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BMP Local Path-ID
draft-younsi-grow-local-path-id-00

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Maxence Younsi , Pierre Francois , Paolo Lucente
Last updated 2023-10-23
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draft-younsi-grow-local-path-id-00
Network Working Group                                          M. Younsi
Internet-Draft                                               P. Francois
Updates: 9069 (if approved)                                    INSA-Lyon
Intended status: Standards Track                              P. Lucente
Expires: 25 April 2024                                               NTT
                                                         23 October 2023

                           BMP Local Path-ID
                   draft-younsi-grow-local-path-id-00

Abstract

   Intelligence is required to track BGP paths throughout the various
   RIBs and VRFs of a routing platform, due to potential attribute
   modifications and the use of BGP multipath.  This document introduces
   the option to identify a path within a router in order to ease
   correlation in monitoring.  A BMPv4 TLV is defined in order to
   communicate this locally significant identifier in monitoring
   messages.

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.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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 25 April 2024.

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Copyright Notice

   Copyright (c) 2023 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 carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Local Path ID . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Local Path ID Properties  . . . . . . . . . . . . . . . .   3
     2.2.  Design Recommendation . . . . . . . . . . . . . . . . . .   3
   3.  Advertising the Local Path ID in BMP  . . . . . . . . . . . .   4
   4.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   When using VRFs and/or BGP Multipath, multiple paths to the same
   destination may be shared among various routing information bases.
   From a collection perspective, tracking the identity of a path thus
   requires some form of modeling, which is subject to inaccuracy.  This
   aspect is exacerbated as path attributes may be modified in the
   process.  This is especially problematic when a PE using BGP
   multipath in VPN instances exports multiple paths for the same
   destination into the default VRF, which were learned from different
   peers.

   While BGP ADD-PATH provides a way to identify paths in BGP multi-path
   scenarios, the scope of ADD-PATH path-id is local to a single BGP
   peering session, and thus cannot be used to distinguish paths
   received over multiple sessions.

   This document introduces a way to identify paths globally within a
   router, allowing operators to not resort to modeling when monitoring
   BGP paths on a router.  In Section 2, we introduce the concept of
   Local Path ID, which is an identifier of a path for a given NLRI,
   which is preserved through the import/export operations performed
   onto them.  In Section 3, we introduce a BMPv4 TLV allowing to
   communicate the value of a Local Path ID on a BMP session.

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2.  Local Path ID

   In this section, we define an identifier called Local Path ID, which
   allows to uniquely identify a path for a given NLRI on a router.

   According to this specification, a path to be advertised by BMP is
   provided with an associated Local Path ID.  The Local Path ID is an
   opaque numerical value with a few properties guaranteeing its
   utility.  The exact approach to generate a Local Path ID is however
   left for the implementation.

2.1.  Local Path ID Properties

   The Local Path ID of each path MUST be unique for a given NLRI.  We
   scope the identifier space to each NLRI to keep it a small value.
   Indeed, most internet routers have at most a few tens of paths for a
   given NLRI.

   The Local Path ID only has a meaning locally on the router generating
   it.

   Once generated, the Local Path ID MUST be preserved between VRFs, and
   Routing Information Bases.  It, however, MUST NOT be exchanged or
   synchronized between routers.

   The value of 0 for a Local Path ID is reserved.

2.2.  Design Recommendation

   In this specification, we recommend making the Local Path ID made of
   two concatenated parts: < process_id | path_discriminator >.

   The process_id is the identifier of the process which produced,
   originated, or received a path.  The process_id allows
   differentiation between path IDs generated in BGP and in other
   processes like an IGP.  Redistributed IGP paths will then have a
   different Local Path ID no matter if BGP or another IGP has chosen
   the same path_discriminator value.  Using the process_id avoids
   requiring interprocess synchronization of path_discriminators or the
   use of a path_discriminator managing process.

   The path_discriminator allows differentiation between different paths
   for a NLRI, coming from the same process (with the same process_id).
   This process originating the path is in charge of guaranteeing the
   uniqueness of the path_discriminator it produces for each path of its
   NLRIs.

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   To ensure traceability in monitoring, processes importing a path
   (like BGP redistribution or VRF imports) SHOULD keep the same Local
   Path ID if provided by the source.

3.  Advertising the Local Path ID in BMP

   The Local Path ID is included in BMPv4 Route Monitoring messages
   [I-D.ietf-grow-bmp-tlv] as an optional TLV, called "Local Path ID
   TLV".

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type (TBD)             |       Length (2 octets)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Index (2 octets)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                         local_path_id                         ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                  Figure 1

   Type  set to TBD

   Length  the length of the Local Path ID, in bytes (TBD static or
      dynamic)

   Index  index of the NLRI in the BGP Update PDU as described by
      [I-D.ietf-grow-bmp-tlv].  The Index MUST refer to a single NLRI
      (no Group TLV).

   local_path_id  the Local Path ID defined in Section 2, on Length
      (Section 3) bytes

   An implementation enabled for Local Path ID usage MUST notify if a
   Local Path ID is unavailable (for any reason) by setting the value
   field to the reserved value of 0.  This means such implementations
   SHOULD always include a Local Path ID TLV (Section 3).

4.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [I-D.ietf-grow-bmp-tlv]
              Lucente, P. and Y. Gu, "TLV support for BMP Route
              Monitoring and Peer Down Messages", Work in Progress,
              Internet-Draft, draft-ietf-grow-bmp-tlv-12, 27 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-grow-
              bmp-tlv-12>.

Authors' Addresses

   Maxence Younsi
   INSA-Lyon
   Villeurbanne
   France
   Email: maxence.younsi@insa-lyon.fr

   Pierre Francois
   INSA-Lyon
   Villeurbanne
   France
   Email: pierre.francois@insa-lyon.fr

   Paolo Lucente
   NTT
   Siriusdreef 70-72
   Hoofddorp, WT 2132
   Netherlands
   Email: paolo@ntt.net

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