BMP Extension for Path Status TLV
draft-ietf-grow-bmp-path-marking-tlv-01

Network Working Group                                         C. Cardona
Internet-Draft                                                P. Lucente
Intended status: Standards Track                                     NTT
Expires: 19 September 2024                                   P. Francois
                                                               INSA-Lyon
                                                                   Y. Gu
                                                                  Huawei
                                                                 T. Graf
                                                                Swisscom
                                                           18 March 2024

                   BMP Extension for Path Status TLV
                draft-ietf-grow-bmp-path-marking-tlv-01

Abstract

   The BGP Monitoring Protocol (BMP) provides an interface for obtaining
   BGP Path information.  BGP Path Information is conveyed within BMP
   Route Monitoring (RM) messages.  This document proposes an extension
   to BMP to convey the status of a path after being processed by the
   BGP process.  This extension makes use of the TLV mechanims described
   in draft-ietf-grow-bmp-tlv [I-D.ietf-grow-bmp-tlv] and
   draft-ietf-grow-bmp-tlv-ebit [I-D.ietf-grow-bmp-tlv-ebit].

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 RFC 2119 [RFC2119] RFC 8174 [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."

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   This Internet-Draft will expire on 19 September 2024.

Copyright Notice

   Copyright (c) 2024 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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Path Status TLV . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  IANA-registered Path Status TLV . . . . . . . . . . . . .   3
     2.2.  Enterprise-specific Path Status TLV . . . . . . . . . . .   6
   3.  Implementation notes  . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Configuration of BMP path marking . . . . . . . . . . . .   7
     3.2.  Paths with no markings  . . . . . . . . . . . . . . . . .   7
     3.3.  Significance of status and origin RIBs  . . . . . . . . .   7
     3.4.  Enterprise-specific status and reasons  . . . . . . . . .   8
     3.5.  Multiple TLVs assigned to the same route. . . . . . . . .   8
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   For a given prefix, multiple paths with different path status, e.g.,
   the "best-path", "back-up path", "invalid", and so on, may co-exist
   in the BGP RIBs after being processed by the BGP decision process.
   The path status information is currently not carried in the BGP
   Update Message RFC4271 [RFC4271] or in the BMP Update Message RFC7854
   [RFC7854].

   External systems can use the path status for various applications.
   The path status is commonly checked by operators when performing
   troubleshooting.  Having such status stored in a centralized system
   can enable the development of tools that facilitate this process.
   Optimisation systems can include the path status in their process,

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   and also use the status as a validation source (since it can compare
   the calculated state to the actual outcome of the network, such as
   primary and backup path).  As a final example, path status
   information can complement other centralized sources of data, for
   example, flow collectors.

   This document defines a so-called Path Status TLV to convey the BGP
   path status to the BMP server.  The BMP Path Status TLV is carried in
   the BMP Route Monitoring (RM) Message.

2.  Path Status TLV

   This document defines two types of Path Status TLVs: one is the IANA-
   registered Path Status TLV, and the other is the Enterprise-specific
   Path Status TLV.

2.1.  IANA-registered Path Status TLV

      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
     +-------------------------------+-------------------------------+
     |E|       Type (15 bits)        |       Length (2 octets)       |
     +---------------------------------------------------------------+
     |        Index (2 octets)       |
     +-------------------------------+-------------------------------+
     |                      Path Status (4 octets)                   |
     +---------------------------------------------------------------+
     |                 Reason Code (2 octets, optional)              |
     +---------------------------------------------------------------+

         Figure 2: Encoding of IANA-Registered Path Status TLV

   *  E bit: For an IANA-registered TLV, the E bit MUST be set to 0
      [I-D.ietf-grow-bmp-tlv-ebit].

   *  Type = TBD2 (15 Bits): indicates that it is the IANA-registered
      Path Status TLV.

   *  Length (2 Octets): indicates the length of the value field of the
      Path Status TLV.  The value field further consists of the Path-
      Status field and Reason Code field.

   *  Index (2 Octets): indicates the prefix that this TLV is
      describing.  Please see [I-D.ietf-grow-bmp-tlv] for details of the
      use of the index field to associate the path marking content with
      one or more NLRIs.

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   *  Path Status (4 Octets): indicates the path status of the BGP
      Update PDU encapsulated in the RM Message.  Currently 10 types of
      path status are defined, as shown in Table 1.  All zeros are
      reserved.

   *  Reason Code (2 Octets, optional): indicates the reason of the path
      status indicated in the Path Status field.  The reason code field
      is optional.  If no reason code is carried, this field is empty.
      If a reason code is carried, the reason code is indicated by a
      2-byte value, which is defined in Table 2.

               +------------+-----------------------------+
               | Value      | Path type                   |
               +------------------------------------------+
               | 0x00000001 | Invalid                     |
               | 0x00000002 | Best                        |
               | 0x00000004 | Non-selected                |
               | 0x00000008 | Primary                     |
               | 0x00000010 | Backup                      |
               | 0x00000020 | Non-installed               |
               | 0x00000040 | Best-external               |
               | 0x00000080 | Add-Path                    |
               | 0x00000100 | Filtered in inbound policy  |
               | 0x00000200 | Filtered in outbound policy |
               | 0x00000400 | Invalid ROV                 |
               | 0x00000800 | Stale                       |
               | 0x00001000 | Suppressed                  |
               +------------+-----------------------------+

               Table 1: IANA-Registered Path Type

                                  Figure 1

   The Path Status field contains a bitmap where each bit encodes a
   specific role of the path.  Multiple bits may be set when multiple
   path status apply to a path.

   *  The best-path is defined in RFC4271 [RFC4271] and the best-
      external path is defined in draft-ietf-idr-best-external
      [I-D.ietf-idr-best-external].

   *  An invalid path is a route that does not enter the BGP decision
      process.

   *  A non-selected path is a route that is not selected in the BGP
      decision process.  Back-up routes are considered non-selected,
      while the best and ECMP routes are not considered as non-selected.

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   *  A primary path is a recursive or non-recursive path whose nexthop
      resolution ends with an adjacency draft-ietf-rtgwg-bgp-pic
      [I-D.ietf-rtgwg-bgp-pic].  A prefix can have more than one primary
      path if multipath is configured
      draft-lapukhov-bgp-ecmp-considerations
      [I-D.lapukhov-bgp-ecmp-considerations].  A best-path is also
      considered as a primary path.

   *  A backup path is also installed in the RIB, but it is not used
      until some or all primary paths become unreachable.  Backup paths
      are used for fast convergence in the event of failures.

   *  A non-installed path refers to the route that is not installed
      into the IP routing table.

   *  For the advertisement of multiple paths for the same address
      prefix without the new paths implicitly replacing any previous
      ones, the add-path status is applied [RFC7911].

   *  Stale refers to a path which has been declared stale by the BGP
      Graceful Restart mechanism as described in Section 4.1 of
      [RFC4724].

   *  Suppressed refers to a path which has been declared suppressed by
      the BGP Route Flap Damping mechanism as described in Section 2.2
      of [RFC2439].

   The path status TLV does not force a BMP client to send any of these
   paths.  It just provides a method to mark the paths that are
   available with their status.

    +----------+-----------------------------------------------------+
    |   Value  | Reason code                                         |
    +----------------------------------------------------------------+
    | [0x0001] | invalid for AS loop                                 |
    | [0x0002] | invalid for unresolvable nexthop                    |
    | [0x0003] | not preferred for Local preference                  |
    | [0x0004] | not preferred for AS Path Length                    |
    | [0x0005] | not preferred for origin                            |
    | [0x0006] | not preferred for MED                               |
    | [0x0007] | not preferred for peer type                         |
    | [0x0008] | not preferred for IGP cost                          |
    | [0x0009] | not preferred for router ID                         |
    | [0x000A] | not preferred for peer address                      |
    | [0x000B] | not preferred for AIGP                              |
    +----------+-----------------------------------------------------+

                   Table 2: IANA-Registered Reason Code

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                                  Figure 2

2.2.  Enterprise-specific Path Status TLV

    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
   +-------------------------------+-------------------------------+
   |E|       Type (15 bits)        |       Length (2 octets)       |
   +-------------------------------+-------------------------------+
   |                      PEN number (4 octets)                    |
   +---------------------------------------------------------------+
   |        Index (2 octets)       |
   +---------------------------------------------------------------+
   |                      Path Status (4 octets)                   |
   +---------------------------------------------------------------+
   |               Reason Code (2 octets, optional)                |
   +---------------------------------------------------------------+

      Figure 3: Encoding of Enterprise-specific Path Status TLV

   *  E bit: For an Enterprise-specific TLV, the E bit MUST be set to 1
      [I-D.ietf-grow-bmp-tlv-ebit].

   *  Type = 1 (15 Bits): indicates that it's the Enterprise-specific
      Path Status TLV.

   *  Length (2 Octets): indicates the length of the value field of the
      Path Status TLV.  The value field further consists of the Path-
      Status field and Reason Code field.

   *  Index (2 Octets): indicates the prefix that this TLV is
      describing.  The index is the encapsulation order, starting from
      0, of the prefix in the BGP Update PDU.

   *  PEN Number (4 octets): indicates the IANA enterprise number IANA-
      PEN.

   *  Path Status (4 Octets): indicates the enterprise-specific path
      status.  The format is to be determined w.r.t. each PEN number.

   *  Reason Code (2 octets, optional): indicates the reasons/
      explanations of the path status indicated in the Path Status
      field.  The format is to be determined w.r.t. each PEN number.

3.  Implementation notes

   The BMP path marking TLV remains optional within BMP implementations.

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   An implementation of the BMP path marking TLV may not fully support
   marking of all status defined in table Figure 1 or any future
   extensions.  Similarly, an implementation may choose to support the
   inclusion of the reason code (for which support is also optional),
   without necessarily incorporating any of the reason codes defined in
   table Figure 2 or future extensions.

   This document refrains from defining mechanisms for signaling the
   status or reason codes an implementation supports.  This could be
   established through external means (e.g. documentation) or
   potentially addressed in a subsequent document.

   The remainder of this section encompasses additional points related
   to the implementation of the BMP Path marking TLV.

3.1.  Configuration of BMP path marking

   Implementations supporting the BMP path marking TLV SHOULD provide an
   option for enabling or disabling the Path Marking TLV over BMP
   sessions.  Furthermore, the configuration options for this TLV SHOULD
   provide the means to enable and disable the transmission of reason
   codes, if the reason code are supported by the implementation.

3.2.  Paths with no markings

   Some BGP routes might not require any type of status or reasons.  For
   example, an unfiltered path obtained via the Adj-RIB-IN may fall
   under this category since there is really nothing to mark for that
   path.  We suggest a couple of approaches for signaling that a path
   has no markings: (1) An implicit form of marking, achieved by
   abstaining from appending any BMP marking TLV pointing toward the
   route. (2) Alternatively, an explicit marking of the packet through a
   TLV containing no marked status and no associated reason code.

3.3.  Significance of status and origin RIBs

   This document refrains from imposing any implementation to mark
   specific status from specific RIBs.  We recognize the diversity among
   implementations; some might be able to mark some status over one RIB
   while other do it on others.  For instance, some might be able to
   mark Adj-RIB-in filtered routes when obtained from the Adj-RIB-IN
   pre, while other could do it only from the Adj-RIB-IN post.  To
   remove ambiguities in implementations, we recommend the meaning of
   status (and reason codes) to not depend on the origin RIB of a route.

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3.4.  Enterprise-specific status and reasons

   Implementations introducing their own status and reason codes are
   advised to adhere to [I-D.ietf-grow-bmp-tlv-ebit] and use ebit and
   vendor specific status and reasons.  Additionally, we recommend all
   implementations to provide comprehensive documentation for these
   codes.

   For scenarios where a path state combines a standard status with an
   enterprise-specific reason code (or vice versa), the following
   alternatives are presented:

   *  Replication of the standard definitions within the enterprise-
      specific space, thus permitting direct marking within the same
      packet using the ebit.
   *  Assigning two TLVs to the same path(s): one containing the
      standard part and another housing the vendor-specific part.

3.5.  Multiple TLVs assigned to the same route.

   We advocate for the employment of TLV grouping wherever feasible.
   The inclusion of all marking information within a single message is
   recommended, except on the case described in section Section 3.4.  In
   situations where multiple TLVs are associated with a single route,
   all markings will be applicable to that route.

4.  Acknowledgments

   We would like to thank Jeff Haas and Maxence Younsi for their
   valuable comments.

5.  IANA Considerations

   This document requests that IANA assign the following new parameters
   to the BMP parameters name space.

   Type = TBD1 (15 Bits): indicates that it is the IANA-registered Path
   Status TLV.

6.  Security Considerations

   It is not believed that this document adds any additional security
   considerations.

7.  Normative References

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   [I-D.ietf-grow-bmp-tlv]
              Lucente, P. and Y. Gu, "BMP v4: TLV support for BMP Route
              Monitoring and Peer Down Messages", Work in Progress,
              Internet-Draft, draft-ietf-grow-bmp-tlv-13, 23 October
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              grow-bmp-tlv-13>.

   [I-D.ietf-grow-bmp-tlv-ebit]
              Lucente, P. and Y. Gu, "Support for Enterprise-specific
              TLVs in the BGP Monitoring Protocol", Work in Progress,
              Internet-Draft, draft-ietf-grow-bmp-tlv-ebit-04, 23
              October 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-grow-bmp-tlv-ebit-04>.

   [I-D.ietf-idr-best-external]
              Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
              Gredler, "Advertisement of the best external route in
              BGP", Work in Progress, Internet-Draft, draft-ietf-idr-
              best-external-05, 3 January 2012,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-
              best-external-05>.

   [I-D.ietf-rtgwg-bgp-pic]
              Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
              Independent Convergence", Work in Progress, Internet-
              Draft, draft-ietf-rtgwg-bgp-pic-20, 1 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
              bgp-pic-20>.

   [I-D.lapukhov-bgp-ecmp-considerations]
              Lapukhov, P. and J. Tantsura, "Equal-Cost Multipath
              Considerations for BGP", Work in Progress, Internet-Draft,
              draft-lapukhov-bgp-ecmp-considerations-12, 28 December
              2023, <https://datatracker.ietf.org/doc/html/draft-
              lapukhov-bgp-ecmp-considerations-12>.

   [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>.

   [RFC2439]  Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
              Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November
              1998, <https://www.rfc-editor.org/info/rfc2439>.

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   [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,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
              Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
              DOI 10.17487/RFC4724, January 2007,
              <https://www.rfc-editor.org/info/rfc4724>.

   [RFC7854]  Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
              Monitoring Protocol (BMP)", RFC 7854,
              DOI 10.17487/RFC7854, June 2016,
              <https://www.rfc-editor.org/info/rfc7854>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [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>.

Authors' Addresses

   Camilo Cardona
   NTT
   164-168, Carrer de Numancia
   08029 Barcelona
   Spain
   Email: camilo@ntt.net

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

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

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   Yunan Gu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: guyunan@huawei.com

   Thomas Graf
   Swisscom
   Binzring 17
   CH-8045 Zurich
   Switzerland
   Email: thomas.graf@swisscom.com

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