| Network Working Group | D. Cheng |
| Internet-Draft | Huawei |
| Intended status: Standards Track | J. Korhonen |
| Expires: April 21, 2017 | Broadcom Corporation |
| M. Boucadair | |
| Orange | |
| S. Sivakumar | |
| Cisco Systems | |
| October 18, 2016 |
RADIUS Extensions for IP Port Configuration and Reporting
draft-ietf-radext-ip-port-radius-ext-14
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 IPFIX Information Element Identifiers.
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].
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 21, 2017.
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
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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 NAT44 [RFC3022], NAT64 [RFC6146], or Dual-Stack Lite AFTR [RFC6333] function. In such case, the CGN IP transport port (e.g., TCP/UDP port) mapping(s) behavior(s) can be part of the configuration information sent from the RADIUS server to the NAS/BNG. The NAS/BNG may also report to the RADIUS Server the IP port mapping behavior applied by the CGN to a user session to the RADIUS server, as part of the accounting information sent from the NAS/BNG to a RADIUS server.
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 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 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 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 [I-D.gundavelli-v6ops-community-wifi-svcs]. For example, a visiting host can be managed by a CPE (Customer Premises Equipment ) 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's extensions, and they are used for separate purposes as follows:
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, UDP, DCCP, and SCTP) that are associated with some RADIUS attributes.
This document focuses on IPv4 address sharing. IPv6 prefix sharing mechanisms (e.g., NPTv6) are out of scope.
This document makes use of the following terms:
These three new attributes are defined in the following sub-sections:
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 guideline in Section 2.7.1 of [RFC6929].
In all the figures describing the RADIUS attributes and TLV formats in the following sub-sections, the fields are transmitted from left to right.
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:
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
Extended-Type
Value
IP-Port-Limit-Info Attribute is associated with the following identifier: 241.Extended-Type(TBD1).
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:
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, the port range is associated with the specific IP transport protocol as specified in the IP-Port-Type TLV, but otherwise is for all IP transport protocols.
If the IP-Port-Ext-IPv4-Addr TLV is included as part of the IP-Port-Range Attribute, the port range as specified is associated with IPv4 address as indicated, but otherwise 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
Extended-Type
Value
The IP-Port-Range attribute is associated with the following identifier: 241.Extended-Type(TBD2).
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:
The attribute contains a 2-byte IP internal port number and a 2-byte 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 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, the port mapping is associated with the specific IP transport protocol as specified in the IP-Port-Type TLV, but otherwise 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
Extended-Type
Value
The IP-Port-Forwarding-Map Attribute is associated with the following identifier: 241.Extended-Type(TBD3).
The TLVs that are included in the three attributes (see Section 3.1) are defined in the following sub-sections. These TLVs use the format defined in [RFC6929]. As the three attributes carry similar data, we have defined a common set of TLVs which 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 Section 3.1.1, Section 3.1.2, and Section 3.1.3 for a list of which TLV is permitted within which parent attribute.
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
Protocol-Number
IP-Port-Type TLV MAY be included in the following Attributes:
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 [RFC4960], DCCP [RFC4340], etc.
The format of IP-Port-Limit TLV is shown in Figure 5. This attribute carries IPFIX Information Element "sourceTransportPortsLimit (TBAx1), 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
sourceTransportPortsLimit
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.TBD1.2.
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
postNATSourceIPv4Address
IP-Port-Ext-IPv4-Addr TLV MAY be included in the following Attributes:
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
sourceIPv4Address
If the internal realm is with 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.TBD3.4.
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
sourceIPv6Address
If the internal realm is with 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.TBD3.5.
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]). The attribute is encoded in 32 bits as per the recommendation in Appendix A.2.1 of [RFC6158].
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
sourceTransportPort
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.TBD3.6.
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]). The attribute is encoded in 32 bits as per the recommendation in Appendix A.2.1 of [RFC6158].
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
postNAPTSourceTransportPort
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.TBD3.7.
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
natEvent
Reserved:
IP-Port-Alloc TLV MUST be included as part of the IP-Port-Range Attribute (refer to Section 3.1.2), identified as 241.TBD2.8.
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]). The attribute is encoded in 32 bits as per the recommendation in Appendix A.2.1 of [RFC6158].
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
portRangeStart
IP-Port-Range-Start TLV is included as part of the IP-Port-Range Attribute (refer to Section 3.1.2), identified as 241.TBD2.9.
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]). The attribute is encoded in 32 bits as per the recommendation in Appendix A.2.1 of [RFC6158].
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
portRangeEnd
IP-Port-Range-End TLV is included as part of the IP-Port-Range Attribute (refer to Section 3.1.2), identified as 241.TBD2.10.
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 (refer to [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
localID
IP-Port-Local-Id TLV MAY be included in the following Attributes:
This section describes some applications and use cases to illustrate the use of the attributes proposed in this document.
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 pass on to the requesting user via PPP or DHCP/DHCPv6.
A CGN function in a broadband network is most likely 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, 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 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.
In the face of 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 IP port limit is also documented in [RFC6888] as a requirement for CGN.
The IP port limit imposed to 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 based 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, acting as a NAS and 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 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 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 IP port limit replaces the previous one.
Figure 16 illustrates how 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
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 its randomization in nature.
At the same time, the CGN device also needs to decide 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 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 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.
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
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 [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 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.
Note that this document targets deployments where a AAA server is responsible de 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 RADIUS protocol is used to configure a forwarding port mapping on a NAT44 device by using RADIUS protocol.
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 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 association. 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 19 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
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 forwarding port mapping
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 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 forwarding port mapping (external port 5000 to internal port 1234) to the CGN device, using 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 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 assign 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 use that port to replace the original source port in outbound IP packets.
For accounting purpose, 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 IP-Port-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 deallocate all TCP/UDP ports as well as the port-forwarding mapping, and send the relevant information to the RADIUS server.
Figure 20 illustrates an example of the flow exchange which occurs when a 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
This document proposes three new RADIUS attributes and their formats are as follows:
Note to IANA: it is assumed that Extended-Type-1 "241" will be used for these attributes.
The following table provides a guide as what type of RADIUS packets that may contain these attributes, and in what quantity.
| Request | Accept | Reject | Challenge | Acct. Request | # | Attribute |
|---|---|---|---|---|---|---|
| 0+ | 0+ | 0 | 0 | 0+ | TBA | IP-Port-Limit-Info |
| 0 | 0 | 0 | 0 | 0+ | TBA | IP-Port-Range |
| 0+ | 0+ | 0 | 0 | 0+ | TBA | 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. |
This document does not introduce any security issue other than the ones already identified in RADIUS [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 to access 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 to be 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 assigned to a given user and which is reported in an IP-Port-Range Attribute, etc. 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.
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].
This document requires new code point assignments for both IPFIX Information Elements and RADIUS attributes as explained in the following sub-sections.
It is assumed that Extended-Type-1 "241" will be used for RADIUS attributes in Section 7.2.
The following is a new IPFIX Information Element as requested by this document (refer to Section 3.2.2) :
The authors request that Attribute Types and Attribute Values defined in this document be registered by the Internet Assigned Numbers Authority (IANA) from the RADIUS namespaces 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 is requested to place them at http://www.iana.org/assignments/radius-types.
Type Name Meaning ---- ---- ------- 241.TBD1 IP-Port-Limit-Info see Section 3.1.1 241.TBD2 IP-Port-Range see Section 3.1.2 241.TBD3 IP-Port-Forwarding-Map see Section 3.1.3
In particular, this document defines three new RADIUS attributes, entitled "IP-Port-Limit-Info" (see Section 3.1.1), "IP-Port-Range" (see Section 3.1.2) and "IP-Port-Forwarding-Map" (see Section 3.1.3), with assigned values of 241.TBD1, 241.TBD2 and 241.TBD3 from the Short Extended Space of [RFC6929]:
This specification requests allocation of the following TLVs:
Name Value Meaning ---- ----- ------- IP-Port-Type 1 see Section 3.2.1 IP-Port-Limit 2 see Section 3.2.2 IP-Port-Ext-IPv4-Addr 3 see Section 3.2.3 IP-Port-Int-IPv4-Addr 4 see Section 3.2.4 IP-Port-Int-IPv6-Addr 5 see Section 3.2.5 IP-Port-Int-Port 6 see Section 3.2.6 IP-Port-Ext-Port 7 see Section 3.2.7 IP-Port-Alloc 8 see Section 3.2.8 IP-Port-Range-Start 9 see Section 3.2.9 IP-Port-Range-End 10 see Section 3.2.10 IP-Port-Local-Id 11 see Section 3.2.11
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.