Re: [Pals] Soliciting reviews for draft-ietf-pals-vccv-for-gal-00.txt

Andy, Stewart and all,
I have read the draft (which is indeed, quite short!), and I have a couple of issues with it which, IMO, the WG should resolve one way or another.

1.       I disagree with the statement in Section 4 “When the PW is a single segment PW, the TTL field of the PW Label Stack Entry (LSE) MUST be set to 2.  TTL=2, rather than the more obvious TTL=1, is used because of legacy hardware considerations.” From my POV

a.       For a single-segment PW, any TTL value excluding 1, can be safely used

b.      TTL=1 in the PW LSE  Is defined in RFC 5085 for VCCV Type 3 (which is not even mentioned in the draft) for single-segment PWs

c.       RFC 6073 also refers to VCCV Type 3 (a.k.a. the TTL-based method)for multi-segment PWs

2.       I see the proposal (in section 5) to place  GAL at the bottom of the label stack for “fat PWs” with the flow PW directly preceding it as highly problematic:

a.       It strictly contradicts RFC 6391 which explicitly states that the flow label is always at the bottom of the label stack

b.      It makes proper treatment of VCCV packets problematic as explained below:

                                                               i.      T-PEs (which are aware of flow labels) would have not just to remove the Flow Label but also to check whether  the next label is  GAL

                                                             ii.      S-PEs of MS-PWs would have to become aware of flow labels while today they may be unaware of flow labels and simply pass these labels transparently (as per Section 6 of RFC 6391)

c.       Some types of forwarding HW are known to be limited to hashing only on the bottom-of-stack label for ECMP:

                                                               i.      Normally (with both “Fat PWs” as per RFC 6391 and with the “ELI/EL scheme” introduced in RFC 6790) this is sufficient since entropy is carried in the bottom-of-stack label in both schemes

                                                             ii.      The proposal in the draft, if accepted, would break normal ECMP behavior for both these schemes with such HW.

d.      In addition:

                                                               i.      The comment about the EL/ELI scheme as being relevant just for “MPLS LSP that carry the PW” is, IMO, incorrect. The only limitation of this scheme is that it cannot be together with the PW Flow Label scheme, but this is hardly restrictive

                                                             ii.      While the proposal in the draft breaks RFC 6391, this RFC  is not even mentioned as being updated (?) by the draft.

Hopefully these comments will be useful for both the authors of the draft and for the WG.

Regards,
       Sasha
Email: Alexander.Vainshtein@ecitele.com
Mobile: 054-9266302

From: Pals [mailto:pals-bounces@ietf.org] On Behalf Of Andrew G. Malis
Sent: Monday, December 22, 2014 4:33 PM
To: pals@ietf.org
Subject: [Pals] Soliciting reviews for draft-ietf-pals-vccv-for-gal-00.txt

PALSers,

i know that you would all like a little something to distract you from the holidays ... :-). Well, maybe not. But anyway, Stewart recently revised the VCCV for GAL draft (see below), and while short (just four pages of real content), we would like to have a good indication that it represents WG consensus, so we need at least some of you out there to read it and comment, even if that comment is "I've reviewed it and looks great to me". As I noted, it's a short draft, so it shouldn't take all that long.

You can read the draft at http://tools.ietf.org/html/draft-ietf-pals-vccv-for-gal-00 .

Thanks,
Stewart and Andy

---------- Forwarded message ----------
From: <internet-drafts@ietf.org<mailto:internet-drafts@ietf.org>>
Date: Wed, Dec 17, 2014 at 12:00 PM
Subject: I-D Action: draft-ietf-pals-vccv-for-gal-00.txt
To: i-d-announce@ietf.org<mailto:i-d-announce@ietf.org>
Cc: pals@ietf.org<mailto:pals@ietf.org>

A New Internet-Draft is available from the on-line Internet-Drafts directories.
 This draft is a work item of the Pseudowire And LDP-enabled Services Working Group of the IETF.

        Title           : VCCV Default CC Types
        Authors         : Thomas D. Nadeau
                          Luca Martini
                          Stewart Bryant
        Filename        : draft-ietf-pals-vccv-for-gal-00.txt
        Pages           : 8
        Date            : 2014-12-17

Abstract:
   This document specifies the default Virtual Circuit Connectivity
   Verification (VCCV) (RFC5085) control channel type to be used when
   the pseudowire control word is present and when it is not present.  A
   new VCCV control channel type using the Generic Associated Channel
   Label (RFC5586) is specified for use when the control word not
   present.

   This document updates RFC4447 and RFC5085.

   Note to be removed at publication: this document started out as
   draft-ietf-pwe3-vccv-for-gal and got to version -02.  When PWE3 was
   absorbed into PALS the next version published was draft-ietf-pals-
   vccv-for-gal-00

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-pals-vccv-for-gal/

There's also a htmlized version available at:
http://tools.ietf.org/html/draft-ietf-pals-vccv-for-gal-00

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org<http://tools.ietf.org>.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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