LDP Extensions for Hub and Spoke Multipoint Label Switched Path
draft-ietf-mpls-mldp-hsmp-06

[Ballot comment]
I think I grok what this thing is doing at a high level.  But the name "hub and spoke multipoint" seems inapt, since there's not actually a hub and spoke topology required, just a reverse path from leaves to root.  Wouldn't something like "P2MP with Upstream Path (PUP)" be more accurate?

The acronym "FEC" is never expanded, and might cause confusion for readers who like error correction.

[Ballot comment]
I am balloting No-Obj based on a quick scan of the document showing no impact on the Internet Area protocols and trust in the RTG ADs doing the right thing.

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-mpls-mldp-hsmp-04. Authors should review the comments and/or questions below.  Please report any inaccuracies and respond to any questions as soon as possible.

IANA's reviewer has the following comments/questions:

We understand that three actions are required upon approval.

ACTION 1:

IANA will register the following in the 0-127 range of the Forwarding Equivalence Class (FEC) Type Name Space registry (Label Distribution Protocol (LDP) Parameters) at http://www.iana.org/assignments/ldp-namespaces:

TBD1  HSMP-upstream  [RFC-to-be]
TB2D  HSMP-downstream  [RFC-to-be]


ACTION 2:

IANA will register the following in the 0x0901-0x3DFF range of the TLV Type Name Space registry (Label Distribution Protocol (LDP) Parameters) at http://www.iana.org/assignments/ldp-namespaces:

TBD1  HSMP LSP Capability Parameter  [RFC-to-be]


ACTION 3:

IANA will register the following in the 0-16383 range of the Sub-TLVs for TLV Types 1 and 16 sub-registry (Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters) at http://www.iana.org/assignments/mpls-lsp-ping-parameters:

TBD1  HSMP-upstream LDP FEC Stack  [RFC-to-be]
TBD2  HSMP-downstream LDP FEC Stack  [RFC-to-be]

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 only to confirm what actions will be performed.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (LDP Extensions for Hub & Spoke Multipoint Label Switched Path) to Proposed Standard

The IESG has received a request from the Multiprotocol Label Switching WG
(mpls) to consider the following document:
- 'LDP Extensions for Hub & Spoke Multipoint Label Switched Path'
  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 2013-12-10. 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

  This draft introduces a hub & spoke multipoint (HSMP) Label Switched
  Path (LSP), which allows traffic both from root to leaf through
  point-to-multipoint (P2MP) LSP and also leaf to root along the
  reverse path.  That means traffic entering the HSMP LSP from
  application/customer at the root node travels downstream to each leaf
  node, exactly as if it is travelling downstream along a P2MP LSP to
  each leaf node.  Upstream traffic entering the HSMP LSP at any leaf
  node travels upstream along the tree to the root, as if it is unicast
  to the root.  The communication among the leaf nodes are not allowed.


The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-mpls-mldp-hsmp/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-mpls-mldp-hsmp/ballot/

The following IPR Declarations may be related to this I-D:

  http://datatracker.ietf.org/ipr/1777/
  http://datatracker.ietf.org/ipr/2191/

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 16 October 2013.

  The MPLS working group requests that:

        LDP Extensions for Hub & Spoke Multipoint Label Switched Path
                      draft-ietf-mpls-mldp-hsmp-03.txt

  is published as an RFC on the standards track.

(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?

  Type of RFC: Proposed Standard.
  Why PS: The document specifies new protocol elements and procedures that
  extend a standard track document. This is clearly a standard tracks document.

(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

  This draft introduces a hub & spoke multipoint (HSMP) Label Switched
  Path (LSP), which allows traffic both from root to leaf through
  point-to-multipoint (P2MP) LSP and also leaf to root along the
  reverse path.  That means traffic entering the HSMP LSP from
  application/customer at the root node travels downstream to each leaf
  node, exactly as if it is travelling downstream along a P2MP LSP to
  each leaf node.  Upstream traffic entering the HSMP LSP at any leaf
  node travels upstream along the tree to the root, as if it is unicast
  to the root.  The communication among the leaf nodes are not allowed.

Working Group Summary

  There were nothing remarkable in the WG process, all decision were
  taken after converged discussions.

Document Quality

  The working group chairs has sent an implementation poll to the
  working group mailing list.
  If/when we have news the Shepherd write-up will be updated.

  For the time being we are aware of implementations and intentions to
  implement.

  The document has been reviewed in the normal wg process,
  all comments has been  fairly easily resolved.

  The MPLS-RT reviewers have Mach Chen and Thomas Morin. The third
  reviewer did not respond)

Personnel

  Shepherd: Loa Andersson
  Responsible AD: Adrian Farrel

(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 twice; once prior to
  making it a working group document. And a second time during working
  group last call.

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

  No, the Shepherd is comfortable with the  reviews of this document.

(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.

  No such reviews necessary.

(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 such 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.

  All the authors has confirmed that they are un-aware of any other IPRs
  other than the one that has been disclosed.

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

  There are two IPR disclosures against this document  (ID # 1777 and
  ID # 2191)

. However, in reallity this is only one disclosure, since the owner of
  the IPR, re-disclosed  when we did the IPR poll, updating the earlier
  disclosure.

(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 working group is behind this document.

(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.)

  Not such threats.

(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 the nits tool clean :)!

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

  No formal reviews required.

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

  Yes - they have been correctly split in normative and informative references.

(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?

  All normative references are too existing RFCs.
  Note: Four informative references are to "work in progress", but to the best
  of the knowledge of the Shepherd these IDs are also well under way
  to become RFCs. All of the "work in progress" references are to IDs
  progressed in other working groups than MPLS:

(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 downward references.

(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 existing RFC will be changed.


(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 well and clearly written. The IANA registries are
  clearly defined.
  However there is one glitch; the registries from which allocations are requested
  contain several ranges

(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.

There are no new registries that require expert review specified in this document.

(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.

  No such reviews.

Hi,

I have done my usual AD review of your document having received the
publication request from the working group. The purpose of the review is
to catch and clean up any issues before the document goes to IETF last
call and IESG evaluation.

The WG chairs tell me that there is at least one implementation and a
few planned implementations, so it is clear we should look at how to
advance this work. At the same time I have a number of issues with the
text that I believe need to be fixed or discussed before we can do that.

Could you please work through the comments below and either produce a
revised document or let me know why I am wrong.

Thanks,
Adrian

===========

You will need to expand some acronyms on first use.
You need to expand them in the Abstract and in the main text even if
they are already expanded in the Abstract.
I see:
LSP
P2MP
OAM
PW
PE
P2P
VPMS
IPTV
FEC
LSR
LER

---

Section 2

All good except would be good to actually expand the acronyms rather
than just explaining them.

Perhaps also give a reference for mLDP.

---

Please read the comments on Sections 3.1 to 3.3, below, and then the
meta-comment that follows.

---

Section 3.1

I believe that the TicToc working group has agreed to change the status
of [I-D.ietf-tictoc-1588overmpls] to be Experimental because it only
describes an approach, and does not have consensus of the MPLS
community.

So I think you should

OLD
  [IEEE1588] over MPLS is defined in [I-D.ietf-tictoc-1588overmpls].
NEW
  [I-D.ietf-tictoc-1588overmpls] describes a possible approach to
  carry [IEEE1588] over an MPLS network.
END

I do believe this use case in as much as timing synchronization benefits
from the forward and reverse paths being identical.  I am less sure that
P2MP timing synchronization is a big requirement, but I am happy to
believe you if you say it is needed.

---

I think you need to do some rewriting in Section 3.2

[I-D.ietf-pwe3-p2mp-pw] expired over a year ago meaning that it has made
no progress for about 20 months. It appears to have been abandoned by
the WG. I think that part of the reason was that the solutions offered
provided too much complexity when the rend result could be achieved more
simply.

This leads to wonder whether your use case is making too many
assumptions.

You could possibly use draft-ietf-pwe3-p2mp-pw-requirements as your
reference, but to be honest with you, that I-D is not in a  good place
either having been sent back to the WG by its AD.

Similarly, [I-D.ietf-l2vpn-vpms-frmwk-requirements] expired more than
six months ago meaning it has made no progress for a year.

You could rewrite this section to establish the requirements in your
text rather than by reference, but IMHO, the best thing is to remove the
whole section.

---

As far as I can tell, section 3.3. does not provide a motivating use
case for this work. It is true that if you do have HSMP it would server
the purpose, but I do not believe that the IGMP messages or the channel
switch messages or whatever have to follow the reverse path of the P2MP
distribution tree.

This makes me think that you have two classes of use case (in the set of
two use cases that remain after the removal of section 3.2). The first
is the type of use case that motivates the invention of HSMP. The second
is the type of use case that shows that HSMP could also be used for
other things. Really, we need to separate these out to see whether there
is real motivation for this work.

Does this mean that the only reason for this work is time distribution
in a multicast network?

---

The comments on Sections 3.1 to 3.3, above, make me wonder about the
value of Section 3. What does it add to the document? Was it intended to
prove that there is a purpose to this work, or was it just trying to
show some ways that HSMP might be used?

If the latter, I recommend simply removing the whole section.

If the former, I think you have failed! :-(
If you *do* want show that there is value in the work (and I don't
believe you need to *if* people are coding/deploying this function) then
I suspect that the real motivation for this work is that it provides
MP2MP functionality with the simplicity of a single hub compared to the
multiple "distributed" hubs of MP2MP LSPs. If you feel the need to show
a purpose, then I think *this* is the topic you need to discuss in
Section 3.

---

Section 4

  HSMP LSP is similar with MP2MP LSP described in [RFC6388], with the
  difference that the leaf LSRs can only send traffic to root node
  along the same path of traffic from root node to leaf node.

This paragraph is very ambiguous.
Is it that the LSRs can only send *traffic*?
Is it that the LSRs can only send *to*the*root*?
Or is it that the LSRs can only send *along*the*same*path*

I think you need

  HSMP LSP is similar to MP2MP LSP described in [RFC6388], with the
  difference that in HSMP, when the leaf LSRs send traffic on the LSP,
  the traffic is first delivered only to the root node and follows the
  reverse path of traffic sent from the root node to the leaf node. The
  root note then distributes the traffic on the P2MP tree to all of the
  leaf nodes.

---

Section 4

  The transmission of packets from the root node of an HSMP LSP
  to the receivers is identical to that of a P2MP LSP.  Traffic from a
  leaf node follows the upstream path toward the root node, along a
  path that traverse the same nodes as the downstream node, but in
  reverse order.

I believe this says that traffic is delivered back to the sender in all
cases. Is that the intent?

This makes for a significant difference between HSMP and MP2MP, doesn't
it? Shouldn't the document make this clearer?

---

Although Figure 1 shows the settings of the U and F bits, I think you
should mention them explicitly. This seems to be important because it
impacts what happens if there is an LSR in the path that does not
support HSMP.

---

Somewhat to my surprise, the use of the HSMP capability TLV is not
described anywhere. Reading between the lines in Section 4.1 I can see
that the new TLV is carried on the Initialization message. I can also
see that an implementation wishing to indicate it supports HSMP includes
the TLV and follow the procedures for indicating capabilities as defined
in RFC 5561.

But I don't find anything saying MUST NOT use HSMP FEC is peer does not
support HSMP.

I also don't understand what happens if I am tying to build an HSMP LSP
and discover that the next hop does not support HSMP. Can I have an
HSMP LSP with a hole in it? Does an LSR finding it cannot advance an
HSMP FEC fail any received HSMP LDP messages? Is there, in fact, an
assumption that all nodes that might be on an HSMP tree will support
HSMP?

I think you need to explain all this. You could look to RFC 6388 for
some suitable wording.

---

Throughout Section 4 the references to 6388 for process may be "obvious"
but are broken.

For example, in 4.3.1 you have

  Determining the upstream LSR for the HSMP LSP  follows the
  procedure for a MP2MP LSP described in [RFC6388] Section 3.3.1.1.

But Section 3.3.1.1 of RFC 6388 says:

  Determining the upstream LDP peer U for an MP2MP LSP  follows
  the procedure for a P2MP LSP described in Section 2.4.1.1.

This is a double indirection, so you should go direct to the source.

For example, later in 4.3.1 you have

  Determining one's HSMP downstream LSR follows the procedure defined
  in [RFC6388] section 3.3.1.2.

But Section 3.3.1.2 of RFC 6388 says

  An LDP peer U that receives an MP2MP-D Label Mapping from an LDP peer
  D will treat D as downstream MP2MP LSR.

which is not helpful in the context of this I-D.

I think the bottom line is that this document needs to be written to
desribe the processes that apply for these extensions.

Looking to the future, there is a strong case to be made that HSMP
might get more traction than MP2MP (since it provides the same user
service with a number of simplifications). If this turns out to be the
case, you do not want this document to need to lean on RFC 6388. It
should be independent. By all means reference 6388 for comparison, but
do not use it to define your processes.

---

I am unconvinced by Section 7. As I read the rest of the document, HSMP
has a high reliance on being able to produce a tree where the leaf-to-
root path is co-routed (in the opposite direction) with the root-to-leaf
path for each leaf. But I don't see anything in the document that
*makes* this happen.

Section 7 seems to expose that the document assumes that co-routing will
happen fortuitously. That is, when it doesn't occur, the network is
requested to detect the fact and scream.

If the main purpose of HSMP is the co-routing, shouldn't this be
factored into the protocol?

If detection and reporting of non-co-routed HSMP LSPs is so important,
shouldn't the protocol enable it? And maybe the LSP shouldn't even come
up?

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 16 October 2013.

  The MPLS working group requests that:

        LDP Extensions for Hub & Spoke Multipoint Label Switched Path
                      draft-ietf-mpls-mldp-hsmp-03.txt

  is published as an RFC on the standards track.

(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?

  Type of RFC: Proposed Standard.
  Why PS: The document specifies new protocol elements and procedures that
  extend a standard track document. This is clearly a standard tracks document.

(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

  This document specifies a hub & spoke multipoint LSP (HSMP LSP),
  which allows traffic both from root to leaf through P2MP LSP and also
  leaf to root along the co-routed reverse path.  That means
  traffic entering the HSMP LSP at the root node travels downstream to
  each leaf node along a P2MP LSP.  Upstream traffic entering the HSMP
  LSP at any leaf node travels upstream along a unicast LSP to the root.
  The leaf to root LSP is co-routed with the P2MP tree, i.e. compared ot the
  traffic from root to leaf, traffic from leaf to root traverse the same nodes,
  but in reverse order.

Working Group Summary

  There were nothing remarkable in the WG process, all decision were
  taken after converged discussions.

Document Quality

  The working group chairs has sent an implementation poll to the
  working group mailing list.
  If/when we have news the Shepherd write-up will be updated.

  For the time being we are aware of implementations and intentions to
  implement.

  The document has been reviewed in the normal wg process,
  all comments has been  fairly easily resolved.

  The MPLS-RT reviewers have Mach Chen and Thomas Morin. The third
  reviewer did not respond)

Personnel

  Shepherd: Loa Andersson
  Responsible AD: Adrian Farrel

(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 twice; once prior to
  making it a working group document. And a second time during working
  group last call.

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

  No, the Shepherd is comfortable with the  reviews of this document.

(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.

  No such reviews necessary.

(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 such 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.

  All the authors has confirmed that they are un-aware of any other IPRs
  other than the one that has been disclosed.

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

  There are two IPR disclosures against this document  (ID # 1777 and
  ID # 2191)

. However, in reallity this is only one disclosure, since the owner of
  the IPR, re-disclosed  when we did the IPR poll, updating the earlier
  disclosure.

(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 working group is behind this document.

(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.)

  Not such threats.

(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 the nits tool clean :)!

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

  No formal reviews required.

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

  Yes - they have been correctly split in normative and informative references.

(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?

  All normative references are too existing RFCs.
  Note: Four informative references are to "work in progress", but to the best
  of the knowledge of the Shepherd these IDs are also well under way
  to become RFCs. All of the "work in progress" references are to IDs
  progressed in other working groups than MPLS:

(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 downward references.

(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 existing RFC will be changed.


(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 well and clearly written. The IANA registries are
  clearly defined.
  However there is one glitch; the registries from which allocations are requested
  contain several ranges

(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.

There are no new registries that require expert review specified in this document.

(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.

  No such reviews.