An Architecture for Use of PCE and the PCE Communication Protocol (PCEP) in a Network with Central Control
draft-ietf-teas-pce-central-control-05

Received changes through RFC Editor sync (changed abstract to 'The Path Computation Element (PCE) is a core component of Software- Defined Networking (SDN) systems. It can compute optimal paths for traffic across a network and can also update the paths to reflect changes in the network or traffic demands.

PCE was developed to derive paths for MPLS Label Switched Paths (LSPs), which are supplied to the head end of the LSP using the Path Computation Element Communication Protocol (PCEP).

SDN has a broader applicability than signaled MPLS traffic-engineered (TE) networks, and the PCE may be used to determine paths in a range of use cases including static LSPs, segment routing, Service Function Chaining (SFC), and most forms of a routed or switched network. It is, therefore, reasonable to consider PCEP as a control protocol for use in these environments to allow the PCE to be fully enabled as a central controller.

This document briefly introduces the architecture for PCE as a central controller, examines the motivations and applicability for PCEP as a control protocol in this environment, and introduces the implications for the protocol. A PCE-based central controller can simplify the processing of a distributed control plane by blending it with elements of SDN and without necessarily completely replacing it.

This document does not describe use cases in detail and does not define protocol extensions: that work is left for other documents.')

Received changes through RFC Editor sync (created alias RFC 8283, changed title to 'An Architecture for Use of PCE and the PCE Communication Protocol (PCEP) in a Network with Central Control', changed abstract to 'The Path Computation Element (PCE) is a core component of Software- Defined Networking (SDN) systems. It can compute optimal paths for traffic across a network and can also update the paths to reflect changes in the network or traffic demands.', changed standardization level to Informational, changed state to RFC, added RFC published event at 2017-12-21, changed IESG state to RFC Published)

[Ballot comment]
I like how clearly this document spells out the nature of the work that is to be performed to adapt PCEP to enable the described network architecture. It's not entirely clear to me what value it has as an archival document (rather than simply being used internally by the working group to guide future development). Has the working group explicitly discussed why they might want this published as an RFC?

This document uses the term "control plane" rather extensively without concretely defining it. While I can infer some things about what is meant, it appears to be intended as a very concrete and specific term. In particular, it seems to diverge from how that term is used in (e.g.) voice networks, to the point of meaning nearly the opposite (that is: I've gathered that it refers to the exchange of routing information on the same paths as are used to exchange traffic). If there is a formal definition of the term in some referenced document, I would think a citation to it would be useful. If not, please take a stab at a formal definition of this term early in this document.

Section 2.1.2 suggests that inter-controller state sync can be achieved by sharing a common back-end database ("...or by using a shared database."). Without further qualifying the database as being also distributed, this simply pushes the single point of failure from the controller to the database. Please add terms to qualify the database itself as being highly-available/distributed.

[Ballot comment]
Just some editorial comments:

- The abstract is unusually long, and seems more like an introduction. The second to last paragraph could almost stand by itself as a useful abstract.

- The terms "southbound" and "northbound" could use definition. (I find these terms cause lots of confusion, since not everyone draws the diagrams with the same idea of what goes on top or bottom.)

- 2.1.1: It's probably too late at this point to change it, but I find the use of "domains" unfortunate. That may be one of the most overloaded terms in the IETF lexicon, if not in that of the networking crowd at large. Since you describe them as "partitions", I think "partitions" would have been better.

- 2.1.2, 2nd to last paragraph: "This is nominally a simple task if
  there are just two controllers, but can actually be quite complex if
  state changes in the network are not to be lost."

That sentence seems self-contradictory. I don't think it's simple, nominally or otherwise.

[Ballot comment]
This topic is not my area (duh, but I mean knowledge, not AD responsibility), and I learned enough to ballot Yes while reviewing.

I find myself wondering why it’s more helpful than some other architecture drafts I’ve reviewed, and note that it’s also pretty close to a forward-looking applicability statement for PCE (re: https://tools.ietf.org/html/rfc2026#section-3.2). No action requested for this document, but something for ADs to think about, when we’re thinking about architecture documents in general.

I did see a couple of places that were not as clear to me as most of the document was.

In https://tools.ietf.org/html/draft-ietf-teas-pce-central-control-04#section-3.1.1, the description is short, which could be fine, but meant I was guessing at a lot of high-level details that I could dig out of https://tools.ietf.org/html/draft-ietf-pce-stateful-pce-21 for myself, but it might be helpful to include a couple of points, like whether the PCCs in this technology are (always?) LSRs participating in the IGP (OSPF or IS-IS), and whether the PCEs are (always?) either LSRs or servers also participating in the IGP, and whether the IGP is (always?) used to set up LSPs, for readers who have a (G)MPLS or MPLS-TE network now, to figure out how it maps at a high level to what they already have. I’m guessing from https://tools.ietf.org/html/draft-ietf-pce-stateful-pce-21#section-5.5, but I’m guessing.

I’m not quite sure what to do with this part of the security considerations:

  In
  short, while the interactions with a PCE-based controller are not
  substantially different to those in any other SDN architecture, the
  security implications of SDN have not been fully discussed or
  described.  Therefore, protocol and applicability work around
  solutions for this architecture must take proper account of these
  concerns.

  It is expected that each new document that is produced for a specific
  use case will also include considerations of the security impacts of
  the use of a PCE-based central controller on the network type and
  services being managed.

If I’m reading this literally, it’s saying that we haven’t finished discussing SDN security considerations in general yet, so each new document will consider the security impact of a PCE-based central controller on the network type and services being managed as an SDN. Is that what was meant?

If I’m reading the manageability considerations section correctly, perhaps it’s worth pointing out what the extension story is for the IGPs that will be used in some of the technologies discussed earlier in the document, if that’s part of this work as well.

[Ballot comment]
Thanks for a clearly written document. While reading the document, I also had a quick look at the teas charter and am wondering how this work is covered by the charter. This shouldn't stop publication, but maybe there is a need to update the charter, especially if more work in this space is expected.

[Ballot comment]
Thanks for a clearly written document. While reading the document, I also had a quick look at the teas charter and am wondering how this work is covered by the charter. This shouldn't stop publication, but maybe there is a need to update the charter, especailly if more work in this space is expected.

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

The IANA Services Operator has reviewed draft-ietf-teas-pce-central-control-03, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any registry actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, we do not object.

If this assessment is not accurate, please respond as soon as possible.

Thank you,

Sabrina Tanamal
IANA Services Specialist

The following Last Call announcement was sent out (ends 2017-08-24):

From: The IESG
To: IETF-Announce
CC: draft-ietf-teas-pce-central-control@ietf.org, db3546@att.com, Vishnu Beeram , teas-chairs@ietf.org, teas@ietf.org, vbeeram@juniper.net
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (An Architecture for Use of PCE and PCEP in a Network with Central Control) to Informational RFC


The IESG has received a request from the Traffic Engineering Architecture and
Signaling WG (teas) to consider the following document: - 'An Architecture
for Use of PCE and PCEP in a Network with Central
  Control'
  as Informational RFC

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 2017-08-24. 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


  The Path Computation Element (PCE) has become established as a core
  component of Software Defined Networking (SDN) systems.  It can
  compute optimal paths for traffic across a network for any definition
  of "optimal" and can also monitor changes in resource availability
  and traffic demands to update the paths.

  Conventionally, the PCE has been used to derive paths for MPLS Label
  Switched Paths (LSPs).  These paths are supplied using the Path
  Computation Element Communication Protocol (PCEP) to the head end of
  the LSP for signaling in the MPLS network.

  SDN has a far broader applicability than just signaled MPLS traffic
  engineered networks, and the PCE may be used to determine paths in a
  wide range of use cases including static LSPs, segment routing,
  service function chaining (SFC), and indeed any form of routed or
  switched network.  It is, therefore, reasonable to consider PCEP as a
  general southbound control protocol for use in these environments to
  allow the PCE to be fully enabled as a central controller.

  This document briefly introduces the architecture for PCE as a
  central controller, examines the motivations and applicability for
  PCEP as a southbound interface, and introduces the implications for
  the protocol.  A PCE-based central controller can simplify the
  processing of distributed control plane by blending it with elements
  of SDN and without necessarily completely replacing it.

  This document does not describe use cases in detail and does not
  define protocol extensions: that work is left for other documents.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-teas-pce-central-control/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-teas-pce-central-control/ballot/


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

> 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)?

Informational.

> Why is this the proper type of RFC? 

This is an architecture document. It discusses the architecture for PCE as
a central controller.

> Is this type of RFC indicated in the title page header?

Yes.

>
> (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.


  The Path Computation Element (PCE) has become established as a core
  component of Software Defined Networking (SDN) systems.  It can
  compute optimal paths for traffic across a network for any definition
  of "optimal" and can also monitor changes in resource availability
  and traffic demands to update the paths.

  Conventionally, the PCE has been used to derive paths for MPLS Label
  Switched Paths (LSPs).  These paths are supplied using the Path
  Computation Element Communication Protocol (PCEP) to the head end of
  the LSP for signaling in the MPLS network.

  SDN has a far broader applicability than just signaled MPLS traffic
  engineered networks, and the PCE may be used to determine paths in a
  wide range of use cases including static LSPs, segment routing,
  service function chaining (SFC), and indeed any form of routed or
  switched network.  It is, therefore, reasonable to consider PCEP as a
  general southbound control protocol for use in these environments to
  allow the PCE to be fully enabled as a central controller.

  This document briefly introduces the architecture for PCE as a
  central controller, examines the motivations and applicability for
  PCEP as a southbound interface, and introduces the implications for
  the protocol.  This document does not describe the use cases in
  detail and does not define protocol extensions: that work is left for
  other documents

> 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?

The progress of the document through the WG has been smooth.
There was some serious debate before the last call with regards
to implications on manageability and on PCEP. The authors addressed
all of these concerns by adding relevant text to the document.


>
> 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?


This document has been discussed and reviewed thoroughly by the WG.
The base PCE architecture and the PCEP protocol have been implemented.
The document that discusses the use-cases for PCE as a central controller
is actively being worked on. While there have been no public statements
on implementation of this new architecture, the authors are from multiple
vendors, and implementation is expected.


> Personnel
>
>  Who is the Document Shepherd?

Vishnu Pavan Beeram

> Who is the Responsible Area Director?

Deborah Brungard

>
> (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.

The Document Shepherd has reviewed the document as part of normal WG progress
and WG last call. The Shepherd believes this document is ready for publication.

>
> (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?

No.

> If so, describe the review that took place.

N/A.

>
> (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.

No specific concerns.

>
> (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, see thread
https://www.ietf.org/mail-archive/web/teas/current/msg02412.html


>
> (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 disclosed.

> (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? 

Solid among those who are interested. "strong concurrence of a few
individuals, with others being silent" is a reasonable
characterization.

> (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 discontent seen.

>
> (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.

The document passes ID nits.

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

N/A.

> (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 was fully reviewed by the document shepherd and is
appropriate for this draft.

> (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.

None.

> (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.

N/A