Re: [tcpm] 793bis wording on TCP keep-alives

Wesley Eddy <wes@mti-systems.com> Tue, 22 October 2019 02:25 UTC

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To: "Scharf, Michael" <Michael.Scharf@hs-esslingen.de>
Cc: "tcpm@ietf.org" <tcpm@ietf.org>
References: <6EC6417807D9754DA64F3087E2E2E03E2D4AF868@rznt8114.rznt.rzdir.fht-esslingen.de>
From: Wesley Eddy <wes@mti-systems.com>
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Date: Mon, 21 Oct 2019 22:25:03 -0400
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Subject: Re: [tcpm] 793bis wording on TCP keep-alives
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Hi Michael, I totally agree with your proposal on this.  The change is 
simple and adds clarity; thanks!  I will put this into my working copy, 
unless there is any disagreement raised in the meantime.


On 10/21/2019 6:37 AM, Scharf, Michael wrote:
> Hi Wes,
>
> after reading Section 3.8.4. "TCP Keep-Alives" in 793bis, I would suggest to copy a bit more text from RFC 1122 to better define keep-alives.
>
> Background: RFC 1122 does not formally define "keep-alive" in the normative part, but it mentions implementation behavior in the DISCUSSION text:
>   
>    Some TCP implementations, however, have included a
>    keep-alive mechanism.  To confirm that an idle
>    connection is still active, these implementations send
>    a probe segment designed to elicit a response from the
>    peer TCP.  Such a segment generally contains SEG.SEQ =
>    SND.NXT-1 and may or may not contain one garbage octet
>    of data.
>   
> In RFC 1122, only this DISCUSSION text describes what a "probe segment" could be and what "garbage octet" implies.
>
> Currently 793bis only copies the normative text from RFC 1122, and therefore it does not define these concepts.
>
> My proposal would be to copy also the cited text from RFC 1122 to 793bis to provide more background, e.g., along the lines of:
>   
> 793bis OLD:
>   
>     Implementors MAY include "keep-alives" in their TCP implementations
>     (MAY-5), although this practice is not universally accepted.  If
>     keep-alives are included, the application MUST be able to turn them
>     on or off for each TCP connection (MUST-24), and they MUST default to
>     off (MUST-25).
>
>    [... and more sections on probe segments and garbage octet...]
>   
> 793bis NEW:
>   
>     Implementors MAY include "keep-alives" in their TCP implementations
>     (MAY-5), although this practice is not universally accepted. Some
>     TCP implementations, however, have included a keep-alive mechanism.
>     To confirm that an idle connection is still active, these implementations
>     send a probe segment designed to elicit a response from the peer TCP.
>     Such a segment generally contains SEG.SEQ = SND.NXT-1 and may or may not
>     contain one garbage octet of data. If keep-alives are included, the
>     application MUST be able to turn them on or off for each TCP connection
>     (MUST-24), and they MUST default to off (MUST-25).
>
>    [... rest of existing text...]
>   
> The additional text is literally taken from RFC 1122 and therefore should not be problematic.
>
> Thanks
>   
> Michael