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Internet Engineering Task Force (IETF)                           T. KingRequest for Comments: 7999                                    C. DietzelCategory: Informational                                           DE-CIXISSN: 2070-1721                                              J. Snijders                                                                     NTT                                                              G. Doering                                                             SpaceNet AG                                                              G. Hankins                                                                   Nokia                                                            October 2016BLACKHOLE CommunityAbstract   This document describes the use of a well-known Border Gateway   Protocol (BGP) community for destination-based blackholing in IP   networks.  This well-known advisory transitive BGP community named   "BLACKHOLE" allows an origin Autonomous System (AS) to specify that a   neighboring network should discard any traffic destined towards the   tagged IP prefix.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 7841.   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/rfc7999.King, et al.                  Informational                     [Page 1]

RFC 7999                   BLACKHOLE Community              October 2016Copyright Notice   Copyright (c) 2016 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 ....................................................31.1. Requirements Language ......................................32. BLACKHOLE Community .............................................43. Operational Recommendations .....................................43.1. IP Prefix Announcements with BLACKHOLE Community Attached ..43.2. Local Scope of Blackholes ..................................43.3. Accepting Blackholed IP Prefixes ...........................54. Vendor Implementation Recommendations ...........................65. IANA Considerations .............................................66. Security Considerations .........................................67. References ......................................................77.1. Normative References .......................................77.2. Informative References .....................................7   Acknowledgements ...................................................8   Authors' Addresses .................................................9King, et al.                  Informational                     [Page 2]

RFC 7999                   BLACKHOLE Community              October 20161.  Introduction   Network infrastructures have been increasingly hampered by DDoS   attacks.  In order to dampen the effects of these DDoS attacks, IP   networks have offered blackholing with BGP [RFC4271] using various   mechanisms such as those described in [RFC3882] and [RFC5635].   DDoS attacks targeting a certain IP address may cause congestion of   links used to connect to adjacent networks.  In order to limit the   impact of such a scenario on legitimate traffic, networks adopted a   mechanism called "BGP blackholing".  A network that wants to trigger   blackholing needs to understand the triggering mechanism adopted by   its neighboring networks.  Different networks provide different   mechanisms to trigger blackholing, including but not limited to pre-   defined blackhole next-hop IP addresses, specific BGP communities, or   out-of-band BGP sessions with a special BGP speaker.   Having several different mechanisms to trigger blackholing in   different networks makes it an unnecessarily complex, error-prone,   and cumbersome task for network operators.  Therefore, a well-known   BGP community [RFC1997] is defined for operational ease.   Having such a well-known BGP community for blackholing also further   simplifies network operations because:   o  Implementing and monitoring blackholing becomes easier when      implementation and operational guides do not cover many variations      to trigger blackholing.   o  The number of support requests from customers about how to trigger      blackholing in a particular neighboring network will be reduced as      the codepoint for common blackholing mechanisms is unified and      well-known.1.1.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to   be interpreted as described in [RFC2119] only when they appear in all   upper case.  They may also appear in lower case or mixed case as   English words, without normative meaning.King, et al.                  Informational                     [Page 3]

RFC 7999                   BLACKHOLE Community              October 20162.  BLACKHOLE Community   This document defines the use of a new well-known BGP transitive   community, BLACKHOLE.   The semantics of this community allow a network to interpret the   presence of this community as an advisory qualification to drop any   traffic being sent towards this prefix.3.  Operational Recommendations3.1.  IP Prefix Announcements with BLACKHOLE Community Attached   Accepting and honoring the BLACKHOLE community, or ignoring it, is a   choice that is made by each operator.  This community MAY be used in   all bilateral and multilateral BGP deployment scenarios.  In a   bilateral peering relationship, use of the BLACKHOLE community MUST   be agreed upon by the two networks before advertising it.  In a   multilateral peering relationship, the decision to honor or ignore   the BLACKHOLE community is to be made according to the operator's   routing policy.  The community SHOULD be ignored, if it is received   by a network that it not using it.   When a network is under DDoS duress, it MAY announce an IP prefix   covering the victim's IP address(es) for the purpose of signaling to   neighboring networks that any traffic destined for these IP   address(es) should be discarded.  In such a scenario, the network   operator SHOULD attach the BLACKHOLE community.   The BLACKHOLE community MAY also be used as one of the trigger   communities in a destination-based Remote Triggered Blackhole (RTBH)   [RFC5635] configuration.3.2.  Local Scope of Blackholes   A BGP speaker receiving an announcement tagged with the BLACKHOLE   community SHOULD add the NO_ADVERTISE or NO_EXPORT community as   defined in [RFC1997], or a similar community, to prevent propagation   of the prefix outside the local AS.  The community to prevent   propagation SHOULD be chosen according to the operator's routing   policy.   Unintentional leaking of more specific IP prefixes to neighboring   networks can have adverse effects.  Extreme caution should be used   when purposefully propagating IP prefixes tagged with the BLACKHOLE   community outside the local routing domain, unless policy explicitly   aims at doing just that.King, et al.                  Informational                     [Page 4]

RFC 7999                   BLACKHOLE Community              October 20163.3.  Accepting Blackholed IP Prefixes   It has been observed in provider networks running BGP that   announcements of IP prefixes longer than /24 for IPv4 and /48 for   IPv6 are usually not accepted on the Internet (seeSection 6.1.3 of   [RFC7454]).  However, blackhole prefix length should be as long as   possible in order to limit the impact of discarding traffic for   adjacent IP space that is not under DDoS duress.  The blackhole   prefix length is typically as specific as possible, /32 for IPv4 or   /128 for IPv6.   BGP speakers in a bilateral peering relationship using the BLACKHOLE   community MUST only accept and honor BGP announcements carrying the   BLACKHOLE community under the two following conditions:   o  The announced prefix is covered by an equal or shorter prefix that      the neighboring network is authorized to advertise.   o  The receiving party agreed to honor the BLACKHOLE community on the      particular BGP session.   In topologies with a route server or other multilateral peering   relationships, BGP speakers SHOULD accept and honor BGP announcements   under the same conditions.   An operator MUST ensure that origin validation techniques (such as   the one described in [RFC6811]) do not inadvertently block legitimate   announcements carrying the BLACKHOLE community.   The BLACKHOLE community is not intended to be used with Network Layer   Reachability Information (NLRI) [RFC5575] to distribute traffic flow   specifications.   The error handling for this community follows the process in   [RFC7606] that causes a malformed community to be treated as   withdrawn.   Operators are encouraged to store all BGP updates in their network   carrying the BLACKHOLE community for long-term analysis or internal   audit purposes.King, et al.                  Informational                     [Page 5]

RFC 7999                   BLACKHOLE Community              October 20164.  Vendor Implementation Recommendations   Without an explicit configuration directive set by the operator,   network elements SHOULD NOT discard traffic destined towards IP   prefixes that are tagged with the BLACKHOLE community.  The operator   is expected to explicitly configure the network element to honor the   BLACKHOLE community in a way that is compliant with the operator's   routing policy.   Vendors MAY provide a shorthand keyword in their configuration   language to reference the well-known BLACKHOLE community attribute   value.  The suggested string to be used is "blackhole".5.  IANA Considerations   The IANA has registered BLACKHOLE in the "BGP Well-known Communities"   registry.      BLACKHOLE (= 0xFFFF029A)   The low-order two octets in decimal are 666, a value commonly   associated with BGP blackholing among network operators.6.  Security Considerations   BGP contains no specific mechanism to prevent the unauthorized   modification of information by the forwarding agent.  This allows   routing information to be modified or removed; it also allows false   information to be added by forwarding agents.  Recipients of routing   information are not able to detect this modification.  BGPsec   [BGPSEC] does not resolve this situation.  Even when BGPsec is in   place, a forwarding agent can alter, add, or remove BGP communities.   The unauthorized addition of the BLACKHOLE community to an IP prefix   by an adversary may cause a denial-of-service attack based on denial   of reachability.   In order to further limit the impact of unauthorized BGP   announcements carrying the BLACKHOLE community, the receiving BGP   speaker SHOULD verify by applying strict filtering (seeSection 6.2.1.1.2 of [RFC7454]) that the peer announcing the prefix   is authorized to do so.  If not, the BGP announcement should be   filtered.King, et al.                  Informational                     [Page 6]

RFC 7999                   BLACKHOLE Community              October 2016   BGP announcements carrying the BLACKHOLE community should only be   accepted and honored if the neighboring network is authorized to   advertise the prefix.  The method of validating announcements is to   be chosen according to the operator's routing policy.   It is RECOMMENDED that operators use best common practices to protect   their BGP sessions, such as the ones in [RFC7454].7.  References7.1.  Normative References   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities              Attribute",RFC 1997, DOI 10.17487/RFC1997, August 1996,              <http://www.rfc-editor.org/info/rfc1997>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A              Border Gateway Protocol 4 (BGP-4)",RFC 4271,              DOI 10.17487/RFC4271, January 2006,              <http://www.rfc-editor.org/info/rfc4271>.   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.              Patel, "Revised Error Handling for BGP UPDATE Messages",RFC 7606, DOI 10.17487/RFC7606, August 2015,              <http://www.rfc-editor.org/info/rfc7606>.7.2.  Informative References   [BGPSEC]   Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol              Specification", Work in Progress,draft-ietf-sidr-bgpsec-protocol-18, August 2016.   [RFC3882]  Turk, D., "Configuring BGP to Block Denial-of-Service              Attacks",RFC 3882, DOI 10.17487/RFC3882, September 2004,              <http://www.rfc-editor.org/info/rfc3882>.   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,              and D. McPherson, "Dissemination of Flow Specification              Rules",RFC 5575, DOI 10.17487/RFC5575, August 2009,              <http://www.rfc-editor.org/info/rfc5575>.King, et al.                  Informational                     [Page 7]

RFC 7999                   BLACKHOLE Community              October 2016   [RFC5635]  Kumari, W. and D. McPherson, "Remote Triggered Black Hole              Filtering with Unicast Reverse Path Forwarding (uRPF)",RFC 5635, DOI 10.17487/RFC5635, August 2009,              <http://www.rfc-editor.org/info/rfc5635>.   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.              Austein, "BGP Prefix Origin Validation",RFC 6811,              DOI 10.17487/RFC6811, January 2013,              <http://www.rfc-editor.org/info/rfc6811>.   [RFC7454]  Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations              and Security",BCP 194,RFC 7454, DOI 10.17487/RFC7454,              February 2015, <http://www.rfc-editor.org/info/rfc7454>.Acknowledgements   The authors would like to gratefully acknowledge many people who have   contributed discussions and ideas to the development of this   document.  They include Petr Jiran, Yordan Kritski, Christian Seitz,   Nick Hilliard, Joel Jaeggli, Christopher Morrow, Thomas Mangin, Will   Hargrave, Niels Bakker, David Farmer, Jared Mauch, John Heasley, and   Terry Manderson.King, et al.                  Informational                     [Page 8]

RFC 7999                   BLACKHOLE Community              October 2016Authors' Addresses   Thomas King   DE-CIX Management GmbH   Lichtstrasse 43i   Cologne  50825   Germany   Email: thomas.king@de-cix.net   Christoph Dietzel   DE-CIX Management GmbH   Lichtstrasse 43i   Cologne  50825   Germany   Email: christoph.dietzel@de-cix.net   Job Snijders   NTT Communications   Theodorus Majofskistraat 100   Amsterdam  1065 SZ   The Netherlands   Email: job@ntt.net   Gert Doering   SpaceNet AG   Joseph-Dollinger-Bogen 14   Munich  80807   Germany   Email: gert@space.net   Greg Hankins   Nokia   777 E. Middlefield Road   Mountain View, CA  94043   United States of America   Email: greg.hankins@nokia.comKing, et al.                  Informational                     [Page 9]