Re: [tcpm] Progressing draft-ietf-tcpm-converters

Yuchung Cheng <ycheng@google.com> Fri, 24 May 2019 15:01 UTC

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From: Yuchung Cheng <ycheng@google.com>
Date: Fri, 24 May 2019 08:00:53 -0700
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To: mohamed.boucadair@orange.com
Cc: Olivier Bonaventure <olivier.bonaventure@tessares.net>, "tcpm@ietf.org Extensions" <tcpm@ietf.org>
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Subject: Re: [tcpm] Progressing draft-ietf-tcpm-converters
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On Thu, May 23, 2019 at 11:34 PM <mohamed.boucadair@orange.com> wrote:
>
> Hi Yuchung,
>
> Please see inline.
>
> Cheers,
> Med
>
> > -----Message d'origine-----
> > De : tcpm [mailto:tcpm-bounces@ietf.org] De la part de Yuchung Cheng
> > Envoyé : jeudi 23 mai 2019 18:38
> > À : Olivier Bonaventure
> > Cc : tcpm@ietf.org Extensions
> > Objet : Re: [tcpm] Progressing draft-ietf-tcpm-converters
> >
> > On Tue, May 21, 2019 at 4:52 AM Olivier Bonaventure
> > <olivier.bonaventure@tessares.net> wrote:
> > >
> > > Yuchung,
> > >
> > > >>
> > > >> We believe that a specialised TCP application should be allowed to
> > use its own cookie inside the payload instead of relying on the TCP header
> > to use fast open. The 0-RTT convert protocol is one example, but there
> > could be others. Looking at other application layer protocols, I noticed
> > that TLS1.3 (rfc8446) also includes a cookie which is mainly designed
> > enable servers to get a confirmation of the reachability of the client IP
> > addresses for DTLS, but the same approach could be used when TLS sends its
> > initial data in the SYN as well.
> > > >>
> > > >> Another point that should be clarified in RFC7413 are how middleboxes
> > should handle SYN packets containing a non-zero payload. According to
> > RFC793, such packets are valid TCP packets. The TFO option, defined in
> > RFC7314 is not and should not be considered as an indication that is
> > required to “authorise” the utilisation of payload inside a SYN packet.
> > During the Prague meeting, Christoph Paasch mentioned at the mike that
> > they have one application that uses data inside the SYN and their
> > measurements indicate that sending this SYN without the TFO option enables
> > it to pass through more middleboxes than when the same SYN contains the
> > TFO option.
> > > >>
> > > >> Another point is the socket API. Currently, Linux and MacOS decouple
> > the transmission of data inside the SYN from the utilisation of the TFO
> > option. This makes it possible for a client to send data inside the SYN
> > without enabling TFO. On Windows, the API seems to force the utilisation
> > of TFO when there is data in the SYN. As indicated earlier, RFC793 does
> > not mandate the presence of the TFO to place data inside the SYN.
> > > >>
> > > >> The approach we are proposing has the benefits of RFC7413 but without
> > its drawbacks. Moreover, given that RFC7413 is Experimental, we don't
> > think that there is a harm if we proceed with the approach 0-rtt convert
> > protocol while the IETF can further tweak and adjust the applicability
> > scope of RFC7413. For example, an update can be proposed to RFC7413 to
> > clarify that specialized application-level protocols could place cookie
> > information in their payload and thus not use the TFO option.
> > > > Just to confirm: you mean an API that
> > > > let application sets the TFO cookie (on either server and client)?
> > >
> > >
> > > No, we suggest to let specific applications use data in the SYN without
> > using the TFO cookie. Those applications can manage their cookie inside
> > the SYN payload if needed. Instead of having TFO cookies that are managed
> > by the TCP stack and have limited size, those specialised protocols would
> > use application-level cookies which can be longer and are managed by these
> > application protocols.
> > I see. though I suppose this requires changing RFC793 of not uploading
> > the data to application until 3WHS completes.
> >
>
> [Med] That constraint can be relaxed following a rationale similar to the one in RFC7413.
>
> Is there any particular reason why a change to RFC793 would be required here but not for RFC7413?
It's an interesting question -

RFC793 long allows data-in-SYN but requires data to be posted after
handshake. RFC7413 relaxes that but also requires a cookie.

So if we think this is an "extension" to TFO, then perhaps extends
RFC7413 not changing RFC793? personally I do think that makes sense.
IMO TFO implementation provides a generic way to do data-in-SYN.
Application can use whatever they prefer to protect or optimize
data-in-SYN. TFO cookie is just a default simple mechanism for
application who finds that acceptable.

>
> > >
> > > > otherwise obviously application can place any data in their TCP
> > payload for its
> > > > purposes.
> > >
> > > This is what we proposed in Prague, i.e. using data in the TCP SYN
> > without the TFO option.
> > >
> > >
> > > Olivier
> > > --
> > >
> > >
> > > Disclaimer: https://www.tessares.net/mail-disclaimer/
> > > <https://www.tessares.net/mail-disclaimer/>
> > >
> > >
> >
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