in the Diameter Base Protocol[RFC3588] to report the bindings per endpoint. This reporting is achieved by sending Diameter Accounting Requests (ACR) [Start, Interim and Stop] from the DNCA Diameter peer within the NAT- device to its associated DNCA Diameter peer within the NAT- controller. The DNCA Diameter peer within the NAT-device sends an ACR Start on receiving a NCR with NC-Request-Type AVP set to INITIAL_REQUEST for a session or on creation of the first binding for a session requested in an earlier NCR. DNCA may send ACR Interim updates, if required, either due to a change in bindings resulting from a NCR with NC- Request-Type AVP set to UPDATE_REQUEST, or periodically as specified in Acct-Interim-Interval by the DNCA Diameter peer within the NAT- Brockners, et al. Expires January 1, 2012 [Page 35] Internet-Draft Diameter NAT Control Application June 2011 controller, or when it creates or tears down bindings. An ACR Stop is sent by the DNCA Diameter peer within the NAT-device on receiving STR. The function of correlating the multiple bindings used by an endpoint at any given time is relegated to the post processor. The DNCA Diameter peer within the NAT-device may trigger an interim accounting record when 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] for exchanging endpoint NAT binding details between the DNCA Diameter peers. DNCA Application ID is used in the accounting commands. ACR contains one or more optional NAT-Control- Record AVP to report the bindings. The NAT-device indicates the number of allocated NAT bindings to NAT-controller using the Current- NAT-Bindings AVP. This number needs to match the number of bindings identified as active within the NAT-Control-Record AVP. 9.2. NAT Control Accounting AVPs In addition to AVPs for ACR specified in [RFC3588], the DNCA Diameter peer within the NAT-device must add the NAT-Control-Record AVP. 9.2.1. NAT-Control-Record The NAT-Control-Record AVP (AVP code TBD) 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: Brockners, et al. Expires January 1, 2012 [Page 36] Internet-Draft Diameter NAT Control Application June 2011 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 DNCA specific AVPs that have to be present in NCR and NCA with NC-Request-Type set to INITIAL_REQUEST or UPDATE_REQUEST. Brockners, et al. Expires January 1, 2012 [Page 37] Internet-Draft Diameter NAT Control Application June 2011 +-------------------+ | Command Code | +-----------------------------------+-------------------+ | Attribute Name NCR NCA | +-------------------------------------------------------+ |NC-Request-Type 1 1 | |NAT-Control-Install 0-1 0 | |NAT-Control-Remove 0-1 0 | |NAT-Control-Definition 0 0 | |Current-NAT-Bindings 0 0 | |Duplicate-Session-Id 0 0-1 | +-------------------------------------------------------+ 10.2. DNCA AVP Table for Session Query request The following table lists 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+ | |Current-NAT-Bindings 0 1 | |Duplicate-Session-Id 0 0 | +-------------------------------------------------------+ 10.3. DNCA AVP Table for Accounting Message The following table lists DNCA specific AVPs, which may or may not be present in ACR and ACA messages. +-------------------+ | Command Code | +-----------------------------------+-------------------+ | Attribute Name ACR ACA | +-------------------------------------------------------+ |NAT-Control-Record 0+ 0 | |Current-NAT-Bindings 1 0 | +-------------------------------------------------------+ 11. IANA Considerations This section contains the namespaces that have either been created in this specification, or the values assigned to existing namespaces Brockners, et al. Expires January 1, 2012 [Page 38] Internet-Draft Diameter NAT Control Application June 2011 managed by IANA. In the subsections below, when we speak about review by a Designated Expert, please note that the designated expert will be assigned by the IESG. Initially, such Expert discussions take place on the AAA WG mailing list. 11.1. Application Identifier This specification assigns the value , 'Diameter NAT Control Application', to the Application Identifier namespace defined in [RFC3588]. See Section 4 for more information. 11.2. Command Codes This specification uses the value from the Command code namespace defined in [RFC3588] for the NAT-Control-Request (NCR), NAT-Control-Answer (NCA) commands. See Section 6.1 and Section 6.2 for more information on these commands. 11.3. AVP Codes This specification assigns the values from the AVP code namespace defined in [RFC3588]. See Figure 15for the assignment of the namespace in this specification. 11.4. Result-Code AVP Values This specification assigns the values (4xxx, 5xxx, 5xxx, 5xxx, 5xxx,5xxx) from the Result-Code AVP value namespace defined in [RFC3588]. See Section 8.2 for the assignment of the namespace in this specification. 11.5. NC-Request-Type AVP As defined in Section 8.7.1, the NC-Request-Type AVP includes Enumerated type values 1 - 3. IANA has created and is maintaining a namespace for this AVP. All remaining values are available for assignment by a Designated Expert [RFC5226]. 11.6. NAT-Control-Binding-Status AVP As defined in Section 8.7.1, the NAT-Control-Binding-Status AVP includes Enumerated type values 1 - 3. IANA has created and is maintaining a namespace for this AVP. All remaining values are available for assignment by a Designated Expert [RFC5226]. Brockners, et al. Expires January 1, 2012 [Page 39] Internet-Draft Diameter NAT Control Application June 2011 12. Security Considerations This document describes procedures for controlling NAT related attributes and parameters by an entity, which is non-local to the device performing NAT. This section discusses security considerations for DNCA interactions between the Diameter peers within a NAT-controller and a NAT-device. Security between NAT- controller and NAT-device has a number of components: authentication, authorization, integrity, and confidentiality. Authentication refers to confirming the identity of an originator for all datagrams received from the originator. Lack of authentication of Diameter messages between the Diameter peers can jeopardize the fundamental service of the peering network elements. A consequence of not authenticating the message sender by the recipient would be that an attacker could spoof the identity of a "legitimate" authorizing entity in order to change the behavior of the receiver. An attacker could for example launch a denial of service attack by setting the maximum number of bindings for a session on the NAT- device to zero; provision bindings on a NAT-device which include IP- addresses already in use in other parts of the network; or request session termination of the Diameter session and hamper a user's connectivity. Lack of authentication of a NAT-device to a NAT- controller could lead to situations where the NAT-device could provide a wrong view of the resources (i.e. NAT-bindings). In addition, templates on the NAT-device specifying pre-defined binding rules could be configured differently than expected by the NAT- controller. Failing of any of the two DNCA Diameter peers to provide the required credentials should be subject to logging. Authorization refers to whether a particular authorizing entity is authorized to signal a network element requests for one or more applications, adhering to a certain policy profile. Failing the authorization process might indicate a resource theft attempt or failure due to administrative and/or credential deficiencies. In either case, the network element should take the proper measures to log such attempts. Integrity is required to ensure that a Diameter message exchanged between the Diameter peers has not been maliciously altered by intermediate devices. The result of a lack of data integrity enforcement in an untrusted environment could be that an impostor will alter the messages exchanged between the peers. This could cause a change of behavior of the peers, including the potential of a denial of service. Confidentiality protection of Diameter messages ensures that the signaling data is accessible only to the authorized entities. When Brockners, et al. Expires January 1, 2012 [Page 40] Internet-Draft Diameter NAT Control Application June 2011 signaling messages between the DNCA Diameter peers traverse untrusted networks, lack of confidentiality will allow eavesdropping and traffic analysis. Diameter offers security mechanisms to deal with the functionality demanded above. DNCA makes use of the capabilities offered by Diameter and the underlying transport protocols to deliver these requirements (see Section 5.1 ). If the DNCA communication traverses untrusted networks, it is assumed that messages between DNCA Diameter peers are secured using either IPsec or TLS. Please refer to [RFC3588], section 13 for details. DNCA Diameter peers MAY perform bilateral authentication, authorization as well as procedures to ensure integrity and confidentiality of the information exchange. It is assumed that the DNCA Diameter peers are typically in the same domain and have a mutual trust set up. This document does not specify a mechanisms for authorization between the DNCA Diameter peers. It is assumed that the DNCA Diameter peers are provided with sufficient information to make an authorization decision. The information can come from various sources, for example the peering devices could store local authentication policy, listing the identities of authorized peers. 13. Acknowledgements The authors would like to thank Miguel A. Garcia, Jouni Korhonen, Matt Lepinski, Avi Lior, Chris Metz, Pallavi Mishra, Lionel Morand, Hannes Tschofenig, Shashank Vikram, 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 Brockners, et al. Expires January 1, 2012 [Page 41] Internet-Draft Diameter NAT Control Application June 2011 a. Reference to pull mode removed, session initiation event clarified in section 4.1 b. added Redirect-* AVPs in NCA command c. Removed reference to Called-Station-Id AVP in NCR command d. Editorial changes e. added support for bindings providing AFT (NAT64) Changes from -02 to -03 a. Editorial changes Changes from -03 to -04 a. Editorial changes suggested in WG last call review b. Removed NCR Request type terminate and replaced with STR c. All references to Auth-Session-State are removed and a new section to describe FSM for Manager and Agent has been added d. Clarified reuse of External address and address pools among multiple subscribers Changes from -04 to -05 a. Removed references to Large Scale NAT as per review comments Changes from -05 to -06 a. Editorial changes Changes from -06 to -07 a. Added a note in section 4.3 stating the state of pre-existing bindings on update failure b. Security considerations are made consistent between sections 5.1 and 12 c. Editorial changes Changes from -07 to -08 Brockners, et al. Expires January 1, 2012 [Page 42] Internet-Draft Diameter NAT Control Application June 2011 a. Added section 4.6 to describe session abort b. Editorial changes c. Nomenclature change: From DNCA Agent/Manager to DNCA Diameter peers identifying the location where they reside (NAT-controller or NAT-device) d. IANA consideration Section format changes e. Updated security section (included considerations directly, rather than referring to Diameter QoS similarities). 15. Normative References [ETSIES283034] ETSI, "Telecommunications and Internet Converged Services and Protocols for Advanced Networks (TISPAN),Network Attachment Sub-System (NASS),e4 interface based on the Diameter protocol.", September 2008. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, "Diameter Network Access Server Application", RFC 4005, August 2005. [RFC4675] Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Attributes for Virtual LAN and Priority Support", RFC 4675, September 2006. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M., and A. Lior, "Traffic Classification and Quality of Service (QoS) Attributes for Diameter", RFC 5777, February 2010. Brockners, et al. Expires January 1, 2012 [Page 43] Internet-Draft Diameter NAT Control Application June 2011 Authors' Addresses Frank Brockners Cisco Hansaallee 249, 3rd Floor DUESSELDORF, NORDRHEIN-WESTFALEN 40549 Germany Email: fbrockne@cisco.com Shwetha Bhandari Cisco Cessna Business Park, Sarjapura Marathalli Outer Ring Road Bangalore, KARNATAKA 560 087 India Email: shwethab@cisco.com Vaneeta Singh 18, Cambridge Road Bangalore 560008 India Email: vaneeta.singh@gmail.com Victor Fajardo Telcordia Technologies 1 Telcordia Drive #1S-222 Piscataway, NJ 08854 USA Email: vf0213@gmail.com Brockners, et al. Expires January 1, 2012 [Page 44]