Re: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed)

Hi Tiru,

thank you for clarification regarding TCP. It seems the this clarification somehow escaped from the
discussion with Mirja (at least I cannot recall it was mentioned).

Regards,
Valery.

> Hi Valery,
> 
> The message transmission parameters including missing-hb-allowed is only for
> UDP transport (not for TCP). For the UDP, she is suggesting us to go with a
> mechanism that checks both side of the connectivity using non-confirmable
> message with ping and pong at the application layer instead of relying on the
> CoAP ping/pong.
> 
> Cheers,
> -Tiru
> 
> > -----Original Message-----
> > From: Dots <dots-bounces@ietf.org> On Behalf Of Valery Smyslov
> > Sent: Friday, July 19, 2019 5:13 PM
> > To: mohamed.boucadair@orange.com; 'Benjamin Kaduk' <kaduk@mit.edu>;
> > dots-chairs@ietf.org; dots@ietf.org
> > Subject: Re: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed)
> >
> >
> >
> > Hi Med,
> >
> > I believe Mirja's main point was that if you use liveness check
> > mechanism in the transport layer, then if it reports that liveness
> > check fails, then it _also_ closes the transport session.
> >
> > Quotes from her emails:
> > "Yes, as Coap Ping is used, the agent should not only conclude that
> > the DOTS signal session is disconnected but also the Coap session and
> > not send any further Coap messages anymore."
> >
> > and
> >
> > "Actually to my understanding this will not work. Both TCP heartbeat
> > and Coap Ping are transmitted reliably. If you don’t receive an ack
> > for these transmissions you are not able to send any additional
> > messages and can only close the connection."
> >
> > I'm not familiar with CoAP, but I suspect she's right about TCP - if
> > TCP layer itself doesn't receive ACK for the sent data after several
> > retransmissions, the connection is closed.
> >
> > As far as I understand the current draft allows underlying liveness
> > check to fail and has a parameter to restart this check several times
> > if this happens. It seems that a new transport session will be created
> > in this case (at least if TCP is used). In my reading of the draft
> > this seems not been assumed, it is assumed that the session remains
> > the same. So, I think that main Mirja's concern is that it won't work (at least
> with TCP).
> >
> > I didn't participate in the WG discussion on this, so I don't know
> > what was discussed regarding this issue. If it was discussed and the
> > WG has come to conclusion that this is not an issue, then I believe
> > more text should be added to the draft so, that people like Mirja, who
> > didn't participate in the discussion, don't have any concerns while reading
> the draft.
> >
> > Regards,
> > Valery.
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: mohamed.boucadair@orange.com
> > > <mohamed.boucadair@orange.com>
> > > Sent: Friday, July 19, 2019 9:57 AM
> > > To: Benjamin Kaduk (kaduk@mit.edu) <kaduk@mit.edu>; dots-
> > > chairs@ietf.org; dots@ietf.org
> > > Subject: Mirja's DISCUSS: Pending Point (AD Help Needed)
> > >
> > > Hi Ben, chairs, all,
> > >
> > > (restricting the discussion to the AD/chairs/WG)
> > >
> > > * Status:
> > >
> > > All DISCUSS points from Mirja's review were fixed, except the one
> > > discussed in this message.
> > >
> > > * Pending Point:
> > >
> > > Rather than going into much details, I consider the following as the
> > > summary of the remaining DISCUSS point from Mirja:
> > >
> > > > I believe there are flaws in the design. First it’s a layer
> > > > violation, but if more an idealistic concern but usually designing
> > > > in layers is a good approach. But more importantly, you end up
> > > > with un-frequent messages which may still terminate the connection
> > > > at some point, while what you want is to simply send messages
> > > > frequently in an unreliable fashion but a low rate until the attack is over.
> > >
> > > * Discussion:
> > >
> > > (1) First of all, let's remind that RFC7252 does not define how CoAP
> > > ping must be used. It does only say:
> > >
> > > ==
> > >       Provoking a Reset
> > >       message (e.g., by sending an Empty Confirmable message) is also
> > >       useful as an inexpensive check of the liveness of an endpoint
> > >       ("CoAP ping").
> > > ==
> > >
> > > How the liveness is assessed is left to applications. So, there is
> > > ** no layer violation **.
> > >
> > > (2) What we need isn't (text from Mirja):
> > >
> > > > to simply send messages frequently in an unreliable fashion but a
> > > > low rate until the attack is over "
> > >
> > > It is actually the other way around. The spec says:
> > >
> > >   "... This is particularly useful for DOTS
> > >    servers that might want to reduce heartbeat frequency or cease
> > >    heartbeat exchanges when an active DOTS client has not requested
> > >    mitigation."
> > >
> > > What we want can be formalized as:
> > >  - Taking into account DDoS traffic conditions, a check to assess
> > > the liveness of the peer DOTS agent + maintain NAT/FW state on
> > > on-path
> > devices.
> > >
> > > An much more elaborated version is documented in SIG-004 of RFC 8612.
> > >
> > > * My analysis:
> > >
> > > - The intended functionality is naturally provided by existing CoAP
> > messages.
> > > - Informed WG decision: The WG spent a lot of cycles when specifying
> > > the current behavior to be meet the requirements set in RFC8612.
> > > - Why not an alternative design: We can always define messages with
> > > duplicated functionality, but that is not a good design approach
> > > especially when there is no evident benefit.
> > > - The specification is not broken: it was implemented and tested.
> > >
> > > And a logistic comment: this issue fits IMHO under the non-discuss
> > > criteria in
> > > https://www.ietf.org/blog/discuss-criteria-iesg-review/#stand-
> > undisc.
> > >
> > > * What's Next?
> > >
> > > As an editor, I don't think a change is needed but I'd like to hear
> > > from Ben, chairs, and the WG.
> > >
> > > Please share your thoughts and whether you agree/disagree with the
> > > above analysis.
> > >
> > > Cheers,
> > > Med
> >
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