Network Working Group M. Boucadair
Internet-Draft C. Jacquenet
Intended status: Standards Track Orange
Expires: July 22, 2016 January 19, 2016

RADIUS Extensions for Network-Assisted Multipath TCP (MPTCP)


One of the promising deployment scenarios for Multipath TCP (MPTCP) is to enable a Customer Premises Equipment (CPE) that is connected to multiple networks (e.g., DSL, LTE, WLAN) to optimize the usage of its network attachments. Because of the lack of MPTCP support at the server side, some service providers consider a network-assisted model that relies upon the activation of a dedicated function called: MPTCP Concentrator.

This document specifies a new Remote Authentication Dial-In User Service (RADIUS) attribute that carries the list of IP addresses that allow CPE devices to reach one or multiple MPTCP Concentrators.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on July 22, 2016.

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Table of Contents

1. Introduction

One of the promising deployment scenarios for Multipath TCP (MPTCP, [RFC6824]) is to enable a Customer Premises Equipment (CPE) that is connected to multiple networks (e.g., DSL, LTE, WLAN) to optimize the usage of such resources, see for example [RFC4908]. This deployment scenario relies on MPTCP proxies located on both the CPE and network sides (Figure 1). MPTCP Proxies deployed in the network play the role of traffic concentrator.

                      IP Network #1                     
 +------------+        _--------_    +------------+   
 |            |       (e.g., LTE )   |            |   
 |   CPE      +======================+            |    
 | (MPTCP     |       (_        _)   |Concentrator|   
 |  Proxy)    |         (_______)    | (MPTCP     |    
 |            |                      |  Proxy)    |------> Internet
 |            |                      |            |
 |            |        IP Network #2 |            |     
 |            |        _--------_    |            |    
 |            |       ( e.g., DSL )  |            |   
 |            +======================+            |
 |            |       (_        _)   |            |
 +-----+------+        (_______)     +------------+
----CPE network----     

Figure 1: “Network-Assisted” MPTCP Design

Within this document, an MPTCP Concentrator (or concentrator) refers to a functional element that is responsible for aggregating the traffic originated by a group of CPEs. This element is located in the network. One or multiple concentrators can be deployed in the network to assist MPTCP-enabled CPEs to establish MPTCP connections via their available network attachments. On the uplink path, the concentrator terminates the MPTCP connections [RFC6824] received from its customer-facing interfaces and transforms these connections into legacy TCP connections [RFC0793] towards upstream servers. On the downlink path, the concentrator turns the legacy server's TCP connection into MPTCP connections towards its customer-facing interfaces.

Both implicit (where a CPE has no specific knowledge of any concentrator deployed in the network) and explicit modes are considered to steer traffic towards an MPTCP Concentrator. This document focuses on the explicit mode that consists in explicitly configuring a CPE with the reachability information of a MPTCP concentrator.

This document specifies a new Remote Authentication Dial-In User Service (RADIUS, [RFC2865]) attribute that carries the MPTCP Concentrator IP address list (Section 2). A sample use case is described in Section 3. In order to accommodate both IPv4 and IPv6 deployment contexts, the same attribute is used to convey an IPv4 or IPv6 address. Note that one or multiple IPv4 and/or IPv6 addresses may be returned to a requesting CPE.

This document assumes that the MPTCP concentrator(s) reachability information can be stored in Authentication, Authorization, and Accounting (AAA) servers while the CPE configuration is usually provided by means of DHCP ([RFC2131][RFC3315]).

This specification assumes an MPTCP Concentrator is reachable through one or multiple IP addresses. As such, a list of IP addresses can be communicated via RADIUS. Also, it assumes the various network attachments provided to an MPTCP-enabled CPE are managed by the same administrative entity.

2. MPTCP RADIUS Attribute

The RADIUS MPTCP-Concentrator attribute contains the IP address of an MPTCP Concentrator that is assigned to a CPE. Because multiple MPTCP Concentrator IP addresses may be provisioned to an authorised CPE (that is a CPE entitled to solicit the resources of a concentrator to establish MPTCP connections), multiple instances of the MPTCP-Concentrator attribute MAY be included; each instance of the attribute carries a distinct IP address.

The format of the MPTCP-Concentrator attribute is shown in Figure 2. The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |     Type      |     Length    |          ip-address ...
   //      ... ip-address          |

Figure 2

The description of the fields is as follows:

  • Type: TBA (see Section 6).
  • Length: 6 or 18.
  • ip-address: This field may include an IPv4 address (32 bits) or an IPv6 address (128 bit) of the MPTCP concentrator.

The MPTCP-Concentrator attribute MUST NOT include multicast and host loopback addresses [RFC6890]. Anycast addresses are allowed to be included in an MPTCP-Concentrator attribute.

The MPTCP-Concentrator Attribute MAY appear in a RADIUS Access-Accept packet. It MAY also appear in a RADIUS Access-Request packet as a hint to the RADIUS server to indicate a preference, although the server is not required to honor such a hint.

The MPTCP-Concentrator Attribute MAY appear in a CoA-Request packet.

The MPTCP-Concentrator Attribute MAY appear in a RADIUS Accounting-Request packet.

The MPTCP-Concentrator Attribute MUST NOT appear in any other RADIUS packet.

3. Sample Use Case

This section does not aim to provide an exhaustive list of deployment scenarios where the use of the RADIUS MPTCP-Concentrator attribute can be helpful. Typical deployment scenarios are described, for instance, in [RFC6911].

Figure 3 shows an example where a CPE is assigned an MPTCP Concentrator. This example assumes that the Network Access Server (NAS) embeds both RADIUS client and DHCPv6 server capabilities.

      CPE                               NAS                      AAA
  DHCPv6 client                      DHCPv6 server              server
       |                                  |                        |
       |---------DHCPv6 Solicit---------->|                        |
       |                                  |----Access-Request ---->|
       |                                  |                        |
       |                                  |<----Access-Accept------|
       |                                  | (MPTCP-Concentrator)   |
       |<-------DHCPv6 Advertisement------|                        |
       |        (OPTION_V6_MPTCP)         |                        |
       |                                  |                        |
       |---------DHCPv6 Request---------->|                        |
       |                                  |                        |
       |<---------DHCPv6 Reply------------|                        |
       |       (OPTION_V6_MPTCP)          |                        |

                    DHCPv6                          RADIUS

Figure 3: Sample Flow Example (1)

Upon receipt of the DHCPv6 Solicit message from a CPE, the NAS sends a RADIUS Access-Request message to the AAA server. Once the AAA server receives the request, it replies with an Access-Accept message (possibly after having sent a RADIUS Access-Challenge message and assuming the CPE is entitled to connect to the network) that carries a list of parameters to be used for this session, and which include MPTCP-Concentrator reachability information (namely a list of IP addresses).

The content of the MPTCP-Concentrator attribute is then used by the NAS to complete the DHCPv6 procedure that the CPE initiated to retrieve information about the MPTCP Concentrator it has been assigned.

Upon change of the MPTCP Concentrator assigned to a CPE, the RADIUS server sends a RADIUS CoA message [RFC5176] that carries the RADIUS MPTCP-Concentrator attribute to the NAS. Once that message is accepted by the NAS, it replies with a RADIUS CoA ACK message. The NAS replaces the old MPTCP Concentrator with the new one.

Figure 4 shows another example where a CPE is assigned an MPTCP Concentrator, but the CPE uses DHCPv6 to retrieve a list of IP addresses of an MPTCP concentrator.

      CPE                               NAS                      AAA
  DHCPv4 client                      DHCPv4 server              server
       |                                  |                        |
       |-----------DHCPDISCOVER---------->|                        |
       |                                  |----Access-Request ---->|
       |                                  |                        |
       |                                  |<----Access-Accept------|
       |                                  | (MPTCP-Concentrator)   |
       |<------------DHCPOFFER------------|                        |
       |         (OPTION_V4_MPTCP)        |                        |
       |                                  |                        |
       |------------DHCPREQUEST---------->|                        |
       |         (OPTION_V4_MPTCP)        |                        |
       |                                  |                        |
       |<-----------DHCPACK---------------|                        |
       |        (OPTION_V4_MPTCP)         |                        |

                     DHCPv4                         RADIUS

Figure 4: Sample Flow Example (2)

Some deployments may rely on the mechanisms defined in [RFC4014] or [RFC7037], which allows a NAS to pass attributes obtained from a RADIUS server to a DHCP server.

4. Security Considerations

RADIUS-related security considerations are discussed in [RFC2865].

MPTCP-related security considerations are discussed in [RFC6824] and [RFC6181].

Traffic theft is a risk if an illegitimate concentrator is inserted in the path. Indeed, inserting an illegitimate concentrator in the forwarding path allows to intercept traffic and can therefore provide access to sensitive data issued by or destined to a host. To mitigate this threat, secure means to discover a concentrator should be enabled.

5. Table of Attributes

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

   Access- Access- Access-  Challenge Accounting #   Attribute
   Request Accept  Reject             Request
   0+      0+      0        0         0+         TBA MPTCP-Concentrator

   CoA-Request CoA-ACK CoA-NACK #   Attribute
   0+          0       0        TBA MPTCP-Concentrator

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

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

6. IANA Considerations

IANA is requested to assign a new RADIUS attribute type from the IANA registry "Radius Attribute Types" located at

  • MPTCP-Concentrator (TBA)

7. Acknowledgements

To be completed.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R. and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, April 2013.

8.2. Informative References

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003.
[RFC4014] Droms, R. and J. Schnizlein, "Remote Authentication Dial-In User Service (RADIUS) Attributes Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Information Option", RFC 4014, DOI 10.17487/RFC4014, February 2005.
[RFC4908] Nagami, K., Uda, S., Ogashiwa, N., Esaki, H., Wakikawa, R. and H. Ohnishi, "Multi-homing for small scale fixed network Using Mobile IP and NEMO", RFC 4908, DOI 10.17487/RFC4908, June 2007.
[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.
[RFC6181] Bagnulo, M., "Threat Analysis for TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6181, DOI 10.17487/RFC6181, March 2011.
[RFC6824] Ford, A., Raiciu, C., Handley, M. and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013.
[RFC6911] Dec, W., Sarikaya, B., Zorn, G., Miles, D. and B. Lourdelet, "RADIUS Attributes for IPv6 Access Networks", RFC 6911, DOI 10.17487/RFC6911, April 2013.
[RFC7037] Yeh, L. and M. Boucadair, "RADIUS Option for the DHCPv6 Relay Agent", RFC 7037, DOI 10.17487/RFC7037, October 2013.

Authors' Addresses

Mohamed Boucadair Orange Rennes, 35000 France EMail:
Christian Jacquenet Orange Rennes, France EMail: