Security Implications of IPv6 Fragmentation with IPv6 Neighbor Discovery
RFC 6980

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Internet Engineering Task Force (IETF)                           F. Gont
Request for Comments: 6980                        SI6 Networks / UTN-FRH
Updates: 3971, 4861                                          August 2013
Category: Standards Track
ISSN: 2070-1721

Security Implications of IPv6 Fragmentation with IPv6 Neighbor Discovery

Abstract

   This document analyzes the security implications of employing IPv6
   fragmentation with Neighbor Discovery (ND) messages.  It updates RFC
   4861 such that use of the IPv6 Fragmentation Header is forbidden in
   all Neighbor Discovery messages, thus allowing for simple and
   effective countermeasures for Neighbor Discovery attacks.  Finally,
   it discusses the security implications of using IPv6 fragmentation
   with SEcure Neighbor Discovery (SEND) and formally updates RFC 3971
   to provide advice regarding how the aforementioned security
   implications can be mitigated.

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 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/rfc6980.

Gont                         Standards Track                    [Page 1]
RFC 6980                ND and IPv6 Fragmentation            August 2013

Copyright Notice

   Copyright (c) 2013 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. Traditional Neighbor Discovery and IPv6 Fragmentation ...........4
   3. SEcure Neighbor Discovery (SEND) and IPv6 Fragmentation .........5
   4. Rationale for Forbidding IPv6 Fragmentation in Neighbor
      Discovery .......................................................6
   5. Specification ...................................................6
   6. Operational Advice ..............................................7
   7. Security Considerations .........................................7
   8. Acknowledgements ................................................8
   9. References ......................................................8
      9.1. Normative References .......................................8
      9.2. Informative References .....................................9
   Appendix A. Message Size When Carrying Certificates ...............10

1.  Introduction

   The Neighbor Discovery Protocol (NDP) is specified in RFC 4861
   [RFC4861].  It is used by both hosts and routers.  Its functions
   include Neighbor Discovery (ND), Router Discovery (RD), address
   autoconfiguration, address resolution, Neighbor Unreachability
   Detection (NUD), Duplicate Address Detection (DAD), and redirection.

   Many of the possible attacks against the Neighbor Discovery Protocol
   are discussed in detail in [RFC3756].  In order to mitigate the
   aforementioned possible attacks, SEcure Neighbor Discovery (SEND) was
   standardized.  SEND employs a number of mechanisms to certify the
   origin of Neighbor Discovery packets and the authority of routers,
   and to protect Neighbor Discovery packets from being the subject of
   modification or replay attacks.

Gont                         Standards Track                    [Page 2]
RFC 6980                ND and IPv6 Fragmentation            August 2013

   However, a number of factors, such as the high administrative
   overhead of deploying trust anchors and the unavailability of SEND
   implementations for many widely deployed operating systems, make SEND
   hard to deploy [Gont-DPSC].  Thus, in many general scenarios, it may
   be necessary and/or convenient to use other mitigation techniques for
   NDP-based attacks.  The following mitigations are currently available
   for NDP attacks:

   o  Static Access Control Lists (ACLs) in switches

   o  Layer-2 filtering of Neighbor Discovery packets (such as RA-Guard
      [RFC6105])

   o  Neighbor Discovery monitoring tools (e.g., NDPMon [NDPMon] and
      ramond [ramond])

   o  Intrusion Prevention Systems (IPS)