Default External BGP (EBGP) Route Propagation Behavior without Policies

Abstract

This document updates RFC 4271 by defining the default behavior of a BGP speaker when there is no Import or Export Policy associated with an External BGP session.

Status of This Memo

This is an Internet Standards Track document.

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). Further information on Internet Standards is available in Section 2 of RFC 7841.

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/rfc8212.

Copyright Notice

Copyright © 2017 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Changes to RFC 4271 . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Transition Considerations for BGP Implementers . . .   6
     A.1.  "N+1 N+2" Release Strategy  . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1. Introduction

BGP routing security issues need to be addressed in order to make the Internet more stable. Route leaks [RFC7908] are part of the problem, but software defects or operator misconfiguration can also contribute. This document updates [RFC4271] so that routes are neither imported nor exported unless specifically enabled by configuration. This change reduces the consequences of these problems and improves the default level of Internet routing security.

Many deployed BGP speakers send and accept any and all route announcements between their BGP neighbors by default. This practice dates back to the early days of the Internet, where operators were permissive in sending routing information to allow all networks to reach each other. As the Internet has become more densely interconnected, the risk of a misbehaving BGP speaker poses significant risks to Internet routing.

This specification intends to improve this situation by requiring the explicit configuration of both BGP Import and Export Policies for any External BGP (EBGP) session such as customers, peers, or confederation boundaries for all enabled address families. Through codification of the aforementioned requirement, operators will benefit from consistent behavior across different BGP implementations.

BGP speakers following this specification do not use or send routes on EBGP sessions, unless specifically configured to do so.

2. Terminology

[RFC4271] describes a Policy Information Base (PIB) that contains local policies that can be applied to the information in the Routing Information Base (RIB). This document distinguishes the type of a policy based on its application.

Import Policy: a local policy to be applied to the information contained in the Adj-RIBs-In. As described in Section 3.2 [RFC4271], the Adj-RIBs-In contain information learned from other BGP speakers, and the application of the Import Policy results in the routes that will be considered in the Decision Process by the local BGP speaker.

Export Policy: a local policy to be applied in selecting the information contained in the Adj-RIBs-Out. As described in Section 3.2 [RFC4271], the Adj-RIBs-Out contain information that has been selected for advertisement to other BGP speakers.

2.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Changes to RFC 4271

This section updates [RFC4271] to specify the default behavior of a BGP speaker when there are no Import or Export Policies associated with a particular EBGP session. A BGP speaker MAY provide a configuration option to deviate from the following updated behaviors.

The following paragraph is added to Section 9.1 (Decision Process) after the fifth paragraph, which ends in "route aggregation and route information reduction":

Routes contained in an Adj-RIB-In associated with an EBGP peer SHALL NOT be considered eligible in the Decision Process if no explicit Import Policy has been applied.

The following paragraph is added to Section 9.1.3 (Phase 3: Route Dissemination) after the third paragraph, which ends in "by means of an UPDATE message (see 9.2).":

Routes SHALL NOT be added to an Adj-RIB-Out associated with an EBGP peer if no explicit Export Policy has been applied.

4. Security Considerations

Permissive default routing policies can result in inadvertent effects such as route leaks [RFC7908], in general resulting in routing of traffic through an unexpected path. While it is possible for an operator to use monitoring to detect unexpected flows, there is no general framework that can be applied. These policies also have the potential to expose software defects or misconfiguration that could have unforeseen technical and business impacting effects.

The update to [RFC4271] specified in this document is intended to eliminate those inadvertent effects. Operators must explicitly configure Import and Export Policies to achieve their expected goals. There is of course no protection against a malicious or incorrect explicit configuration.

The security considerations described in [RFC4271] and the vulnerability analysis discussed in [RFC4272] also apply to this document.

5. IANA Considerations

This document does not require any IANA actions.

6. References

6.1. Normative References

   [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>.
   
   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <http://www.rfc-editor.org/info/rfc8174>.

6.2. Informative References

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <http://www.rfc-editor.org/info/rfc4272>.
   
   [RFC7908]  Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
              and B. Dickson, "Problem Definition and Classification of
              BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
              2016, <http://www.rfc-editor.org/info/rfc7908>.

Appendix A. Transition Considerations for BGP Implementers

This appendix is not normative.

For an implementer, transitioning to a compliant BGP implementation may require a process that can take several years.

It is understood and acknowledged that operators who are taking advantage of an undefined behavior will always be surprised by changes to said behavior.

A.1. "N+1 N+2" Release Strategy

An implementer could leverage an approach described as the "N+1 and N+2" release strategy. In release N+1, the implementer introduces a new default configuration parameter to indicate that the BGP speaker is operating in "ebgp insecure-mode". In addition to the introduction of the new parameter, an implementer could begin to display informational warnings to the operator that certain parts of the configuration are incomplete. In release N+1, operators of the BGP implementation become aware that a configurable default exists in the implementation, and can prepare accordingly. In release N+2 or later, the inverse of the previous default configuration parameter that was introduced in release N+1 becomes the new default.

As a result, any new installation of release N+2 will adhere to this document. Installations upgraded from version release N+1 will adhere to the previous insecure behavior, if no modification was made to the "ebgp insecure-mode" configuration parameter.

Acknowledgments

The authors would like to thank the following people for their comments, support and review: Shane Amante, Christopher Morrow, Robert Raszuk, Greg Skinner, Adam Chappell, Sriram Kotikalapudi, Brian Dickson, Jeffrey Haas, John Heasley, Ignas Bagdonas, Donald Smith, Alvaro Retana, John Scudder, and Dale Worley.

Contributors

The following people contributed to successful deployment of the solution described in this document:

Jakob Heitz
Cisco

Email:

          jheitz@cisco.com

Ondrej Filip
CZ.NIC

   Email: ondrej.filip@nic.cz

Authors' Addresses

   Jared Mauch
   Akamai Technologies
   8285 Reese Lane
   Ann Arbor  Michigan 48103
   United States of America

Email:

          jared@akamai.com
   
   Job Snijders
   NTT Communications
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands

Email:

          job@ntt.net
   
   Greg Hankins
   Nokia
   777 E. Middlefield Road
   Mountain View, CA  94043
   United States of America
   
   Email: greg.hankins@nokia.com