AS Path Prepending
draft-ietf-grow-as-path-prepending-00

Document Type Active Internet-Draft (grow WG)
Last updated 2020-09-08
Replaces draft-mcbride-grow-as-path-prepend
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Network Working Group                                         M. McBride
Internet-Draft                                                 Futurewei
Intended status: Best Current Practice                         D. Madory
Expires: March 12, 2021                                           Oracle
                                                             J. Tantsura
                                                                  Apstra
                                                               R. Raszuk
                                                            Bloomberg LP
                                                                   H. Li
                                                                     HPE
                                                       September 8, 2020

                           AS Path Prepending
                 draft-ietf-grow-as-path-prepending-00

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 12, 2021.

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Internet-Draft             AS Path Prepending             September 2020

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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
     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 . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Memory  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Errant announcement . . . . . . . . . . . . . . . . . . .   7
   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
   NEXT_HOP attribute are passed unmodified.

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