Internet Engineering Task Force (IETF) J. Mauch
Request for Comments: 8212 Akamai
Updates: 4271 J. Snijders
Category: Standards Track NTT
ISSN: 2070-1721 G. Hankins
July 2017Default External BGP (EBGP) Route Propagation Behavior without Policies
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
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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[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
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
The security considerations described in [RFC4271] and the
vulnerability analysis discussed in [RFC4272] also apply to this
5. IANA Considerations
This document does not require any IANA actions.
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,
[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,
[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>.
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.
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.
The following people contributed to successful deployment of the
solution described in this document:
8285 Reese Lane
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