Internet Engineering Task Force (IETF)
Request for Comments: 8045
Category: Standards Track
ISSN: 2070-1721

D. Cheng
Huawei
J. Korhonen
Broadcom Corporation
M. Boucadair
Orange
S. Sivakumar
Cisco Systems
January 2017

RADIUS Extensions for IP Port Configuration and Reporting

Abstract

This document defines three new RADIUS attributes. For devices that implement IP port ranges, these attributes are used to communicate with a RADIUS server in order to configure and report IP transport ports as well as mapping behavior for specific hosts. This mechanism can be used in various deployment scenarios such as Carrier-Grade NAT, IPv4/IPv6 translators, Provider WLAN gateway, etc. This document defines a mapping between some RADIUS attributes and IP Flow Information Export (IPFIX) Information Element identifiers.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8045.

Copyright Notice

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.

   1. Introduction ....................................................4
   2. Terminology .....................................................5
      2.1. Requirements Language ......................................6
   3. Extensions of RADIUS Attributes and TLVs ........................7
      3.1. Extended Attributes for IP Ports ...........................7
           3.1.1. IP-Port-Limit-Info Attribute ........................7
           3.1.2. IP-Port-Range Attribute .............................9
           3.1.3. IP-Port-Forwarding-Map Attribute ...................12
      3.2. RADIUS TLVs for IP Ports ..................................15
           3.2.1. IP-Port-Type TLV ...................................16
           3.2.2. IP-Port-Limit TLV ..................................17
           3.2.3. IP-Port-Ext-IPv4-Addr TLV ..........................18
           3.2.4. IP-Port-Int-IPv4-Addr TLV ..........................19
           3.2.5. IP-Port-Int-IPv6-Addr TLV ..........................20
           3.2.6. IP-Port-Int-Port TLV ...............................21
           3.2.7. IP-Port-Ext-Port TLV ...............................22
           3.2.8. IP-Port-Alloc TLV ..................................23
           3.2.9. IP-Port-Range-Start TLV ............................24
           3.2.10. IP-Port-Range-End TLV .............................25
           3.2.11. IP-Port-Local-Id TLV ..............................25
   4. Applications, Use Cases, and Examples ..........................27
      4.1. Managing CGN Port Behavior Using RADIUS ...................27
           4.1.1. Configure IP Port Limit for a User .................27
           4.1.2. Report IP Port Allocation/Deallocation .............29
           4.1.3. Configure Port Forwarding Mapping ..................31
           4.1.4. An Example .........................................33
      4.2. Report Assigned Port Set for a Visiting UE ................35
   5. Table of Attributes ............................................36
   6. Security Considerations ........................................36
   7. IANA Considerations ............................................37
      7.1. New IPFIX Information Elements ............................37
      7.2. New RADIUS Attributes .....................................38
      7.3. New RADIUS TLVs ...........................................38
   8. References .....................................................39
      8.1. Normative References ......................................39
      8.2. Informative References ....................................40
   Acknowledgments ...................................................43
   Authors' Addresses ................................................43

1. Introduction

In a broadband network, customer information is usually stored on a RADIUS server [RFC2865]. At the time when a user initiates an IP connection request, if this request is authorized, the RADIUS server will populate the user's configuration information to the Network Access Server (NAS), which is often referred to as a Broadband Network Gateway (BNG) in broadband access networks. The Carrier- Grade NAT (CGN) function may also be implemented on the BNG. Within this document, the CGN may perform Network Address Translation from IPv4 Clients to IPv4 Servers (NAT44) [RFC3022], NAT from IPv6 Clients to IPv4 Servers (NAT64) [RFC6146], or Dual-Stack Lite Address Family Transition Router (AFTR) [RFC6333] function. In such case, the CGN IP transport port (e.g., TCP/UDP port) mapping behaviors can be part of the configuration information sent from the RADIUS server to the NAS/BNG. As part of the accounting information sent from the NAS/BNG to a RADIUS server, the NAS/BNG may also report the IP port mapping behavior applied by the CGN to a user session.

When IP packets traverse the CGN, it performs mapping on the IP transport (e.g., TCP/UDP) source port as required. An IP transport source port, along with a source IP address, destination IP address, destination port, and protocol identifier, if applicable, uniquely identify a mapping. Since the number space of IP transport ports in the CGN's external realm is shared among multiple users assigned with the same IPv4 address, the total number of a user's simultaneous IP mappings is likely to be subject to a port quota (see Section 5 of [RFC6269]).

The attributes defined in this document may also be used to report the assigned port range in some deployments, such as Provider WLAN [WIFI-SERVICES]. For example, a visiting host can be managed by Customer Premises Equipment (CPE), which will need to report the assigned port range to the service platform. This is required for identification purposes (see TR-146 [TR-146] for more details).

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

   1.  IP-Port-Limit-Info: This attribute may be carried in a RADIUS
   
       Access-Accept, Access-Request, Accounting-Request, or CoA-Request
       packet.  The purpose of this attribute is to limit the total
       number of IP source transport ports allocated to a user and
       associated with one or more IPv4 or IPv6 addresses.

IP-Port-Range: This attribute may be carried in a RADIUS Accounting-Request packet. The purpose of this attribute is for an address-sharing device (e.g., a CGN) to report to the RADIUS server the range of IP source transport ports that have been allocated or deallocated for a user. The port range is bound to an external IPv4 address.

   3.  IP-Port-Forwarding-Map: This attribute may be carried in RADIUS
       Access-Accept, Access-Request, Accounting-Request, or CoA-Request
       packet.  The purpose of this attribute is to specify how an IP
       internal source transport port, together with its internal IPv4
       or IPv6 address, are mapped to an external source transport port
       along with the external IPv4 address.

IPFIX Information Elements [RFC7012] can be used for IP flow identification and representation over RADIUS. This document provides a mapping between some RADIUS TLVs and IPFIX Information Element identifiers. A new IPFIX Information Element is defined by this document (see Section 3.2.2).

IP protocol numbers (refer to [ProtocolNumbers]) can be used for identification of IP transport protocols (e.g., TCP [RFC793], UDP [RFC768], Datagram Congestion Control Protocol (DCCP) [RFC4340], and Stream Control Transmission Protocol (SCTP) [RFC4960]) that are associated with some RADIUS attributes.

This document focuses on IPv4 address sharing. Mechanisms for IPv6 prefix sharing (e.g., IPv6-to-IPv6 Network Prefix Translation (NPTv6)) are out of scope.

2. Terminology

This document makes use of the following terms:

IP Port: This refers to an IP transport port (e.g., a TCP port number or UDP port number).

IP Port Type: This refers to the IP transport protocol as indicated by the IP transport protocol number. Refer to [ProtocolNumbers].

IP Port Limit: This denotes the maximum number of IP ports for a specific (or all) IP transport protocol(s) that a device supporting port ranges can use when performing port number mappings for a specific user/host. Note that this limit is usually associated with one or more IPv4/IPv6 addresses.

IP Port Range: This specifies a set of contiguous IP ports indicated by the lowest numerical number and the highest numerical number, inclusively.

Internal IP Address: This refers to the IP address that is used by a host as a source IP address in an outbound IP packet sent towards a device supporting port ranges in the internal realm. The internal IP address may be IPv4 or IPv6.

External IP Address: This refers to 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. This document assumes that the external IP address is an IPv4 address.

Internal Port: This is an IP transport port that is allocated by a host or application behind an address-sharing device for an outbound IP packet in the internal realm.

External Port: This is an IP transport port that is allocated by an address-sharing device 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.

External Realm: This refers to the networking segment where external IP addresses are used as source addresses of outbound packets forwarded by an address-sharing device.

Internal Realm: This refers to the networking segment that is behind an address-sharing device and where internal IP addresses are used.

Mapping: This denotes a relationship between an internal IP address, internal port, and protocol, as well as an external IP address, external port, and protocol.

Address-Sharing Device: This is a device that is capable of sharing an IPv4 address among multiple users. A typical example of this device is a CGN, CPE, Provider WLAN gateway, etc.

2.1. 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].

3. Extensions of RADIUS Attributes and TLVs

These three new attributes are defined in the following subsections:

   1.  IP-Port-Limit-Info Attribute

IP-Port-Range Attribute

   3.  IP-Port-Forwarding-Map Attribute

All these attributes are allocated from the RADIUS "Extended Type" code space per [RFC6929].

These attributes and their embedded TLVs (refer to Section 3.2) are defined with globally unique names and follow the guidelines in Section 2.7.1 of [RFC6929].

In all the figures describing the RADIUS attributes and TLV formats in the following subsections, the fields are transmitted from left to right.

3.1. Extended Attributes for IP Ports

3.1.1. IP-Port-Limit-Info Attribute

This attribute is of type "tlv" as defined in the RADIUS Protocol Extensions [RFC6929]. It contains some sub-attributes, and the requirements are as follows:

   o  The IP-Port-Limit-Info Attribute MAY contain the IP-Port-Type TLV
   
      (see Section 3.2.1).
   
   o  The IP-Port-Limit-Info Attribute MUST contain the
      IP-Port-Limit TLV (see Section 3.2.2).
   
   o  The IP-Port-Limit-Info Attribute MAY contain the
      IP-Port-Ext-IPv4-Addr TLV (see Section 3.2.3).

The IP-Port-Limit-Info Attribute specifies the maximum number of IP ports, as indicated in IP-Port-Limit TLV, of a specific IP transport protocol, as indicated in IP-Port-Type TLV, and associated with a given IPv4 address, as indicated in IP-Port-Ext-IPv4-Addr TLV, for an end user.

Note that when IP-Port-Type TLV is not included as part of the IP-Port-Limit-Info Attribute, the port limit applies to all IP transport protocols.

Note also that when IP-Port-Ext-IPv4-Addr TLV is not included as part of the IP-Port-Limit-Info Attribute, the port limit applies to all the IPv4 addresses managed by the address-sharing device, e.g., a CGN or NAT64 device.

The IP-Port-Limit-Info Attribute MAY appear in an Access-Accept packet. It MAY also appear in an Access-Request packet as a preferred maximum number of IP ports indicated by the device supporting port ranges co-located with the NAS, e.g., a CGN or NAT64.

The IP-Port-Limit-Info Attribute MAY appear in a CoA-Request packet.

The IP-Port-Limit-Info Attribute MAY appear in an Accounting-Request packet.

The IP-Port-Limit-Info Attribute MUST NOT appear in any other RADIUS packet.

The format of the IP-Port-Limit-Info Attribute is shown in Figure 1.

    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    | Extended-Type |    Value ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1

   Type

   Length

This field indicates the total length in octets of all fields of this attribute, including the Type, Length, Extended-Type, and the entire length of the embedded TLVs.

   Extended-Type

   Value

This field contains a set of TLVs as follows:

      IP-Port-Type TLV

This TLV contains a value that indicates the IP port type. Refer to Section 3.2.1.

      IP-Port-Limit TLV

This TLV contains the maximum number of IP ports of a specific IP port type and associated with a given IPv4 address for an end user. This TLV MUST be included in the IP-Port-Limit-Info Attribute. Refer to Section 3.2.2. This limit applies to all mappings that can be instantiated by an underlying address- sharing device without soliciting any external entity. In particular, this limit does not include the ports that are instructed by an Authentication, Authorization, and Accounting (AAA) server.

      IP-Port-Ext-IPv4-Addr TLV

This TLV contains the IPv4 address that is associated with the IP port limit contained in the IP-Port-Limit TLV. This TLV is optionally included as part of the IP-Port-Limit-Info Attribute. Refer to Section 3.2.3.

IP-Port-Limit-Info Attribute is associated with the following identifier: 241.5.

3.1.2. IP-Port-Range Attribute

This attribute is of type "tlv" as defined in the RADIUS Protocol Extensions [RFC6929]. It contains some sub-attributes and the requirement is as follows:

   o  The IP-Port-Range Attribute MAY contain the IP-Port-Type TLV (see
      Section 3.2.1).
   
   o  The IP-Port-Range Attribute MUST contain the IP-Port-Alloc TLV
      (see Section 3.2.8).

For port allocation, the IP-Port-Range Attribute MUST contain both the IP-Port-Range-Start TLV (see Section 3.2.9) and the IP-Port-Range-End TLV (see Section 3.2.10). For port deallocation, the IP-Port-Range Attribute MAY contain both of these two TLVs; if the two TLVs are not included, it implies that all ports that were previously allocated are now all deallocated.

The IP-Port-Range Attribute MAY contain the IP-Port-Ext-IPv4-Addr TLV (see Section 3.2.3).

   o  The IP-Port-Range Attribute MAY contain the IP-Port-Local-Id TLV
      (see Section 3.2.11).

The IP-Port-Range Attribute contains a range of contiguous IP ports. These ports are either to be allocated or deallocated depending on the Value carried by the IP-Port-Alloc TLV.

If the IP-Port-Type TLV is included as part of the IP-Port-Range Attribute, then the port range is associated with the specific IP transport protocol as specified in the IP-Port-Type TLV, but otherwise it is for all IP transport protocols.

If the IP-Port-Ext-IPv4-Addr TLV is included as part of the IP-Port-Range Attribute, then the port range as specified is associated with the IPv4 address as indicated, but otherwise it is for all IPv4 addresses by the address-sharing device (e.g., a CGN device) for the end user.

This attribute can be used to convey a single IP transport port number: in such case, the Value of the IP-Port-Range-Start TLV and the IP-Port-Range-End TLV, respectively, contain the same port number.

The information contained in the IP-Port-Range Attribute is sent to RADIUS server.

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

The IP-Port-Range Attribute MUST NOT appear in any other RADIUS packet.

The format of the IP-Port-Range Attribute is shown in Figure 2.

    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    | Extended-Type |    Value ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2

   Type

   Length

This field indicates the total length in octets of all fields of this attribute, including the Type, Length, Extended-Type, and the entire length of the embedded TLVs.

   Extended-Type

   Value

This field contains a set of TLVs as follows:

      IP-Port-Type TLV

This TLV contains a value that indicates the IP port type. Refer to Section 3.2.1.

      IP-Port-Alloc TLV

This TLV contains a flag to indicate the range of the specified IP ports for either allocation or deallocation. This TLV MUST be included as part of the IP-Port-Range Attribute. Refer to Section 3.2.8.

      IP-Port-Range-Start TLV

This TLV contains the smallest port number of a range of contiguous IP ports. To report the port allocation, this TLV MUST be included together with IP-Port-Range-End TLV as part of the IP-Port-Range Attribute. Refer to Section 3.2.9.

      IP-Port-Range-End TLV

This TLV contains the largest port number of a range of contiguous IP ports. To report the port allocation, this TLV MUST be included together with IP-Port-Range-Start TLV as part of the IP-Port-Range Attribute. Refer to Section 3.2.10.

      IP-Port-Ext-IPv4-Addr TLV

This TLV contains the IPv4 address that is associated with the IP port range, as is collectively indicated in the IP-Port-Range-Start TLV and the IP-Port-Range-End TLV. This TLV is optionally included as part of the IP-Port-Range Attribute. Refer to Section 3.2.3.

      IP-Port-Local-Id TLV

This TLV contains a local significant identifier at the customer premise, such as the Media Access Control (MAC) address, interface ID, VLAN ID, PPP sessions ID, VPN Routing and Forwarding (VRF) ID, IP address/prefix, etc. This TLV is optionally included as part of the IP-Port-Range Attribute. Refer to Section 3.2.11.

The IP-Port-Range Attribute is associated with the following identifier: 241.6.

3.1.3. IP-Port-Forwarding-Map Attribute

This attribute is of type "tlv" as defined in the RADIUS Protocol Extensions [RFC6929]. It contains some sub-attributes and the requirement is as follows:

   o  The IP-Port-Forwarding-Map Attribute MAY contain the
      IP-Port-Type TLV (see Section 3.2.1).
   
   o  The IP-Port-Forwarding-Map Attribute MUST contain both
      IP-Port-Int-Port TLV (see Section 3.2.6) and the
      IP-Port-Ext-Port TLV (see Section 3.2.7).

If the internal realm is with an IPv4 address family, the IP-Port-Forwarding-Map Attribute MUST contain the IP-Port-Int-IPv4-Addr TLV (see Section 3.2.4); if the internal realm is with an IPv6 address family, the IP-Port-Forwarding-Map Attribute MUST contain the IP-Port-Int-IPv6-Addr TLV (see Section 3.2.5).

   o  The IP-Port-Forwarding-Map Attribute MAY contain the
      IP-Port-Ext-IPv4-Addr TLV (see Section 3.2.3).
   
   o  The IP-Port-Forwarding-Map Attribute MAY contain the
      IP-Port-Local-Id TLV (see Section 3.2.11).

The attribute contains a two-octet IP internal port number and a two-octet IP external port number. The internal port number is associated with an internal IPv4 or IPv6 address that MUST always be included. The external port number is associated with a specific external IPv4 address if included, but otherwise it is associated with all external IPv4 addresses for the end user.

If the IP-Port-Type TLV is included as part of the IP-Port-Forwarding-Map Attribute, then the port mapping is associated with the specific IP transport protocol as specified in the IP-Port-Type TLV, but otherwise it is for all IP transport protocols.

The IP-Port-Forwarding-Map Attribute MAY appear in an Access-Accept packet. It MAY also appear in an Access-Request packet to indicate a preferred port mapping by the device co-located with NAS. However, the server is not required to honor such a preference.

The IP-Port-Forwarding-Map Attribute MAY appear in a CoA-Request packet.

The IP-Port-Forwarding-Map Attribute MAY also appear in an Accounting-Request packet.

The IP-Port-Forwarding-Map Attribute MUST NOT appear in any other RADIUS packet.

The format of the IP-Port-Forwarding-Map Attribute is shown in Figure 3.

    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    | Extended-Type |    Value ....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3

   Type

   Length

This field indicates the total length in octets of all fields of this attribute, including the Type, Length, Extended-Type, and the entire length of the embedded TLVs.

   Extended-Type

   Value

This field contains a set of TLVs as follows:

      IP-Port-Type TLV

This TLV contains a value that indicates the IP port type. Refer to Section 3.2.1.

      IP-Port-Int-Port TLV

This TLV contains an internal IP port number associated with an internal IPv4 or IPv6 address. This TLV MUST be included together with IP-Port-Ext-Port TLV as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.6.

      IP-Port-Ext-Port TLV

This TLV contains an external IP port number associated with an external IPv4 address. This TLV MUST be included together with IP-Port-Int-Port TLV as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.7.

      IP-Port-Int-IPv4-Addr TLV

This TLV contains an IPv4 address that is associated with the internal IP port number contained in the IP-Port-Int-Port TLV. For the internal realm with an IPv4 address family, this TLV MUST be included as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.4.

      IP-Port-Int-IPv6-Addr TLV

This TLV contains an IPv6 address that is associated with the internal IP port number contained in the IP-Port-Int-Port TLV. For the internal realm with an IPv6 address family, this TLV MUST be included as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.5.

      IP-Port-Ext-IPv4-Addr TLV

This TLV contains an IPv4 address that is associated with the external IP port number contained in the IP-Port-Ext-Port TLV. This TLV MAY be included as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.3.

      IP-Port-Local-Id TLV

This TLV contains a local significant identifier at the customer premise, such as MAC address, interface ID, VLAN ID, PPP sessions ID, VRF ID, IP address/prefix, etc. This TLV is optionally included as part of the IP-Port-Forwarding-Map Attribute. Refer to Section 3.2.11.

The IP-Port-Forwarding-Map Attribute is associated with the following identifier: 241.7.

3.2. RADIUS TLVs for IP Ports

The TLVs that are included in the three attributes (see Section 3.1) are defined in the following subsections. These TLVs use the format defined in [RFC6929]. As the three attributes carry similar data, we have defined a common set of TLVs that are used for all three attributes. That is, the TLVs have the same name and number when encapsulated in any one of the three parent attributes. See Sections 3.1.1, 3.1.2, and 3.1.3 for a list of which TLV is permitted within which parent attribute.

   The encoding of the Value field of these TLVs follows the
   recommendation of [RFC6158].  In particular, IP-Port-Type,
   IP-Port-Limit, IP-Port-Int-Port, IP-Port-Ext-Port, IP-Port-Alloc,
   IP-Port-Range-Start, and IP-Port-Range-End TLVs are encoded in
   32 bits as per the recommendation in Appendix A.2.1 of [RFC6158].

3.2.1. IP-Port-Type TLV

The format of IP-Port-Type TLV is shown in Figure 4. This attribute carries the IP transport protocol number defined by IANA (refer to [ProtocolNumbers]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV-Type    |     Length    |        Protocol-Number
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Protocol-Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4

   TLV-Type

   Length
   
      Six octets
   
   Protocol-Number

Integer. This field contains the data (unsigned8) of the protocol number defined in [ProtocolNumbers], right justified, and the unused bits in this field MUST be set to zero. Protocols that do not use a port number (e.g., the Resource Reservation Protocol (RSVP) or IP Encapsulating Security Payload (ESP)) MUST NOT be included in the IP-Port-Type TLV.

IP-Port-Type TLV MAY be included in the following attributes:

   o  IP-Port-Limit-Info Attribute, identified as 241.5.1 (see
      Section 3.1.1)
   
   o  IP-Port-Range Attribute, identified as 241.6.1 (see Section 3.1.2)
   
   o  IP-Port-Forwarding-Map Attribute, identified as 241.7.1 (see
      Section 3.1.3)

When the IP-Port-Type TLV is included within a RADIUS attribute, the associated attribute is applied to the IP transport protocol as indicated by the Protocol-Number only, such as TCP, UDP, SCTP, DCCP, etc.

3.2.2. IP-Port-Limit TLV

The format of IP-Port-Limit TLV is shown in Figure 5. This attribute carries IPFIX Information Element 458, "sourceTransportPortsLimit", which indicates the maximum number of IP transport ports as a limit for an end user to use that is associated with one or more IPv4 or IPv6 addresses.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV-Type    |     Length    |    sourceTransportPortsLimit
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        sourceTransportPortsLimit  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5

   TLV-Type

   Length
   
      Six octets
   
   sourceTransportPortsLimit

Integer. This field contains the data (unsigned16) of sourceTransportPortsLimit (458) defined in IPFIX, right justified, and the unused bits in this field MUST be set to zero.

IP-Port-Limit TLV MUST be included as part of the IP-Port-Limit-Info Attribute (refer to Section 3.1.1), identified as 241.5.2.

3.2.3. IP-Port-Ext-IPv4-Addr TLV

The format of IP-Port-Ext-IPv4-Addr TLV is shown in Figure 6. This attribute carries IPFIX Information Element 225, "postNATSourceIPv4Address", which is the IPv4 source address after NAT operation (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV-Type    |    Length     |    postNATSourceIPv4Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        postNATSourceIPv4Address   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6

   TLV-Type

   Length
   
      Six octets
   
   postNATSourceIPv4Address

Integer. This field contains the data (ipv4Address) of postNATSourceIPv4Address (225) defined in IPFIX.

IP-Port-Ext-IPv4-Addr TLV MAY be included in the following attributes:

   o  IP-Port-Limit-Info Attribute, identified as 241.5.3 (see
      Section 3.1.1)
   
   o  IP-Port-Range Attribute, identified as 241.6.3 (see Section 3.1.2)
   
   o  IP-Port-Forwarding-Mapping Attribute, identified as 241.7.3 (see
      Section 3.1.3)

3.2.4. IP-Port-Int-IPv4-Addr TLV

The format of IP-Port-Int-IPv4 TLV is shown in Figure 7. This attribute carries IPFIX Information Element 8, "sourceIPv4Address", which is the IPv4 source address before NAT operation (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV-Type    |     Length    |       sourceIPv4Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         sourceIPv4Address         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 7

   TLV-Type

   Length
   
      Six octets
   
   sourceIPv4Address

Integer. This field contains the data (ipv4Address) of sourceIPv4Address (8) defined in IPFIX.

If the internal realm is with an IPv4 address family, the IP-Port-Int-IPv4-Addr TLV MUST be included as part of the IP-Port-Forwarding-Map Attribute (refer to Section 3.1.3), identified as 241.7.4.

3.2.5. IP-Port-Int-IPv6-Addr TLV

The format of IP-Port-Int-IPv6-Addr TLV is shown in Figure 8. This attribute carries IPFIX Information Element 27, "sourceIPv6Address", which is the IPv6 source address before NAT operation (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV-Type    |     Length    |        sourceIPv6Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                             sourceIPv6Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                             sourceIPv6Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                             sourceIPv6Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           sourceIPv6Address       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 8

   TLV-Type

   Length
   
      Eighteen octets
   
   sourceIPv6Address

IPv6 address (128 bits). This field contains the data (ipv6Address) of sourceIPv6Address (27) defined in IPFIX.

If the internal realm is with an IPv6 address family, the IP-Port-Int-IPv6-Addr TLV MUST be included as part of the IP-Port-Forwarding-Map Attribute (refer to Section 3.1.3), identified as 241.7.5.

3.2.6. IP-Port-Int-Port TLV

The format of IP-Port-Int-Port TLV is shown in Figure 9. This attribute carries IPFIX Information Element 7, "sourceTransportPort", which is the source transport number associated with an internal IPv4 or IPv6 address (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |      sourceTransportPort
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           sourceTransportPort     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9

   TLV-Type

   Length
   
      Six octets
   
   sourceTransportPort

Integer. This field contains the data (unsigned16) of sourceTransportPort (7) defined in IPFIX, right justified, and unused bits MUST be set to zero.

   IP-Port-Int-Port TLV MUST be included as part of the
   IP-Port-Forwarding-Map Attribute (refer to Section 3.1.3),
   identified as 241.7.6.

3.2.7. IP-Port-Ext-Port TLV

The format of IP-Port-Ext-Port TLV is shown in Figure 10. This attribute carries IPFIX Information Element 227, "postNAPTSourceTransportPort", which is the transport number associated with an external IPv4 address (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |  postNAPTSourceTransportPort
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      postNAPTSourceTransportPort  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10

   TLV-Type

   Length
   
      Six octets
   
   postNAPTSourceTransportPort

Integer. This field contains the data (unsigned16) of postNAPTSourceTransportPort (227) defined in IPFIX, right justified, and unused bits MUST be set to zero.

   IP-Port-Ext-Port TLV MUST be included as part of the
   IP-Port-Forwarding-Map Attribute (refer to Section 3.1.3),
   identified as 241.7.7.

3.2.8. IP-Port-Alloc TLV

The format of IP-Port-Alloc TLV is shown in Figure 11. This attribute carries IPFIX Information Element 230, "natEvent", which is a flag to indicate an action of NAT operation (refer to [IPFIX]).

When the value of natEvent is "1" (Create event), it means to allocate a range of transport ports; when the value is "2", it means to deallocate a range of transports ports. For the purpose of this TLV, no other value is used.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |            natEvent
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               natEvent            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11

   TLV-Type

   Length
   
      Six octets
   
   natEvent

Integer. This field contains the data (unsigned8) of natEvent (230) defined in IPFIX, right justified, and unused bits MUST be set to zero. It indicates the allocation or deallocation of a range of IP ports as follows:

         0: Reserved
         1: Allocation
         2: Deallocation

IP-Port-Alloc TLV MUST be included as part of the IP-Port-Range Attribute (refer to Section 3.1.2), identified as 241.6.8.

3.2.9. IP-Port-Range-Start TLV

The format of IP-Port-Range-Start TLV is shown in Figure 12. This attribute carries IPFIX Information Element 361, "portRangeStart", which is the smallest port number of a range of contiguous transport ports (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |         portRangeStart
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             portRangeStart        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 12

   TLV-Type

   Length
   
      Six octets
   
   portRangeStart

Integer. This field contains the data (unsigned16) of portRangeStart (361) defined in IPFIX, right justified, and unused bits MUST be set to zero.

   IP-Port-Range-Start TLV is included as part of the IP-Port-Range
   Attribute (refer to Section 3.1.2), identified as 241.6.9.

3.2.10. IP-Port-Range-End TLV

The format of IP-Port-Range-End TLV is shown in Figure 13. This attribute carries IPFIX Information Element 362, "portRangeEnd", which is the largest port number of a range of contiguous transport ports (refer to [IPFIX]).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |          portRangeEnd
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              portRangeEnd         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13

   TLV-Type

   Length
   
      Six octets
   
   portRangeEnd

Integer. This field contains the data (unsigned16) of portRangeEnd (362) defined in IPFIX, right justified, and unused bits MUST be set to zero.

   IP-Port-Range-End TLV is included as part of the IP-Port-Range
   Attribute (refer to Section 3.1.2), identified as 241.6.10.

3.2.11. IP-Port-Local-Id TLV

The format of IP-Port-Local-Id TLV is shown in Figure 14. This attribute carries a string called "localID", which is a local significant identifier as explained below.

The primary issue addressed by this TLV is that there are CGN deployments that do not distinguish internal hosts by their internal IP address alone but use further identifiers for unique subscriber identification. For example, this is the case if a CGN supports overlapping private or shared IP address spaces (as described in [RFC1918] and [RFC6598]) for internal hosts of different subscribers. In such cases, different internal hosts are identified and mapped at the CGN by their IP address and/or another identifier, for example, the identifier of a tunnel between the CGN and the subscriber. In these scenarios (and similar ones), the internal IP address is not sufficient to demultiplex connections from internal hosts. An additional identifier needs to be present in the IP-Port-Range Attribute and IP-Port-Forwarding-Mapping Attribute in order to uniquely identify an internal host. The IP-Port-Local-Id TLV is used to carry this identifier.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    TLV-Type   |     Length    |        localID ....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14

   TLV-Type

   Length

Variable number of octets

   localID

String. The data type of this field is string (refer to [RFC8044]). This field contains the data that is a local significant identifier at the customer premise, such as MAC address, interface ID, VLAN ID, PPP sessions ID, VRF ID, IP address/prefix, or another local significant identifier.

IP-Port-Local-Id TLV MAY be included in the following Attributes if it is necessary to identify the subscriber:

   o  IP-Port-Range Attribute, identified as 241.6.11 (see
      Section 3.1.2)
   
   o  IP-Port-Forwarding-Mapping Attribute, identified as 241.7.11 (see
      Section 3.1.3)

4. Applications, Use Cases, and Examples

This section describes some applications and use cases to illustrate the use of the attributes proposed in this document.

4.1. Managing CGN Port Behavior Using RADIUS

In a broadband network, customer information is usually stored on a RADIUS server, and the BNG acts as a NAS. The communication between the NAS and the RADIUS server is triggered by a user when it 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 configuration information specific to that user back to the NAS, where some of the information would be passed on to the requesting user via PPP or DHCP/DHCPv6.

A CGN function in a broadband network is most likely to be co-located on a BNG. In that case, parameters for CGN port 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, a CGN operation status such as CGN port allocation and deallocation for a specific user on the BNG can also be transmitted back to the RADIUS server for accounting purposes using the RADIUS protocol.

The 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 subsections, we describe how to manage CGN behavior using the RADIUS protocol, with required RADIUS extensions proposed in Section 3.

4.1.1. Configure IP Port Limit for a User

In the face of an IPv4 address shortage, there are currently proposals to multiplex multiple users' connections over a number of shared IPv4 addresses, such as Carrier Grade NAT [RFC6888], Dual-Stack Lite [RFC6333], NAT64 [RFC6146], etc. As a result, a single IPv4 public address may be shared by hundreds or even thousands of users. As indicated in [RFC6269], it is therefore necessary to impose limits on the total number of ports available to an individual user to ensure that the shared resource, i.e., the IPv4 address, remains available in some capacity to all the users using it. The support of an IP port limit is also documented in [RFC6888] as a requirement for CGN.

The IP port limit imposed on an end user may be on the total number of IP source transport ports or a specific IP transport protocol as defined in Section 3.1.1.

The per-user IP port limit is configured on a RADIUS server, along with other user information such as credentials.

When a user signs in to the Internet service successfully, the IP port limit for the subscriber is passed by the RADIUS server to the BNG, which is acting as a NAS and is co-located with the CGN using the IP-Port-Limit-Info RADIUS attribute (defined in Section 3.1.1) along with other configuration parameters. While some parameters are passed to the user, the IP port limit is recorded on the CGN device for imposing the usage of IP transport ports for that user.

Figure 15 illustrates how the RADIUS protocol is used to configure the maximum number of TCP/UDP ports for a given user on a CGN device.

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

Figure 15: RADIUS Message Flow for Configuring CGN Port Limit

The IP port limit created on a CGN device for a specific user using a RADIUS extension may be changed using a RADIUS CoA message [RFC5176] that carries the same RADIUS attribute. The CoA message may be sent from the RADIUS server directly to the NAS, and once a RADIUS CoA ACK message is accepted and sent back, the new IP port limit replaces the previous one.

Figure 16 illustrates how the RADIUS protocol is used to increase the TCP/UDP port limit from 1024 to 2048 on a CGN device for a specific user.

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

Figure 16: RADIUS Message Flow for Changing a User's CGN Port Limit

4.1.2. Report IP Port Allocation/Deallocation

Upon obtaining the IP port limit for a user, the CGN device needs to allocate an IP transport port for the user when receiving a new IP flow sent from that user.

As one practice, a CGN may allocate a block of IP ports for a specific user, instead of one port at a time, and within each port block the ports may be randomly distributed or in consecutive fashion. When a CGN device allocates a block of transport ports, the information can be easily conveyed to the RADIUS server by a new RADIUS attribute called the IP-Port-Range (defined in Section 3.1.2). The CGN device may allocate one or more IP port ranges, where each range contains a set of numbers representing IP transport ports and the total number of ports MUST be less or equal to the associated IP port limit imposed for that user. A CGN device may choose to allocate a small port range and allocate more at a later time as needed; such practice is good because of its randomization in nature.

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

When a user initiates an IP flow, the CGN device randomly selects a transport port number from the associated and pre-allocated IP port range for that user to replace the original source port number 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 IP ports that have been allocated for a specific user but are not currently in use, and with that, the CGN device must send the information of the deallocated IP port range along with the shared IPv4 address to the RADIUS server.

Figure 17 illustrates how the RADIUS protocol is used to report a set of ports allocated and deallocated, respectively, by a NAT64 device for a specific user to the RADIUS server. 2001:db8:100:200::/56 is the IPv6 prefix allocated to this user. In order to limit the usage of the NAT64 resources on a per-user basis for fairness of resource usage (see REQ-4 of [RFC6888]), port range allocations are bound to the /56 prefix, not to the source IPv6 address of the request. The NAT64 device is configured with the per-user port limit policy by some means (e.g., subscriber-mask [RFC7785]).

   Host                      NAT64/NAS                     AAA
    |                         BNG                         Server
    |                          |                             |
    |                          |                             |
    |----Service Request------>|                             |
    |                          |                             |
    |                          |-----Access-Request -------->|
    |                          |                             |
    |                          |<----Access-Accept-----------|
    |<---Service Granted ------|                             |
    |    (other parameters)    |                             |
   ...                        ...                           ...
    |                          |                             |
    |                          |                             |
    |                (NAT64 decides to allocate              |
    |                 a TCP/UDP port range for the user)     |
    |                          |                             |
    |                          |-----Accounting-Request----->|
    |                          |    (IP-Port-Range           |
    |                          |     for allocation)         |
   ...                        ...                           ...
    |                          |                             |
    |                (NAT64 decides to deallocate            |
    |                 a TCP/UDP port range for the user)     |
    |                          |                             |
    |                          |-----Accounting-Request----->|
    |                          |    (IP-Port-Range           |
    |                          |     for deallocation)       |
    |                          |                             |

Figure 17: RADIUS Message Flow for Reporting NAT64

Allocation/Deallocation of a Port Set

4.1.3. Configure Port Forwarding 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 and allow IP packets of applications from outside a CGN device to pass through and be "port forwarded" to the correct user located behind the CGN device.

The Port Control Protocol (PCP) [RFC6887], 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 deployments, all users need is a few (typically just one) pre-configured port mappings for applications at home, such as a web cam; 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 propagate the information to the associated CGN device.

Note that this document targets deployments where a AAA server is responsible for instructing NAT mappings for a given subscriber and does not make any assumption about the host's capabilities with regards to port forwarding control. This deployment is complementary to PCP given that PCP targets a different deployment model where an application (on the host) controls its mappings in an upstream CPE, CGN, firewall, etc.

Figure 18 illustrates how the RADIUS protocol is used to configure a port forwarding mapping on a NAT44 device.

   Host                     CGN/NAS                           AAA
    |                         BNG                            Server
    |                          |                               |
    |----Service Request------>|                               |
    |                          |                               |
    |                          |---------Access-Request------->|
    |                          |                               |
    |                          |<--------Access-Accept---------|
    |                          |   (IP-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------>|
    |                          |    (IP-Port-Forwarding-Map)   |

Figure 18: RADIUS Message Flow for Configuring

a Port Forwarding Mapping

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

Figure 19 illustrates how the 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

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

Figure 19: RADIUS Message Flow for Changing

a User's Port Forwarding Mapping

4.1.4. An Example

An Internet Service Provider (ISP) assigns TCP/UDP 500 ports for the user Joe. This number is the limit that can be used for TCP/UDP ports on a CGN device for Joe and it is configured on a RADIUS server. Also, Joe asks for a pre-defined port forwarding mapping on the CGN device for his web cam applications (external port 5000 maps to internal port 1234).

When Joe successfully connects to the Internet service, the RADIUS server conveys the TCP/UDP port limit (500) and the port forwarding mapping (external port 5000 to internal port 1234) to the CGN device using the IP-Port-Limit-Info Attribute and IP-Port-Forwarding-Map Attribute, respectively, carried by an Access-Accept message to the BNG where NAS and CGN are co-located.

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

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

When Joe works on more applications with more outbound IP mappings and the port pool (3500-3540) is close to exhaust, the CGN device 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 IP-Port-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 IP-Port-Limit-Info Attribute with 1000 ports to the CGN device; the CGN device in turn sends back a CoA-ACK message. With that, Joe enjoys more available TCP/UDP ports for his applications.

When Joe is not using his service, most of the IP mappings are closed with their associated TCP/UDP ports released on the CGN device, which then sends the relevant information back to the RADIUS server using the IP-Port-Range Attribute carried by the Accounting-Request message.

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

When Joe disconnects from his Internet service, the CGN device will deallocate 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 20 illustrates an example of the flow exchange that occurs when the visiting User Equipment (UE) connects to a CPE offering WLAN service.

For identification purposes (see [RFC6967]), once the CPE assigns a port set, it issues a RADIUS message to report the assigned port set.

   UE         CPE             CGN                          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-...------------------->|
    |           |    (IP-Port-Range                          |
    |           |     for allocation)                        |
   ...          |             ...                           ...
    |           |              |                             |
    |           |              |                             |
    |   (CPE withdraws a TCP/UDP port                        |
    |   range for a visiting UE)                             |
    |           |                                            |
    |           |--Accounting-Request-...------------------->|
    |           |    (IP-Port-Range                          |
    |           |     for deallocation)                      |
    |           |                                            |

Figure 20: RADIUS Message Flow for Reporting CPE

Allocation/Deallocation of a Port Set to a Visiting UE

5. Table of Attributes

This document proposes three new RADIUS attributes, and their formats are as follows:

   o  IP-Port-Limit-Info: 241.5

IP-Port-Range: 241.6

   o  IP-Port-Forwarding-Map: 241.7

The following table provides a guide as to what type of RADIUS packets may contain these attributes and in what quantity.

   Request Accept Reject Challenge Acct.    #     Attribute
                                   Request
   0+      0+     0      0         0+       241.5 IP-Port-Limit-Info
   0       0      0      0         0+       241.6 IP-Port-Range
   0+      0+     0      0         0+       241.7 IP-Port-Forwarding-Map

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

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

6. Security Considerations

This document does not introduce any security issue other than the ones already identified in RADIUS documents [RFC2865] and [RFC5176] for CoA messages. Known RADIUS vulnerabilities apply to this specification. For example, if RADIUS packets are sent in the clear, an attacker in the communication path between the RADIUS client and server may glean information that it will use to prevent a legitimate user from accessing the service by appropriately setting the maximum number of IP ports conveyed in an IP-Port-Limit-Info Attribute; exhaust the port quota of a user by installing many mapping entries (IP-Port-Forwarding-Map Attribute); prevent incoming traffic from being delivered to its legitimate destination by manipulating the mapping entries installed by means of an IP-Port-Forwarding-Map Attribute; discover the IP address and port range that are assigned to a given user and reported in an IP-Port-Range Attribute; and so on. The root cause of these attack vectors is the communication between the RADIUS client and server.

The IP-Port-Local-Id TLV includes an identifier of which the type and length is deployment and implementation dependent. This identifier might carry privacy-sensitive information. It is therefore RECOMMENDED to utilize identifiers that do not have such privacy concerns.

If there is any error in a RADIUS Accounting-Request packet sent from a RADIUS client to the server, the RADIUS server MUST NOT send a response to the client (refer to [RFC2866]). Examples of the errors include the erroneous port range in the IP-Port-Range Attribute, inconsistent port mapping in the IP-Port-Forwarding-Map Attribute, etc.

This document targets deployments where a trusted relationship is in place between the RADIUS client and server with communication optionally secured by IPsec or Transport Layer Security (TLS) [RFC6614].

7. IANA Considerations

Per this document, IANA has made new code point assignments for both IPFIX Information Elements and RADIUS attributes as explained in the following subsections.

7.1. New IPFIX Information Elements

The following IPFIX Information Element has been registered (refer to Section 3.2.2):

sourceTransportPortsLimit:

Name: sourceTransportPortsLimit

Element ID: 458

Description: This Information Element contains the maximum number of IP source transport ports that can be used by an end user when sending IP packets; each user is associated with one or more (source) IPv4 or IPv6 addresses. This Information Element is particularly useful in address-sharing deployments that adhere to REQ-4 of [RFC6888]. Limiting the number of ports assigned to each user ensures fairness among users and mitigates the denial-of-service attack that a user could launch against other users through the address-sharing device in order to grab more ports.

Data type: unsigned16

      *  Data type semantics: totalCounter
      
      *  Data type unit: ports

Data value range: from 1 to 65535

7.2. New RADIUS Attributes

The Attribute Types defined in this document have been registered by IANA from the RADIUS namespace as described in the "IANA Considerations" section of [RFC3575], in accordance with BCP 26 [RFC5226]. For RADIUS packets, attributes, and registries created by this document, IANA has placed them at <http://www.iana.org/assignments/radius-types>.

In particular, this document defines three new RADIUS attributes, as follows, from the Short Extended Space of [RFC6929]:

   Type      Description             Data Type   Reference
   ----      -----------             ---------   ---------
   241.5     IP-Port-Limit-Info      tlv         Section 3.1.1
   241.6     IP-Port-Range           tlv         Section 3.1.2
   241.7     IP-Port-Forwarding-Map  tlv         Section 3.1.3

7.3. New RADIUS TLVs

IANA has created a new registry called "RADIUS IP Port Configuration and Reporting TLVs". All TLVs in this registry have one or more parent RADIUS attributes in nesting (refer to [RFC6929]). This registry contains the following TLVs:

      Value  Description           Data Type    Reference
      -----  -----------           ---------    ---------
      0      Reserved
      1      IP-Port-Type          integer      Section 3.2.1
      2      IP-Port-Limit         integer      Section 3.2.2
      3      IP-Port-Ext-IPv4-Addr ipv4addr     Section 3.2.3
      4      IP-Port-Int-IPv4-Addr ipv4addr     Section 3.2.4
      5      IP-Port-Int-IPv6-Addr ipv4addr     Section 3.2.5
      6      IP-Port-Int-Port      integer      Section 3.2.6
      7      IP-Port-Ext-Port      integer      Section 3.2.7
      8      IP-Port-Alloc         integer      Section 3.2.8
      9      IP-Port-Range-Start   integer      Section 3.2.9
      10     IP-Port-Range-End     integer      Section 3.2.10
      11     IP-Port-Local-Id      string       Section 3.2.11
      12-255 Unassigned

The registration procedure for this registry is Standards Action as defined in [RFC5226].

8. References

8.1. Normative References

   [IPFIX]    IANA, "IP Flow Information Export (IPFIX) Entities",
              <http://www.iana.org/assignments/ipfix/>.

[ProtocolNumbers]

              IANA, "Protocol Numbers",
              <http://www.iana.org/assignments/protocol-numbers/>.
   
   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.
   
   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <http://www.rfc-editor.org/info/rfc2865>.
   
   [RFC3575]  Aboba, B., "IANA Considerations for RADIUS (Remote
              Authentication Dial In User Service)", RFC 3575,
              DOI 10.17487/RFC3575, July 2003,
              <http://www.rfc-editor.org/info/rfc3575>.
   
   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.
   
   [RFC6929]  DeKok, A. and A. Lior, "Remote Authentication Dial In User
              Service (RADIUS) Protocol Extensions", RFC 6929,
              DOI 10.17487/RFC6929, April 2013,
              <http://www.rfc-editor.org/info/rfc6929>.
   
   [RFC7012]  Claise, B., Ed., and B. Trammell, Ed., "Information Model
              for IP Flow Information Export (IPFIX)", RFC 7012,
              DOI 10.17487/RFC7012, September 2013,
              <http://www.rfc-editor.org/info/rfc7012>.
   
   [RFC8044]  DeKok, A., "Data Types in RADIUS", RFC 8044,
              DOI 10.17487/RFC8044, January 2017,
              <http://www.rfc-editor.org/info/rfc8044>.

8.2. Informative References

   [RFC768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <http://www.rfc-editor.org/info/rfc768>.
   
   [RFC793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.
   
   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.
   
   [RFC2866]  Rigney, C., "RADIUS Accounting", RFC 2866,
              DOI 10.17487/RFC2866, June 2000,
              <http://www.rfc-editor.org/info/rfc2866>.
   
   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              DOI 10.17487/RFC3022, January 2001,
              <http://www.rfc-editor.org/info/rfc3022>.
   
   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340,
              DOI 10.17487/RFC4340, March 2006,
              <http://www.rfc-editor.org/info/rfc4340>.
   
   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <http://www.rfc-editor.org/info/rfc4960>.
   
   [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,
              DOI 10.17487/RFC5176, January 2008,
              <http://www.rfc-editor.org/info/rfc5176>.
   
   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <http://www.rfc-editor.org/info/rfc6146>.
   
   [RFC6158]  DeKok, A., Ed., and G. Weber, "RADIUS Design Guidelines",
              BCP 158, RFC 6158, DOI 10.17487/RFC6158, March 2011,
              <http://www.rfc-editor.org/info/rfc6158>.
   
   [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
              P. Roberts, "Issues with IP Address Sharing", RFC 6269,
              DOI 10.17487/RFC6269, June 2011,
              <http://www.rfc-editor.org/info/rfc6269>.
   
   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee,
              "Dual-Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
              <http://www.rfc-editor.org/info/rfc6333>.
   
   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, DOI 10.17487/RFC6598,
              April 2012, <http://www.rfc-editor.org/info/rfc6598>.
   
   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,
              <http://www.rfc-editor.org/info/rfc6614>.
   
   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <http://www.rfc-editor.org/info/rfc6887>.
   
   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <http://www.rfc-editor.org/info/rfc6888>.
   
   [RFC6967]  Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Potential Solutions for Revealing a Host
              Identifier (HOST_ID) in Shared Address Deployments",
              RFC 6967, DOI 10.17487/RFC6967, June 2013,
              <http://www.rfc-editor.org/info/rfc6967>.
   
   [RFC7785]  Vinapamula, S. and M. Boucadair, "Recommendations for
              Prefix Binding in the Context of Softwire Dual-Stack
              Lite", RFC 7785, DOI 10.17487/RFC7785, February 2016,
              <http://www.rfc-editor.org/info/rfc7785>.
   
   [TR-146]   Broadband Forum, "TR-146: Subscriber Sessions", Broadband
              Forum Technical Report 146, Issue 1, May 2013,
              <http://www.broadband-forum.org/technical/
              download/TR-146.pdf>.

[WIFI-SERVICES]

              Gundavelli, S., Grayson, M., Seite, P., and Y. Lee,
              "Service Provider Wi-Fi Services Over Residential
              Architectures", Work in Progress,
              draft-gundavelli-v6ops-community-wifi-svcs-06, April 2013.

Acknowledgments

Many thanks to Dan Wing, Roberta Maglione, Daniel Derksen, David Thaler, Alan DeKok, Lionel Morand, and Peter Deacon for their useful comments and suggestions.

Special thanks to Lionel Morand for the Shepherd review and to Kathleen Moriarty for the AD review.

Thanks to Carl Wallace, Tim Chown, and Ben Campbell for the detailed review.

Authors' Addresses

   Dean Cheng
   Huawei
   2330 Central Expressway
   Santa Clara, California  95050
   United States of America
   
   Email: dean.cheng@huawei.com
   
   Jouni Korhonen
   Broadcom Corporation
   3151 Zanker Road
   San Jose, California  95134
   United States of America
   
   Email: jouni.nospam@gmail.com

Mohamed Boucadair
Orange
Rennes
France

   Email: mohamed.boucadair@orange.com

Senthil Sivakumar
Cisco Systems
7100-8 Kit Creek Road
Research Triangle Park, North Carolina
United States of America

Email:

          ssenthil@cisco.com

RADIUS Extensions for IP Port Configuration and Reporting

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction

2. Terminology

2.1. Requirements Language

3. Extensions of RADIUS Attributes and TLVs

3.1. Extended Attributes for IP Ports

3.1.1. IP-Port-Limit-Info Attribute

Figure 1

3.1.2. IP-Port-Range Attribute

Figure 2

3.1.3. IP-Port-Forwarding-Map Attribute

Figure 3

3.2. RADIUS TLVs for IP Ports

3.2.1. IP-Port-Type TLV

Figure 4

3.2.2. IP-Port-Limit TLV

Figure 5

3.2.3. IP-Port-Ext-IPv4-Addr TLV

Figure 6

3.2.4. IP-Port-Int-IPv4-Addr TLV

Figure 7

3.2.5. IP-Port-Int-IPv6-Addr TLV

Figure 8

3.2.6. IP-Port-Int-Port TLV

Figure 9

3.2.7. IP-Port-Ext-Port TLV

Figure 10

3.2.8. IP-Port-Alloc TLV

Figure 11

3.2.9. IP-Port-Range-Start TLV

Figure 12

3.2.10. IP-Port-Range-End TLV

Figure 13

3.2.11. IP-Port-Local-Id TLV

Figure 14

4. Applications, Use Cases, and Examples

4.1. Managing CGN Port Behavior Using RADIUS

4.1.1. Configure IP Port Limit for a User

4.1.2. Report IP Port Allocation/Deallocation

Figure 17: RADIUS Message Flow for Reporting NAT64

Allocation/Deallocation of a Port Set

4.1.3. Configure Port Forwarding Mapping

Figure 18: RADIUS Message Flow for Configuring

a Port Forwarding Mapping

Figure 19: RADIUS Message Flow for Changing

a User's Port Forwarding Mapping

4.1.4. An Example

4.2. Report Assigned Port Set for a Visiting UE

Figure 20: RADIUS Message Flow for Reporting CPE

Allocation/Deallocation of a Port Set to a Visiting UE

5. Table of Attributes

6. Security Considerations

7. IANA Considerations

7.1. New IPFIX Information Elements

7.2. New RADIUS Attributes

7.3. New RADIUS TLVs

8. References

8.1. Normative References

8.2. Informative References

Acknowledgments

Authors' Addresses