AS Path Prepending
draft-ietf-grow-as-path-prepending-02
Network Working Group M. McBride
Internet-Draft Futurewei
Intended status: Best Current Practice D. Madory
Expires: May 5, 2021 Oracle
J. Tantsura
Apstra
R. Raszuk
Bloomberg LP
H. Li
HPE
J. Heitz
Cisco
November 1, 2020
AS Path Prepending
draft-ietf-grow-as-path-prepending-02
Abstract
AS Path Prepending provides a tool to manipulate the BGP AS_Path
attribute through prepending multiple entries of an AS. AS Path
Prepending is used to deprioritize a route or alternate path. By
prepending the local ASN multiple times, ASs can make advertised AS
paths appear artificially longer. Excessive AS Path Prepending has
caused routing issues in the internet. This document provides
guidance,to the internet community, with how best to utilize AS Path
Prepending in order to avoid negatively affecting the internet.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 5, 2021.
McBride, et al. Expires May 5, 2021 [Page 1]
Internet-Draft AS Path Prepending November 2020
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problems . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Excessive Prepending . . . . . . . . . . . . . . . . . . 4
3.2. Prepending during a routing leak . . . . . . . . . . . . 5
3.3. Prepending to All . . . . . . . . . . . . . . . . . . . . 5
3.4. Memory . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Errant announcement . . . . . . . . . . . . . . . . . . . 6
4. Alternatives to AS Path Prepend . . . . . . . . . . . . . . . 7
5. Best Practices . . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Border Gateway Protocol (BGP) [RFC4271] specifies the AS_PATH
attribute which enumerates ASs a route update has traversed. If the
UPDATE message is propagated over an external link, then the local AS
number is prepended to the AS_PATH attribute, and the NEXT_HOP
attribute is updated with an IP address of the router that should be
used as a next hop to the network. If the UPDATE message is
propagated over an internal link, then the AS_PATH attribute and the
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