RFC 7999

BLACKHOLE Community

📅 published October 2016, from ietf

🎀 RFC 7999: BLACKHOLE Community ✨

Okay bestie, this one is an Informational RFC from the IETF, numbered 7999 and dated October 2016 🦋 It was written by T. King, C. Dietzel (DE-CIX), J. Snijders (NTT), G. Doering (SpaceNet AG), and G. Hankins (Nokia). Its ISSN is 2070-1721. The header doesn't list anything it obsoletes or updates, so no drama there 💅

Abstract 🌸

So this doc is all about using a well-known Border Gateway Protocol (BGP) community for destination-based blackholing in IP networks 🫶 The community is called "BLACKHOLE", and it's an advisory transitive BGP community. It lets an origin Autonomous System (AS) tell a neighboring network that it should discard any traffic headed toward the tagged IP prefix 🔥

Status of This Memo 📜

This document is not an Internet Standards Track specification. It's published for informational purposes, so chill 🧚

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community, and it got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every document the IESG approves is a candidate for any level of Internet Standard, so see Section 2 of RFC 7841 if you want the full story 🤓

Info about the current status of this document, any errata, and how to give feedback on it lives at http://www.rfc-editor.org/info/rfc7999 💜

Copyright (c) 2016 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, because 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 they are provided without warranty as described in the Simplified BSD License 📋

Table of Contents 🧾

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................3
   2. BLACKHOLE Community .............................................4
   3. Operational Recommendations .....................................4
      3.1. IP Prefix Announcements with BLACKHOLE Community Attached ..4
      3.2. Local Scope of Blackholes ..................................4
      3.3. Accepting Blackholed IP Prefixes ...........................5
   4. Vendor Implementation Recommendations ...........................6
   5. IANA Considerations .............................................6
   6. Security Considerations .........................................6
   7. References ......................................................7
      7.1. Normative References .......................................7
      7.2. Informative References .....................................7
   Acknowledgements ...................................................8
   Authors' Addresses .................................................9

1. Introduction 🌈

Network infrastructures have been getting absolutely smashed by DDoS attacks 💀 To soften the blow, IP networks have offered blackholing with BGP [RFC4271] using various mechanisms, such as the ones described in [RFC3882] and [RFC5635].

DDoS attacks aimed at a certain IP address can congest the links used to connect to adjacent networks. To limit the damage that does to legit traffic, networks adopted a mechanism called "BGP blackholing" 😭 A network that wants to trigger blackholing needs to understand the triggering mechanism its neighboring networks use. Different networks offer different ways 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 a bunch of different triggers in different networks is unnecessarily complex, error-prone, and cumbersome for network operators, honestly so messy 🙈 So a well-known BGP community [RFC1997] was defined for operational ease 👑

A well-known BGP community for blackholing also makes network operations way simpler, because:

  • Implementing and monitoring blackholing gets easier when implementation and operational guides don't have to cover a ton of variations for triggering blackholing 🍓
  • Customers will file fewer support requests asking how to trigger blackholing in a particular neighboring network, since 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 💅

2. BLACKHOLE Community 🦋

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

The semantics of this community let a network read the presence of this community as an advisory qualification to drop any traffic being sent toward this prefix ✨

3. Operational Recommendations 🧚

3.1. IP Prefix Announcements with BLACKHOLE Community Attached 📣

Accepting and honoring the BLACKHOLE community, or ignoring it, is a choice 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 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) to signal to neighboring networks that any traffic destined for these IP address(es) should be discarded 🚨 In that 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 that receives 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 the prefix from propagating outside the local AS. The community used 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, so be extremely careful 🙃 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.

3.3. 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 (see Section 6.1.3 of [RFC7454]). However, blackhole prefix length should be as long as possible 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:

  • The announced prefix is covered by an equal or shorter prefix that the neighboring network is authorized to advertise.
  • 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], which 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 🗂️💜

⏭️ Part 2 is coming next, with Section 4 onward, the references, and the appendices!

6. Security Considerations 🔥

okay bestie, this is the serious part, so let's be real 🫶. BGP has no specific mechanism to stop the forwarding agent from messing with information 💀. That means routing info can be modified or removed, and forwarding agents can add false info, and the people receiving the routes literally cannot tell it happened. not ideal 😭. BGPsec [BGPSEC] does not fix this either. Even with BGPsec in place, a forwarding agent can still 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. Someone sneaking that community onto a prefix can knock it offline for everyone, so this one is a big deal 💀🌈.

To further limit the impact of unauthorized BGP announcements carrying the BLACKHOLE community, the receiving BGP speaker SHOULD verify, by applying strict filtering (see Section 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 ✨. Think of it as a bouncer checking the guest list 💅.

BGP announcements carrying the BLACKHOLE community should only be accepted and honored if the neighboring network is authorized to advertise the prefix 🦋. How you validate announcements is up to the operator's routing policy, so pick the method that fits your setup 🎀.

It is RECOMMENDED that operators use best common practices to protect their BGP sessions, such as the ones in [RFC7454] 👑💜. Protect your sessions, bestie, it's giving responsible networking 🫶✨.

7. References

7.1. 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>.

[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 🎀✨. Everyone who helped shape this one deserves a flower crown 💐👑.

Authors' 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.com
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