Operational Neighbor Discovery Problems
RFC 6583

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Internet Engineering Task Force (IETF)                      I. Gashinsky
Request for Comments: 6583                                        Yahoo!
Category: Informational                                       J. Jaeggli
ISSN: 2070-1721                                                    Zynga
                                                               W. Kumari
                                                            Google, Inc.
                                                              March 2012

                Operational Neighbor Discovery Problems

Abstract

   In IPv4, subnets are generally small, made just large enough to cover
   the actual number of machines on the subnet.  In contrast, the
   default IPv6 subnet size is a /64, a number so large it covers
   trillions of addresses, the overwhelming number of which will be
   unassigned.  Consequently, simplistic implementations of Neighbor
   Discovery (ND) can be vulnerable to deliberate or accidental denial
   of service (DoS), whereby they attempt to perform address resolution
   for large numbers of unassigned addresses.  Such denial-of-service
   attacks can be launched intentionally (by an attacker) or result from
   legitimate operational tools or accident conditions.  As a result of
   these vulnerabilities, new devices may not be able to "join" a
   network, it may be impossible to establish new IPv6 flows, and
   existing IPv6 transported flows may be interrupted.

   This document describes the potential for DoS in detail and suggests
   possible implementation improvements as well as operational
   mitigation techniques that can, in some cases, be used to protect
   against or at least alleviate the impact of such attacks.

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/rfc6583.

Gashinsky, et al.             Informational                     [Page 1]
RFC 6583                 Operational ND Problems              March 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 ..............................................3
   2. The Problem .....................................................3
   3. Terminology .....................................................4
   4. Background ......................................................5
   5. Neighbor Discovery Overview .....................................6
   6. Operational Mitigation Options ..................................7
      6.1. Filtering of Unused Address Space ..........................7
      6.2. Minimal Subnet Sizing ......................................7
      6.3. Routing Mitigation .........................................8
      6.4. Tuning of the NDP Queue Rate Limit .........................8
   7. Recommendations for Implementors ................................8
      7.1. Prioritize NDP Activities ..................................9
      7.2. Queue Tuning ..............................................10
   8. Security Considerations ........................................11
   9. Acknowledgements ...............................................11
   10. References ....................................................11
      10.1. Normative References .....................................11
      10.2. Informative References ...................................11

Gashinsky, et al.             Informational                     [Page 2]
RFC 6583                 Operational ND Problems              March 2012

1.  Introduction

   This document describes implementation issues with IPv6's Neighbor
   Discovery protocol that can result in vulnerabilities when a network