[tcpm] Francesca Palombini's No Objection on draft-ietf-tcpm-rfc793bis-25: (with COMMENT)

Francesca Palombini via Datatracker <noreply@ietf.org> Wed, 22 September 2021 21:19 UTC

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Subject: [tcpm] Francesca Palombini's No Objection on draft-ietf-tcpm-rfc793bis-25: (with COMMENT)
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Francesca Palombini has entered the following ballot position for
draft-ietf-tcpm-rfc793bis-25: No Objection

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----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

Thank you for the work on this document. I only have minor comments, and some
questions.

I have divided comments into "minor" (including the questions) and "nits".
Neither require replies strictly speaking, please feel free to address as you
see fit. I will appreciate answers to my questions, to improve my
understanding. If any clarification comes out of it, I hope it will help
improve the document.

Francesca

## minor

1. -----

Figure 1

FP: The figure's capture is "TCP Header Format", but Options and Data are
included as well.

2. -----

Figure 2

FP: For consistency, I would have kept the same style as in Figure 1.
Additionally, the IPv4 fields below do not have their size explicitly
specified, so using the same type of formatting as in Figure 1 would help, IMO.

3. -----

       0
       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |       0       |
      +-+-+-+-+-+-+-+-+

FP: More of a question than a comment: how come this change, compared to RFC
793? Any particular reason, or was it only for readability?

4. -----

FP: This is surely me missing something but, in section 3.5 I see:

   4.  ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK>       --> ESTABLISHED

   5.  ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK><DATA> --> ESTABLISHED

which is followed by:

   Note that the sequence number of the segment in line 5 is the same as
   in line 4 because the ACK does not occupy sequence number space (if
   it did, we would wind up ACKing ACKs!).

However, later on, in Figure 13:

   2.  (Close)                                              (Close)
       FIN-WAIT-1  --> <SEQ=100><ACK=300><CTL=FIN,ACK>  ... FIN-WAIT-1
                   <-- <SEQ=300><ACK=100><CTL=FIN,ACK>  <--
                   ... <SEQ=100><ACK=300><CTL=FIN,ACK>  -->

   3.  CLOSING     --> <SEQ=101><ACK=301><CTL=ACK>      ... CLOSING
                   <-- <SEQ=301><ACK=101><CTL=ACK>      <--
                   ... <SEQ=101><ACK=301><CTL=ACK>      -->

I am confused why in this case, in line 3, ACK does in fact occupy sequence
number space. What am I missing?

## nit

5. -----

   Initial Sequence Number Selection

FP: I assume this (and following) was not numbered to keep it as close as
possible to the original RFC, is that right? For readability, I would suggest
numbering these subsections.