| Internet Engineering Task Force | F. Brockners |
| Internet-Draft | S. Bhandari |
| Intended status: Standards Track | Cisco |
| Expires: October 20, 2012 | V. Singh |
| V. Fajardo | |
| Telcordia Technologies | |
| April 20, 2012 |
Diameter Network Address and Port Translation Control Application
draft-ietf-dime-nat-control-16
This document describes the framework, messages, and procedures for the Diameter Network address and port translation Control Application. This Diameter application allows per endpoint control of Network Address Translators and Network Address and Port Translators, which are added to networks to cope with IPv4-address space depletion. This Diameter application allows external devices to configure and manage a Network Address Translator device - expanding the existing Diameter-based AAA and policy control capabilities with a Network Address Translators and Network Address and Port Translators control component. These external devices can be network elements in the data plane such as a Network Access Server, or can be more centralized control plane devices such as AAA-servers. This Diameter application establishes a context to commonly identify and manage endpoints on a gateway or server, and a Network Address Translator and Network Address and Port Translator device. This includes, for example, the control of the total number of Network Address Translator bindings allowed or the allocation of a specific Network Address Translator binding for a particular endpoint. In addition, it allows Network Address Translator devices to provide information relevant to accounting purposes.
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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 time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 20, 2012.
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Internet service providers deploy Network Address Translators (NATs) and Network Address and Port Translators (NAPTs) [RFC3022] in their networks. A key motivation for doing so is the depletion of available public IPv4 addresses. This document defines a Diameter application allowing providers to control the behavior of NAT and NAPT devices that implement IPv4-to-IPv4 network address and port translation [RFC2663] as well as stateful IPv6-to-IPv4 address family translation as defined in [RFC2663], [RFC6145], and [RFC6146]. The use of a Diameter application allows for simple integration into the existing Authentication, Authorization and Accounting (AAA) environment of a provider.
The Diameter Network address and port translation Control Application (DNCA) offers the following capabilities:
With the above capabilities, DNCA qualifies as a MIDCOM protocol [RFC3303], [RFC3304], [RFC5189] for middle boxes which perform NAT. The MIDCOM protocol evaluation [RFC4097] evaluated Diameter as a candidate protocol for MIDCOM. DNCA provides the extensions to the Diameter base protocol [RFC3588] following the MIDCOM protocol requirements, such as the support of NAT-specific rule transport, support for oddity of mapped ports, as well as support for consecutive range port numbers. DNCA adds to the MIDCOM protocol capabilities in that it allows to maintain the reference to an endpoint representing a user or subscriber in the control operation, enabling the control of the behavior of a NAT-device on a per endpoint basis. Following the requirements of different operators and deployments, different management protocols are employed. Examples include e.g. SNMP [RFC3411] and NETCONF [RFC6241] which can both be used for device configuration. Similarly, DNCA is complementing existing MIDCOM implementations, offering a MIDCOM protocol option for operators with an operational environment that is Diameter-focused which desire to use Diameter to perform per endpoint NAT control. Note that in case an operator uses multiple methods and protocols to configure a NAT-device, such as for example command line interface, SNMP, NETCONF, or PCP, along with DNCA specified in this document, the operator MUST ensure that the configurations performed using the different methods and protocols do not conflict in order to ensure a proper operation of the NAT service.
This document is structured as follows: Section 2 lists terminology, while Section 3 provides an introduction to DNCA and its overall deployment framework. Sections 4 to 8 cover DNCA specifics, with Section 4 describing session management, Section 5 the use of the Diameter base protocol, Section 6 new commands, Section 7 Attribute Value Pairs(AVPs) used, and Section 8 accounting aspects. Section 9 presents AVP occurrence tables. IANA and security considerations are addressed in Sections 10 and 11.
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:
Figure 1 shows a typical network deployment for IPv4-Internet access. A user’s IPv4 host (i.e. endpoint) gains access to the Internet though a NAS, which facilitates the authentication of the endpoint and configures the endpoints’s connection according to the authorization and configuration data received from the AAA-server upon successful authentication. Public IPv4 addresses are used throughout the network. DNCA manages an endpoint that represents a network element or device or IPv4 host, associated with a subscriber, a user or a group of users. An endpoint is represented by a single access-session on a NAS. DNCA assumes a 1:1 relationship between an endpoint, the access-session it represents, and the associated DNCA session.
+---------+
| |
| AAA |
| |
+---------+
|
|
|
|
+---------+ +---------+ +----------+
| IPv4 | | | | IPv4 |
| Host |----------| NAS |-------------| Internet |
| | | | | |
+---------+ +---------+ +----------+
<-------------------- Public IPv4 ---------------------->
Figure 2 depicts the deployment scenario where a service provider places a NAT between the host and the public Internet. The objective is to provide the customer with connectivity to the public IPv4 Internet. The NAT-device performs network address and port (and optionally address family) translation, depending on whether the access network uses private IPv4 addresses or public IPv6 addresses, to public IPv4 addresses. Note that there may be more than one NAS, NAT-device, or AAA-entity in a deployment, although the figures only depict one entity each for clarity.
If the NAT-device would be put in place without any endpoint awareness, the service offerings of the service provider could be impacted as detailed in [I-D.ietf-behave-lsn-requirements]. This includes cases like:
+---------+
| |
| AAA |
| |
+---------+
|
|
|
|
+--------+ +---------+ +--------+ +----------+
| IPv4 |----| |----| NAT- |----| IPv4- |
| Host | | NAS | | device | | Internet |
| | | | | | | |
+--------+ +---------+ +--------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 2 shows a typical deployment for IPv4-Internet access involving a NAT-device within the service provider network. The figure describes two scenarios: One where an IPv4-host (with a private IPv4 address) accesses the IPv4-Internet, as well as one where an IPv6-host accesses the IPv4-Internet.
DNCA runs between two DNCA Diameter peers. One DNCA Diameter peer resides within the NAT-device, the other DNCA Diameter peer resides within a NAT-controller (discussed in Section 3.3). DNCA allows per endpoint control and management of NAT within the NAT-device. Based on Diameter, DNCA integrates well with the suite of Diameter applications deployed for per endpoint authentication, authorization, accounting, and policy control in service provider networks.
DNCA offers:
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.
DNCA can be deployed in different ways. DNCA supports deployments with "n" NAT-controllers and "m" NAT-devices, with n and m equal to or greater than 1. From a DNCA perspective an operator should ensure that the session representing a particular endpoint is atomic. Any deployment MUST ensure that for any given endpoint only a single DNCA NAT-controller and is active at any point in time. This is to ensure that NAT-devices controlled by multiple NAT-controllers do not receive conflicting control requests for a particular endpoint, or would be unclear which NAT-controller to send accounting information to. Operational considerations MAY require an operator to use alternate control mechanisms or protocols such as SNMP or manual configuration via a Command-Line-Interface to apply per-endpoint NAT-specific configuration, like for example static NAT-bindings. For these cases, the NAT-device MUST allow the operator to configure a policy how configuration conflicts are resolved. Such a policy could for example specify that manually configured NAT-bindings using the Command-Line-Interface always take precedence over those configured using DNCA.
Two common deployment scenarios are outlined in Figure 3 (“integrated deployment”) and Figure 4 (“autonomous deployment”). Per the note above, multiple instances of NAT-controllers and NAT-devices could be deployed. The figures only show single instances for reasons of clarity. The two shown scenarios differ in which entity fulfills the role of the NAT-controller. Within the figures (C) denotes the network element performing the role of the NAT-controller.
The integrated deployment approach hides the existence of the NAT-device from external servers, such as the AAA-server. It is suited for environments where minimal changes to the existing AAA deployment are desired. The NAS and the NAT-device are Diameter peers supporting the DNCA. The Diameter peer within the NAS, performing the role of the NAT-controller, initiates and manages sessions with the NAT-device, exchanges NAT specific configuration information and handles reporting and accounting information. The NAS receives reporting and accounting information from the NAT-device. With this information, the NAS can provide a single accounting record for the endpoint. A system correlating the accounting information received from the NAS and NAT-device would not be needed.
An example network attachment for an integrated NAT deployment can be described as follows: An endpoint connects to the network, with the NAS being the point of attachment. After successful authentication, the NAS receives endpoint related authorization data from the AAA-server. A portion of the authorization data applies to per endpoint configuration on the NAS itself, another portion describes authorization and configuration information for NAT control aimed at the NAT-device. The NAS initiates a DNCA session to the NAT-device and sends relevant authorization and configuration information for the particular endpoint to the NAT-device. This can comprise NAT-bindings, which have to be pre-established for the endpoint, or management related configuration, such as the maximum number of NAT-bindings allowed for the endpoint. The NAT-device sends its per endpoint accounting information to the NAS, which aggregates the accounting information received from the NAT-device with its local accounting information for the endpoint into a single accounting stream towards the AAA-server.
+---------+
| |
| AAA |
| |
+---------+
|
|
|
+--------+ +---------+ +--------+ +----------+
| | | (C) | | | | |
| Host |----| NAS |----| NAT- |----| IPv4- |
| | | | | device | | Internet |
+--------+ +---------+ +--------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 3 shows examples of integrated deployments. The figure describes two scenarios: One where an IPv4-host (with a private IPv4 address) accesses the IPv4-Internet, as well as one where an IPv6-host accesses the IPv4-Internet.
The autonomous deployment approach decouples endpoint management on the NAS and NAT-device. In the autonomous deployment approach, the AAA-system and the NAT-device are the Diameter peers running the DNCA. The AAA-system also serves as NAT-controller. It manages the connection to the NAT-device, controls the per endpoint configuration, and also receives accounting and reporting information from the NAT-device. Different from the integrated deployment scenario, the autonomous deployment scenario does not “hide” the existence of the NAT-device from the AAA infrastructure. Here two accounting streams are received by the AAA-server for one particular endpoint, one from the NAS, and one from the NAT-device.
+---------+
| (C) |
| AAA |---------
| | |
+---------+ |
| |
| |
| |
+--------+ +---------+ +---------+ +----------+
| IPv4/ | | | | | | IPv4 |
| IPv6 |----| NAS |----| NAT- |----| Internet |
| Host | | | | device | | |
+--------+ +---------+ +---------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 4 shows examples of autonomous deployments. The figure describes two scenarios: One where an IPv4-host (with a private IPv4 address) accesses the IPv4-Internet, as well as one where an IPv6-host accesses the IPv4-Internet.
Note that this section forward references some of the commands and AVPs defined for DNCA. Please refer to Section 6 and Section 8 for details. DNCA runs between a Diameter peer residing in a NAT-controller and a Diameter peer residing in a NAT-device. Note that, per what was already mentioned above, each DNCA session between Diameter peers in a NAT-controller and a NAT-device represents a single endpoint, with an endpoint being either a network element, a device or an IPv4 host associated with a subscriber, a user, or a group of users. The Diameter peer within the NAT-controller is always the control requesting entity: It initiates, updates, or terminates the sessions. Sessions are initiated when the NAT-controller learns about a new endpoint (i.e., host) that requires a NAT service. This could for example be due to the entity hosting the NAT-controller receiving authentication, authorization, or accounting requests for or from the endpoint. Alternate methods that could trigger session setup include local configuration, receipt of a packet from a formerly unknown IP-address, etc.
The DNCA Diameter peer within the NAT-controller establishes a session with the DNCA Diameter peer within the NAT-device to control the behavior of the NAT function within the NAT-device. During session establishment, the DNCA Diameter peer within the NAT-controller passes along configuration information to DNCA Diameter peer within the NAT-device. The session configuration information comprises the maximum number of bindings allowed for the endpoint associated with this session, a set of pre-defined NAT bindings to be established for this endpoint, or a description of the address pool, that external addresses are to be allocated from.
The DNCA Diameter peer within the NAT-controller generates a NAT-Control Request (NCR) message to the DNCA Diameter peer within the NAT-device with NC-Request-Type AVP set to INITIAL_REQUEST to initiate a Diameter NAT control session. On receipt of a NCR the DNCA Diameter peer within the NAT-device sets up a new session for the endpoint associated with the endpoint classifier(s) contained in the NCR. The DNCA Diameter peer within the NAT-device notifies its DNCA Diameter peer within the NAT-controller about successful session setup using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS. Figure 5 shows the initial protocol interaction between the two DNCA Diameter peers.
The initial NAT-Control-Request MAY contain configuration information for the session, which specifies the behavior of the NAT-device for the session. The configuration information that MAY be included, comprises:
In certain cases, the NAT-device may not be able to perform the tasks requested within the NCR. These include the following:
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| |
Trigger |
| |
| NCR |
|------------------------------------------>|
| |
| |
| |
| |
| If Able to comply
| with Request then
| Create session state
| |
| |
| NCA |
|<------------------------------------------|
| |
| |
Note: The DNCA Diameter peer within the NAT-device creates session state only if it is able to comply with the NCR. On success it will reply with an NCA with Result-Code set to DIAMETER_SUCCESS.
Session update is performed if the NAT-controller desires to change the behavior of the NAT-device for an existing session. Session update could be used, for example, to change the number of allowed bindings for a particular session, or establish or remove a pre-defined binding.
The DNCA Diameter peer within the NAT-controller generates a NCR message to the DNCA Diameter peer within the NAT-device with NC-Request-Type AVP set to UPDATE_REQUEST upon receiving a trigger signal. If the session is updated successfully, the DNCA Diameter peer within the NAT-device notifies the DNCA Diameter peer within the NAT-controller about the successful session update using a NAT-Control Answer (NCA) message with Result-Code set to DIAMETER_SUCCESS.Figure 6 shows the protocol interaction between the two DNCA Diameter peers.
In certain cases, the NAT-device may not be able to perform the tasks requested within the NCR. These include the following:
Note: Already established bindings for the session SHOULD 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 |
|------------------------------------------>|
| |
| |
| If able to comply
| with the request:
| Update session state
| |
| |
| NCA |
|<------------------------------------------|
| |
A Session and NAT-binding query MAY be used by the DNCA Diameter peer within the NAT-controller to either retrieve information on the current bindings for a particular session at the NAT-device or discover the session identifier for a particular external IP address/port pair.
A DNCA Diameter peer within the NAT-controller starts a session query by sending an NCR message with NC-Request-Type AVP set to QUERY_REQUEST. Figure 7 shows the protocol interaction between the DNCA Diameter peers.
Two types of query requests exist. The first type of query request uses the session ID as input parameter to the query. It is to allow the DNCA Diameter peer within the NAT-controller to retrieve the current set of bindings for a specific session. The second type of query request is used to retrieve the session identifiers, along with the associated bindings, matching a criteria. This enables the DNCA Diameter peer within the NAT-controller to find those sessions, which utilize a specific external or internal IP-address.
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| |
DNCA Session Established |
| |
| NCR |
|------------------------------------------>|
| |
| |
| |
| |
| Look up corresponding session
| and associated NAT-bindings
| |
| NCA |
|<------------------------------------------|
| |
| |
| |
Similar to session initiation, session tear down MUST be initiated by the DNCA Diameter peer within the NAT-controller. The DNCA Diameter peer sends a Session Terminate Request (STR) message to its peer within the NAT-device upon receiving a trigger signal. The source of the trigger signal is outside the scope of this document. As part of STR message processing the DNCA Diameter peer within the NAT-device MAY send an accounting stop record reporting all bindings. All the NAT-bindings belonging to the session MUST be removed and the session state MUST be cleaned up. The DNCA Diameter peer within the NAT-device MUST notify its DNCA Diameter peer in the NAT-controller about successful session termination using a Session Terminate Answer (STA) message with Result-Code set to DIAMETER_SUCCESS. Figure 8 shows the protocol interaction between the two DNCA Diameter peers.
If a DNCA Diameter peer within a NAT-device receives a STR and fails to find a matching session, the DNCA Diameter peer MUST return a STA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
Trigger |
| |
| STR |
|------------------------------------------->|
| |
| |
| |
| |
| |
| Send accounting stop |
|<-------------------------------------------|
| reporting all session bindings |
| |
| |
| Remove NAT-bindings
| of session
| |
| Terminate session /
| Remove session state
| |
| |
| |
| STA |
|<-------------------------------------------|
| |
| |
An Abort-Session-Request (ASR) message is sent from the DNCA Diameter peer within the NAT-device to the DNCA Diameter peer within the NAT-controller when it is unable to maintain a session due to resource limitations. The DNCA Diameter peer within the NAT-controller MUST acknowledge successful session abort using a Abort Session Answer (ASA) message with Result-Code set to DIAMETER_SUCCESS. Figure 9 shows the protocol interaction between the DNCA Diameter peers. The DNCA Diameter peers will start a session termination procedure as described in Section 4.4 following an ASA with Result-Code set to DIAMETER_SUCCESS.
If the DNCA Diameter peer within a NAT-controller receives an ASR but fails to find a matching session, it MUST return an ASA with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID. If the DNCA Diameter peer within the NAT-controller is unable to comply with the ASR for any other reason, an ASA with Result-Code set to DIAMETER_UNABLE_TO_COMPLY MUST be returned.
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| Trigger
| |
| ASR |
|<-------------------------------------------|
| |
| |
| |
| ASA |
|------------------------------------------->|
| |
| |
| |
| On successful ASA |
|<------Session Termination Procedure------->|
This document does not specify the behavior in case the NAT-device and NAT-controller, or their respective DNCA Diameter peers are out of sync or lose state. This could happen for example if one of the entities restarts, in case of a (temporary) loss of network connectivity etc. Example failure cases include the following:
The Diameter Base Protocol defined by [RFC3588] applies with the clarifications listed in the present specification.
For secure transport of Diameter messages, the recommendations in [RFC3588] apply.
DNCA Diameter peers SHOULD verify their identity during the Capabilities Exchange Request procedure.
A DNCA Diameter peer within the NAT-device SHOULD verify that a DNCA Diameter peer that issues a NCR command is allowed to do so based on:
Accounting functionality (accounting session state machine, related command codes and AVPs) is defined in Section 9 below.
Each DNCA session MUST have a globally unique Session-ID as defined in [RFC3588], which MUST NOT be changed during the lifetime of a DNCA session. The Diameter Session-ID serves as the global endpoint identifier. The DNCA Diameter peers maintain state associated with the Session-ID. This globally unique Session-ID is used for updating, accounting, and terminating the session. A DNCA session MUST NOT have more than one outstanding request at any given instant. A DNCA Diameter peer sends an Abort-Session-Request as defined in [RFC3588] if it is unable to maintain sessions due to resource limitation.
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.
Diameter nodes conforming to this specification MUST advertise support for DNCA by including the value of TBD.APP-ID in the Auth-Application-Id of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer command[RFC3588].
The following commands are used to establish, maintain and query NAT-bindings.
The NAT-Control Request (NCR) command, indicated by the command field set to TBD.COM-CODE and the "R" bit set in the Command Flags field, is sent from the DNCA Diameter peer within the NAT-controller to the DNCA Diameter peer within the NAT-device in order to install NAT-bindings.
User-Name, Logical-Access-Id, Physical-Access-ID, Framed-IP-Address, Framed-IPv6-Prefix, Framed-Interface-Id, EGRESS-VLANID, NAS-Port-ID, Address-Realm, Calling-Station-ID AVPs serve as identifiers for the endpoint.
Message format:
< NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
{ Auth-Application-Id }
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Destination-Host }
{ NC-Request-Type }
[ Session-Id ]
[ Origin-State-Id ]
*1 [ NAT-Control-Remove ]
*1 [ NAT-Control-Install ]
[ NAT-External-Address ]
[ User-Name ]
[ Logical-Access-Id ]
[ Physical-Access-ID ]
[ Framed-IP-Address ]
[ Framed-IPv6-Prefix ]
[ Framed-Interface-Id ]
[ EGRESS-VLANID]
[ NAS-Port-ID]
[ Address-Realm ]
[ Calling-Station-ID ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ AVP ]
The NAT-Control-Answer (NCA) command, indicated by the Command-Code field set to TBD.COM-CODE and the "R" bit cleared in the Command Flags field, is sent by the DNCA Diameter peer within the NAT-device in response to NAT-Control-Request command.
Message format:
<NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
{ Origin-Host }
{ Origin-Realm }
{ Result-Code }
[ Session-Id ]
[ NC-Request-Type ]
* [ NAT-Control-Definition ]
[ Current-NAT-Bindings ]
[ Origin-State-Id ]
[ Error-Message ]
[ Error-Reporting-Host ]
* [ Failed-AVP ]
* [ Proxy-Info ]
[ Duplicate-Session-ID ]
* [ Redirect-Host]
[ Redirect-Host-Usage ]
[ Redirect-Max-Cache-Time ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ Failed-AVP ]
* [ AVP ]
This section contains a set of finite state machines, representing the life cycle of a DNCA session, which MUST be observed by all implementations of the DNCA Diameter application. The DNCA Diameter peers are stateful and the state machine maintained is similar to the stateful Client and Server authorization state machine described in [RFC3588]. When a session is moved to the Idle state, any resources that were allocated for the particular session must be released. Any event not listed in the state machines MUST be considered as an error condition, and an answer, if applicable, MUST be returned to the originator of the message.
In the state table, the event 'Failure to send NCR' means that the DNCA Diameter peer within the NAT-controller is unable to send the NCR command to the desired destination. This could be due to the peer being down, or due to the peer sending back the transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of an NCA.
In the state table "FAILED NCA" means that the DNCA Diameter peer within the NAT-device was not able to honor the corresponding NCR. This can happen due to any transient and permanent error at the NAT-device or its associated DNCA Diameter peer within indicated by the following error Result-Code values: RESOURCE_FAILURE, UNKNOWN_BINDING_TEMPLATE_NAME, MAX_BINDINGS_SET_FAILURE, BINDING_FAILURE, MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT, SESSION_EXISTS, INSUFFICIENT_CLASSIFIERS.
The following state machine is observed by a DNCA Diameter peer within a NAT-controller. The state machine description uses the term "access session" to describe the connectivity service offered to the endpoint or host. "Access session" should not be confused with the Diameter session ID.
DNCA Diameter peer within a NAT-controller
State Event Action New State
-------------------------------------------------------------
Idle New endpoint detected that Send Pending
requires NAT Control NCR
Initial
Request
Idle ASR Received Send ASA Idle
for unknown session with
Result-Code
= UNKNOWN_
SESSION_ID
Pending Successful NCA Setup Open
received complete
Pending Successful NCA Send STR Discon
received
but peer unable to provide
service
Pending Error processing successful Send STR Discon
NCA
Pending Failed Clean up Idle
NCA received
Open NAT control Send Open
update required NCR Update
Request
Open Successful Open
NCA received
Open Failed Clean up Idle
NCA received
Open Access session end detected Send STR Discon
Open ASR Received, Send ASA Discon
access session will be with
terminated Result-Code
= SUCCESS,
Send STR
Open ASR Received, Send ASA Open
access session will not with
be terminated Result-Code
!= SUCCESS
Discon ASR Received Send ASA Idle
Discon STA Received Discon. Idle
endpoint
The following state machine is observed by a DNCA Diameter peer within a NAT-device.
DNCA Diameter peer within a NAT-device
State Event Action New State
-------------------------------------------------------------
Idle NCR Query request Send Idle
received, and successful
able to provide requested NCA
NAT Binding report
Idle NCR received Send Open
and able to successful
provide requested NCA
NAT control service
Idle NCR request Send Idle
received, and failed
unable to provide requested NCA
NAT control service
Open NCR request Send Open
received, and successful
able to provide requested NCA
NAT control service
Open NCR request Send Idle
received, and failed
unable to provide requested NCA,
NAT control service Clean up
Open Unable to continue Send ASR Discon
providing requested
NAT control service
Open Unplanned loss of session/ Clean up Idle
connection to DNCA Diameter
peer in NAT controller
detected (e.g. due to Diameter
watchdog notification)
Discon Failure to send ASR Wait, Discon
resend ASR
Discon ASR successfully sent and Clean up Idle
ASA Received with Result-Code
Not ASA Received None No change
Discon
Any STR Received Send STA, Idle
Clean up
The following table describes the AVPs reused from Diameter Base Protocol [RFC3588]; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4.
+---------+
| AVP |
| Flag |
| rules |
+-----------------------------------------------|-----+---+---------+
| AVP | | | |
| Attribute Name Code Data Type |MUST |MAY| Encr |
+-----------------------------------------------+-----+---+---------+
|Acct-Interim-Interval 85 Unsigned32 | M | P | Y |
|Auth-Application-Id 258 Unsigned32 | M | P | N |
|Destination-Host 293 DiamIdent | M | P | N |
|Destination-Realm 283 DiamIdent | M | P | N |
|Error-Message 281 UTF8String | M | P | N |
|Error-Reporting-Host 294 DiamIdent | M | P | N |
|Failed-AVP 279 Grouped | M | P | N |
|Origin-Host 264 DiamIdent | M | P | N |
|Origin-Realm 296 DiamIdent | M | P | N |
|Origin-State-Id 278 Unsigned32 | M | P | N |
|Proxy-Info 284 Grouped | M | P | N |
|Result-Code 268 Unsigned32 | M | P | N |
|Route-Record 282 DiamIdent | M | | N |
|Session-Id 263 UTF8String | M | P | Y |
|User-Name 1 UTF8String | M | P | Y |
+-----------------------------------------------+-----+---+---------+
Table 1: DIAMETER AVPs used from Diameter base
The Auth-Application-Id AVP (AVP Code 258) is assigned by IANA to Diameter applications. The value of the Auth-Application-Id for the Diameter NAT Control Application is TBD.APP-ID. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
This section defines new values for the Result-Code AVP that SHALL be supported by all Diameter implementations that conform to the present document.
No new Result-Code AVP value is defined within this category.
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:
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:
MAX_BINDINGS_SET_FAILURE (TBD.RCX)
The following table describes the AVPs reused from the Diameter Network Access Server Application [RFC4005]; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4.
+---------------------+
| AVP Flag rules |
+------------------+------+------------|----+-----+----+-----|----+
| | AVP | | | |SHLD| MUST| |
| Attribute Name | Code | Value Type|MUST| MAY | NOT| NOT|Encr|
|------------------|------|------------|----+-----+----+-----|----|
| NAS-Port | 5 | Unsigned32 | M | P | | V | Y |
| NAS-Port-Id | 87 | UTF8String | M | P | | V | Y |
| Calling-Station- | 31 | UTF8String | M | P | | V | Y |
| Id | | | | | | | |
| Framed-IP-Address| 8 | OctetString| M | P | | V | Y |
| Framed-Interface-| 96 | Unsigned64 | M | P | | V | Y |
| Id | | | | | | | |
| Framed-IPv6- | 97 | OctetString| M | P | | V | Y |
| Prefix | | | | | | | |
+------------------+------+------------|----+-----+----+-----|----+
Table 2: Reused NASREQ Diameter application AVPs. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
The following table describes the AVPs reused from "RADIUS Attributes for Virtual LAN and Priority Support" specification [RFC4675]; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4.
+---------------------+
| AVP Flag rules |
+------------------+------+------------|----+-----+----+-----|----+
| | AVP | | | |SHLD| MUST| |
| Attribute Name | Code | Value Type|MUST| MAY | NOT| NOT|Encr|
|------------------|------|------------|----+-----+----+-----|----|
| Egress-VLANID | 56 | OctetString| M | P | | V | Y |
+------------------+------+------------|----+-----+----+-----|----+
Table 3: Reused attributes from RFC 4675. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
The following table describes the AVPs reused from the Traffic Classification and Quality of Service (QoS) Attributes for Diameter [RFC5777]; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4.
+---------+
| AVP |
| Flag |
| rules |
+-----------------------------------------------|-----+---+---------+
| AVP | | | |
| Attribute Name Code Data Type |MUST |MAY| Encr |
+-----------------------------------------------+-----+---+---------+
|Port 530 Integer32 | M | P | Y |
|Protocol 513 Enumerated | M | P | Y |
|Direction 514 Enumerated | M | P | Y |
+-----------------------------------------------+-----+---+---------+
Table 4: Reused QoS-attributes. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
The following table describes the AVPs reused from the Diameter e4 Application [ETSIES283034]; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4. The Vendor-ID field in these AVP header will be set to ETSI (13019).
+---------+
| AVP |
| Flag |
| rules |
+-----------------------------------------------|-----+---+---------+
| AVP | | | |
| Attribute Name Code Data Type |MUST |MAY| Encr |
+-----------------------------------------------+-----+---+---------+
|Address-Realm 301 OctetString | M,V | | Y |
|Logical-Access-Id 302 OctetString | V | M | Y |
|Physical-Access-ID 313 UTF8String | V | M | Y |
+-----------------------------------------------+-----+---+---------+
Table 5: Reused AVPs from Diameter e4 application. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
The following table describes the new Diameter AVPs defined in this document; their AVP Code values, types, and possible flag values; and whether the AVP MAY be encrypted. The [RFC3588] specifies the AVP Flag rules for AVPs in section 4.5. The Diameter AVP rules are defined in the [RFC3588], section 4. The AVPs defined here MUST NOT have the V bit in the AVP Flag set.
+---------+
| AVP |
| Flag |
| rules |
+--------------------------------------------------|-----+---+------+
| AVP | | | |
| Attribute Name Code Data Type |MUST |MAY| Encr |
+--------------------------------------------------+-----+---+------+
|NC-Request-Type TBD.AX 8.7.1 Enumerated | M | P | Y |
|NAT-Control-Install TBD.AX 8.7.2 Grouped | M | P | Y |
|NAT-Control-Remove TBD.AX 8.7.3 Grouped | M | P | Y |
|NAT-Control-Definition TBD.AX 8.7.4 Grouped | M | P | Y |
|NAT-Internal-Address TBD.AX 8.7.5 Grouped | M | P | Y |
|NAT-External-Address TBD.AX 8.7.6 Grouped | M | P | Y |
|Max-NAT-Bindings TBD.AX 8.7.7 Unsigned32 | M | P | Y |
|NAT-Control- TBD.AX 8.7.8 OctetString| M | P | Y |
| Binding-Template | | | |
|Duplicate- TBD.AX 8.7.9 UTF8String | M | P | Y |
| Session-ID | | | |
|NAT-External-Port- TBD.AX 8.7.10 Enumerated | M | P | Y |
| Style | | | |
|NAT-Control-Record TBD.AX 9.2.1 Grouped | M | P | Y |
|NAT-Control- TBD.AX 9.2.2 Enumerated | M | P | Y |
| Binding-Status | | | |
|Current-NAT-Bindings TBD.AX 9.2.3 Unsigned32 | M | P | Y |
+--------------------------------------------------+-----+---+------+
Table 6: New Diameter AVPs. Please refer to [RFC3588] for the definition of the Diameter AVP flag rules and the associated abbreviations used in the table.
The NC-Request-Type AVP (AVP Code TBD.AX) is of type Enumerated and contains the reason for sending the NAT-Control-Request command. It shall be present in all NAT-Control-Request messages.
The following values are defined:
The NAT-Control AVP (AVP code TBD.AX) is of type Grouped, and it is used to activate or install NAT bindings. It also contains Max-NAT-Bindings that defines the maximum number of NAT bindings allowed for an endpoint and the NAT-Control-Binding-Template that references a predefined template on the NAT-device that may contain static binding, a maximum number of bindings allowed, an IP-address pool from which external binding addresses should be allocated, etc. If the NAT-External-Port-Style AVP is present, then the NAT-device MUST select the external ports for the NAT-Bindings as per the style specified. The NAT-External-Port-Style is applicable for NAT-Bindings defined by the NAT-Control-Definition AVPs whose NAT-External-Address or Port AVPs within the NAT-External-Address are unspecified.
AVP format:
NAT-Control-Install ::= < AVP Header: TBD.AX >
* [ NAT-Control-Definition ]
[ NAT-Control-Binding-Template ]
[ Max-NAT-Bindings ]
[ NAT-External-Port-Style ]
* [ AVP ]
The NAT-Control-Remove AVP (AVP code TBD.AX) is of type Grouped, and it is used to deactivate or remove NAT-bindings. At least one of the two AVPs (NAT-Control-Definition AVP, NAT-Control-Binding-Template AVP) SHOULD be present in the NAT-Control-Remove AVP.
AVP format:
NAT-Control-Remove ::= < AVP Header: TBD.AX >
* [ NAT-Control-Definition ]
[ NAT-Control-Binding-Template ]
* [ AVP ]
The NAT-Control-Definition AVP (AVP code TBD.AX) is of type Grouped, and it describes a binding.
The NAT-Control-Definition AVP uniquely identifies the binding between the DNCA Diameter peers.
If both the NAT-Internal-Address and NAT-External-Address AVP(s) are supplied, it is a pre-defined binding.
If the NAT-External-Address AVP is not specified then the NAT-device MUST select the external port as per the NAT-External-Port-Style AVP, if present in the NAT-Control-Definition AVP.
The Protocol AVP describes the transport protocol for the binding. The NAT-Control-Definition AVP can contain either zero or one Protocol AVP. If the Protocol AVP is omitted and if both internal and external IP-address are specified then the binding reserves the IP-addresses for all transport protocols.
The Direction AVP is of type Enumerated. It specifies the direction for the binding. The values of the enumeration applicable in this context are: "IN","OUT". If Direction AVP is OUT or absent, the NAT-Internal-Address refers to the IP-address of the endpoint that needs to be translated. If Direction AVP is "IN", NAT-Internal-Address is the destination IP-address that has to be translated.
AVP format:
NAT-Control-Definition ::= < AVP Header: TBD.AX >
{ NAT-Internal-Address }
[ Protocol ]
[ Direction ]
[ NAT-External-Address ]
[ Session-Id ]
* [ AVP ]
The NAT-Internal-Address AVP (AVP code TBD.AX) is of type Grouped. It describes the internal IP-address and port for a binding. Framed-IPV6-Prefix and Framed-IP-Address AVPs are mutually exclusive.
AVP format:
NAT-Internal-Address ::= < AVP Header: TBD.AX >
[ Framed-IP-Address ]
[ Framed-IPv6-Prefix ]
[ Port]
* [ AVP ]
The NAT-External-Address AVP (AVP code TBD.AX) is of type Grouped, and it describes the external IP-address and port for a binding. The external IP-address specified in this attribute can be reused for multiple endpoints by specifying the same address in the respective NAT-External-Address AVPs. If the external IP-address is not specified and the NAT-External-Port-Style AVP is specified in the NAT-Control-Definition AVP then the NAT-device MUST select external port as per the NAT-External-Port-Style AVP.
AVP format:
NAT-External-Address ::= < AVP Header: TBD.AX >
[ Framed-IP-Address ]
[ Port ]
* [ AVP ]
The Max-NAT-Bindings AVP (AVP code TBD.AX) is of type Unsigned32. It indicates the maximum number of NAT-bindings allowed for a particular endpoint.
The NAT-Control-Binding-Template AVP (AVP code TBD.AX) is of type OctetString. It defines a name for a policy template that is predefined at the NAT-device. Details on the contents and structure of the template and configuration are outside the scope of this document. The policy to which this AVP refers to may contain NAT-bindings, IP-address pool for allocating the external IP-address of a NAT-binding, and maximum number of allowed NAT-bindings. Such policy template can be reused by specifying the same NAT-Control-Binding-Template AVP in the corresponding NAT-Control-Install AVPs of multiple endpoints.
The Duplicate-Session-Id AVP (AVP Code TBD.AX) is of type UTF8String. It is used to report errors and contains the Session-Id of an existing session.
The NAT-External-Port-Style AVP (AVP Code TBD.AX) is of type Enumerated and contains the style to be followed while selecting the external port for a NAT-Binding relative to the internal port.
The following values are defined:
The DNCA reuses session based accounting as defined in the Diameter Base Protocol[RFC3588] to report the bindings per endpoint. This reporting is achieved by sending Diameter Accounting Requests (ACR) [Start, Interim and Stop] from the DNCA Diameter peer within the NAT-device to its associated DNCA Diameter peer within the NAT-controller.
The DNCA Diameter peer within the NAT-device sends an ACR Start on receiving a NCR with NC-Request-Type AVP set to INITIAL_REQUEST for a session or on creation of the first binding for a session requested in an earlier NCR. DNCA may send ACR Interim updates, if required, either due to a change in bindings resulting from a NCR with NC-Request-Type AVP set to UPDATE_REQUEST, or periodically as specified in Acct-Interim-Interval by the DNCA Diameter peer within the NAT-controller, or when it creates or tears down bindings. An ACR Stop is sent by the DNCA Diameter peer within the NAT-device on receiving STR.
The function of correlating the multiple bindings used by an endpoint at any given time is relegated to the post processor.
The DNCA Diameter peer within the NAT-device may trigger an interim accounting record when the maximum number of bindings, if received in an NCR, is reached.
The ACR and ACA messages are reused as defined in the Diameter Base Protocol [RFC3588] for exchanging endpoint NAT binding details between the DNCA Diameter peers. The DNCA Application IDs is used in the accounting commands. ACR contains one or more optional NAT-Control-Record AVPs to report the bindings. The NAT-device indicates the number of allocated NAT bindings to the NAT-controller using the Current-NAT-Bindings AVP. This number needs to match the number of bindings identified as active within the NAT-Control-Record AVP.
In addition to AVPs for ACR specified in [RFC3588], the DNCA Diameter peer within the NAT-device must add the NAT-Control-Record AVP.
The NAT-Control-Record AVP (AVP code TBD.AX) is of type Grouped. It describes a binding and its status. If NAT-Control-Binding-Status is set to Created, Event-Timestamp indicates the binding creation time. If NAT-Control-Binding-Status is set to Removed, Event-Timestamp indicates the binding removal time. If NAT-Control-Binding-Status is active, Event-Timestamp need not be present; if a value is present, it indicates that binding is active at the given time.
NAT-Control-Record ::= < AVP Header: TBD.AX >
{ NAT-Control-Definition }
{ NAT-Control-Binding-Status }
[ Event-Timestamp ]
The NAT-Control-Binding-Status AVP (AVP code TBD.AX) is of type enumerated. It indicates the status of the binding - created, removed, or active.
The following values are defined:
The Current-NAT-Bindings AVP (AVP code TBD.AX) is of type Unsigned32. It indicates the number of NAT bindings active on the NAT-device.
The following sections present the AVPs defined in this document and specify the Diameter messages in which they can be present. Note: AVPs that can only be present within a Grouped AVP are not represented in this table.
The table uses the following symbols:
The following table lists DNCA specific AVPs that have to be present in NCRs and NCAs with NC-Request-Type set to INITIAL_REQUEST or UPDATE_REQUEST.
+-------------------+
| Command Code |
+-----------------------------------+-------------------+
| Attribute Name NCR NCA |
+-------------------------------------------------------+
|NC-Request-Type 1 1 |
|NAT-Control-Install 0-1 0 |
|NAT-Control-Remove 0-1 0 |
|NAT-Control-Definition 0 0 |
|Current-NAT-Bindings 0 0 |
|Duplicate-Session-Id 0 0-1 |
+-------------------------------------------------------+
Note that any combination of "NAT-Control-Install" and "NAT-Control-Remove" AVPs could be present in an update or initial requests. Consider the following examples:
The following table lists DNCA specific AVPs that have to be present in NCRs and NCAs 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-External-Address 0+ 0 |
|Current-NAT-Bindings 0 1 |
|Duplicate-Session-Id 0 0 |
+-------------------------------------------------------+
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 |
+-------------------------------------------------------+
This section contains the namespaces that have either been created in this specification, or the values assigned to existing namespaces managed by IANA.
In the subsections below, when we speak about review by a Designated Expert, please note that the designated expert will be assigned by the IESG. Initially, such Expert discussions take place on the AAA WG mailing list.
This specification assigns the value <TBD.APP-ID>, 'Diameter NAT Control Application', to the Application Identifier namespace defined in [RFC3588]. See Section 4 for more information.
This specification uses the value <TBD.COM-CODE> from the Command code namespace defined in [RFC3588] for the NAT-Control-Request (NCR), NAT-Control-Answer (NCA) commands. See Section 6.1 and Section 6.2 for more information on these commands.
This specification assigns the values <TBD.AX> from the AVP code namespace defined in [RFC3588]. See Section 8.7 for the assignment of the namespace in this specification.
This specification assigns the values <TBD.RCX> (4xxx, 5xxx, 5xxx, 5xxx, 5xxx,5xxx) from the Result-Code AVP value namespace defined in [RFC3588]. See Section 8.2 for the assignment of the namespace in this specification.
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].
As defined in Section 8.7.10, the NAT-External-Port-Style AVP includes Enumerated type value 1. IANA has created and is maintaining a namespace for this AVP. All remaining values are available for assignment by a Designated Expert [RFC5226].
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].
This document describes procedures for controlling NAT related attributes and parameters by an entity, which is non-local to the device performing NAT. This section discusses security considerations for DNCA. This includes the interactions between the Diameter peers within a NAT-controller and a NAT-device as well as general considerations for NAT-control in a service provider network.
Security between a NAT-controller and a NAT-device has a number of components: authentication, authorization, integrity, and confidentiality.
Authentication refers to confirming the identity of an originator for all datagrams received from the originator. Lack of authentication of Diameter messages between the Diameter peers can jeopardize the fundamental service of the peering network elements. A consequence of not authenticating the message sender by the recipient would be that an attacker could spoof the identity of a "legitimate" authorizing entity in order to change the behavior of the receiver. An attacker could for example launch a denial of service attack by setting the maximum number of bindings for a session on the NAT-device to zero; provision bindings on a NAT-device which include IP-addresses already in use in other parts of the network; or request session termination of the Diameter session and hamper an endpoint's (i.e. a user's) connectivity. Lack of authentication of a NAT-device to a NAT-controller could lead to situations where the NAT-device could provide a wrong view of the resources (i.e. NAT-bindings). In addition, NAT Binding Predefined template on the NAT-device could be configured differently than expected by the NAT-controller. Failing of any of the two DNCA Diameter peers to provide the required credentials should be subject to logging. The corresponding logging infrastructure of the operator SHOULD be built in a way that it can mitigate potential denial of service attacks resulting from large amounts of logging events. This could include proper dimensioning of the logging infrastructure combined with policing the maximum amount of logging events accepted by the logging system to a threshold which the system is known to be able to handle.
Authorization refers to whether a particular authorizing entity is authorized to signal a network element requests for one or more applications, adhering to a certain policy profile. Failing the authorization process might indicate a resource theft attempt or failure due to administrative and/or credential deficiencies. In either case, the network element should take the proper measures to log such attempts.
Integrity is required to ensure that a Diameter message exchanged between the Diameter peers has not been maliciously altered by intermediate devices. The result of a lack of data integrity enforcement in an untrusted environment could be that an impostor will alter the messages exchanged between the peers. This could cause a change of behavior of the peers, including the potential of a denial of service.
Confidentiality protection of Diameter messages ensures that the signaling data is accessible only to the authorized entities. When signaling messages between the DNCA Diameter peers traverse untrusted networks, lack of confidentiality will allow eavesdropping and traffic analysis.
Diameter offers security mechanisms to deal with the functionality demanded above. DNCA makes use of the capabilities offered by Diameter and the underlying transport protocols to deliver these requirements (see Section 5.1). If the DNCA communication traverses untrusted networks, messages between DNCA Diameter peers SHOULD be secured using either IPsec or TLS. Please refer to [RFC3588], section 13 for details. DNCA Diameter peers SHOULD perform bilateral authentication, authorization as well as procedures to ensure integrity and confidentiality of the information exchange. In addition the Session-Id chosen for a particular Diameter session SHOULD be chosen in a way that it is hard to guess in order to mitigate issues through potential message replay.
DNCA Diameter peers SHOULD have a mutual trust setup. This document does not specify a mechanisms for authorization between the DNCA Diameter peers. The DNCA Diameter peers SHOULD be provided with sufficient information to make an authorization decision. The information can come from various sources, for example the peering devices could store local authentication policy, listing the identities of authorized peers.
Any mechanism or protocol providing control of a NAT-device, and DNCA is an example of such a control mechanism, could allow for misuse of the NAT-device given that it enables the definition of per-destination or per-source rules. Misuse could include anti-competitive practices among providers, censorship, crime, etc. NAT-control could be used as a tool for preventing or redirecting access to particular sites. For instance, by controlling the NAT bindings, one could ensure that endpoints aren't able to receive particular flows, or that those flows are redirected to a relay that snoops or tampers with traffic instead of directly forwarding the traffic to the intended endpoint. In addition one could set up a binding in a way that the source IP address used is one of a relay so that traffic coming back can be snooped on or interfered with. The operator also needs to consider security threats resulting from unplanned termination of the DNCA session. Unplanned session termination, which could e.g. happen due to an attacker taking down the NAT-controller, leads to the NAT-device cleaning up the state associated with this session after a grace period. If the grace period is set to zero, the endpoint will experience an immediate loss of connectivity to services reachable through the NAT-device following the termination of the DNCA session.The protections on DNCA and its Diameter protocol exchanges don't prevent such abuses of NAT-control. Prevention of mis-use or mis-configuration of a NAT-device by an authorized NAT-controller is beyond the scope of this protocol specification. A service provider deploying DNCA needs to make sure that higher layer processes and procedures are put in place which allow them to detect and mitigate misuses.
This section shows example DNCA message content and exchange.
Figure 29 depicts a typical call flow for DNCA session establishment.
In this example, the NAT-controller:
endpoint NAT-Controller (within NAS) NAT-device | | | | | | | 1. Trigger | | |--------------------------->| | | +-------------------------------------+ | | | 2. Determine that NAT control | | | | is required for the endpoint | | | +-------------------------------------+ | | | | | | | | ................................... | .| 3. Diameter Base CER/CEA |. | .|<----------------------------->|. | ................................... | | | | | | | | 4. NCR | | |------------------------------>| | | | | | 5. DNCA session | | established | | | | | 6. NCA | | |<------------------------------| | | | | | | | 7. Data traffic | |----------------------------------------------------------->| | | | | | | | | 8. NAT Bindings | | created as per | | directives in the | | DNCA session | | |
Detailed description of the steps shown in Figure 29:
< NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
Session-Id = "natC.example.com:33041;23432;"
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "nat-device.example.com"
NC-Request-Type = INITIAL_REQUEST
User-Name = "subscriber_example1"
Framed-IP-Address = "192.0.2.1"
NAT-Control-Install = {
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 80
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 80
}
}
Max-NAT-Bindings = 100
NAT-Control-Binding-Template = "local-policy"
}
<NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
Session-Id = "natC.example.com:33041;23432;"
Origin-Host = "nat-device.example.com"
Origin-Realm = "example.com"
NC-Request-Type = INITIAL_REQUEST
Result-Code = DIAMETER_SUCCESS
This section gives an example for a DNCA session update: A new set of NAT-bindings is requested for an existing session. The request contains a directive ( the "NAT-External-Port-Style" AVP set to FOLLOW_INTERNAL_PORT_STYLE) that directs the NAT-device to maintain port-sequence and port-oddity for the newly created NAT-bindings. In the example shown, the internal ports are UDP port 1036 and 1037. The NAT-device follows the directive selects the external ports accordingly. The NAT-device would for example create a mapping of 192.0.2.1:1036 to 198.51.100.1:5056 and 192.0.2.1:1037 to 198.51.100.1:5057, thereby maintaining port oddity (1036->5056, 1037->5057) and sequence ( the consecutive internal ports 1036 and 1037 map to the consecutive external ports 5056 and 5057).
< NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
Session-Id = "natC.example.com:33041;23432;"
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "nat-device.example.com"
NC-Request-Type = UPDATE_REQUEST
NAT-Control-Install = {
NAT-Control-Definition = {
Protocol = UDP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 1035
}
}
NAT-Control-Definition = {
Protocol = UDP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 1036
}
}
NAT-External-Port-
Style = FOLLOW_INTERNAL_PORT_STYLE
}
This section shows an example for DNCA session query for a subscriber whose internal IP-Address is 192.0.2.1.
< NC-Request > ::= < Diameter Header: TBD.COM-CODE, REQ, PXY>
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "nat-device.example.com"
NC-Request-Type = QUERY_REQUEST
Framed-IP-Address = "192.0.2.1"
The NAT-device constructs an NCA to report all currently active NAT-bindings whose internal address is 192.0.2.1.
<NC-Answer> ::= < Diameter Header: TBD.COM-CODE, PXY >
Origin-Host = "nat-device.example.com"
Origin-Realm = "example.com"
NC-Request-Type = QUERY_REQUEST
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 80
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 80
}
Session-Id = "natC.example.com:33041;23432;"
}
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 1036
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 5056
}
Session-Id = "natC.example.com:33041;23432;"
}
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 1037
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 5057
}
Session-Id = "natC.example.com:33041;23432;"
}
In this example the NAT-controller decides to terminate the previously established DNCA session. This could for example be the case as a result of an access session (e.g. a PPP session) associated with an endpoint been torn down.
NAT-Controller NAT-device
| |
| |
+--------------+ |
| 1. Trigger | |
+--------------+ |
| |
| |
| 2. STR |
|-------------------------------------->|
| |
| 3. DNCA session
| lookup
| 4. ACR |
|<--------------------------------------|
| |
| 5. ACA |
|-------------------------------------->|
| |
| |
| 6. DNCA bindings
| and session cleanup
| |
| 7. STA |
|<--------------------------------------|
| |
The following steps describe the sequence of events for tearing down the DNCA session in the example above:
< STR > ::= < Diameter Header: 275, REQ, PXY>
Session-Id = "natC.example.com:33041;23432;"
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "nat-device.example.com"
Termination-Cause = DIAMETER_LOGOUT
< ACR > ::= < Diameter Header: 271, REQ, PXY>
Session-Id = "natC.example.com:33041;23432;"
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "nat-device.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "natC.example.com"
Accounting-Record-Type = STOP_RECORD
Accounting-Record-Number = 1
NAT-Control-Record = {
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 5001
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 7777
}
}
NAT-Control-Binding-Status = Removed
}
<ACA> ::= < Diameter Header: 271, PXY >
Session-Id = "natC.example.com:33041;23432;"
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Result-Code = DIAMETER_SUCCESS
Accounting-Record-Type = STOP_RECORD
Accounting-Record-Number = 1
<STA> ::= < Diameter Header: 275, PXY >
Session-Id = "natC.example.com:33041;23432;"
Origin-Host = "nat-device.example.com"
Origin-Realm = "example.com"
Result-Code = DIAMETER_SUCCESS
The authors would like to thank Jari Arkko, Wesley Eddy, Stephen Farrell, Miguel A. Garcia, David Harrington, Jouni Korhonen, Matt Lepinski, Avi Lior, Chris Metz, Pallavi Mishra, Lionel Morand, Robert Sparks, Martin Stiemerling, Dave Thaler, Hannes Tschofenig, Sean Turner, Shashank Vikram, Greg Weber, and Glen Zorn for their input on this document.
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