Network Working Group T. King
Internet-Draft C. Dietzel
Intended status: Standards Track DE-CIX Management GmbH
Expires: May 4, 2016 J. Snijders
G. Döring
SpaceNet AG
G. Hankins
November 2015

BLACKHOLE BGP Community for Blackholing


This document describes the use of a well-known Border Gateway Protocol (BGP) community for blackholing at IP networks and Internet Exchange Points (IXP). This well-known advisory transitive BGP community, namely BLACKHOLE, allows an origin AS to specify that a neighboring IP network or IXP should blackhole a specific IP prefix.

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 or mixed case as English words, without normative meaning.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

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This Internet-Draft will expire on May 4, 2016.

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

The network infrastructure has been getting hammered by DDoS attacks for years. In order to block DDoS attacks, IP networks have offered BGP blackholing to neighboring networks (iBGP scenarios [RFC3882] and RTBH filtering [RFC5635]), much like some IXPs have recently started to do.

DDoS attacks targeting a certain IP network may cause congestion of links used to connect to other networks. In order to limit the impact of such a scenario on legitimate traffic, IP networks and IXPs adopted a mechanism called BGP blackholing. A network that wants to trigger blackholing needs to understand the triggering mechanism adopted by its neighboring IP networks and IXPs. Different IP networks and IXPs provide different BGP mechanisms to trigger blackholing, including pre-defined blackhole next- hop IP addresses and pre-defined BGP communities.

Having several different mechanisms to trigger blackholing at different IP networks and IXPs 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 supports IP networks and IXPs because

Making it considerably easier for network operators to utilize blackholing makes operations easier.

2. BLACKHOLE Attribute

This document defines the use of a new well-known BGP transitive community, BLACKHOLE.

The semantics of this attribute 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 Recommendations

3.1. IP Prefix Announcements with BLACKHOLE Community Attached

When an IP 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 IP networks or IXPs that any traffic destined for these IP address(es) should be discarded. In such a scenario, the network operator SHOULD attach BLACKHOLE BGP community.

3.2. Local Scope of Blackholes

A BGP speaker receiving a BGP announcement tagged with the BLACKHOLE BGP community SHOULD add a NO_ADVERTISE, NO_EXPORT or similar community to prevent propagation of this route outside the local AS.

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 BGP community outside the local routing domain.

3.3. Accepting Blackholed IP Prefixes

It has been observed that announcements of IP prefixes larger than /24 for IPv4 and /48 for IPv6 are usually not accepted on the Internet (see section 6.1.3 [RFC7454]). However, blackhole routes should be as small as possible in order to limit the impact of discarding traffic for adjacent IP space that is not under DDoS duress. Typically, the blackhole route's prefix length is as specific as /32 for IPv4 and /128 for IPv6.

BGP speakers SHOULD only accept and honor BGP announcements carrying the BLACKHOLE community if the announced prefix is covered by a shorter prefix for which the neighboring network is authorized to advertise.

3.4. IXPs: Peering at Route Servers

Many IXPs provide the so-called policy control feature as part of their route servers [I-D.ietf-idr-ix-bgp-route-server] (see e.g. the LINX website). Policy control allows members to specify, by using BGP communities, which ASNs connected to the route server receive a particular BGP announcement.

Combined usage of the BGP communities for blackholing and policy control allows a fine-grained control of a blackhole.

In some implementations of blackholing at IXPs, the route server after receiving a BGP announcement tagged with the BLACKHOLE BGP community rewrites the next-hop IP address to the pre-defined blackholing IP address before redistributing the announcement.

4. IANA Considerations

The IANA is requested to register BLACKHOLE as a well-known BGP community with global significance:

The low-order two octets in decimal are 666, amongst IP network operators a value commonly associated with BGP blackholing.

5. 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, removed, or false information to be added by forwarding agents. Recipients of routing information are not able to detect this modification. Also, RPKI [RFC6810] and BGPSec [I-D.ietf-sidr-bgpsec-overview] do not fully resolve this situation. For instance, BGP communities can still be added or altered by a forwarding agent even if RPKI and BGPSec are in place.

The BLACKHOLE BGP community does not alter this situation.

A new additional attack vector is introduced into BGP by using the BLACKHOLE BGP community: denial of service attacks for IP prefixes.

The unauthorized addition of the BLACKHOLE BGP community to an IP prefix by a forwarding agent may cause a denial of service attack based on denial of reachability. The denial of service will happen if an IP network or IXP offering blackholing is traversed. However, denial of service attack vectors to BGP are not new as the injection of false routing information is already possible.

In order to further limit the impact of unauthorized BGP announcements carrying the BLACKHOLE BGP community, the receiving BGP speaker SHOULD verify by applying strict filtering (see section [RFC7454]) that the peer announcing the prefix is authorized to do so. If not, the BGP announcement should be filtered out.

The presence of this BLACKHOLE BGP community may introduce a resource exhaustion attack to BGP speakers. If a BGP speaker receives many IP prefixes containing the BLACKHOLE BGP community, its internal resources such as CPU power and/or memory might get consumed, especially if usual prefix sanity checks (e.g. such as IP prefix length or number of prefixes) are disabled (see Section 3.3).

6. References

6.1. Normative References

[RFC1997] Chandra, R., Traina, P. and T. Li, "BGP Communities Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

6.2. Informative References

[I-D.ietf-idr-ix-bgp-route-server] Jasinska, E., Hilliard, N., Raszuk, R. and N. Bakker, "Internet Exchange BGP Route Server", Internet-Draft draft-ietf-idr-ix-bgp-route-server-09, October 2015.
[I-D.ietf-sidr-bgpsec-overview] Lepinski, M., "An Overview of BGPsec", Internet-Draft draft-ietf-sidr-bgpsec-overview-07, June 2015.
[RFC3882] Turk, D., "Configuring BGP to Block Denial-of-Service Attacks", RFC 3882, DOI 10.17487/RFC3882, September 2004.
[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.
[RFC6810] Bush, R. and R. Austein, "The Resource Public Key Infrastructure (RPKI) to Router Protocol", RFC 6810, DOI 10.17487/RFC6810, January 2013.
[RFC7454] Durand, J., Pepelnjak, I. and G. Doering, "BGP Operations and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454, February 2015.

Appendix A. Acknowledgements

The authors gratefully acknowledges the contributions of:

Authors' Addresses

Thomas King DE-CIX Management GmbH Lichtstrasse 43i Cologne, 50825 Germany EMail:
Christoph Dietzel DE-CIX Management GmbH Lichtstrasse 43i Cologne, 50825 Germany EMail:
Job Snijders NTT Communications, Inc. Theodorus Majofskistraat 100 Amsterdam, 1065 SZ NL EMail:
Gert Döring SpaceNet AG Joseph-Dollinger-Bogen 14 Munich, 80807 Germany EMail:
Greg Hankins Alcatel-Lucent 777 E. Middlefield Road Mountain View, CA 94043 USA EMail: