RADIUS over TCP
RFC 6613

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Internet Engineering Task Force (IETF)                          A. DeKok
Request for Comments: 6613                                    FreeRADIUS
Category: Experimental                                          May 2012
ISSN: 2070-1721

                            RADIUS over TCP

Abstract

   The Remote Authentication Dial-In User Server (RADIUS) protocol has,
   until now, required the User Datagram Protocol (UDP) as the
   underlying transport layer.  This document defines RADIUS over the
   Transmission Control Protocol (RADIUS/TCP), in order to address
   handling issues related to RADIUS over Transport Layer Security
   (RADIUS/TLS).  It permits TCP to be used as a transport protocol for
   RADIUS only when a transport layer such as TLS or IPsec provides
   confidentiality and security.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   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/rfc6613.

DeKok                         Experimental                      [Page 1]
RFC 6613                     RADIUS over TCP                    May 2012

Copyright Notice

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

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

Table of Contents

   1. Introduction ....................................................3
      1.1. Applicability of Reliable Transport ........................4
      1.2. Terminology ................................................6
      1.3. Requirements Language ......................................6
   2. Changes to RADIUS ...............................................6
      2.1. Packet Format ..............................................7
      2.2. Assigned Ports for RADIUS/TCP ..............................7
      2.3. Management Information Base (MIB) ..........................8
      2.4. Detecting Live Servers .....................................8
      2.5. Congestion Control Issues ..................................9
      2.6. TCP Specific Issues ........................................9
           2.6.1. Duplicates and Retransmissions .....................10
           2.6.2. Head of Line Blocking ..............................11
           2.6.3. Shared Secrets .....................................11
           2.6.4. Malformed Packets and Unknown Clients ..............12
           2.6.5. Limitations of the ID Field ........................13
           2.6.6. EAP Sessions .......................................13
           2.6.7. TCP Applications Are Not UDP Applications ..........14
   3. Diameter Considerations ........................................14
   4. Security Considerations ........................................14
   5. References .....................................................15
      5.1. Normative References ......................................15
      5.2. Informative References ....................................15

DeKok                         Experimental                      [Page 2]
RFC 6613                     RADIUS over TCP                    May 2012

1.  Introduction

   The RADIUS protocol is defined in [RFC2865] as using the User
   Datagram Protocol (UDP) for the underlying transport layer.  While
   there are a number of benefits to using UDP as outlined in [RFC2865],
   Section 2.4, there are also some limitations:

      *  Unreliable transport.  As a result, systems using RADIUS have
         to implement application-layer timers and retransmissions, as
         described in [RFC5080], Section 2.2.1.

      *  Packet fragmentation.  [RFC2865], Section 3, permits RADIUS
         packets up to 4096 octets in length.  These packets are larger
         than the common Internet MTU (576), resulting in fragmentation