Hi Ketan,
thank you for your detailed review and thoughtful comments. I'll work on
addressing your concerns and will bring proposed updates for the discussion.

Regards,
Greg

On Tue, Jul 16, 2024 at 6:35 PM Ketan Talaulikar <ketant.i...@gmail.com>
wrote:

> Hello All,
>
> Please find below the shepherd review for this document as asked for by
> the chairs.
>
> Thanks,
> Ketan
>
>
> Major:
>
> 1) Alignment to SR Policy [RFC9256] terms is needed (e.g., what is
> monitored is individual SLs instead of "tunnels"). The operations and
> interactions between the SR Policy framework and BFD is required to be
> specified -
> somewhat on similar lines as what RFC5882 did. SR Policy as defined in
> [RFC9256] consists
> of candidate paths which in turn contains one or more segment list. The BFD
> monitoring is done for each individual segment list. When the BFD detects
> that
> a segment list is down, it is considered invalid and taken out from the
> forwarding. When all segment lists in a CP are down, then the CP is down
> and
> another CP path would need to be evaluated. This also means that, when
> enabled, BFD validation augments the CP validation as
> specified in section 5 of RFC9256.
>
> 2) There is no Target FEC stack defined for Segment Lists for SR Policy.
> Something that carries the < Headend, Endpoint, Color, <CP identifiers>, <
> SL
> identifiers/stack> > so that the egress LER can setup a BFD control
> session context
> for each of the segment lists of an SR Policy. Note that the egress LER
> can be
> the endpoint for a large number of SR Policies from multiple headends and
> each
> of these SR Policies can have multiple CPs and in turn multiple SLs. So,
> how
> is LSP Ping able to bootstrap the BFD control session for each of these
> individual SLs on the Egress LER?
>
> Editorial:
>
> a) The document seems to have started as LSP ping bootstrap for SR
> Policies and
> then evolved to include almost all BFD flavors in it. Suggest to fix the
> abstract,
> introduction and the section headings accordingly. The common aspects can
> be
> in their own independent sessions. I have provided some suggestions.
>
> Please find below the detailed review in idnits output
>
> 2 SPRING Working Group                                           G. Mirsky
> 3 Internet-Draft                                                  Ericsson
> 4 Intended status: Experimental                                J. Tantsura
> 5 Expires: 19 October 2024                                           NVDIA
> 6                                                           I. Varlashkin
> 7                                                                  Google
> 8                                                                 M. Chen
> 9                                                                  Huawei
> 10                                                              J. Wenying
> 11                                                                    CMCC
> 12                                                           17 April 2024
>
> 14  Bidirectional Forwarding Detection (BFD) in Segment Routing Networks
> 15                          Using MPLS Dataplane
>
> < major > The title should be corrected as BFD for SR Policies ?
>
> 16                        draft-ietf-spring-bfd-10
>
> 18 Abstract
>
> 20   Segment Routing (SR) architecture leverages the paradigm of source
> 21   routing.  It can be realized in the Multiprotocol Label Switching
> 22   (MPLS) network without any change to the data plane.  A segment is
> 23   encoded as an MPLS label, and an ordered list of segments is encoded
> 24   as a stack of labels.  Bidirectional Forwarding Detection (BFD) is
> 25   expected to monitor any existing path between systems.  This document
> 26   defines how to use Label Switched Path (LSP) Ping to bootstrap a BFD
> 27   session, optional control of the selection of a segment list as the
> 28   reverse direction of the BFD session, applicability of BFD Demand
> 29   mode, and Seamless BFD in the SR-MPLS domain.  Also, the document
> 30   describes the use of the BFD Echo function with the BFD Control
> 31   packet payload.
>
> < editorial > Please consider breaking down or rephrasing the last two
> sentences in the abstract for better readability. Perhaps something on the
> lines of ... This document describes the use of BFD for monitoring
> individual
> segment lists of candidate paths of an SR Policy. It documents the
> use of various BFD flavors and features such as ...
>
>
> 92 1.  Introduction
>
> 94   [RFC5880], [RFC5881], and [RFC5883] defined the operation of
> 95   Bidirectional Forwarding Detection (BFD) protocol between the two
> 96   systems over IP networks.  [RFC5884] and [RFC7726] set rules for
> 97   using BFD Asynchronous mode over point-to-point (p2p) Multiprotocol
> 98   Label Switching (MPLS) Label Switched Path (LSP).  These latter
> 99   standards implicitly assume that the remote BFD system, which is at
> 100   the egress Label Edge Router (LER), will use the shortest path route
> 101   regardless of the path the BFD system at the ingress LER uses to send
> 102   BFD Control packets towards it.  Throughout this document, references
> 103   to ingress LER and egress LER are used, respectively, as a shortened
> 104   version of the "BFD system at the ingress/egress LER".
>
> 106   This document defines the use of LSP Ping for Segment Routing
> 107   networks over the MPLS data plane [RFC8287] to bootstrap and control
> 108   path of a BFD session from the egress to ingress LER using Segment
> 109   Routing tunnel with MPLS data plane (SR-MPLS).
>
> < editorial > Please use SR Policy terminology instead of "Segment Routing
> Tunnel" for consistency with RFC9256. See major (1) above. What is
> monitored
> is Segment Lists.
>
> < editorial > Please also introduce the other flavors and features of BFD
> that
> are specified in this document.
>
> 111   [RFC9256] defines the SR Policy architecture.  When analyzing the
> 112   applicability of a BFD-based mechanism for detecting network failures
> 113   in a Segment Routing domain, it is essential to identify the SR
> 114   Policy elements monitored by the BFD.  Concluding from the definition
> 115   of BFD in [RFC5880], in an SR domain, BFD, in its modes and
> 116   functions, monitors not the SR Policy, as defined in [RFC9256], but a
> 117   segment list that is a constituent of the candidate path of the
> 118   particular SR Policy.  That is the context used throughout the
> 119   document.
>
> < major > Please consider rephrasing the 2nd last sentence for clarity.
> Also
> see major (1) above.
>
>
> 156 2.  Bootstrapping BFD Session over Segment Routed Tunnel with MPLS Data
> 157    Plane
>
> < editorial > Consider revising this section title to "BFD control session
> setup" ... or something like that.
>
> 159   Use of an LSP Ping to bootstrap BFD over MPLS LSP is required, as
> 160   documented in [RFC5884], to establish an association between a fault
> 161   detection message, i.e., BFD Control message, and the Forwarding
> 162   Equivalency Class (FEC) of a single label stack LSP in case of
> 163   Penultimate Hop Popping or when the egress LER distributes the
> 164   Explicit NULL label to the penultimate hop router.  The Explicit NULL
> 165   label is not advertised as a Segment Identifier (SID) by an SR node
> 166   but, as demonstrated in section 3.1 [RFC8660] if the operation at the
> 167   penultimate hop is NEXT; then the egress SR node will receive an IP
> 168   encapsulated packet.  Thus the conclusion is that LSP Ping MUST be
> 169   used to bootstrap a BFD session in an SR-MPLS domain if there are no
>
> < minor > I am not following the logic here. It is clear that the
> knowledge of
> the FEC is required to setup the proper BFD session context at the egress
> LER
> and this is something that LSP ping provides. I am not sure if the rest of
> the
> explanation is needed or even correct? E.g, even if there is no PHP, the
> last
> label may be an adj-sid or prefix-sid and not provide a context for the SR
> segment list.
>
> 170   other means to bootstrap the BFD session, e.g., using an extension to
> 171   a dynamic routing protocol as described in [RFC9026] and [RFC9186].
>
> 173   As demonstrated in [RFC8287], the introduction of Segment Routing
> 174   network domains with an MPLS data plane requires three new sub-TLVs
> 175   that MAY be used with Target FEC TLV [RFC8029].  Section 6.1
> 176   addresses the use of the new sub-TLVs in Target FEC TLV in LSP ping
> 177   and LSP traceroute.  For the case of LSP ping, the [RFC8287] states
> 178   that:
>
> 180      The initiator, i.e., ingress LER, MUST include FEC(s)
> 181      corresponding to the destination segment.
>
> 183      The initiator MAY include FECs corresponding to some or all of
> 184      segments imposed in the label stack by the ingress LER to
> 185      communicate the segments traversed.
>
> 187   It has been noted in [RFC5884] that a BFD session monitors for
> 188   defects particular <MPLS LSP, FEC> tuple.  [RFC7726] clarified how to
> 189   establish and operate multiple BFD sessions for the same <MPLS LSP,
> 190   FEC> tuple.  Because only the ingress LER is aware of the SR-based
> 191   explicit route, the egress LER can associate the LSP ping with BFD
> 192   Discriminator TLV with only one of the FECs it advertised for the
> 193   particular segment.  Thus this document clarifies that:
>
> 195      When LSP Ping is used to bootstrapping a BFD session for SR-MPLS
> 196      tunnel the FEC corresponding to the segment to be associated with
> 197      the BFD session MUST be as the very last sub-TLV in the Target FEC
> 198      TLV.
>
> < major > This is OK when the target FEC is the PrefixSID of the LER.
> However,
> it does not work for SLs of SR Policies. See major (2) above.
>
> 200   Encapsulation of a BFD Control packet in Segment Routing network with
> 201   MPLS data plane MUST follow Section 7 [RFC5884] when the IP/UDP
> 202   header used and MUST follow Section 3.4 [RFC6428] without IP/UDP
> 203   header being used.
>
> 205 3.  Use BFD Reverse Path TLV over Segment Routed MPLS Tunnel
>
> < editorial > Consider the section title "BFD Directed Return Path for SR
> Policy SLs" ... or something like that.
>
> 207   For BFD over MPLS LSP case, per [RFC5884], egress LER MAY send BFD
> 208   Control packet to the ingress LER either over IP network or an MPLS
> 209   LSP.  Similarly, for the case of BFD over p2p SR-MPLS tunnel, the
> 210   egress LER MAY route BFD Control packet over the IP network, as
> 211   described in [RFC5883], or transmit over a segment tunnel, as
> 212   described in Section 7 [RFC5884].  In some cases, there may be a need
> 213   to direct egress LER to use a specific path for the reverse direction
> 214   of the BFD session by using the BFD Reverse Path TLV and following
> 215   all procedures as defined in [I-D.ietf-mpls-bfd-directed].
>
> < minor > The draft-ietf-mpls-bfd-directed does not describe what TLVs (or
> FECs) need to be used for the reverse path for SR Policy SLs. Since the
> intention
> is to use the new Non-FEC Path TLV then consider making section 4 as a
> sub-section of section 3 - same goes for rest of the text related to BFD
> directed mode of operations.
>
> 217 4.  Use Non-FEC Path TLV
>
> 219   For the case of MPLS data plane, Segment Routing Architecture
> 220   [RFC8402] explains that "a segment is encoded as an MPLS label.  An
> 221   ordered list of segments is encoded as a stack of labels."
>
> 223   This document defines a new optional Non-FEC Path TLV.  The format of
> 224   the Non-FEC Path TLV is presented in Figure 1
> 225       0                   1                   2                   3
> 226       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
> 227      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 228      |    Non-FEC Path TLV Type      |           Length              |
> 229      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 230      |                                                               |
> 231      ~                          Non-FEC Path                         ~
> 232      |                                                               |
> 233      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> 235                     Figure 1: Non-FEC Path TLV Format
>
> 237   Non-FEC Path TLV Type is two octets in length and has a value of TBD1
> 238   (to be assigned by IANA as requested in Section 10.1).
>
> 240   Length field is two octets long and defines the length in octets of
> 241   the Non-FEC Path field.
>
> 243   Non-FEC Path field contains a sub-TLV.  Any Non-FEC Path sub-TLV
> 244   (defined in this document or to be defined in the future) for Non-FEC
> 245   Path TLV type MAY be used in this field.  None or one sub-TLV MAY be
> 246   included in the Non-FEC Path TLV.  If no sub-TLV has been found in
>
> < minor > Perhaps ... one and only one sub-TLV MUST be included ...
>
> 247   the Non-FEC Path TLV, the egress LER MUST revert to using the reverse
> 248   path selected based on its local policy.  If there is more than one
> 249   sub-TLV, then the Return Code in echo reply MUST be set to value TBD3
> 250   "Too Many TLVs Detected" (to be assigned by IANA as requested in
> 251   Table 4).
>
> 253   Non-FEC Path TLV MAY be used to specify the reverse path of the BFD
> 254   session identified in the BFD Discriminator TLV.  If the Non-FEC Path
> 255   TLV is present in the echo request message the BFD Discriminator TLV
> 256   MUST be present as well.  If the BFD Discriminator TLV is absent when
> 257   the Non-FEC Path TLV is included, then it MUST be treated as
> 258   malformed Echo Request, as described in [RFC8029].
>
> 260   This document defines the Segment Routing MPLS Tunnel sub-TLV that
> 261   MAY be used with the Non-FEC Path TLV.  The format of the sub-TLV is
> 262   presented in Figure 2.
>
> 264     0                   1                   2                   3
> 265     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
> 266    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 267    |  SR MPLS Tunnel sub-TLV Type  |           Length              |
> 268    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 269    |                   SID Entry 1 (Top of Stack)                  |
> 270    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 271    |                           SID Entry 2                         |
> 272    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 273    ~                                                               ~
> 274    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 275    |                   SID Entry N (Bottom of Stack)               |
> 276    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> 278               Figure 2: Segment Routing MPLS Tunnel sub-TLV
>
> 280   The Segment Routing MPLS Tunnel sub-TLV Type is two octets in length,
> 281   and has a value of TBD2 (to be assigned by IANA as requested in
> 282   Section 10.1).
>
> 284   The egress LER MUST use the Value field as label stack for BFD
> 285   Control packets for the BFD session identified by the source IP
> 286   address of the MPLS LSP Ping packet and the value in the BFD
> 287   Discriminator TLV.  Label Entries MUST be in network order.
>
> < major > The naming of the fields in the figure is not consistent with the
> description above. If the "SID entry" is a label, then please call it so.
> SID
> can be either an index value (into SRGB) or a label value per Segment
> Routing Arch.
>
> 289 5.  BFD Reverse Path TLV over Segment Routed MPLS Tunnel with Dynamic
> 290    Control Plane
>
> 292   When Segment Routed domain with MPLS data plane uses distributed
> 293   tunnel computation BFD Reverse Path TLV MAY use Target FEC sub-TLVs
> 294   defined in [RFC8287].
>
> < major > Is this really required? Does it not complicate things at both
> ends, why not just use the label stack directly in this case as well ?
>
> 296 6.  Applicability of BFD Demand Mode in SR-MPLS Domain
>
> 298   Sections 6.6 and 6.18.4 of [RFC5880] define how Demand mode of BFD
> 299   can be used to monitor uni-directional MPLS LSP.  Similar procedures
> 300   can be following in SR-MPLS to monitor uni-directional SR tunnels:
>
> 302   *  an ingress SR node bootstraps BFD session over SR-MPLS in Async
> 303      BFD mode;
>
> 305   *  once BFD session is Up, the ingress SR node switches the egress
> 306      LER into the Demand mode by setting D field in BFD Control packet
> 307      it transmits;
>
> 309   *  if the egress LER detects the failure of the BFD session, it sends
> 310      its BFD Control packet to the ingress SR node over the IP network
> 311      with a Poll sequence;
>
> 313   *  if the ingress SR node receives a BFD Control packet from the
> 314      remote node in a Demand mode with Poll sequence and Diag field
> 315      indicating the failure, the ingress SR node transmits BFD Control
> 316      packet with Final over IP and switches the BFD over SR-MPLS back
> 317      into Async mode, sending BFD Control packets one per second.
>
> 319 7.  Using BFD to Monitor Point-to-Multipoint SR Policy
>
> 321   [I-D.ietf-spring-sr-replication-segment] defined variants of SR
>
> < minor > Please update the reference to the RFC
>
> 322   Policy to deliver point-to-multipoint (p2mp) services.  For the given
> 323   p2mp segment [RFC8562] can be used if, for example, leaves have an
> 324   alternative source of the multicast service flow to select.  In such
> 325   a scenario, a leaf may switch to using the alternative flow after
> 326   p2mp BFD detects the failure in the working multicast path.  For
> 327   scenarios where it is required for the root to monitor the state of
> 328   the multicast tree [RFC8563] can be used.  The root may use the
> 329   detection of the failure of the multicast tree to the particular leaf
> 330   to restore the path for that leaf or re-instantiate the whole
> 331   multicast tree.
>
> 333   An essential part of using p2mp BFD is the bootstrapping the BFD
> 334   session at all the leaves.  The root, acting as the MultipointHead,
> 335   MAY use LSP Ping with the BFD Discriminator TLV.  Alternatively,
> 336   extensions to routing protocols, e.g., BGP, or management plane,
> 337   e.g., Path Computation Element Protocol, MAY be used to associate the
> 338   particular p2mp segment with MultipointHead's Discriminator.
> 339   Extensions for routing protocols and management plane are for further
> 340   study.
>
> < major > I don't see a normative reference
> to draft-ietf-pim-p2mp-policy-ping
>
> 342 8.  Use of Echo BFD in SR-MPLS
>
> 344   Echo-BFD [RFC5880] can be used to monitor a segment list of the
> 345   particular SR Policy between the local and the remote BFD peers.  As
> 346   defined in [RFC5880], the remote BFD system does not process the
> 347   payload of an Echo BFD.  Thus it is the local system that
> 348   demultiplexes the Echo BFD packet matching it to the appropriate BFD
> 349   session and detects missing Echo BFD packets.  A BFD Control packet
> 350   MAY be used as the payload of Echo BFD.  This specification defines
> 351   the use of Echo BFD in SR-MPLS network with BFD Control packet as the
> 352   payload.  The use of other types of Echo BFD payload is outside the
> 353   scope of this document.  Because the remote BFD system does not
> 354   process Echo BFD, the value of the Your Discriminator field MUST be
> 355   set to the discriminator the local BFD system assigned to the given
> 356   BFD session.  My Discriminator field MUST be zeroed.  Authentication
> 357   MUST be set according to the configuration of the BFD session.  To
> 358   ensure that the Echo BFD packet is returned to the sender without
> 359   being processed, the sender MAY use a Binding SID (BSID) [RFC8402]
> 360   that has been bound with the SR Policy that ensures the return of a
> 361   packet to that particular node.  A BSID MAY be associated with the SR
> 362   Policy that is the reverse to the SR Policy programmed onto the BFD
> 363   Echo packet by the sender.
>
> < major > Could you describe how the encapsulation of the BFD packet is
> done at the
>  sender along with this BSID for the return path?
>
> 365 9.  Use of S-BFD in SR-MPLS
>
> 367   Seamless BFD (S-BFD), defined in [RFC7880], maintains essential
> 368   characteristics and elements of the base BFD mechanism described in
> 369   [RFC5880] with a lighter approach to instantiating a BFD session
> 370   between BFD peers.  Similar to the BFD Asynchronous mode, S-BFD is
> 371   capable of monitoring a segment list of a p2p SR Policy.
>
> 373   Considering that a particular SR Policy can include multiple
> 374   candidate paths, which, in turn, have one or more segment lists, it
> 375   could be beneficial to monitor each segment list independently.  To
> 376   achieve that, S-BFD Reflector advertises My Discriminator value.
> 377   Then, the S-BFD Initiator uses the advertised My Discriminator value
> 378   as Your Discriminator value in the BFD Control messages transmitted
> 379   over the segment list of the SR Policy.  Furthermore, the S-BFD
> 380   Initiator assigns a unique My Discriminator for each S-BFD session
> 381   monitoring a segment list.  S-BFD Reflector transmits BFD Control
> 382   messages as IP/UDP packets, taking advantage of the available
> 383   resilience mechanisms of the IP network.  From that point, to
> 384   minimize the detection of failures in the IP network that do not
> 385   affect the monitored segment list, it is reasonable not to use defect
> 386   detection intervals that are close to the IP network repair time.
> 387   Instead, having an S-BFD detection interval three times longer than
> 388   the IP network repair time is practical.
>
> < major > Is this aspect for return path not relevant to all forms of BFD
> when
> using an IP return path? Why is it only in this particular section?
>
> < major > Perhaps text can be picked from
> https://datatracker.ietf.org/doc/html/draft-ali-spring-bfd-sr-policy-10
> that
> covers the SBFD operations in greater detail.
>
> < major > There are multiple BFD flavors described but there isn't a
> section
> that covers the pros/cons of their usage and applicability. Is that
> something
> that could be added?
>
> < major > SR Policy scale is generally expected to be higher than RSVP-TE
> tunnels since the state is only present on the headend. Then we have CPs
> and
> SLs. Can the draft cover the scalability aspects of the different BFD
> flavors?
>
>
> 390 10.  IANA Considerations
>
> 392 10.1.  Non-FEC Path TLV
>
> 394   IANA is requested to assign new TLV type from the from Standards
> 395   Action range of the registry "Multiprotocol Label Switching
> 396   Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
> 397   TLVs" as defined in Table 1.
>
> 399               +=======+==================+===============+
> 400               | Value | TLV Name         | Reference     |
> 401               +=======+==================+===============+
> 402               |  TBD1 | Non-FEC Path TLV | This document |
> 403               +-------+------------------+---------------+
>
>
> < minor > I note that there is an implementation reported and in
> production by a vendor while
> code points are still not allocated. Could you please get this clarified
> and if there is already some
> code point being squatted upon? I couldn't find the early allocation as
> indicated in the implementation
> report section.
>
> 405                      Table 1: New Non-FEC Path TLV
>
> 407   IANA is requested to create new Non-FEC Path sub-TLV registry for
> the
> 408   Non-FEC Path TLV, as described in Table 2.
>
> 410   +=============+===============+=====================================+
> 411   | Range       |  Registration | Note                                |
> 412   |             |   Procedures  |                                     |
> 413   +=============+===============+=====================================+
> 414   | 0-16383     |   Standards   | This range is for mandatory         |
> 415   |             |     Action    | TLVs or for optional TLVs           |
> 416   |             |               | that require an error               |
> 417   |             |               | message if not recognized.          |
> 418   +-------------+---------------+-------------------------------------+
> 419   | 16384-31743 | Specification | Experimental RFC needed             |
> 420   |             |    Required   |                                     |
> 421   +-------------+---------------+-------------------------------------+
> 422   | 32768-49161 |   Standards   | This range is for optional          |
> 423   |             |     Action    | TLVs that can be silently           |
> 424   |             |               | dropped if not recognized.          |
> 425   +-------------+---------------+-------------------------------------+
> 426   | 49162-64511 | Specification | Experimental RFC needed             |
> 427   |             |    Required   |                                     |
> 428   +-------------+---------------+-------------------------------------+
> 429   | 64512-65535 |  Private Use  |                                     |
> 430   +-------------+---------------+-------------------------------------+
>
> 432                   Table 2: Non-FEC Path sub-TLV registry
>
> 434   IANA is requested to allocate the following values from the Non-FEC
> 435   Path sub-TLV registry as defined in Table 3.
>
> 437      +=======+=====================================+===============+
> 438      | Value | Description                         | Reference     |
> 439      +=======+=====================================+===============+
> 440      | 0     | Reserved                            | This document |
> 441      +-------+-------------------------------------+---------------+
> 442      |  TBD2 | Segment Routing MPLS Tunnel sub-TLV | This document |
> 443      +-------+-------------------------------------+---------------+
> 444      | 65535 | Reserved                            | This document |
> 445      +-------+-------------------------------------+---------------+
>
> 447                Table 3: New Segment Routing Tunnel sub-TLV
>
> 449 10.2.  Return Code
>
> 451   IANA is requested to create Non-FEC Path sub-TLV sub-registry for the
> 452   new Non-FEC Path TLV and assign a new Return Code value from the
> 453   "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
> 454   Ping Parameters" registry, "Return Codes" sub-registry, as follows
> 455   using a Standards Action value.
>
> 457           +========+=========================+===============+
> 458           | Value  | Description             | Reference     |
> 459           +========+=========================+===============+
> 460           | X TBD3 | Too Many TLVs Detected. | This document |
> 461           +--------+-------------------------+---------------+
>
> 463                         Table 4: New Return Code
>
> 465 11.  Implementation Status
>
> 467   Note to RFC Editor: This section MUST be removed before publication
> 468   of the document.
>
> 470   This section records the status of known implementations of the
> 471   protocol defined by this specification at the time of posting of this
> 472   Internet-Draft, and is based on a proposal described in [RFC7942].
> 473   The description of implementations in this section is intended to
> 474   assist the IETF in its decision processes in progressing drafts to
> 475   RFCs.  Please note that the listing of any individual implementation
> 476   here does not imply endorsement by the IETF.  Furthermore, no effort
> 477   has been spent to verify the information presented here that was
> 478   supplied by IETF contributors.  This is not intended as, and must not
> 479   be construed to be, a catalog of available implementations or their
> 480   features.  Readers are advised to note that other implementations may
> 481   exist.
>
> 483   According to [RFC7942], "this will allow reviewers and working groups
> 484   to assign due consideration to documents that have the benefit of
> 485   running code, which may serve as evidence of valuable experimentation
> 486   and feedback that have made the implemented protocols more mature.
> 487   It is up to the individual working groups to use this information as
> 488   they see fit".
>
> 490   - The organization responsible for the implementation: ZTE
> 491   Corporation.
>
> 493   - The implementation's name ROSng SW empowers traditional routers,
> 494   e.g., ZXCTN 6000.
>
> 496   - A brief general description: A list of SIDs can be specified as the
> 497   Return Path for an SR-MPLS tunnel.
>
> 499   - The implementation's level of maturity: production.
>
> 501   - Coverage: complete
>
> 503   - Version compatibility: draft-mirsky-spring-bfd-06.
>
> 505   - Licensing: proprietary.
>
> 507   - Implementation experience: Appreciate Early Allocation of values
> 508   for Non-FEC TLV and Segment Routing MPLS Tunnel sub-TLV (using
> 509   Private Use code points).
>
> 511   - Contact information: Qian Xin qian.x...@zte.com.cn
>
> 513   - The date when information about this particular implementation was
> 514   last updated: 12/16/2019
>
> < minor > The implementation reference is to a very old document version
> that has
> gone through several changes. Is the "complete" coverage accurate? Please
> consider
> polling the WG to get an updated implementation status for the various BFD
> flavors/sections
> in this document.
>
> 516 12.  Security Considerations
>
> 518   Security considerations discussed in [RFC5880], [RFC5884], [RFC7726
> ],
> 519   and [RFC8029] apply to this document.
>
> < minor > I think some more text would be required here to cover SR
> specific
> aspects? Right now, it is only BFD specific.
>
>
>
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