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Routing Loop Attack Using IPv6 Automatic Tunnels: Problem Statement and Proposed Mitigations
RFC 6324

Internet Engineering Task Force (IETF)                        G. Nakibly
Request for Comments: 6324                                        NEWRSC
Category: Informational                                       F. Templin
ISSN: 2070-1721                             Boeing Research & Technology
                                                             August 2011

           Routing Loop Attack Using IPv6 Automatic Tunnels:
               Problem Statement and Proposed Mitigations

Abstract

   This document is concerned with security vulnerabilities in IPv6-in-
   IPv4 automatic tunnels.  These vulnerabilities allow an attacker to
   take advantage of inconsistencies between the IPv4 routing state and
   the IPv6 routing state.  The attack forms a routing loop that can be
   abused as a vehicle for traffic amplification to facilitate denial-
   of-service (DoS) attacks.  The first aim of this document is to
   inform on this attack and its root causes.  The second aim is to
   present some possible mitigation measures.  It should be noted that
   at the time of this writing there are no known reports of malicious
   attacks exploiting these vulnerabilities.  Nonetheless, these
   vulnerabilities can be activated by accidental misconfiguration.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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/rfc6324.

Nakibly & Templin             Informational                     [Page 1]
RFC 6324                   Routing Loop Attack               August 2011

Copyright Notice

   Copyright (c) 2011 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 ....................................................2
   2. A Detailed Description of the Attack ............................4
   3. Proposed Mitigation Measures ....................................6
      3.1. Verification of Endpoint Existence .........................6
           3.1.1. Neighbor Cache Check ................................6
           3.1.2. Known IPv4 Address Check ............................7
      3.2. Operational Measures .......................................7
           3.2.1. Avoiding a Shared IPv4 Link .........................7
           3.2.2. A Single Border Router ..............................8
           3.2.3. A Comprehensive List of Tunnel Routers ..............9
           3.2.4. Avoidance of On-Link Prefixes .......................9
      3.3. Destination and Source Address Checks .....................15
           3.3.1. Known IPv6 Prefix Check ............................16
   4. Recommendations ................................................17
   5. Security Considerations ........................................17
   6. Acknowledgments ................................................18
   7. References .....................................................18
      7.1. Normative References ......................................18
      7.2. Informative References ....................................19

1.  Introduction

   IPv6-in-IPv4 tunnels are an essential part of many migration plans
   for IPv6.  They allow two IPv6 nodes to communicate over an IPv4-only
   network.  Automatic tunnels that assign IPv6 prefixes with stateless
   address mapping properties (hereafter called "automatic tunnels") are
   a category of tunnels in which a tunneled packet's egress IPv4
   address is embedded within the destination IPv6 address of the
   packet.  An automatic tunnel's router is a router that respectively
   encapsulates and decapsulates the IPv6 packets into and out of the
   tunnel.

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