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Internet Engineering Task Force (IETF)                       N. HilliardRequest for Comments: 6666                                          INEXCategory: Informational                                      D. FreedmanISSN: 2070-1721                                                 Claranet                                                             August 2012A Discard Prefix for IPv6Abstract   Remote triggered black hole filtering describes a method of   mitigating the effects of denial-of-service attacks by selectively   discarding traffic based on source or destination address.  Remote   triggered black hole routing describes a method of selectively re-   routing traffic into a sinkhole router (for further analysis) based   on destination address.  This document updates the "IPv6 Special   Purpose Address Registry" by explaining why a unique IPv6 prefix   should be formally assigned by IANA for the purpose of facilitating   IPv6 remote triggered black hole filtering and routing.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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6666.Hilliard & Freedman           Informational                     [Page 1]

RFC 6666                   IPv6 Discard Prefix               August 2012Copyright Notice   Copyright (c) 2012 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1. Introduction ....................................................21.1. Notational Conventions .....................................32. A Discard Prefix for IPv6 .......................................33. Operational Implications ........................................44. IANA Considerations .............................................45. Security Considerations .........................................46. References ......................................................56.1. Normative References .......................................56.2. Informative References .....................................51.  Introduction   Remote Triggered Black Hole (RTBH) filtering describes a class of   methods of blocking IP traffic either from a specific source   ([RFC5635]) or to a specific destination ([RFC3882]) on a network.   RTBH routing describes a class of methods of re-routing IP traffic   destined to the attacked/targeted host to a special path (tunnel)   where a sniffer could capture the traffic for analysis.  Both of   these methods operate by setting the next-hop address of an IP packet   with a specified source or destination address to be a unicast prefix   that is connected locally or remotely to a router's discard, null, or   tunnel interface.  Typically, reachability information for this   prefix is propagated throughout an autonomous system using a dynamic   routing protocol such as BGP ([RFC3882]).  By deploying RTBH systems   across a network, traffic to or from specific destinations may be   selectively black-holed or re-routed to a sinkhole device in a manner   that is efficient, scalable, and straightforward to implement.Hilliard & Freedman           Informational                     [Page 2]

RFC 6666                   IPv6 Discard Prefix               August 2012   On some networks, operators configure RTBH installations using   [RFC1918] address space or the address blocks reserved for   documentation in [RFC5737].  This approach is inadequate because RTBH   configurations are not documentation, but rather operationally   important features of many public-facing production networks.   Furthermore, [RFC3849] specifies that the IPv6 documentation prefix   should be filtered in both local and public contexts.  On this basis,   it is suggested that both private network address blocks and the   documentation prefixes described in [RFC5737] are inappropriate for   RTBH configurations and that a dedicated IPv6 prefix should be   assigned instead.   This document updates the "IPv6 Special Purpose Address Registry"   [IANA-IPV6REG].1.1.  Notational Conventions   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 [RFC2119].2.  A Discard Prefix for IPv6   For the purposes of implementing an IPv6 RTBH configuration, a   unicast address block is required.  There are currently no IPv6   unicast address blocks that are specifically nominated for the   purposes of implementing such RTBH systems.   While it could be argued that there are other addresses and address   prefixes that could be used for this purpose (e.g., documentation   prefixes, private address space), or that an operator could assign an   address block from their own address space for this purpose, there is   currently no operational clarity on what address block would be   appropriate or inappropriate to use for this purpose.  By assigning a   globally unique discard prefix for IPv6, the IETF will introduce good   practice for the implementation of IPv6 RTBH configurations and will   facilitate operational clarity by allowing operators to implement   consistent and deterministic inter-domain prefix and traffic   filtering policies for black-holed traffic.   As [RFC3882] and [RFC5635] describe situations where more than one   discard address may be used for implementing multiple RTBH scenarios,   a single address is not sufficient to cover all likely RTBH   situations.  Consequently, an address block is required.Hilliard & Freedman           Informational                     [Page 3]

RFC 6666                   IPv6 Discard Prefix               August 20123.  Operational Implications   This assignment MAY be carried in a dynamic routing protocol within   an autonomous system.  The assignment SHOULD NOT be announced to or   accepted from third-party autonomous systems, and IPv6 traffic with a   destination address within this prefix SHOULD NOT be forwarded to or   accepted from third-party autonomous systems.  If the prefix or a   subnet of the prefix is inadvertently announced to or accepted from a   third-party autonomous system, this may cause excessive volumes of   traffic to pass unintentionally between the two networks, which would   aggravate the effect of a denial-of-service attack.   On networks that implement IPv6 remote triggered black holes, some or   all of this network block MAY be configured with a next-hop   destination of a discard or null interface on any or all IPv6 routers   within the autonomous system.4.  IANA Considerations   Per this document, IANA has recorded the allocation of the IPv6   address prefix 0100::/64 as a Discard-Only Prefix in the "Internet   Protocol Version 6 Address Space" and added the prefix to the "IANA   IPv6 Special Purpose Address Registry" [IANA-IPV6REG].  No end party   has been assigned to this prefix.  The prefix has been allocated from   ::/3.5.  Security Considerations   As the prefix specified in this document ought not normally be   transmitted or accepted over inter-domain BGP sessions for the   reasons described inSection 3, it is usually appropriate to include   this prefix in inter-domain BGP prefix filters [RFC3704] or otherwise   ensure the prefix is neither transmitted to nor accepted from a   third-party autonomous system.Hilliard & Freedman           Informational                     [Page 4]

RFC 6666                   IPv6 Discard Prefix               August 20126.  References6.1.  Normative References   [IANA-IPV6REG]              Internet Assigned Numbers Authority, "IPv6 Special Purpose              Address Registry", 2012, <http://www.iana.org/assignments/iana-ipv6-special-registry>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3882]  Turk, D., "Configuring BGP to Block Denial-of-Service              Attacks",RFC 3882, September 2004.   [RFC5635]  Kumari, W. and D. McPherson, "Remote Triggered Black Hole              Filtering with Unicast Reverse Path Forwarding (uRPF)",RFC 5635, August 2009.6.2.  Informative References   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,              and E. Lear, "Address Allocation for Private Internets",BCP 5,RFC 1918, February 1996.   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed              Networks",BCP 84,RFC 3704, March 2004.   [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix              Reserved for Documentation",RFC 3849, July 2004.   [RFC5737]  Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks              Reserved for Documentation",RFC 5737, January 2010.Hilliard & Freedman           Informational                     [Page 5]

RFC 6666                   IPv6 Discard Prefix               August 2012Authors' Addresses   Nick Hilliard   INEX   4027 Kingswood Road   Dublin  24   IE   EMail: nick@inex.ie   David Freedman   Claranet   21 Southampton Row, Holborn   London  WC1B 5HA   UK   EMail: david.freedman@uk.clara.netHilliard & Freedman           Informational                     [Page 6]