Re: Genart last call review of draft-ietf-sfc-nsh-19

["Carlos Pignataro (cpignata)" <[e-mail]>]

Thanks to you, Dan!

—
Carlos Pignataro, [e-mail]<mailto:[e-mail]>

“Sometimes I use big words that I do not fully understand, to make myself sound more photosynthesis."

On Aug 31, 2017, at 11:56 PM, Dan Romascanu <[e-mail]<mailto:[e-mail]>> wrote:

Hi Carlos,

Thank you for addressing my comments. Your suggested edits seem to address
the issues.

Regards,

Dan


On Fri, Sep 1, 2017 at 3:55 AM, Carlos Pignataro (cpignata) <
[e-mail]<mailto:[e-mail]>> wrote:

Hi, Dan,

Many thanks for your detailed and valuable review, and apologies for the
delay in Ack-ing and responding.

Please see inline.

—
Carlos Pignataro, [e-mail]<mailto:[e-mail]>

“Sometimes I use big words that I do not fully understand, to make myself
sound more photosynthesis."

On Aug 22, 2017, at 11:34 AM, Dan Romascanu <[e-mail]<mailto:[e-mail]>> wrote:

Reviewer: Dan Romascanu
Review result: Almost Ready

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.

For more information, please see the FAQ at

<https://trac.ietf.org/trac/gen/wiki/GenArtfaq>.

Document: draft-ietf-sfc-nsh-19
Reviewer: Dan Romascanu
Review Date: 2017-08-22
IETF LC End Date: 2017-08-25
IESG Telechat date: 2017-09-14

Summary:

This document describes the header (called Network Service Header - NSH)
to be
inserted in packets and frames in order to create packets and frames that
realize service functions described by other SFC documents. It needs to
be read
in conjunction with RFC 7665 and other documents as the SFC control
plane I-D
in order to make sense of the required functionality. This part of the
SFC
solution seems almost ready, but a few issues mentioned below need in my
opinion clarification before the document is approved.

Thank you for this summary — you raise good points.


Major issues:

1. Section 11.1 claims: 'An IEEE EtherType, 0x894F, has been allocated
for
NSH'. I could not find this value in the tables displayed by the IEEE
Registration Authority (RAC) - for example at
http://standards-oui.ieee.org/ethertype/eth.txt. Neither does IANA at
https://www.iana.org/assignments/ieee-802-numbers/ieee-802-numbers.xhtml
(which
would not be in any case the authoritative source). Can you please
indicate the
source that this is indeed a confirmed IEEE EtherType registration.

I am not sure how often that page is updated, but the same link you
include, http://standards-oui.ieee.org/ethertype/eth.txt, shows:

0x894F
894F: NSH (Network Service Header). Reference: draft-ietf-sfc-nsh-18

Granted, that registration will be updated with the RFC number instead of
the I-D, when it publishes.


2. Section 5 refers to ietf-rtgwg-dt-encap which is expired. If I
understand
correctly the status of this work, there is a design team in place in the
Routing Area created to look at common issues for the different data
plane
encapsulations being discussed in various WGs including SFC. This leaves
the
issue unsettled at this stage and this may be a problem for a standards
track
document. I suggest that first the reference to the expired document is
removed, second that the issue is marked as 'open' and subject for
future work.


Good suggestion. Instead of removing the reference all together, we can
mark it as exemplifying of one approach.

Minor issues:

1.  Two values 'Experiment 1' and 'Experiment 2' are defined in section
2.2 and
11.2.5 for the Next Protocol. This seems a little odd. Why 2? Why are
they
defined at the end of the range? Maybe there is an explanation for those
who
know the history but for an un-initiated reader or a future implementer
this
seems odd.

There is no strong rational behind the number of values (two) or the
location (towards the end of the range). There are two values as it seems
appropriate given the same of the number space (2 out of 256).

Perhaps, it’s somewhat following common practice started at
https://tools.ietf.org/html/rfc3692#section-2.1 (2 values for and 8-bit
field, closer to the end).


2. In Section 2.2 I see:

All other flag fields, marked U, are unassigned and available for
 future use, see Section 11.2.1.  Unassigned bits MUST be set to zero
 upon origination, and MUST be ignored and preserved unmodified by
 other NSH supporting elements.  Elements which do not understand the
 meaning of any of these bits MUST NOT modify their actions based on
 those unknown bits.

The way the last sentence is written it seems to open the path for
elements
that claim to 'understand' the meaning of some Unassigned bit to modify
its
behavior based upon it. This does not seem good, as at transmission all
Unassigned bits MUST be set to zero. I would suggest to make the
statement
simpler and just say that at reception all elements MUST NOT modify their
actions based on these bits.


Very good point, and good improvement. Applied.

3. In Section 2.2 I see:

0xF - This value is reserved for experimentation and testing, as per
 [RFC3692].  Implementations not explicitly configured to be part of
 an experiment SHOULD silently discard packets with MD Type 0xF.

Why is this a SHOULD and not a MUST?


To use MUSTs very sparingly and leave a little bit of leeway for
experimentation, following appropriate justification.

4. I believe that  [I-D.ietf-sfc-control-plane] needs to be a Normative
Reference. There are several places in the document (e.g. in Section
2.3) where
this document is referred to describe behavior or actions related to the
fields
of the header.


The control plane I-D is, by WG decision, intended to not be normative as
NSH is the data plane independent of the CP spec.

I see that [I-D.ietf-sfc-control-plane] is cited in two places:

1.
      [I-D.ietf-sfc-control-plane] provides an example of such in

2.
  process.  These considerations are deployment-specific.  However, the
  control plane is entitled to instruct SFC-aware SFs with the data
  structure of context header together with its scoping (see
  Section 3.3.3 of [I-D.ietf-sfc-control-plane]).


We already caught the issue with #2 and changed it to, in our working copy
working with the chairs, to:

  process.  These considerations are deployment-specific.  However, the
  control plane is entitled to instruct SFC-aware SFs with the data
  structure of context header together with its scoping (see e.g.,
  Section 3.3.3 of [I-D.ietf-sfc-control-plane]).

As that’s one possible, and non-normative way, out of many ways.

5. The version number has only two bits assigned. Moreover, this document
reserves already two values without any explanation why (only 00 is
mandatory
to use, as far as I understand). This needs to be explained (maybe
'historical'
reasons - but unclear for future readers and users) and may be a
limitation as
the protocol develops.

The version field is indeed a two-bit field. One reserved and will not be
used. One used by this spec, and two unassigned ones.

We really expect to not be bumping up version number ofter — or ever…


Nits/editorial comments:

1. Please make sure that acronyms are expanded at first occurrence (e.g