Elwyn,
This is a great review. Thank you.
Please see inline.
Deborah,
We will be queueing edits, let me know when you’d want us to post an updated
revision.
On Apr 10, 2016, at 1:26 PM, Elwyn Davies <elw...@dial.pipex.com> wrote:
I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair. Please treat these comments just
like any other last call comments.
Apologies for the slightly late review - I was stricken by a stomach bug.
I hope you are feeling better!
For more information, please see the FAQ at
<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
Document: draft-ietf-l2tpext-sbfd-discriminator-03.txt
Reviewer: Elwyn Davies
Review Date: 2016/04/10
IETF LC End Date: 2016/04/05
IESG Telechat date: (if known) -
Summary: Almost ready. There are a number of acronyms that need expansion and I
am unclear how an implementation of S-BFD getting its discriminators via L2TPv3
would know what entities the advertised discriminators (whether one or many)
should be associated with. This probably just needs a single sentence to sort
it out, but I found the existing wording to be either inappropriate or just
plain wrong.
These items, with the exception of the acronym expansion, have already been
discussed. See below line-by-line responses to each of these potential issues,
as well as a set of HTML diffs from the working copy, FYI.
Nearly Major Issue:
Question:
The format allows multiple discriminators to be sent in one message. Looking
at the S-BFD base draft (s3), it is implied that if a S-BFD module is dealing
with multiple discriminators they would be associated with multiple different
entities. How would the receiver know what entity each of the discriminators
was supposed to be associated with? It seems to me that the receiver would
want to know this but I may not have understood what is going on here. I guess
one way would be to use a part of the discriminator bit pattern but I don't
know if this might make it more difficult to achieve uniqueness in a domain.
Alternatively a purpose provided field could be sent in addition to each
discriminator, or different AVP IDs used for well-known purposes.
Thanks for raising this — although this was discussed and addressed, it might
not be self-evident. See the next comment.
The sentence at the end of para 4 of s2.1:
When multiple S-BFD discriminators are
advertised, the mechanism to choose a subset of specific
discriminator(s) is out of scope for this document.
may be associated with this question but I am not sure
Indeed, this is the relevant paragraph.
This paragraph was also added to other related documents (ISIS, OSPF), and goes
hand-in-hand with the following paragraph from draft-ietf-bfd-seamless-base-08:
The use of multiple S-BFD
discriminators by a single network node is therefore discouraged
until a means of learning the mapping is defined.
Now, that said, it is clear that if it created confusion in this review, this
can also create future confusion.
(1) which end is supposed to be choosing - is the Initiator choosing which to
advertise or the Responder choosing which to 'do something with', and
(2) it seems to me that the L2TPv3 receiver or its associated S-BFD module
would be deciding on some well-defined basis which entities were associated
with which designator rather than just making an arbitrary choice.
I suggest that a sentence indicating how the association of discriminators to
entities is done (or even that it needs to be done but how it is done is out of
scope) needs to be added, and the sentence above needs to be clarified or
subsumed in this new part (unless either of the more draconian alternatives
suggested above is thought to be appropriate).
To really minimize the chance of that future confusion, I agree with your
suggestion. I added such sentence and reworded the paragraph a bit. Further
comments on the proposed text most welcome.
Minor issues:
None
Nits/editorial comments:
Abstract: I'm afraid you are going to have expand the acronyms AVP, L2TP and BFD
here. References to RFC 5880 and the new S-BFD draft RFC would also be helpful - in
the form "(RFC 5880, I-D.ietf-bfd-seamless-base)”.
Acronyms expanded. Since the Abstract should not have citations, I am hesitant
to add anything else. It is clearly in the Introduction.
s1.1: The L2TP message names used in s2.1 and elsewhere (ICRQ, ICRP, OCRQ,
OCRP) need to be expanded - here would be as good as anywhere.
S1.1 already specifies expectations to readers, which include these L2TP
messages:
1.1. Terminology
The reader is expected to be very familiar with the terminology and
protocol constructs defined in S-BFD (see Section 2 of
[I-D.ietf-bfd-seamless-base]) and L2TPv3 (see Section 1.3 of
[RFC3931]).
But sure, will expand on first use as well.
s2.1: Need to expand AVP and ID.
Seems a bit repetitive, but done.
Thanks,
— Carlos.
