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Versions: 00 01 02 03 04 05 06 07 draft-cheng-radext-ip-port-radius-ext

Network Working Group                                           D. Cheng
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                             J. Korhonen
Expires: April 20, 2013                           Nokia Siemens Networks
                                                            M. Boucadair
                                                          France Telecom
                                                        October 17, 2012


       RADIUS Extensions for Port Set Configuration and Reporting
                draft-cheng-behave-cgn-cfg-radius-ext-04

Abstract

   This document defines new RADIUS attributes that can be used by a
   device implementing port ranges to communicate with a RADIUS server
   to configure and/or report TCP/UDP port sets and ICMP identifiers
   mapping behavior for specific hosts.  This mechanism can be used in
   various deployment scenarios such as CGN, NAT64, Provider WiFi
   Gateway, etc.

   This document does not make any assumption about the deployment
   context.

Requirements Language

   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 RFC 2119 [RFC2119].

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
   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 April 20, 2013.

Copyright Notice



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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  RADIUS Attributes  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Port-Session-Limit Attribute . . . . . . . . . . . . . . .  6
     3.2.  Port-Session-Range Attribute . . . . . . . . . . . . . . .  7
     3.3.  Port-Forwarding-Map Attribute  . . . . . . . . . . . . . .  9
   4.  Applications, Use Cases and Examples . . . . . . . . . . . . . 11
     4.1.  Managing CGN Port Behavior using RADIUS  . . . . . . . . . 11
       4.1.1.  Configure CGN Session Limit  . . . . . . . . . . . . . 12
       4.1.2.  Report CGN Session Allocation or De-allocation . . . . 14
       4.1.3.  Configure CGN Forwarding Port Mapping  . . . . . . . . 16
       4.1.4.  An Example . . . . . . . . . . . . . . . . . . . . . . 18
     4.2.  Report Assigned Port Set for a Visiting UE . . . . . . . . 19
   5.  Table of Attributes  . . . . . . . . . . . . . . . . . . . . . 20
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  RADIUS Attributes  . . . . . . . . . . . . . . . . . . . . 21
     7.2.  Name Spaces  . . . . . . . . . . . . . . . . . . . . . . . 21
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 21
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23












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1.  Introduction

   In a broadband network, customer information is usually stored on a
   RADIUS server [RFC2865] and at the time when a user initiates an IP
   connection request, the RADIUS server will populate the user's
   configuration information to the Network Access Server (NAS), which
   is usually co-located with the Border Network Gateway (BNG), after
   the connection request is granted.  The Carrier Grade NAT (CGN)
   function may also implemented on the BNG, and therefore CGN TCP/UDP
   port (or ICMP identifier) mapping behavior can be configured on the
   RADIUS server as part of the user profile, and populated to the NAS
   in the same manner.  In addition, during the operation, the CGN can
   also convey port/identifier mapping behavior specific to a user to
   the RADIUS server, as part of the normal RADIUS accounting process.

   The CGN device that communicates with a RADIUS server using RADIUS
   extensions defined in this document may perform NAT44 [RFC3022],
   NAT64 [RFC6146], or Dual-Stack Lite AFTR [RFC6333] function.

   For the CGN example, when IP packets traverse a CGN, it would perform
   TCP/UDP source port mapping or ICMP identifier mapping as required.
   A TCP/ UDP source port or ICMP identifier, along with source IP
   address, destination IP address, destination port and protocol
   identifier if applicable, uniquely identify a session.  Since the
   number space of TCP/UDP ports and ICMP identifiers in CGN's external
   realm is shared among multiple users assigned with the same IPv4
   address, the total number of a user's simultaneous IP sessions is
   likely to subject to port quota.

   The attributes defined in this document may also be used to report
   the assigned port set in some deployment such as Provider WiFi
   [I-D.gundavelli-v6ops-community-wifi-svcs].  For example, a visiting
   host can be managed by a CPE which will need to report the assigned
   port set to the service platform.  This is required for
   identification purposes (see WT-146 for example).

   This document proposes three new RADIUS attributes as RADIUS
   protocol's extensions, and they are used for separate purposes as
   follows:

   o  A session limit is configured on a RADIUS server based on service
      agreement with a subscriber, and this parameter imposes the limit
      of total number of TCP/UDP ports and/or ICMP identifiers that the
      subscriber can use.  Alternately, a separate session limit may be
      configured to limit the number of TCP ports, UDP ports, or the sum
      of the two, and ICMP identifiers, respectively, that the user can
      use.  The session limit is carried by a new RADIUS attribute Port-
      Session-Limit, which is included in a RADIUS Access-Accept message



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      sent by the RADIUS server to port-based device.  This new RADIUS
      attribute can also be included in a RADIUS CoA message sent by the
      RADIUS server to the port-based device in order to change the
      session limit previously configured.

   o  A port-based device may allocate or de-allocate a set of TCP/UDP
      ports or ICMP identifiers for a specific subscriber.  When it does
      so, the associated session range along with the shared IPv4
      address can be conveyed to the RADIUS server as part of the
      accounting process.  These parameters are carried by a new RADIUS
      attribute Port-Session-Range, which is included in a RADIUS
      Accounting- Request message sent by the port-based device to the
      RADIUS server.

   o  A user may require the port-based device to perform port
      forwarding function, i.e., a port mapping is pre-configured on the
      port-based so that inbound IP packets sent by some applications
      from the port-based external realm can pass through that device
      and reach the user.  The port mapping information includes the
      port-based device internal port, external port, and may also
      include the associated internal IPv4 or IPv6 address, and is
      carried by a new RADIUS attribute Port- Forwarding-Map, which is
      included in a RADIUS Access-Accept message sent by the RADIUS
      server to the port-based device.  This new RADIUS attribute can
      also be included in a RADIUS CoA message sent by the RADIUS server
      to the port-based device in order to change the forwarding port
      mapping previously configured.


2.  Terminology

   Some terms that are used in this document are listed as follows:

   o  Session Limit - This is the maximum number of TCP ports, or UDP
      ports, or the total of the two, or ICMP identifiers, or the total
      of the three, that a device supporting port ranges can use when
      performing mapping on TCP/ UDP ports or ICMP identifiers for a
      specific user.

   o  Session Range - This specifies a set of TCP/UDP port numbers or
      ICMP identifiers, indicated by the port/identifier with the
      smallest numerical number and the port/identifier with the largest
      numerical number, inclusively.

   o  Internal IP Address - The IP address that is used as a source IP
      address in an outbound IP packet sent toward a device supporting
      port ranges in the internal realm.  In IPv4 case, it is typically
      a private address [RFC1918].



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   o  External IP Address - The IP address that is used as a source IP
      address in an outbound IP packet after traversing a device
      supporting port ranges in the external realm.  In IPv4 case, it is
      typically a global and routable IP address.

   o  Internal Port - The internal port is a UDP or TCP port, or an ICMP
      identifier, which is allocated by a host or application behind a
      device supporting port ranges for an outbound IP packet in the
      internal realm.

   o  External Port - The external port is a UDP or TCP port, or an ICMP
      identifier, which is allocated by a device supporting port ranges
      upon receiving an outbound IP packet in the internal realm, and is
      used to replace the internal port that is allocated by a user or
      application.

   o  External realm - The networking segment where IPv4 public
      addresses are used in respective of the device supporting port
      ranges.

   o  Internal realm - The networking segment that is behind a device
      supporting port ranges and where IPv4 private addresses are used.

   o  Mapping - This term in this document associates with a device
      supporting port ranges for a relationship between an internal IP
      address, internal port and the protocol, and an external IP
      address, external port, and the protocol.

   o  Port-based device - A device that is capable of providing IP
      address and TCP/UDP port mapping services and in particular, with
      the granularity of one or more subsets within the 16-bit TCP/UDP
      port number range.  A typical example of this device can be a CGN,
      CPE, Provider WiF Gateway, etc.

   Note the terms "internal IP address", "internal port", "internal
   realm", "external IP address", "external port", "external realm", and
   "mapping" and their semantics are the same as in [I-D.ietf-pcp-base],
   and [I-D.ietf-behave-lsn-requirements].


3.  RADIUS Attributes

      [Discussion: should these attributes be allocated from the
      extended RADIUS attribute code space?]

      [Discussion: Should we define a dedicated attribute
      (port_set_policies) to configure the following policies: (1)
      enforce port randomization, (2) include/exclude the WKP in the



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      port assignment, (3) preserve parity, (4) quota for explicit port
      mapping, (5) DSCP marking policy, (6) Port hold down timer, (7)
      port hold down pool, etc.  Perhaps we don't need to cover all
      these parameters.]

3.1.  Port-Session-Limit Attribute

   This attribute is of type complex [RFC6158] and specifies the limit
   of TCP ports, or UDP ports, or the sum of the two, or ICMP
   identifiers, or the sum of the three, which is configured on a device
   supporting port ranges corresponding to a specific subscriber.

   The Port-Session-Limit MAY appear in an Access-Accept packet, it MAY
   also appear in an Access-Request packet as a hint by the device
   supporting port ranges, which is co-allocated with the NAS, to the
   RADIUS server as a preference, although the server is not required to
   honor such a hint.

   The Port-Session-Limit MAY appear in an CoA-Request packet.

   The Port-Session-Limit MAY appear in an Accounting-Request packet.

   The Port-Session-Limit MUST NOT appear in any other RADIUS packets.

   The format of the Port-Session-Limit RADIUS attribute format is shown
   below.  The fields are transmitted from left to right.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |      ST       |    Session
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Limit     |
   +-+-+-+-+-+-+-+-+

   Type:

        TBA1 for Port-Session-Limit.

   Length:

        5 octets.  This field indicates the total length in octets of
        this attribute including the Type and the Length field.

   ST (Session Type):





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        This one octet field contains an enumerated value that indicates
        the applicability of the Session Limit as follows:

        0:

             The limit as specified is applied to each transport
             protocol (TCP/UDP) and ICMP Identifiers as a whole.

        1:

             The limit as specified is applied to TCP and UDP ports.

        2:

             The limit as specified is applied to TCP ports.

        3:

             The limit as specified is applied to UDP ports.

        4:

             The limit as specified is applied to ICMP Identifiers.

        5-255:

             These values are undefined.

   Session Limit:

        This field contains the maximum number that is imposed to the
        transport sessions depending on the value in the Session Type
        (ST) field, that the specific user can use.

3.2.  Port-Session-Range Attribute

   This attribute is type of complex [RFC6158] and contains a range of
   numbers for TCP ports or UDP ports, or both, or for ICMP Identifiers,
   which has been allocated or de-allocated by a device supporting port
   ranges for a given subscriber, along with an external IPv4 address
   that is associated with any TCP/UDP port or ICMP identifier in the
   range.

   In some CGN deployment scenarios as described such as L2NAT
   [I-D.miles-behave-l2nat] and DS-Extra-Lite
   [I-D.arkko-dual-stack-extra-lite], parameters at a customer premise
   such as MAC address, interface ID, VLAN ID, PPP session ID, IPv6
   prefix, VRF ID, etc., may also be required to pass to the RADIUS



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   server as part of the accounting record.

   The Port-Session-Range MAY appear in an Accounting-Request packet.

   The Port-Session-Range MUST NOT appear in any other RADIUS packets.

   The port range follows the encoding specified in [RFC6431]; as such
   both contiguous and non-contiguous port sets are supported.

   The format of the Port-Session-Range RADIUS attribute format is shown
   below.  The fields are transmitted from left to right.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |       ST      |A| Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Port Range Mask          |      Port Range Value         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     External IPv4 Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Local Session ID ....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--

   Type:

        TBA2 for Port-Session-Range.

   Length:

        12 octets plus the length of optional field Local Session ID.
        This field indicates the total length in octets of this
        attribute including the Type and the Length field.

   ST (Session Type):

        This one octet field contains an enumerated value that indicates
        the semantics of the session range.  The values follow the
        Session Type encoding defined in Section 3.1 except that the
        following values are not valid in scope of this attribute:

        0:

             The limit as specified is applied to the sum of TCP ports,
             UDP ports, and ICMP Identifiers as a whole.

   A-bit Flag:



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        This field is set to 0 or 1, indicates that the session range
        has been allocated or de-allocated, respectively, by the device
        supporting port ranges.

   Reserved:

        This field MUST be set to zero by the sender and ignored by the
        receiver.

   Port Range Mask:

        The Port Range Mask indicates the position of the bits that are
        used to build the Port Range Value.  By default, no PRM value is
        assigned.  The 1 values in the Port Range Mask indicate by their
        position the significant bits of the Port Range Value.  Refer to
        [RFC6431] for more details.

   Port Range Value:

        The PRV indicates the value of the significant bits of the Port
        Mask.  By default, no PRV is assigned.  Refer to [RFC6431] for
        more details.

   External IPv4 Address:

        This is an optional field.  If present, this field contains the
        IPv4 address assigned to the associated subscriber to be used in
        the external realm.  If set to 0/0, the allocation address
        policy is local to the device supporting port ranges.

   Local Session ID:

        This is an optional field and if presents, it contains a local
        session identifier at the customer premise, such as MAC address,
        interface ID, VLAN ID, PPP sessions ID, VRF ID, IPv6 address/
        prefix, etc.  The length of this field equals to the total
        attribute length minus 12 octets.  If this field is not present,
        the port range policies must be enforced to all subscribers
        using a local subscriber identifier.

3.3.  Port-Forwarding-Map Attribute

   This attribute is type of complex [RFC6158] and contains a 16-bit
   Internal Port that identifies the source TCP/UDP port number of an IP
   packet sent by the user, or the destination port number of an IP
   packet destined to the user, and in both cases, the IP packet travels
   behind the NAT device.  Also they contain a 16-bit Configured
   External Port that identifies the source TCP/UDP port number of an IP



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   packet sent by the user, or the destination port number of an IP
   packet destined to the user, and in both cases, the IP packet travels
   outside of the NAT device.  In addition, the attribute may contain a
   32-bit IPv4 address or a 128-bit IPv6 address, respectively, as their
   respective NAT mappings internal IP address.  Together, the port pair
   and IP address determine the port mapping rule for a specific IP flow
   that traverses a NAT device.

   The attribute MAY appear in an Access-Accept packet, and may also
   appear in an Accounting-Request packet.  In either case, the
   attribute MUST NOT appear more than once in a single packet.

   The attribute MUST NOT appear in any other RADIUS packets.

   The format of the Port-Forwarding-Map RADIUS attribute format is
   shown below.  The fields are transmitted from left to right.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |      AF       |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Internal Port         |    Configured External Port   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Internal IP Address  .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:

        TBA3 for Port-Forwarding-Map.

   Length:

        This field indicates the total length in octets of this
        attribute including the Type and the Length field.  Depending on
        the value of the AF field, the length could be 8, 12 or 24
        octets.

   AF (Address Family):

        This one octet field contains a value that indicates address
        family of the internal IP address at the mapping as follows:

        0:

             There is no internal address attached.




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        1:

             The internal address is an IPv4 address.

        2:

             The internal address is an IPv6 address.

        3-255:

             Unused.

        [Discussion: should we use IANA assigned protocol numbers here?]

   Reserved:

        This field is set to zero by the sender and ignored by the
        receiver.

   Internal Port:

        This field contains the internal port for the CGN mapping.

   Configured External Port:

        This field contains the external port for the CGN mapping.

   Internal IP Address:

        This field may or may not present, and when it does, contains
        the internal IPv4 or IPv6 address for the CGN mapping.


4.  Applications, Use Cases and Examples

   This section describes some applications and use cases to illustrate
   the use of the RADIUS port set attributes.

4.1.  Managing CGN Port Behavior using RADIUS

   In a broadband network, customer information is usually stored on a
   RADIUS server, and the BNG hosts the NAS.  The communication between
   the NAS and the RADIUS server is triggered by a subscriber when the
   user signs in to the Internet service, where either PPP or DHCP/
   DHCPv6 is used.  When a user signs in, the NAS sends a RADIUS Access-
   Request message to the RADIUS server.  The RADIUS server validates
   the request, and if the validation succeeds, it in turn sends back a
   RADIUS Access-Accept message.  The Access-Accept message carries



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   configuration information specific to that user, back to the NAS,
   where some of the information would pass on to the requesting user
   via PPP or DHCP/DHCPv6.

   A CGN function in a broadband network would most likely reside on a
   BNG.  In that case, parameters for CGN port/identifier mapping
   behavior for users can be configured on the RADIUS server.  When a
   user signs in to the Internet service, the associated parameters can
   be conveyed to the NAS, and proper configuration is accomplished on
   the CGN device for that user.

   Also, CGN operation status such as CGN port/identifier allocation and
   de-allocation for a specific user on the BNG can also be transmitted
   back to the RADIUS server for accounting purpose using the RADIUS
   protocol.

   RADIUS protocol has already been widely deployed in broadband
   networks to manage BNG, thus the functionality described in this
   specification introduces little overhead to the existing network
   operation.

   In the following sub-sections, we describe how to manage CGN behavior
   using RADIUS protocol, with required RADIUS extensions proposed in
   Section 3.

4.1.1.  Configure CGN Session Limit

   In the face of IPv4 address shortage, there are currently proposals
   to multiplex multiple subscribers' connections over a smaller number
   of shared IPv4 addresses, such as Carrier Grade NAT
   [I-D.ietf-behave-lsn-requirements], Dual-Stack Lite [RFC6333], NAT64
   [RFC6146], etc.  As a result, a single IPv4 public address may be
   shared by hundreds or even thousands of subscribers.  As indicated in
   [RFC6269], it is therefore necessary to impose limits on the total
   number of ports available to an individual subscriber to ensure that
   the shared resource, i.e., the IPv4 address remains available in some
   capacity to all the subscribers using it, and port limiting is also
   documented in [I-D.ietf-behave-lsn-requirements] as a requirement.

   There are two practical granularities to impose such a limit.  One is
   to define a session limit that is imposed to the total number of TCP
   and UDP ports, plus the number of ICMP identifiers, for a specific
   subscriber.  Alternatively, a session limit can be specified for the
   sum of TCP ports and UDP ports, or a separate session limit for TCP
   ports and UDP ports, respectively, and another session limit for ICMP
   identifiers.

   The per-subscriber based session limit(s) is configured on a RADIUS



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   server, along with other user information such as credentials.  The
   value of these session limit(s) is based on service agreement and its
   specification is out of the scope of this document.

   When a subscriber signs in to the Internet service successfully, the
   session limit(s) for the subscriber is passed to the BNG based NAS,
   where CGN also locates, using a new RADIUS attribute called Port-
   Session-Limit (defined in Section 3.1), along with other
   configuration parameters.  While some parameters are passed to the
   subscriber, the session limit(s) is recorded on the CGN device for
   imposing the usage of TCP/UDP ports and ICMP identifiers for that
   subscriber.

   Figure 1 illustrates how RADIUS protocol is used to configure the
   maximum number of TCP/UDP ports for a given subscriber on a NAT44
   device.


   User                    NAT44/NAS                       AAA
    |                         BNG                         Server
    |                          |                             |
    |                          |                             |
    |----Service Request------>|                             |
    |                          |                             |
    |                          |-----Access-Request -------->|
    |                          |                             |
    |                          |<----Access-Accept-----------|
    |                          |     (Port-Session-Limit)    |
    |                          |     (for TCP/UDP ports)     |
    |<---Service Granted ------|                             |
    |    (other parameters)    |                             |
    |                          |                             |
    |                  (NAT44 external port                  |
    |                   allocation and                       |
    |                   IPv4 address assignment)             |
    |                          |                             |

      Figure 1: RADIUS Message Flow for Configuring NAT44 Port Limit

   The session limit(s) created on a CGN device for a specific user
   using RADIUS extension may be changed using RADIUS CoA message
   [RFC5176] that carries the same RADIUS attribute.  The CoA message
   may be sent from the RADIUS server directly to the NAS, which once
   accepts and sends back a RADIUS CoA ACK message, the new session
   limit replaces the previous one.

   Figure 2 illustrates how RADIUS protocol is used to increase the TCP/
   UDP port limit from 1024 to 2048 on a NAT44 device for a specific



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   user.



   User                     NAT/NAS                           AAA
    |                         BNG                            Server
    |                          |                               |
    |              TCP/UDP Port Limit (1024)                   |
    |                          |                               |
    |                          |<---------CoA Request----------|
    |                          |       (Port-Session-Limit)    |
    |                          |       (for TCP/UDP ports)     |
    |                          |                               |
    |              TCP/UDP Port Limit (2048)                   |
    |                          |                               |
    |                          |---------CoA Response--------->|
    |                          |                               |

   Figure 2: RADIUS Message Flow for changing a user's NAT44 port limit

4.1.2.  Report CGN Session Allocation or De-allocation

   Upon obtaining the session limit(s) for a subscriber, the CGN device
   needs to allocate a TCP/UDP port or an ICMP identifiers for the
   subscriber when receiving a new IP flow sent from that subscriber.

   As one practice, a CGN may allocate a bulk of TCP/UDP ports or ICMP
   identifiers once at a time for a specific user, instead of one port/
   identifier at a time, and within each session bulk, the ports/
   identifiers may be randomly distributed or in consecutive fashion.
   When a CGN device allocates bulk of TCP/UDP ports and ICMP
   identifiers, the information can be easily conveyed to the RADIUS
   server by a new RADIUS attribute called the CGN-Session-Range
   (defined in Section 3.2).  The CGN device may allocate one or more
   TCP/UDP port ranges or ICMP identifier ranges, or generally called
   session ranges, where each range contains a set of numbers
   representing TCP/UDP ports or ICMP identifiers, and the total number
   of sessions must be less or equal to the associated session limit
   defined for that subscriber.  A CGN device may choose to allocate a
   small session range, and allocate more at a later time as needed;
   such practice is good because its randomization in nature.

   At the same time, the CGN device also needs to decide the shared IPv4
   address for that subscriber.  The shared IPv4 address and the pre-
   allocated session range are both passed to the RADIUS server.

   When a subscriber initiates an IP flow, the CGN device randomly
   selects a TCP/UDP port or ICMP identifier from the associated and



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   pre-allocated session range for that subscriber to replace the
   original source TCP/UDP port or ICMP identifier, along with the
   replacement of the source IP address by the shared IPv4 address.

   A CGN device may decide to "free" a previously assigned set of TCP/
   UDP ports or ICMP identifiers that have been allocated for a specific
   subscriber but not currently in use, and with that, the CGN device
   must send the information of the de-allocated session range along
   with the shared IPv4 address to the RADIUS server.

   Figure 3 illustrates how RADIUS protocol is used to report a set of
   ports allocated and de-allocated, respectively, by a NAT44 device for
   a specific user to the RADIUS server.


   Host                    NAT44/NAS                       AAA
    |                         BNG                         Server
    |                          |                             |
    |                          |                             |
    |----Service Request------>|                             |
    |                          |                             |
    |                          |-----Access-Request -------->|
    |                          |                             |
    |                          |<----Access-Accept-----------|
    |<---Service Granted ------|                             |
    |    (other parameters)    |                             |
   ...                        ...                           ...
    |                          |                             |
    |                          |                             |
    |                (NAT44 decides to allocate              |
    |                 a TCP/UDP port range for the user)     |
    |                          |                             |
    |                          |-----Accounting-Request----->|
    |                          |    (Port-Session-Range      |
    |                          |     for allocation)         |
   ...                        ...                           ...
    |                          |                             |
    |                (NAT44 decides to de-allocate           |
    |                 a TCP/UDP port range for the user)     |
    |                          |                             |
    |                          |-----Accounting-Request----->|
    |                          |    (Port-Session-Range      |
    |                          |     for de-allocation)      |
    |                          |                             |

       Figure 3: RADIUS Message Flow for reporting NAT44 allocation/
                        de-allocation of a port set




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4.1.3.  Configure CGN Forwarding Port Mapping

   In most scenarios, the port mapping on a NAT device is dynamically
   created when the IP packets of an IP connection initiated by a user
   arrives.  For some applications, the port mapping needs to be pre-
   defined allowing IP packets of applications from outside a CGN device
   to pass through and "port forwarded" to the correct user located
   behind the CGN device.

   Port Control Protocol [I-D.ietf-pcp-base], provides a mechanism to
   create a mapping from an external IP address and port to an internal
   IP address and port on a CGN device just to achieve the "port
   forwarding" purpose.  PCP is a server-client protocol capable of
   creating or deleting a mapping along with a rich set of features on a
   CGN device in dynamic fashion.  In some deployment, all users need is
   a few, typically just one pre-configured port mapping for
   applications such as web cam at home, and the lifetime of such a port
   mapping remains valid throughout the duration of the customer's
   Internet service connection time.  In such an environment, it is
   possible to statically configure a port mapping on the RADIUS server
   for a user and let the RADIUS protocol to propagate the information
   to the associated CGN device.

   Figure 4 illustrates how RADIUS protocol is used to configure a
   forwarding port mapping on a NAT44 device by using RADIUS protocol.


























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   Host                     NAT/NAS                           AAA
    |                         BNG                            Server
    |                          |                               |
    |----Service Request------>|                               |
    |                          |                               |
    |                          |---------Access-Request------->|
    |                          |                               |
    |                          |<--------Access-Accept---------|
    |                          |   (Port-Forwarding-Map)       |
    |<---Service Granted ------|                               |
    |    (other parameters)    |                               |
    |                          |                               |
    |                 (Create a port mapping                   |
    |                  for the user, and                       |
    |                  associate it with the                   |
    |                  internal IP address                     |
    |                  and external IP address)                |
    |                          |                               |
    |                          |                               |
    |                          |------Accounting-Request------>|
    |                          |    (Port-Forwarding-Map)      |

      Figure 4: RADIUS Message Flow for configuring a forwarding port
                                  mapping

   A port forwarding mapping that is created on a CGN device using
   RADIUS extension as described above may also be changed using RADIUS
   CoA message [RFC5176] that carries the same RADIUS associate.  The
   CoA message may be sent from the RADIUS server directly to the NAS,
   which once accepts and sends back a RADIUS CoA ACK message, the new
   port forwarding mapping then replaces the previous one.

   Figure 5 illustrates how RADIUS protocol is used to change an
   existing port mapping from (a:X) to (a:Y), where "a" is an internal
   port, and "X" and "Y" are external ports, respectively, for a
   specific user with a specific IP address















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   Host                     NAT/NAS                           AAA
    |                         BNG                            Server
    |                          |                               |
    |                    Internal IP Address                   |
    |                    Port Map (a:X)                        |
    |                          |                               |
    |                          |<---------CoA Request----------|
    |                          |    (Port-Forwarding-Map)      |
    |                          |                               |
    |                    Internal IP Address                   |
    |                    Port Map (a:Y)                        |
    |                          |                               |
    |                          |---------CoA Response--------->|
    |                          |    (Port-Forwarding-Map)      |

      Figure 5: RADIUS Message Flow for changing a user's forwarding
                               port mapping

4.1.4.  An Example

   An Internet Service Provider (ISP) assigns TCP/UDP 500 ports for the
   subscriber Joe. This number is the limit that can be used for TCP/UDP
   ports on a NAT44 device for Joe, and is configured on a RADIUS
   server.  Also, Joe asks for a pre-defined port forwarding mapping on
   the NAT44 device for his web cam applications (external port 5000
   maps to internal port 80).

   When Joe successfully connects to the Internet service, the RADIUS
   server conveys the TCP/UDP port limit (1000) and the forwarding port
   mapping (external port 5000 to internal port 80) to the NAT44 device,
   using Port-Session-Limit attribute and Port-Forwarding-Map attribute,
   respectively, carried by an Access-Accept message to the BNG where
   NAS and CGN co-located.

   Upon receiving the first outbound IP packet sent from Joe's laptop,
   the NAT44 device decides to allocate a small port pool that contains
   40 consecutive ports, from 3500 to 3540, inclusively, and also assign
   a shared IPv4 address 192.0.2.15, for Joe. The NAT44 device also
   randomly selects one port from the allocated range (say 3519) and use
   that port to replace the original source port in outbound IP packets.

   For accounting purpose, the NAT44 device passes this port range
   (3500-3540) and the shared IPv4 address 192.0.2.15 together to the
   RADIUS server using Port-Session-Range attribute carried by an
   Accounting-Request message.

   When Joe works on more applications with more outbound IP sessions
   and the port pool (3500-3540) is close to exhaust, the NAT44 device



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   allocates a second port pool (8500-8800) in a similar fashion, and
   also passes the new port range (8500-8800) and IPv4 address
   192.0.2.15 together to the RADIUS server using Port-Session-Range
   attribute carried by an Accounting-Request message.  Note when the
   CGN allocates more ports, it needs to assure that the total number of
   ports allocated for Joe is within the limit.

   Joe decides to upgrade his service agreement with more TCP/UDP ports
   allowed (up to 1000 ports).  The ISP updates the information in Joe's
   profile on the RADIUS server, which then sends a CoA-Request message
   that carries the Port-Session-Limit attribute with 1000 ports to the
   NAT44 device; the NAT44 device in turn sends back a CoA-ACK message.
   With that, Joe enjoys more available TCP/UDP ports for his
   applications.

   When Joe travels, most of the IP sessions are closed with their
   associated TCP/UDP ports released on the NAT44 device, which then
   sends the relevant information back to the RADIUS server using Port-
   Session-Range attribute carried by Accounting-Request message.

   Throughout Joe's connection with his ISP Internet service,
   applications can communicate with his web cam at home from external
   realm directly traversing the pre-configured mapping on the CGN
   device.

   When Joe disconnects from his Internet service, the CGN device will
   de-allocate all TCP/UDP ports as well as the port-forwarding mapping,
   and send the relevant information to the RADIUS server.

4.2.  Report Assigned Port Set for a Visiting UE

   Figure 6 illustrates an example of the flow exhange which occurs when
   a visiting UE connects to a CPE offering WiFi service.

   For identification purposes (see
   [I-D.ietf-intarea-nat-reveal-analysis]), once the CPE assigns a port
   set, it issues a RADIUS message to report the assigned port set.














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   UE         CPE             NAS                          AAA
    |                         BNG                         Server
    |                          |                             |
    |                          |                             |
    |----Service Request------>|                             |
    |                          |                             |
    |                          |-----Access-Request -------->|
    |                          |                             |
    |                          |<----Access-Accept-----------|
    |<---Service Granted ------|                             |
    |    (other parameters)    |                             |
   ...          |             ...                           ...
    |<---IP@----|              |                             |
    |           |              |                             |
    |   (CPE assigns a TCP/UDP port                          |
    |   range for this visiting UE)                          |
    |           |                                            |
    |           |--Accounting-Request-...------------------->|
    |           |    (Port-Session-Range                     |
    |           |     for allocation)                        |
   ...          |             ...                           ...
    |           |              |                             |
    |           |              |                             |
    |   (CPE withdraws a TCP/UDP port                        |
    |   range for a visiting UE)                             |
    |           |                                            |
    |           |--Accounting-Request-...------------------->|
    |           |    (Port-Session-Range                     |
    |           |     for de-allocation)                     |
    |           |                                            |

        Figure 6: RADIUS Message Flow for reporting CPE allocation/
               de-allocation of a port set to a visiting UE


5.  Table of Attributes

   The following table provides a guide as the attributes may be found
   in which kinds of RADIUS packets, and in what quantity.

   Request Accept Reject Challenge Acct.        #    Attribute
                                   Request
   0-1     0-1    0      0         0-1          TBA1 Port-Session-Limit
   0       0      0      0         0-1          TBA2 Port-Session-Range
   0-1     0-1    0      0         0-1          TBA3 Port-Forwarding-Map

   The following table defines the meaning of the above table entries.




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   0   This attribute MUST NOT be present in packet.
   0+  Zero or more instances of this attribute MAY be present in
       packet.
   0-1 Zero or one instance of this attribute MAY be present in packet.


6.  Security Considerations

   This document does not introduce any security issue than what has
   been identified in [RFC2865].


7.  IANA Considerations

7.1.  RADIUS Attributes

   This document requires new code point assignment for the three new
   RADIUS attributes as follows:

   o  Port-Session-Limit

   o  Port-Session-Range

   o  Port-Forwarding-Map

7.2.  Name Spaces

   This document establishes a new name space for Session Type (see
   Section 3.1 for the initial reservation of values.  The allocation of
   future values is according to RFC Required policy [RFC5226].


8.  Acknowledgements

   Many thanks to Dan Wing, Roberta Maglione, Daniel Derksen, and David
   Thaler for their useful comments and suggestions.


9.  References

9.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC5176]  Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
              Aboba, "Dynamic Authorization Extensions to Remote
              Authentication Dial In User Service (RADIUS)", RFC 5176,
              January 2008.

9.2.  Informative References

   [I-D.arkko-dual-stack-extra-lite]
              Arkko, J., Eggert, L., and M. Townsley, "Scalable
              Operation of Address Translators with Per-Interface
              Bindings", draft-arkko-dual-stack-extra-lite-05 (work in
              progress), February 2011.

   [I-D.gundavelli-v6ops-community-wifi-svcs]
              Gundavelli, S., Grayson, M., Seite, P., and Y. Lee,
              "Service Provider Wi-Fi Services Over Residential
              Architectures",
              draft-gundavelli-v6ops-community-wifi-svcs-04 (work in
              progress), April 2012.

   [I-D.ietf-behave-lsn-requirements]
              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common requirements for Carrier Grade NATs
              (CGNs)", draft-ietf-behave-lsn-requirements-09 (work in
              progress), August 2012.

   [I-D.ietf-intarea-nat-reveal-analysis]
              Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Solution Candidates to Reveal a Host
              Identifier (HOST_ID) in Shared Address Deployments",
              draft-ietf-intarea-nat-reveal-analysis-04 (work in
              progress), August 2012.

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-28 (work in progress), October 2012.

   [I-D.miles-behave-l2nat]
              Miles, D. and M. Townsley, "Layer2-Aware NAT",
              draft-miles-behave-l2nat-00 (work in progress),
              March 2009.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network



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              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6158]  DeKok, A. and G. Weber, "RADIUS Design Guidelines",
              BCP 158, RFC 6158, March 2011.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269,
              June 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6431]  Boucadair, M., Levis, P., Bajko, G., Savolainen, T., and
              T. Tsou, "Huawei Port Range Configuration Options for PPP
              IP Control Protocol (IPCP)", RFC 6431, November 2011.


Authors' Addresses

   Dean Cheng
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, California  95050
   USA

   Email: dean.cheng@huawei.com


   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  FIN-02600
   Finland

   Email: jouni.nospam@gmail.com






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   Mohamed Boucadair
   France Telecom
   Rennes
   France

   Email: mohamed.boucadair@orange.com













































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