Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing
draft-ietf-pce-segment-routing-16

[Ballot comment]
I can guess what

  This mechanism is useful in Software Defined
  Networking (SDN) applications, such as on-demand engineering, or
  bandwidth calendaring.

means, but I'm guessing. Is there a reference for "on-demand engineering" or "bandwidth calendaring"?

[Ballot discuss]
I am balloting DISCUSS because I think that there are some technical and clarity issues that makes understanding, and potentially implementing this document hard.  I also want to discuss the "backwards compatibility" and the use of TLVs as sub-TLVs in PCEP as introduced in this document.

(1) MSD Definition.  The MSD may be learned from a variety of sources, including the SR-PCE-CAPABILITY sub-TLV defined in this document.  It is important then for the MSD to be defined consistently everywhere.  Please use the BMI-MSD definition from rfc8491.


(2) Ability to signal the MSD per link, not just per node.  Clearly the calculation of paths through specific links (using an Adjacency SID, for example) would require that information (if different/lower from what the node may support).

Note that §6.1 seems to assume that the MSD will normally be advertised through different mechanisms, and it uses that to work around the fact that there's no link-specific information: "Furthermore, whenever a PCE learns the MSD for a link via different means, it MUST use that value for that link regardless of the MSD value exchanged in the SR-PCE-CAPABILITY sub-TLV."  However, the text doesn't mandate the IGP/BGP-LS information to be available to the PCE.  IOW, as written, the specification can't guarantee the proper calculation of paths that require the PCE to consider link MSDs.


(3) Extensibility to advertise other MSD-Types. [This point is not DISCUSS-worthy, but I'm including it here since I'm already talking about the MSD.]

rfc8491 (aka I-D.ietf-isis-segment-routing-msd) and I-D.ietf-ospf-segment-routing-msd encode the MSD advertisement as a pair: MSD-Type and MSD-Value, with the expectation that "new MSD-Types will be defined to signal additional capabilities, e.g., entropy labels, SIDs that can be imposed through recirculation, or SIDs associated with another data plane such as IPv6."  IOW, the encoding is reusable with other dataplanes.  I peeked into draft-negi-pce-segment-routing-ipv6 [*] and i don't see anything in there that couldn't be signaled using the SR-PCE-CAPABILITY sub-TLV defined here (+ the MSD_Value).  I think this is important for consistency.

[*] I realize that draft-negi-pce-segment-routing-ipv6 is not even a WG document, but it is the only potential reference I found to what a different dataplane might look line.


(4) §6.2.2 (Interpreting the SR-ERO):

  o  If the subobjects contain NAI only, then the PCC first converts
    each NAI into a SID index value by looking it up in its local
    database, and then proceeds as above.

I believe that this step in the interpretation of the SR-ERO is not properly specified.

Which "local database" are you referring to?  §6.2.2.1 mentions the SR-DB (when talking about errors)...but the specification should be clear about which database and what the specific procedure is.

For example, what is the specific process that the PCC needs to follow to convert a Node ID/IP address to the SID/MPLS label?  What if the SR-DB doesn't contain an SID associated to the specific Node ID/IP address?  How should the router react to that?  This case is not covered in the Error Handling section (6.2.2.1) either.

A pointer to the SR-DB (as defined in I-D.ietf-spring-segment-routing-policy) is not enough because it is composed of optional information (according to the description in §3 (Segment Routing Database)).  This document should be specific about what information must be contained in the SR-DB for the conversion to be successful.

The requirement of the information to be contained in the SR-DB makes I-D.ietf-spring-segment-routing-policy a Normative reference.


(5) §7 (Backward Compatibility)  "Some implementations, which are compliant with an earlier version of this specification..."

I understand that there may be implementations that are non-compliant with this specification out in the field.  However, why is this document making accommodations for them?  Not only are these implementations not compliant with this document, but are also non compliant with rfc8408, which implies the use of a new sub-TLV per PST.

I didn't find a discussion on the mailing list related to this issue.  Specifying alternate behavior to accommodate non-compliant implementations is not the best way to define new functionality.  If the support for those old implementations was an imperative then the new functionality should have been fully specified to seamlessly interoperate with what is already deployed.  The current result is two ways to do the same thing...

While I would prefer for this "backwards compatibility" not to be built into the specification, I am looking for discussion in the WG and a better justification that the current one (which can be reduced to "non-compliant implementations exist, so we need to fit them in here somehow").


(6) sub-TLV Space for the PATH-SETUP-TYPE-CAPABILITY TLV

rfc8408 failed to set up a sub-TLV registry for the PATH-SETUP-TYPE-CAPABILITY TLV.  The bigger issue is that it also doesn't say that other PCE TLVs can be used as sub-TLVs (nor does it prohibit that).  The Type for the SR-PCE-CAPABILITY sub-TLV is allocated from the PCEP TLV Type Indicators registry, making it a TLV.  I also couldn't find any mention of sub-TLVs in rfc5440, or the potential intent to have a single space from which both TLVs and sub-TLVs could come.

The question is: are all TLVs (defined in the PCEP TLV Type Indicators registry) able to be used as sub-TLVs?  This question is general, but also specific to the PATH-SETUP-TYPE-CAPABILITY TLV.  At a minimum, it should be made clear which can be used with the PATH-SETUP-TYPE-CAPABILITY TLV -- because this is the first document to define a new PST and sub-TLV, it seems appropriate to Update rfc8408 here...but rfc5440 may also need an Update.

[Ballot comment]
These comments don't raise to the level of a DISCUSS, but I would like to also see them addressed.

(1) [nit] "Both node segments and adjacency segments can be used for SR Traffic Engineering (SR-TE)." I find the use of SR-TE (instead of simply SR) gratuitous and potentially confusing; it introduces a new term which doesn't represent new functionality as compared to exiting segment routing documents.


(2) "This document is relevant to the MPLS forwarding plane only."  I believe that I-D.ietf-spring-segment-routing-mpls should be a Normative reference.


(3) In §3, the first two paragraphs have redundant text:

"In an SR network, the ingress node of an SR path prepends an SR header to all outgoing packets.  The SR header consists of a list of SIDs (or MPLS labels in the context of this document)....In SR networks, an ingress node of an SR path prepends an SR header to all outgoing packets.  The SR header consists of a list of SIDs (or MPLS labels in the context of this document)."


(4) §3: "...the PCEP messages (e.g., Path Computation Request, Path Computation Reply, Path Computation Report, Path Computation Update, Path Computation Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231], [RFC8281], and any other applicable PCEP specifications."  I'm not sure what behavior is being specified here -- IOW, why do we need Normative language?  This document defines the extensions referred to here, so the format should already be compliant with the RFCs mentioned.  s/MUST/must


(5) Following up from the last point...  §4 seems to address that MUST by saying that there's no requirement for "changes in the format of the PCReq and PCRep messages specified in [RFC5440], PCInitiate message specified in [RFC8281], and PCRpt and PCUpd messages specified in [RFC8231]."  I find this section unnecessary.


(6) [nit] §5.3.1 defines the "L Flag"...  §6.1, for example, uses "L flag" to refer to the L bit (§5.1.1).  Please try to be consistent to avoid confusion...or even better, use a different letter.


(7) §5.1.1 says that a "PCEP speaker SHOULD indicate its support of the function described in this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV...[and]...MUST also include the SR-PCE-CAPABILITY sub-TLV"...but §6.1 then says that "if a PCE receives an SR-PCE-CAPABILITY sub-TLV with the L flag and MSD both set to zero then it MUST assume that the PCC is not capable of imposing a SID stack of any depth and hence is not SR-TE capable".  Wait, the sub-TLV is included because the TLV says that it supports SR.  Isn't this then a contradiction??  What good is it to signal support if the node is "not capable of imposing a SID stack of any depth"?  Shouldn't this combination result in an error message?


(8) §6.2.2  "According to [I-D.ietf-spring-segment-routing-policy], each SR-ERO subobject in the sequence identifies a segment that the traffic will be directed to, in the order given."

The SR-ERO subobject is defined in this document, so its interpretation is of obvious importance.  Because of that, I think that the text above makes the reference Normative.

However, I looked in I-D.ietf-spring-segment-routing-policy and I find no mention of the SR-ERO, ERO, or sequence.  The only related text (that I could find) is the generic one about SR being an "ordered list of segments"...so I think that the reference to I-D.ietf-spring-segment-routing-policy is out of place.

Suggestion: replace the reference to I-D.ietf-spring-segment-routing-policy with a reference to rfc8402.


(9) §6.2.2 "If the subobjects contain SID index values, then the PCC converts them into the corresponding MPLS labels by following the procedure defined in [I-D.ietf-spring-segment-routing-mpls]."  I think this statement requires I-D.ietf-spring-segment-routing-mpls to be a Normative reference.


(10) §6.2.2  Only the third procedure ends with "...and then directs the packet to the segment identified by the first SID", which is the obvious next step, but the text is only talking about the conversion.  Either make sure that it is clear that all the processes continue with sending, or take this piece of text out.  Be consistent.


(11) §5.5 "...the PCE MUST minimize the SID depth of the computed path."  If the B bit is not set (meaning not bound), what behavior is this phrase standardizing?  Given that we're not standardizing the computation done by the PCE, how can it be enforced?


(12) §8.1 (Controlling the Path Setup Type)  I find this section out of place in this document.  rfc8408 is the document that specifies the support for multiple path setup methods...while this document adds the SR-related type.  If kept, then I think this document should be tagged to Update rfc8408.

[Ballot comment]
Section 8.4 strikes me as a little odd for an archival document -- presumably draft-ietf-pce-pcep-yang either will or will not include the listed items, so the recommendations will either be out-of-date or false once draft-ietf-pce-pcep-yang is published.

[Ballot comment]
Hello,

thank you for this document. I have few comments/questions:

Could you elaborate on what you mean by: "or to perform a specific service on the packet."

s/A Segment Routed path/A Segment Routing path/

  In SR networks, an ingress node of an SR path prepends an SR header to
  all outgoing packets.  The SR header consists of a list of SIDs (or
  MPLS labels in the context of this document).
This appears twice in two consecutive paragraphs at the beginning of section 3.

I'm not a native english speaker but I find the use of "ERO subobject" confusing when used to refer to the SR-ERO subobject.
Maybe say the "the (SR-ERO) subobject of the ERO".

  Length:  Contains the total length of the subobject in octets,
      including the L, Type and Length fields.  The Length MUST be at
      least 8, and MUST be a multiple of 4.  An SR-ERO subobject MUST
      contain at least one of a SID or an NAI.  The length should
      include the SID and NAI fields if and only if they are not absent.
I am confused about the minimum length. L, Type and Length use 2 octets. What bring this to 8 considering that a SID is 4?
Also the last sentence is very confusing. It seems normal not to count something which is not there. No need to say so. The current statement seems to contradict the preceding sentence in fact, so I'd just remove it.

      *  A 4 octet MPLS label, where the 20 most significant bits encode
        the label value per [RFC3032].
s/MPLS label/MPLS Label Stack Entry/

I believe it is too late to change but I find L=1 meaning "no limit" is *very* confusing. For me L stands for Limit and when L=1 there is a limit, when L=0 there is none.

On the metric object.
You have the requirement that "the PCE MUST minimize the SID depth". This is a non actionable requirement. You need to set a bound. I very much understand that the bound is the specified sid depth (and you say it properly afterwards ("the PCE MUST NOT return a path whose SID depth exceeds the given metric-value"), but still the sentence I point to is a non actionable requirement which you may want to reformulate.

  If a PCEP session is established with a non-zero default MSD value,
  then the PCC MUST NOT send an MSD METRIC object with an MSD greater
  than the session's default MSD.
Out of curiosity, why do you forbid that case?

[Ballot comment]
Abstract

                  This document specifies extensions to the Path
  Computation Element Communication Protocol (PCEP) that allow a
  stateful PCE to compute and initiate Traffic Engineering (TE) paths,
  as well as a PCC to request a path subject to certain constraints and
  optimization criteria in SR networks.

Why are we talking about TE paths now instead of SR?

Section 1

  Several types of segment are defined.  A node segment represents an
  ECMP-aware shortest-path to a specific node, and is always identified
  uniquely within the SR/IGP domain.  [...]

A path to a node is only going to be unique if the starting node is also
included, is it not?

Section 3

The sentences:

  In an SR network, the ingress node of an SR path prepends an SR
  header to all outgoing packets.  The SR header consists of a list of
  SIDs (or MPLS labels in the context of this document).

Appear virtually unchanged in both the start of the first paragraph and the
middle of the second paragraph; is this duplication really needed?

  A PCC MAY include an RRO containing the recorded LSP in PCReq and
  PCRpt messages as specified in [RFC5440] and [RFC8231], respectively.
  This document defines a new RRO subobject for SR networks.  The
  methods used by a PCC to record the SR-TE LSP are outside the scope
  of this document.

It's not entirely clear that we need to define a standard container to
carry site-local data when a site-local container could also be used.

Section 5.2

Please expand SRP (and RP, for that matter) on first usage.
(Interestingly, https://www.rfc-editor.org/materials/abbrev.expansion.txt
does not seem to have the correct expansion for this usage.)

Section 5.3.1

      *  C: If the M bit and the C bit are both set to 1, then the TC,
        S, and TTL fields in the MPLS label stack entry are specified
        by the PCE.  However, a PCC MAY choose to override these values
        according its local policy and MPLS forwarding rules.  If the M
        bit is set to 1 but the C bit is set to zero, then the TC, S,
        and TTL fields MUST be ignored by the PCC.  The PCC MUST set
        these fields according to its local policy and MPLS forwarding
        rules.  [...]

Must be ignored in incoming messages received from where?

Isn't the 'F' bit fully redundant with NT?

Section 5.3.2

Do we need to say anything about which node is the reference point for
evaluating "local" and "remote" w.r.t. IP addresses?  (Maybe we
don't, since these are always unidirectional adjacencies, right?)

Section 6.1

  If a PCC sets the N flag to 1, then the PCE MAY send an SR-ERO
  subobject containing NAI and no SID (see Section 6.2).  Otherwise,
  the PCE MUST NOT send an SR-ERO subobject containing NAI and no SID.

Sets the N flag in what message?

                                                If a PCE receives an
  SR-PCE-CAPABILITY sub-TLV with the L flag set to 1 then it MUST
  ignore the MSD field and MUST assume that the sender can impose a SID
  stack of any depth.  [...]

nit: this second MUST seems like overkill; "and assumes" would probably
work fine.  (Similarly for the following case.)

It's interesting that the routing protocols' MSD value supersedes the
PCE-obtained one, given that all three (IS-IS, OSPF, and BGP-LS) documents
have text to the effect of "PCEP provides a way to get this, but if PCEP is
not used you can use our thing", which a naive reader would take to mean
that PCEP is intended to be the primary distribution mechanism.

Section 7

Is there some history regarding making it MUST-level mandatory to treat
top-level SR-CAPABILITY-TLV in OPEN for backwards-compatibility (as opposed
to SHOULD-level but leaving open the option of a strict implementation)?
(The guidance for what to do when both forms appear seems good to have at
MUST-level, to me.)

Section 9

RFC 8281's security considerations incorporate those of RFC 8231 by
reference; we could save the reader a step and also mention it at the
toplevel here.

I don't think it's a good idea to just refer to "the security mechanisms of
[RFC 5440] and [RFC8281]", since there are qualitative differences between
the TCP authentication schemes and the full-on encryption provided by TLS
and IPsec.  (Also, what exactly are the security mechanisms of RFC8281
supposed to be -- a quick look only sees the new guidance to apply resource
limits?)  The second paragraph only requires integrity protection to avoid
the vulnerability mentioned there, but the third paragraph requires
confidentiality protection to preent the attack.

Section 10.6

RFC 8408 does not "request" the creation of the registry; IANA has already
created the registry.  I would just say "[RFC8408] created a sub-registry
[...]" but the smaller change to "requested" would be okay, too.

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has completed its review of draft-ietf-pce-segment-routing-14. If any part of this review is inaccurate, please let us know.

The IANA Functions Operator has a question about one of the actions requested in the IANA Considerations section of this document.

The IANA Functions Operator understands that, upon approval of this document, there are eleven actions which we must complete.

First, in the Subobject type - 20 EXPLICIT_ROUTE - Type 1 Explicit Route subregistry of the Class Names, Class Numbers, and Class Types registry on the Resource Reservation Protocol (RSVP) Parameters registry page located at:

https://www.iana.org/assignments/rsvp-parameters/

the existing temporary registration for:

Value: 36
Description: SR-ERO

will be made permanent and its reference changed to [ RFC-to-be ].

Second, in the Subobject type - 21 ROUTE_RECORD - Type 1 Route Record subregistry of the Class Names, Class Numbers, and Class Types registry on the Resource Reservation Protocol (RSVP) Parameters registry page located at:

https://www.iana.org/assignments/rsvp-parameters/

the existing temporary registration for:

Value: 36
Description: SR-RRO

will be made permanent and its reference changed to [ RFC-to-be ].

Third, a new registry is to be created called the PCEP SR-ERO NAI Types registry. The new registry will be created on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

The new registry is to be maintained using IETF Review as defined in RFC8126.

IANA Question --> What is the range of values for the new registry? Are any reserved or unallocated?

There are initial registrations in the new registry as follows:

Value Description Reference
---------------+-----------------------------+-----------------
0 NAI is absent. [ RFC-to-be ]
1 NAI is an IPv4 node ID. [ RFC-to-be ]
2 NAI is an IPv6 node ID. [ RFC-to-be ]
3 NAI is an IPv4 adjacency. [ RFC-to-be ]
4 NAI is an IPv6 adjacency. [ RFC-to-be ]
5 NAI is an unnumbered [ RFC-to-be ]
adjacency with IPv4 node IDs.

Fourth, a new registry is to be created called the SR-ERO Flag Field registry. The new registry will be created on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

The new registry is to be maintained using Standards Action as defined in RFC8126.

IANA Question --> How many bits will be in the new Flag Field registry? Are any reserved?

There are initial registrations in the new registry as follows:


Bit Description Reference
-------+---------------------+---------------
0-7 Unassigned
8 NAI is absent (F) [ RFC-to-be ]
9 SID is absent (S) [ RFC-to-be ]
10 SID specifies TC, S [ RFC-to-be ]
and TTL in addition
to an MPLS label (C)
11 SID specifies an MPLS [ RFC-to-be ]
label (M)

Fifth, in the PCEP-ERROR Object Error Types and Values registry also on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

the following Error-values in Error-type 10 (Reception of an invalid object.) will be made permanent and have their reference changed to [ RFC-to-be ].

Error-Type Meaning
---------- -------
10 Reception of an invalid object
Error-value = 2: Bad label value
Error-value = 3: Unsupported number
of SR-ERO
subobjects
Error-value = 4: Bad label format
Error-value = 5: ERO mixes SR-ERO
subobjects with
other subobject
types
Error-value = 6: Both SID and NAI
are absent in SR-
ERO subobject
Error-value = 7: Both SID and NAI
are absent in SR-
RRO subobject
Error-value = 9: MSD exceeds the
default for the
PCEP session
Error-value = 10: RRO mixes SR-RRO
subobjects with
other subobject
types

Sixth, also in the PCEP-ERROR Object Error Types and Values registry also on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

nine, new registrations will be made for Error-type 10 (Reception of an invalid object.) The nine, new registrations are as follows:

Error-Type Meaning
---------- -------
10 Reception of an invalid object.

Error-value = [ TBD-at-Registration ]: Missing PCE-SR-
CAPABILITY sub-TLV
Error-value = [ TBD-at-Registration ]: Unsupported NAI
Type in SR-ERO
subobject
Error-value = [ TBD-at-Registration ]: Unknown SID
Error-value = [ TBD-at-Registration ]: NAI cannot be
resolved to a SID
Error-value = [ TBD-at-Registration ]: Could not find SRGB
Error-value = [ TBD-at-Registration ]: SID index exceeds
SRGB size
Error-value = [ TBD-at-Registration ]: Could not find SRLB
Error-value = [ TBD-at-Registration ]: SID index exceeds
SRLB size
Error-value = [ TBD-at-Registration ]: Inconsistent SIDs
in SR-ERO / SR-RRO
subobjects

For each of these new Error-values the reference will be set to [ RFC-to-be ].

Seventh, IANA notes that this draft originally had an early allocation for Error-value? (Malformed object) in the above list. IANA has registered this value as part of the IAN Actions for RFC8408.

Eighth, in the PCEP TLV Type Indicators registry also on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

the existing temporary registration for:

Value Meaning Reference
------------------------- ---------------------------- --------------
26 SR-PCE-CAPABILITY TEMPORARY

will be made permanent and its reference changed to [ RFC-to-be ].

Ninth, in the PCEP Path Setup Types registry also on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

a single, new registration is to be made as follows:

Value: [ TBD-at-Registration ]
Description: Traffic engineering path is setup using Segment Routing.
Reference: [ RFC-to-be ]

IANA notes that the authors have requested the value 1 for this new registration.

Tenth, in the METRIC Object T Field regsitry also on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

the existing, temporary registration for:

Value: 11
Description: Segment-ID (SID) Depth.

will be made permanent and its reference changed to [ RFC-to-be ].

Eleventh, a new registry is to be created called the SR Capability Flag Field registry. The new registry will be created on the Path Computation Element Protocol (PCEP) Numbers registry page located at:

https://www.iana.org/assignments/pcep/

The new registry is to be maintained using Standards Action as defined in RFC8126.

IANA Question --> How many bits will be in the new Flag Field registry? Are any reserved?

There are initial registrations in the new registry as follows:


Bit Description Reference

0-5 Unassigned
6 Node or Adjacency [ RFC-to-be ]
Identifier (NAI) is
supported (N)
7 Unlimited Maximum SID [ RFC-to-be ]
Depth (L)

The IANA Functions Operator understands that these are the only actions required to be completed upon approval of this document.

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is meant only to confirm the list of actions that will be performed.


Thank you,

Sabrina Tanamal
Senior IANA Services Specialist

The following Last Call announcement was sent out (ends 2018-10-29):

From: The IESG
To: IETF-Announce
CC: dhruv.ietf@gmail.com, db3546@att.com, Dhruv Dhody , pce@ietf.org, pce-chairs@ietf.org, draft-ietf-pce-segment-routing@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (PCEP Extensions for Segment Routing) to Proposed Standard


The IESG has received a request from the Path Computation Element WG (pce) to
consider the following document: - 'PCEP Extensions for Segment Routing'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2018-10-29. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the beginning of
the Subject line to allow automated sorting.

Abstract


  Segment Routing (SR) enables any head-end node to select any path
  without relying on a hop-by-hop signaling technique (e.g., LDP or
  RSVP-TE).  It depends only on "segments" that are advertised by Link-
  State Interior Gateway Protocols (IGPs).  A Segment Routed Path can
  be derived from a variety of mechanisms, including an IGP Shortest
  Path Tree (SPT), explicit configuration, or a Path Computation
  Element (PCE).  This document specifies extensions to the Path
  Computation Element Communication Protocol (PCEP) that allow a
  stateful PCE to compute and initiate Traffic Engineering (TE) paths,
  as well as a PCC to request a path subject to certain constraints and
  optimization criteria in SR networks.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-pce-segment-routing/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-pce-segment-routing/ballot/


No IPR declarations have been submitted directly on this I-D.

Document Writeup for Working Group Documents

As required by RFC 4858, this is the current template for the Document Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard, Internet Standard, Informational, Experimental, or Historic)? Why is this the proper type of RFC? Is this type of RFC indicated in the title page header?

    Proposed Standard. This is appropriate because the draft specifies protocol
    extensions. The title page identifies the draft as Standards Track.

(2) The IESG approval announcement includes a Document Announcement Write-Up. Please provide such a Document Announcement Write-Up. Recent examples can be found in the "Action" announcements for approved documents. The approval announcement contains the following sections:

Technical Summary:

Relevant content can frequently be found in the abstract and/or introduction of the document. If not, this may be an indication that there are deficiencies in the abstract or introduction.

    [RFC8402] specify the Segment Routing (SR) architecture that enables
    any head-end node to select any path without relying on a hop-by-hop
    signaling technique. [RFC8402] also identified PCEP a possible mechanism
    for a central controller to instruct the network. This documents specify
    the PCEP extention to support Segment Routing.


Working Group Summary:

Was there anything in WG process that is worth noting? For example, was there controversy about particular points or were there decisions where the consensus was particularly rough?

    No controversies. A 2nd WG LC was issued after the draft had a substantial
    change after the 1st call. The shepherd review also led to simplification
    of text. The authors handled all comments raised. The consensus behind the
    document is good.

Document Quality:

Are there existing implementations of the protocol? Have a significant number of vendors indicated their plan to implement the specification? Are there any reviewers that merit special mention as having done a thorough review, e.g., one that resulted in important changes or a conclusion that the document had no substantive issues? If there was a MIB Doctor, Media Type or other expert review, what was its course (briefly)? In the case of a Media Type review, on what date was the request posted?

    There are several PCEP implementations supporting Segment Routing. This
    includes commercial as well as open source implementations. There
    was also a discussion related to backward compatibility as related to
    some implementations before RFC8408 was published.

    Substantial review was done by Adrian Farrel and Dhruv Dhody.

Personnel:

Who is the Document Shepherd? Who is the Responsible Area Director?

    Dhruv Dhody is the document shepherd.
    Deborah Brungard is the responsible area director.

(3) Briefly describe the review of this document that was performed by the Document Shepherd. If this version of the document is not ready for publication, please explain why the document is being forwarded to the IESG.

    In my opinion, the document is ready. The shepherd review provided
    comments and suggestion to the authors which were handled during the latest
    update.

(4) Does the document Shepherd have any concerns about the depth or breadth of the reviews that have been performed?

    No

(5) Do portions of the document need review from a particular or from broader perspective, e.g., security, operational complexity, AAA, DNS, DHCP, XML, or internationalization? If so, describe the review that took place.

    The usual Routing Directorate's review is expected.

(6) Describe any specific concerns or issues that the Document Shepherd has with this document that the Responsible Area Director and/or the IESG should be aware of? For example, perhaps he or she is uncomfortable with certain parts of the document, or has concerns whether there really is a need for it. In any event, if the WG has discussed those issues and has indicated that it still wishes to advance the document, detail those concerns here.

    The text related to handling of SID list is independent of the protocol.
    During shephered review, these details were removed for the PCE WG document
    and instead referenced from the SPRING WG I-Ds.

(7) Has each author confirmed that any and all appropriate IPR disclosures required for full conformance with the provisions of BCP 78 and BCP 79 have already been filed. If not, explain why?

    Yes.

(8) Has an IPR disclosure been filed that references this document? If so, summarize any WG discussion and conclusion regarding the IPR disclosures.

    No IPR disclosures for this document.

(9) How solid is the WG consensus behind this document? Does it represent the strong concurrence of a few individuals, with others being silent, or does the WG as a whole understand and agree with it?

    The document triggered various discussions and it has been carefully
    reviewed by a few interested individuals. Overall it can be considered as a
    consensus of the WG as a whole.

(10) Has anyone threatened an appeal or otherwise indicated extreme discontent? If so, please summarise the areas of conflict in separate email messages to the Responsible Area Director. (It should be in a separate email because this questionnaire is publicly available.)

    No

(11) Identify any ID nits the Document Shepherd has found in this document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts Checklist). Boilerplate checks are not enough; this check needs to be thorough.

    None.

(12) Describe how the document meets any required formal review criteria, such as the MIB Doctor, media type, and URI type reviews.

    Not Applicable

(13) Have all references within this document been identified as either normative or informative?

    Yes.

(14) Are there normative references to documents that are not ready for advancement or are otherwise in an unclear state? If such normative references exist, what is the plan for their completion?

    No.

(15) Are there downward normative references references (see RFC 3967)? If so, list these downward references to support the Area Director in the Last Call procedure.

    No.

(16) Will publication of this document change the status of any existing RFCs? Are those RFCs listed on the title page header, listed in the abstract, and discussed in the introduction? If the RFCs are not listed in the Abstract and Introduction, explain why, and point to the part of the document where the relationship of this document to the other RFCs is discussed. If this information is not in the document, explain why the WG considers it unnecessary.

    No.

(17) Describe the Document Shepherd's review of the IANA considerations section, especially with regard to its consistency with the body of the document. Confirm that all protocol extensions that the document makes are associated with the appropriate reservations in IANA registries. Confirm that any referenced IANA registries have been clearly identified. Confirm that newly created IANA registries include a detailed specification of the initial contents for the registry, that allocations procedures for future registrations are defined, and a reasonable name for the new registry has been suggested (see RFC 5226).

    The IANA section is clear. It mixes existing early allocation, new request
    and import from another I-D in an precise manner.

(18) List any new IANA registries that require Expert Review for future allocations. Provide any public guidance that the IESG would find useful in selecting the IANA Experts for these new registries.

    Not Applicable.

(19) Describe reviews and automated checks performed by the Document Shepherd (to validate sections of the document written in a formal language, such as (XML code, BNF rules, MIB definitions, etc.)

    Not Applicable.

Request for posting confirmation emailed to previous authors: Wim Henderickx , Jonathan Hardwick , Edward Crabbe , Robert Raszuk , Victor Lopez , Jan Medved , pce-chairs@ietf.org, Jeff Tantsura , Clarence Filsfils , Siva Sivabalan

Request for posting confirmation emailed to previous authors: "Jan Medved" , "Siva Sivabalan" , "Jeff Tantsura" , "Wim Henderickx" , "Clarence Filsfils" , pce-chairs@ietf.org, "Victor Lopez" , "Jonathan Hardwick"