Re: [tcpm] 793bis ready to go?

tuexen@fh-muenster.de Sat, 20 February 2021 20:56 UTC

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From: tuexen@fh-muenster.de
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Date: Sat, 20 Feb 2021 21:56:00 +0100
Cc: Markku Kojo <kojo=40cs.helsinki.fi@dmarc.ietf.org>, Michael Scharf <Michael.Scharf@hs-esslingen.de>, Wesley Eddy <wes@mti-systems.com>, tcpm IETF list <tcpm@ietf.org>
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To: "Scheffenegger, Richard" <rs.ietf@gmx.at>
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Subject: Re: [tcpm] 793bis ready to go?
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> On 18. Feb 2021, at 14:59, Scheffenegger, Richard <rs.ietf@gmx.at> wrote:
> 
> One more nit, around dealing with data-in-SYN,ACK
> 
> 793bis (page 71) has this text, which unfortunately doesn have any
> RFC2119 language.
> 
> But in short, it seems to require the transmission of a pure ACK just
> for the SYN bit, and a 2nd ACK right afterwards (step 6) to acknowledge
> the data.
> 
> The FBSD implementation was found to skip over the ACK-only-the-SYN
> intermediate step (which must be acceptable, as that ACK may get lost in
> the network), sending out only the cummulative ACK for SYN and data,
> after having transitioned into ESTABLISHED.
Hi,

I really prefer the FreeBSD behaviour. A TCP stack should not need to send
two segments at the same time when handling the event of a single segment reception.

Best regards
Michael, as an individual
> 
> But strictly speaking, this behavior is a deviation from 793 / 793bis.
> 
> Perhaps a "and should send it" would do, to allow this behavior,
> conserving one pure ACK...
> 
> Best regards,
>   Richard
> 
> 
> 
> If the state is SYN-SENT then
> 
>         first check the ACK bit
> 
>            If the ACK bit is set
> :
> :
> fourth check the SYN bit
> 
>            This step should be reached only if the ACK is ok, or there
>            is no ACK, and it the segment did not contain a RST.
> 
>            If the SYN bit is on and the security/compartment is
> >>>         acceptable then, RCV.NXT is set to SEG.SEQ+1, IRS is set to
>            SEG.SEQ.  SND.UNA should be advanced to equal SEG.ACK (if
>            there is an ACK), and any segments on the retransmission
>            queue that are thereby acknowledged should be removed.
> 
>            If SND.UNA > ISS (our SYN has been ACKed), change the
>            connection state to ESTABLISHED, form an ACK segment
> 
> >>>            <SEQ=SND.NXT><ACK=RCV.NXT><CTL=ACK>
> 
>            and send it.  Data or controls that were queued for
>            transmission may be included.  If there are other controls
> or text in the segment then continue processing at the sixth
>            step below where the URG bit is checked, otherwise return.
> 
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