Media Access Control (MAC) Address Withdrawal over Static Pseudowire
draft-ietf-pals-mpls-tp-mac-wd-03

[Ballot comment]
I agree with the Gen-ART review from Ralph Droms; there are points where this document could be clearer. The one case that I felt personally strongly about was the part about what number the sequence numbers must start from. The text makes the reader wonder if one should read it literally, or if the starting number is handled differently. It would be better to be explicit.

I have balloted no-obj for this document, but would very much like to see the discussion with Ralph continue and some changes based on the comments adopted.

[Ballot comment]
I also agree with the SecDir review (Stephen already provided a link) and would like to see the security considerations specific to this draft added.

[Ballot comment]

- The secdir review [1] raised a few points that deserve a
response I think, did I miss the response?

  [1] https://www.ietf.org/mail-archive/web/secdir/current/msg06097.html

- Where in the referenced RFCs in the security considerations
is the DoS potential of MAC address withdrawal covered?

[Ballot comment]
Just a few editorial comments:

- Please expand PW, H-VPLS and PBB-VPLS on first mention. (The abbreviation list is helpful, but it's still good to expand them in place on first mention.)

- section 1, first paragraph:

s/withdrawl/withdrawal

- section 3: "A single bit (called A-bit) is set to indicate if a MAC withdraw message is for ACK"

I don't understand what this means, and I don't find any further explanation of the A-Bit. Do you mean to say that the MAC withdraw message requires an ACK? Isn't that always true? If the A-bit is already defined elsewhere, a citation would be helpful.

- Paragraph starting with "Only half of the sequence number space is used. "

It seems odd to find that between the descriptions of the A and R bits. Does it relate to the A-Bit, or does it stand alone? (I gather the latter.)

- There's an empty "Informative References" section.

[Ballot comment]
I have some comments that, while non-blocking, I would like to see addressed before publication.

1. Section 3. (MAC Withdraw OAM Message)  I don't understand why "when sequence number wraps, all MAC addresses are flushed".  Presumably, the wrap in the sequence number would be the result of a new MAC List TLV, so why would all the addresses be flushed and not just the ones on the list?  What am I missing?

2. Section 4.1. (Operation of Sender)  "…if a need to send a new MAC withdraw message with updated sequence number arises then retransmission of the older unacknowledged withdraw message MUST be suspended and retransmit time for the new sequence number MUST be initiated."  That sounds fine to me, but I have a related question.  Should the contents of the withdraw message include both the un-ack'ed list as well as the new addresses?  It is not clear from the text above.  I ask this in light of the text in Section 3 that reads: "The receipt of same or lower sequence number message is responded with ACK but does not cause removal of MAC addresses."  IOW, if the un-ack'ed list is not included in the new message then those addresses may not be withdrawn.

3. Also in 4.1. "The 'R' reset bit is set in the first MAC withdraw…"  I'm assuming the Sequence Number with the R-bit set will always be 1, is that true?  Does the text mean that there will in fact be a MAC List TLV if the R-bit is set?  Later in Section 4.2 it says that a message "…with 'R' bit set…MAC withdraw message processing is performed as described above."  All this seems problematic due to the text ("above") that says: "If the sequence number in the received message is smaller than or equal to the value in the register, the MAC TLV(s) is/are not processed."  IOW, of the R-bit is set (assuming Sew Number = 1), then the Seq Number will be smaller than whatever was received before and the MAC TLV will not be processed.  The logic doesn't seem to work for me..

4. Security Considerations.  I traced all the way back to RFC4385, where it hints at the ability of an attacker to disrupt the PW by misusing the associated channel..but couldn't find an authoritative reference to whether spoofing or changing the messages in flight is an issue.  I'm worried about the ability of someone to, for example, inject/modify the MAC List, or simply change the R-bit setting.  I may just be paranoid, so please point me in the right direction.

[Ballot discuss]
I expect that this is a very simple and quick Discuss to deal with.

1) In Sec 4.1, it first says "The retransmission MUST be
  ceased anytime when ACK is received or after three retries." which is fine but
then - "For instance, 1 second
  retransmission with three retries in absence of ACK response is
  suggested in this document.  However, incremental backoff with higher
  number of retries is also feasible and may be worth consideration to
  address the scale issues.  This document does not mandate a strict
  guideline since there are no interoperability implications."

CLEARLY, using MUST is more than a gentle suggestion - but is exactly
mandating a strict guideline.

Please fix either the MUST or the remaining text.

[Ballot comment]
Just total nit-level stuff here, mostly unexpanded abbreviations that should be expanded. 

Note to responsible AD: While "MAC", by itself, still needs to be expanded (because of multiple possible meanings), "MAC address", as a unit, probably qualifies for flagging in the RFC Editor's abbreviation list as not requiring expansion.

-- Abstract --
PW, VPLS, H-VPLS
(Because the abstract has to stand alone.)

-- Introduction --
PBB.  It would also help to have a forward pointer to Section 2, though I honestly don't know how to do that without having it look silly.

-- Section 2 --
For MPLS, "Multiprotocol" (one word, no capital "P") is the preferred spelling.
For PW, "Pseudowire" (no capital "W") is the preferred spelling.

-- Section 3 --
H-VPLS

-- Section 4.2 --

  A MAC withdraw message with 'R' bit set MUST be processed by
  resetting the send and receive sequence number first.

I suggest making it "the send-and-receive sequence number" (with hyphens), so no one thinks there are two sequence numbers (and gets confused by it not being "numbers").

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

IANA has completed its review of draft-ietf-pals-mpls-tp-mac-wd-02. If any part of this review is inaccurate, please let us know.

IANA understands that upon approval of this document, there are two actions which need to be completed.

First, in the MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types) subregistry of the Generic Associated Channel (G-ACh) Parameters registry located at:

http://www.iana.org/assignments/g-ach-parameters/

a new type is to be registered as follows:

Value: [ TBD-at-Registraion ]
Description: MAC Withdraw OAM Message
Reference: [ RFC-to-be ]

IANA notes that the value 0x0028 is requested (and is currently available) for this registration.

Second, a new registry is to be created called the MAC Withdraw sub-TLV registry. This will be a subregistry of the Generic Associated Channel (G-ACh) Parameters registry located at:

http://www.iana.org/assignments/g-ach-parameters/

The registry will be managed via the following policies:

The value 0 and the values 16,384 to 65,535 are reserved and not available for assignments. The range 1 to 16,383 is available for assignments, with the "Standards Action" policy as defined in RFC 5226.

There are initial registrations in the new subregistry as follows:

Type Description Reference
-------- ---------------------------------------- ---------------
0 Reserved (not available for allocation) [ RFC-to-be ]
1 Sequence Number [ RFC-to-be ]
2-16383 Unassigned
16384-65635 Reserved (not available for allocation) [ RFC-to-be ]

IANA understands that these two actions are the only ones 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 only to confirm what actions will be performed. 

Please note that IANA cannot reserve specific values. However, early allocation is available for some types of registrations. For more information, please see RFC 7120.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (MAC Address Withdrawal over Static Pseudowire) to Proposed Standard


The IESG has received a request from the Pseudowire And LDP-enabled
Services WG (pals) to consider the following document:
- 'MAC Address Withdrawal over Static Pseudowire'
  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 2015-10-19. 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 document specifies a mechanism to signal MAC address withdrawal
  notification using PW Associated Channel (ACH).  Such notification is
  useful when statically provisioned PWs are deployed in VPLS/H-VPLS
  environment.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-pals-mpls-tp-mac-wd/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-pals-mpls-tp-mac-wd/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)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

Proposed Standard

(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 mechanism to signal MAC address withdrawal
  notification using PW Associated Channel (ACH).  Such notification is
  useful when statically provisioned PWs are deployed in VPLS/H-VPLS
  environment.

Working Group Summary

This draft was previously in the L2VPN WG before being moved to the PALS WG. It was a typical draft, with most of the technical comments being made as it progressed through several revisions as an individual draft. As a result, it was in pretty good shape when it reached PALS WG LC. Both PALS chairs reviewed the draft in detail and provided comments, which were addressed by the authors prior to IESG submission.

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?

As noted above, both PALS chairs reviewed the draft in detail and provided comments, which have been addressed. The chairs are aware of at least one implementation in active use, and there may be others as well.

Personnel

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

Andy Malis, 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 shepherd (also WG co-chair) reviewed the draft in detail and provided comments that have been addressed. The shepherd is pleased with the document quality.

(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.

No.

(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 concerns or issues. The draft's functionality is very useful and is in active use.

(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 disclosures have been filed.

(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? 

There is solid consensus.

(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.

There is a warning that one page is one line too long. This will be fixed by the RFC Editor.

(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.

None.

(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.

N/A

(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 Considerations section follows the instructions in RFC 5226. There is one new channel type requested from the "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types)" registry. A specific previously undefined value has been requested, that is the value that was used to implement the draft. The draft defines a new Sequence Number TLV and a new sub-registry to assign values to the TLV.

(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, the new sub-registry only requires Standards Action for new assignments.

(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