



Network Working Group                                         C. Cardona
Internet-Draft                                                P. Lucente
Intended status: Standards Track                                     NTT
Expires: 16 November 2026                                    P. Francois
                                                               INSA-Lyon
                                                                   Y. Gu
                                                                  Huawei
                                                                 T. Graf
                                                                Swisscom
                                                             15 May 2026


                   BMP Extension for Path Status TLV
                draft-ietf-grow-bmp-path-marking-tlv-05

Abstract

   The BGP Monitoring Protocol (BMP) provides an interface for obtaining
   BGP path information, which is conveyed through BMP Route Monitoring
   (RM) messages.  This document specifies a BMP extension to convey the
   status of a path after being processed by the BGP process.

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 [RFC2119] and RFC8174 [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 16 November 2026.





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Copyright Notice

   Copyright (c) 2026 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Path Status TLV encoding  . . . . . . . . . . . . . . . . . .   3
   3.  IANA encoding of Path Status TLV  . . . . . . . . . . . . . .   4
     3.1.  IANA path status codes  . . . . . . . . . . . . . . . . .   4
     3.2.  IANA reason codes . . . . . . . . . . . . . . . . . . . .   6
   4.  Path Marking Statistics . . . . . . . . . . . . . . . . . . .   7
     4.1.  Per-Status Counters . . . . . . . . . . . . . . . . . . .   7
     4.2.  Generic Path Status Counters  . . . . . . . . . . . . . .   8
   5.  Implementation notes  . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Configuration of BMP Path Marking . . . . . . . . . . . .   9
     5.2.  Scalability and churn . . . . . . . . . . . . . . . . . .   9
     5.3.  Paths with no markings  . . . . . . . . . . . . . . . . .   9
     5.4.  Path markings applicability and consistency . . . . . . .  10
       5.4.1.  Significance of status and origin RIBs  . . . . . . .  10
     5.5.  Multiple TLVs assigned to the same route. . . . . . . . .  10
     5.6.  Enterprise-specific status  . . . . . . . . . . . . . . .  10
     5.7.  Multiple reason codes . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Implementation Status  . . . . . . . . . . . . . . .  15
     A.1.  Huawei VRP NE8000 . . . . . . . . . . . . . . . . . . . .  15
     A.2.  pmacct BMP Collector  . . . . . . . . . . . . . . . . . .  15
     A.3.  NetGauze and Wireshark Decoders . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16







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1.  Introduction

   Multiple paths with different path statuses (e.g., the "best path",
   "backup path", "invalid", and so on) may co-exist for a given prefix
   in the BGP RIBs after being processed by the BGP decision process.
   The path status information is not carried in the BGP UPDATE Message
   [RFC4271] or in the BMP Route Monitoring Message [RFC7854].

   External systems can use the path status for various applications.
   For example, operators commonly use path status during
   troubleshooting.  Having such status stored and tracked enables the
   development of tools that facilitate this process.  Optimization
   systems can consider path status in their process, e.g., as a
   validation source (since it can compare the calculated state to the
   actual outcome of the network, such as primary and backup path).
   Moreover, path status information can complement other centralized
   sources of data.  For example, flow collectors can leverage it to
   identify the exact forwarding paths, yielding more accurate traffic
   matrices than existing methods.

   This document defines a Path Status TLV to convey the BGP path status
   to a BMP server.  The BMP Path Status TLV is carried in the BMP Route
   Monitoring (RM) Message [RFC7854].

2.  Path Status TLV encoding

   The path status TLV follows the common header defined in
   [I-D.ietf-grow-bmp-tlv] and [I-D.ietf-grow-bmp-tlv-ebit].

      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
     +-------------------------------+-------------------------------+
     |            Common TLV Header (Variable bits)                  |
     +---------------------------------------------------------------+
     |                      Path Status (4 octets)                   |
     +---------------------------------------------------------------+
     | Reason Code (2 oct., opt.)    |
     +-------------------------------+

         Figure 2: Encoding of Path Status TLV

   *  The common TLV header that can encode IANA-registered TLV or
      Enterprise-specific markings using [I-D.ietf-grow-bmp-tlv-ebit].









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   *  Path Status (4 Octets): indicates the path status of the BGP
      Update PDU encapsulated in the RM Message.  The path status is
      encoded using a bitmap where each bit position encodes a specific
      role of the path.  Multiple bits may be set when multiple path
      statuses apply to a path.  All zeros are reserved for paths with
      no marking.

   *  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 not
      included.  If a reason code is carried, the reason code is
      indicated by a two-byte value.

3.  IANA encoding of Path Status TLV

3.1.  IANA path status codes

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

                   Table 1: IANA-Registered Path Status





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   Table 1 includes a list of IANA status codes.  This list might be
   extended.  An explanation of each of the types is included next:

   *  An invalid route is a route that does not enter the BGP decision
      process as indicated in Section 9.1.2 of RFC4271 [RFC4271].

   *  The best route is defined in Section 9.1 of RFC4271 [RFC4271].

   *  Nonselected routes are those that are not selected in the BGP
      decision process.  Backup routes are considered nonselected, while
      the best and primary routes are not considered as nonselected.

   *  A primary route is a path used for traffic forwarding.  See
      draft-ietf-rtgwg-bgp-pic [I-D.ietf-rtgwg-bgp-pic].  A prefix can
      have more than one primary path when multipath is configured
      draft-lapukhov-bgp-ecmp-considerations
      [I-D.lapukhov-bgp-ecmp-considerations].  The best path is also a
      primary path.

   *  A backup path is 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 primary path failures.

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

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

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

   *  Filtered in inbound policy routes are those that are filtered in
      the Adj-RIB-In policy.

   *  Filtered in outbound policy routes are those that are filtered in
      the Adj-RIB-Out policy.

   *  Stale routes refer to paths which have been declared stale by the
      BGP Graceful Restart mechanism, as described in Section 4.1 of
      [RFC4724].

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





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3.2.  IANA reason codes

   Table 2 includes a list of IANA reason codes.  This list can be
   extended in future documents.  This document includes a brief
   explanation of each code and the path status they are intended to
   explain.  Please see Section 5.4 for notes on potentially
   inconsistencies in the path marking data.

   *  Invalid routes due to AS loop and unresolvable nexthop are defined
      in Section 9.1.2 of [RFC4271].  These codes target routes of type
      "Invalid".

   *  The reason codes starting with 'not preferred' are aimed at paths
      not selected as best, and describe the reason they were ranked
      lower in the decision process.  AIGP is explained in RFC7311
      [RFC7311].  The rest of the codes are described in Section 9.1.2.2
      of [RFC4271].

             +========+=====================================+
             | Value  | Reason Code                         |
             +========+=====================================+
             | 0x0001 | Invalid due to AS loop              |
             +--------+-------------------------------------+
             | 0x0002 | Invalid due to 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 Codes






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4.  Path Marking Statistics

   This section defines statistics to account and summarize Path Status
   TLV in the BGP Local-RIB.  The statistics specified in this section
   are exported by BMP speakers using the Stats Reports message type
   defined in Section 4.8 of [RFC7854].

   Unless otherwise stated, all counters defined in this section are
   unsigned 64-bit integers.  Counters are maintained per BMP session
   and per monitored peer.  The reset behavior of these counters (for
   example, upon BMP session restart or operator-triggered reset)
   follows the general semantics of BMP Stats Reports as defined in
   RFC7854 [RFC7854].

4.1.  Per-Status Counters

   For each IANA-registered Path Status bit defined in Table 1, an
   implementation SHOULD maintain a counter that reflects the number of
   paths currently marked with that status.  These counters are
   conceptually similar to the per-status gauges defined for primary,
   backup, stale, and suppressed routes in the BMP RIB statistics
   document [I-D.ietf-grow-bmp-bgp-rib-stats].

   The following counters are defined:

   *  Type = TBD1: Current number of paths for which the Path Status TLV
      has the Invalid status bit set.

   *  Type = TBD2: Current number of paths for which the Path Status TLV
      has the Best status bit set.

   *  Type = TBD3: Current number of paths for which the Path Status TLV
      has the Nonselected status bit set.

   *  Type = TBD4: Current number of paths for which the Path Status TLV
      has the Primary status bit set.

   *  Type = TBD5: Current number of paths for which the Path Status TLV
      has the Backup status bit set.

   *  Type = TBD6: Current number of paths for which the Path Status TLV
      has the Non-installed status bit set.

   *  Type = TBD7: Current number of paths for which the Path Status TLV
      has the Best-external status bit set.

   *  Type = TBD8: Current number of paths for which the Path Status TLV
      has the Add-Path status bit set.



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   *  Type = TBD9: Current number of paths for which the Path Status TLV
      has the Filtered in inbound policy status bit set.

   *  Type = TBD10: Current number of paths for which the Path Status
      TLV has the Filtered in outbound policy status bit set.

   *  Type = TBD11: Current number of paths for which the Path Status
      TLV has the Stale status bit set.

   *  Type = TBD12: Current number of paths for which the Path Status
      TLV has the Suppressed status bit set.

   Since the Path Status field is encoded as a bitmap, multiple status
   bits can be set for a single path.  The corresponding per-status
   counters are incremented independently; that is, a single path may
   contribute to more than one per-status counter.

4.2.  Generic Path Status Counters

   In addition to the per-status counters defined above, the following
   generic counters MAY be maintained by a BMP implementation:

   *  Type = TBD13: Current number of paths that carry a Path Status TLV
      with at least one status bit set (that is, paths that are
      explicitly marked).

   *  Type = TBD14: Current number of paths that either do not carry a
      Path Status TLV or carry a Path Status TLV with all bits set to
      zero.

5.  Implementation notes

   The BMP path marking TLV remains optional within BMP implementations.

   An implementation of the BMP path marking TLV may not fully support
   marking of all statuses defined in Table 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 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 covers additional points related to the
   implementation of the BMP Path Marking TLV.



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5.1.  Configuration of BMP Path Marking

   Implementations supporting the BMP Path Marking TLV should provide an
   option for enabling/disabling the Path Marking TLV over BMP
   monitoring sessions.  Furthermore, the configuration options for this
   TLV should provide the means to enable/disable the transmission of
   reason codes, if the reason codes are supported by the
   implementation.

5.2.  Scalability and churn

   The Path Marking TLV introduces metadata on the routes, which could
   increase the churn (Section 8.1.6 of RFC4098 [RFC4098]) of paths
   within the BMP session.  For instance, if BMP Path Marking is
   configured, and a non-installed path changes status to a backup
   route, the device should send an update about this path with the new
   markings, even if its BGP attributes remain unchanged.  Enabling
   reason codes could additionally increase the churn.  Churn could be
   more pronounced during the start of a BGP session, where the device
   is processing all available routes.

   If churn is undesired, an implementation could make use of "state
   compression" to hide state until paths converge (Section 5 of
   [RFC7854]).  It could also initially send BMP routes without the path
   marking TLV, even if it were configured, and then add them once the
   implementation considers the path to be stable enough.  This document
   does not provide a definitive solution for churn since it depends on
   the capabilities of an implementation and the requirements of an
   operator.

5.3.  Paths with no markings

   Some BGP routes might not require any type of status or reasons.  For
   example, a path in Adj-RIB-In where the BGP best path decision has
   not been applied yet, falls under this category, since there is
   really nothing to mark for that path.  This document suggests
   applying an explicit marking of this route, by attaching a BMP path
   marking TLV with no bits set.  This will help BMP monitor stations to
   differentiate this case from those in which markings are not
   configured, or not yet attached by the device.











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5.4.  Path markings applicability and consistency

   The status and reason codes from Table 1 and Table 2 are included
   based on use cases from network operators and defined following the
   most relevant protocol references available.  While implementations
   are strongly encouraged to align with these code definitions, this
   document does not enforce strict validity rules for code combinations
   to accommodate the diversity of BGP implementations.

   The experience during testing of this TLV revealed scenarios where
   implementations might combine codes differently than originally
   anticipated.  For example, one test implementation marked routes with
   both 'Invalid' and 'Best' status bits set, which is contradictory
   from the point of view of [RFC4271], but made sense for their
   specific implementation.

   Operators should apply their own validation checks on the data from
   TLVs and discuss potential inconsistencies with their vendors, and
   raise bugs if applicable.

5.4.1.  Significance of status and origin RIBs

   This document refrains from imposing on any implementation the
   requirement to mark specific status from specific RIBs.  Some
   implementations might be able to mark some status over one RIB while
   others 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-
   policy, while others could do it only from the Adj-RIB-In post-
   policy.  To remove ambiguities in implementations, it is recommended
   that the meaning of status (and reason codes) does not depend on the
   origin RIB of a route.

5.5.  Multiple TLVs assigned to the same route.

   We advocate for the use of TLV grouping wherever feasible
   (Section 5.2.1 of [I-D.ietf-grow-bmp-tlv]).  The inclusion of all
   marking information within a single message is recommended.  In
   situations where multiple TLVs are associated with a single route,
   all markings and reasons will be applicable to that route.

5.6.  Enterprise-specific status

   Implementations introducing their own status and reason codes are
   advised to adhere to [I-D.ietf-grow-bmp-tlv-ebit] and use the
   enterprise-bit (ebit) for vendor-specific status and reasons.






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   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.

5.7.  Multiple reason codes

   The path marking TLV was not designed to optimally hold more than one
   reason code per path.  However, if needed by a specific use case, the
   implementation can use two or more path markings TLVs for the same
   path listing the multiple reasons that apply to it.

6.  Acknowledgments

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

7.  IANA Considerations

   This document requests that IANA assign the following new TLV type to
   the BMP Route Monitoring TLVs.

   Type = 5: indicates that this is the IANA-registered Path marking
   TLV.  The value field is defined in Section 2.

   RFC Editor and IANA registry note: The registry is created with
   Section 10 of [I-D.ietf-grow-bmp-tlv] and populated with initial
   values 1-4.  This document adds value 5 to the registry.  Please
   remove this sentence before publishing the document as RFC.

   In addition, this document requests IANA to assign new statistic
   types in the BMP Statistics Types (https://www.iana.org/assignments/
   bmp-parameters/bmp-parameters.xhtml#statistics-types) registry, part
   of the BMP parameters (https://www.iana.org/assignments/bmp-
   parameters/bmp-parameters.xhtml) registry group, for the Path Marking
   Statistics defined in Section 4.

   Unless otherwise stated, all statistics defined below are 64-bit
   unsigned integer gauges whose Stat Data value field and Stat Length
   follow the rules defined in Section 4.8 of [RFC7854].





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   This document requests IANA to assign the following new BMP
   Statistics Types and to update the registry to reference the RFC
   number of this document:

   *  Type TBD1: Current number of paths for which the Path Status TLV
      has the Invalid status bit set.

   *  Type TBD2: Current number of paths for which the Path Status TLV
      has the Best status bit set.

   *  Type TBD3: Current number of paths for which the Path Status TLV
      has the Nonselected status bit set.

   *  Type TBD4: Current number of paths for which the Path Status TLV
      has the Primary status bit set.

   *  Type TBD5: Current number of paths for which the Path Status TLV
      has the Backup status bit set.

   *  Type TBD6: Current number of paths for which the Path Status TLV
      has the Non-installed status bit set.

   *  Type TBD7: Current number of paths for which the Path Status TLV
      has the Best-external status bit set.

   *  Type TBD8: Current number of paths for which the Path Status TLV
      has the Add-Path status bit set.

   *  Type TBD9: Current number of paths for which the Path Status TLV
      has the Filtered in inbound policy status bit set.

   *  Type TBD10: Current number of paths for which the Path Status TLV
      has the Filtered in outbound policy status bit set.

   *  Type TBD11: Current number of paths for which the Path Status TLV
      has the Stale status bit set.

   *  Type TBD12: Current number of paths for which the Path Status TLV
      has the Suppressed status bit set.

   *  Type TBD13: Current number of paths that carry a Path Status TLV
      with at least one status bit set (paths that are explicitly
      marked).

   *  Type TBD14: Current number of paths that either do not carry a
      Path Status TLV or carry a Path Status TLV with all bits set to
      zero.




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8.  Security Considerations

   Using the path status information may affect other applications which
   rely on this information for operational decisions.  Operators should
   secure BMP sessions and control access to TLV data to mitigate these
   risks.

9.  References

9.1.  Normative References

   [I-D.ietf-grow-bmp-bgp-rib-stats]
              Srivastava, M., Liu, Y., Lin, C., and J. Li, "Advanced BGP
              Monitoring Protocol (BMP) Statistics Types", Work in
              Progress, Internet-Draft, draft-ietf-grow-bmp-bgp-rib-
              stats-17, 3 December 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-grow-
              bmp-bgp-rib-stats-17>.

   [I-D.ietf-grow-bmp-tlv]
              Lucente, P., Gu, Y., Younsi, M., and P. Francois, "BMP v4:
              Extended TLV Support for BGP Monitoring Protocol (BMP)",
              Work in Progress, Internet-Draft, draft-ietf-grow-bmp-tlv-
              20, 2 March 2026, <https://datatracker.ietf.org/doc/html/
              draft-ietf-grow-bmp-tlv-20>.

   [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-06, 17
              January 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-grow-bmp-tlv-ebit-06>.

   [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>.

   [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>.





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   [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>.

   [RFC7311]  Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
              "The Accumulated IGP Metric Attribute for BGP", RFC 7311,
              DOI 10.17487/RFC7311, August 2014,
              <https://www.rfc-editor.org/info/rfc7311>.

   [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>.

9.2.  Informative References

   [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., Mohapatra, P., and Y. Qu, "BGP
              Prefix Independent Convergence", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-bgp-pic-23, 15 February
              2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
              rtgwg-bgp-pic-23>.

   [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-13, 6 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-lapukhov-bgp-
              ecmp-considerations-13>.




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   [RFC4098]  Berkowitz, H., Davies, E., Ed., Hares, S., Krishnaswamy,
              P., and M. Lepp, "Terminology for Benchmarking BGP Device
              Convergence in the Control Plane", RFC 4098,
              DOI 10.17487/RFC4098, June 2005,
              <https://www.rfc-editor.org/info/rfc4098>.

Appendix A.  Implementation Status

   Note to the Editor: Please remove this section before publication.

   This section records the status of known implementations of the BMP
   Path Marking TLV specified in this document.  The information is
   based on interoperability and testbed activities, including the
   Swisscom IETF Daisy testbed, and is intended to help reviewers and
   operators understand current implementation and deployment status.
   This section is non-normative.

A.1.  Huawei VRP NE8000

   Huawei implemented the BMP Path Marking TLV, including Path Status
   and Path Reason, on NE8000 platforms running VRP R025C00SPC305T and
   subsequent R025C10 test images.

   The implementation exports Path Marking information in BMP Route
   Monitoring messages for IPv4 and IPv6 unicast, as well as VPNv4 and
   VPNv6 Local-RIB.  Support includes ADD-PATH and VPN peer
   distinguishers.

   In the test environment, BMP sessions were established from NE8000
   PEs to a collector and configured to monitor Adj-RIB-In and Adj-RIB-
   Out, both pre-policy and post-policy, as well as VPNv4 and VPNv6
   Local-RIB across multiple VRF instances.

   The implementation was exercised against a set of path selection
   scenarios, including best path, backup path, non-installed paths, and
   policy-filtered paths.  The exported Path Status bits, such as Best,
   Nonselected, Primary, Backup, and Non-installed, and the
   corresponding Path Reason codes, for example not preferred due to
   local preference or router ID, were verified against the
   corresponding VRF RIB and BGP routing state.

A.2.  pmacct BMP Collector

   The BMP collector used in the implementation is pmacct with support
   for the Path Marking TLVs as defined in this document.






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   The implementation includes updates to align TLV type and value
   handling with the current draft, as well as changes to the TLV
   parsing logic to correctly process Path Status and Path Reason
   information in BMP Route Monitoring messages.

   In the implementation tests, the collector is configured to receive
   BMP sessions and export decoded data as JSON logs, including Path
   Marking TLVs where available.  This allows comparison between the BGP
   path state observed on the NE8000, for example best, backup, non-
   installed, or policy-filtered, and the corresponding BMP-exported
   Path Status and Reason values.

A.3.  NetGauze and Wireshark Decoders

   NetGauze is used as an independent BMP decoder to validate the
   encoding of Path Marking TLVs.  Updates were made to improve BMPv4
   support, including handling of ADD-PATH for IPv4/IPv6 MPLS unicast,
   Loc-RIB Peer Up messages, and general BMP message parsing.  These
   changes help decode and inspect Route Monitoring messages carrying
   Path Status and Path Reason TLVs.

   Wireshark nightly builds are used to inspect BMP Route Monitoring
   messages and verify the presence and decoding of Path Marking TLVs,
   including VPN peer distinguishers and SAFI-specific updates.
   Improvements in BMP TLV and Group TLV decoding help inspect VRF
   context and associated path-marking information.

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








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


   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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