draft-ietf-grow-bmp-path-marking-tlv.xml

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<rfc category="std" docName="draft-ietf-grow-bmp-path-marking-tlv-latest"
     ipr="trust200902">
  <front>
    <title abbrev="BMP path status tlv">BMP Extension for Path Status
    TLV</title>

    <author fullname="Camilo Cardona" initials="C." surname="Cardona">
      <organization>NTT</organization>

      <address>
        <postal>
          <street>164-168, Carrer de Numancia</street>

          <city>Barcelona</city>

          <code>08029</code>

          <country>Spain</country>
        </postal>

        <email>camilo@ntt.net</email>
      </address>
    </author>

    <author fullname="Paolo Lucente" initials="P." surname="Lucente">
      <organization>NTT</organization>

      <address>
        <postal>
          <street>Siriusdreef 70-72</street>

          <city>Hoofddorp</city>

          <region>WT</region>

          <code>2132</code>

          <country>Netherlands</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>paolo@ntt.net</email>

        <uri/>
      </address>
    </author>

    <author fullname="Pierre Francois" initials="P." surname="Francois">
      <organization>INSA-Lyon</organization>

      <address>
        <postal>
          <street/>

          <city>Lyon</city>

          <code/>

          <country>France</country>
        </postal>

        <email>Pierre.Francois@insa-lyon.fr</email>
      </address>
    </author>

    <author fullname="Yunan Gu" initials="Y. " surname="Gu">
      <organization>Huawei</organization>

      <address>
        <postal>
          <street>Huawei Bld., No.156 Beiqing Rd.</street>

          <city>Beijing</city>

          <code>100095</code>

          <country>China</country>
        </postal>

        <email>guyunan@huawei.com</email>
      </address>
    </author>

    <author fullname="Thomas Graf" initials="T. " surname="Graf">
      <organization>Swisscom</organization>

      <address>
        <postal>
          <street>Binzring 17</street>

          <city>Zurich</city>

          <code>8045</code>

          <country>Switzerland</country>
        </postal>

        <email>thomas.graf@swisscom.com</email>
      </address>
    </author>

    <date day="16" month="September" year="2024"/>

    <abstract>
      <t>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 <xref
      target="I-D.ietf-grow-bmp-tlv">draft-ietf-grow-bmp-tlv</xref> and <xref
      target="I-D.ietf-grow-bmp-tlv-ebit">draft-ietf-grow-bmp-tlv-ebit</xref>.
      </t>
    </abstract>

    <note title="Requirements Language">
      <t>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
      <xref target="RFC2119">RFC 2119</xref> <xref target="RFC8174">RFC
      8174</xref> when, and only when, they appear in all capitals, as shown
      here.</t>
    </note>
  </front>

  <middle>
    <section title="Introduction">
      <t>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 <xref target="RFC4271">RFC4271</xref> or in the BMP Update
      Message <xref target="RFC7854">RFC7854</xref>.</t>

      <t>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, 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.</t>

      <t>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.</t>
    </section>

    <section title="Path Status TLV">
      <t>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.</t>

      <section title="IANA-registered Path Status TLV">
        <t><figure>
            <artwork align="center"><![CDATA[ 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 ]]></artwork>
          </figure><list style="symbols">
            <t>E bit: For an IANA-registered TLV, the E bit MUST be set to
                0 <xref target="I-D.ietf-grow-bmp-tlv-ebit"/>.</t>

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

            <t>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.</t>

            <t>Index (2 Octets): indicates the prefix that this TLV is describing.
            Please see <xref target="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.</t>

            <t>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.</t>

            <t>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.</t>
          </list><figure anchor="status_codes">
            <artwork align="center"><![CDATA[+------------+-----------------------------+
| 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 ]]></artwork>
          </figure>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.</t>

        <t><list style="symbols">
            <t>The best-path is defined in <xref
            target="RFC4271">RFC4271</xref> and the best-external path is
            defined in <xref
            target="I-D.ietf-idr-best-external">draft-ietf-idr-best-external</xref>.</t>

            <t>An invalid path is a route that does not enter the BGP decision
            process.</t>

            <t>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.</t>

            <t>A primary path is a recursive or non-recursive path whose
            nexthop resolution ends with an adjacency <xref
            target="I-D.ietf-rtgwg-bgp-pic">draft-ietf-rtgwg-bgp-pic</xref>. A
            prefix can have more than one primary path if multipath is
            configured <xref
            target="I-D.lapukhov-bgp-ecmp-considerations">draft-lapukhov-bgp-ecmp-considerations</xref>.
            A best-path is also considered as a primary path.</t>

            <t>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.</t>

            <t>A non-installed path refers to the route that is not installed
            into the IP routing table.</t>

            <t>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 <xref target="RFC7911"/>.</t>

            <t>Stale refers to a path which has been declared stale by the BGP
            Graceful Restart mechanism as described in Section 4.1 of <xref
            target="RFC4724"/>.</t>

            <t>Suppressed refers to a path which has been declared suppressed
            by the BGP Route Flap Damping mechanism as described in Section
            2.2 of <xref target="RFC2439"/>.</t>
          </list>

          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.

<figure anchor="reasons_codes">
            <artwork align="center"><![CDATA[+----------+-----------------------------------------------------+
|   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 ]]></artwork>
          </figure></t>
      </section>

      <section title="Enterprise-specific Path Status TLV">
        <t><figure>
            <artwork><![CDATA[ 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]]></artwork>
          </figure><list style="symbols">
            <t>E bit: For an Enterprise-specific TLV, the E bit MUST be set to
                1 <xref target="I-D.ietf-grow-bmp-tlv-ebit"/>.</t>

            <t>Type = 1 (15 Bits): indicates that it's the Enterprise-specific
            Path Status TLV.</t>

            <t>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.</t>

            <t>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.</t>

            <t>PEN Number (4 octets): indicates the IANA enterprise number
            IANA-PEN.</t>

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

            <t>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.</t>
          </list></t>
      </section>
    </section>

    <section title="Implementation notes">

        <t>The BMP path marking TLV remains optional within BMP
            implementations.</t>

        <t>An implementation of the BMP path marking TLV may not fully support
        marking of all status defined in table <xref target="status_codes"/> 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 <xref target="reasons_codes"/> or future
                extensions.</t>

        <t>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.</t>

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

        <section title="Configuration of BMP path marking">

            <t>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.</t>

        </section>

        <section title="Paths with no markings">

            <t>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.</t>

        </section>

        <section title="Significance of status and origin RIBs">

            <t>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.</t>

        </section>

        <section title="Enterprise-specific status and reasons" anchor="ebit_mixed">

            <t>Implementations introducing their own status and reason codes
            are advised to adhere to <xref
                target="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.</t>

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

            <t> 
                <ul spacing="compact"> 
                    <li>Replication of the standard
            definitions within the enterprise-specific space, thus permitting
                    direct marking within the same packet using the ebit.</li> 
                <li>Assigning two TLVs to the same path(s): one containing the standard
                    part and another housing the vendor-specific part.</li> 
                </ul>
            </t>

        </section>

        <section title="Multiple TLVs assigned to the same route.">

            <t>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 <xref target="ebit_mixed"/>. In situations where
                    multiple TLVs are associated with a single route, all
                    markings will be applicable to that route.</t>

        </section>
    </section>

    <section title="Acknowledgments">
      <t>We would like to thank Jeff Haas and  Maxence Younsi for their
          valuable comments.</t>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This document requests that IANA assign the following new parameters
      to the BMP parameters name space.</t>

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

    <section anchor="Security" title="Security Considerations">
      <t>It is not believed that this document adds any additional security
      considerations.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.2119.xml"?>

      <?rfc include="reference.RFC.8174.xml"?>

      <?rfc include='reference.RFC.4271.xml'?>

      <?rfc include='reference.RFC.7854.xml'?>

      <?rfc include='reference.I-D.ietf-idr-best-external.xml'?>

      <?rfc include='reference.I-D.ietf-grow-bmp-tlv.xml'?>

      <?rfc include='reference.I-D.ietf-rtgwg-bgp-pic.xml'?>

      <?rfc include='reference.I-D.lapukhov-bgp-ecmp-considerations.xml'?>

      <?rfc include='reference.RFC.7911.xml'?>

      <?rfc include='reference.RFC.4724.xml'?>

      <?rfc include='reference.RFC.2439.xml'?>

      <?rfc include='reference.I-D.ietf-grow-bmp-tlv-ebit.xml'?>
    </references>
  </back>
</rfc>