Re: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed)
"Konda, Tirumaleswar Reddy" <TirumaleswarReddy_Konda@McAfee.com> Tue, 23 July 2019 06:41 UTC
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From: "Konda, Tirumaleswar Reddy" <TirumaleswarReddy_Konda@McAfee.com>
To: "mohamed.boucadair@orange.com" <mohamed.boucadair@orange.com>, Benjamin Kaduk <kaduk@mit.edu>, Valery Smyslov <valery@smyslov.net>
CC: "dots-chairs@ietf.org" <dots-chairs@ietf.org>, "dots@ietf.org" <dots@ietf.org>
Thread-Topic: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed)
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Date: Tue, 23 Jul 2019 06:41:07 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/dots/4I4nul_8umIzYz1PfrgU04dkivg>
Subject: Re: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed)
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> -----Original Message----- > From: mohamed.boucadair@orange.com > <mohamed.boucadair@orange.com> > Sent: Tuesday, July 23, 2019 11:02 AM > To: Konda, Tirumaleswar Reddy > <TirumaleswarReddy_Konda@McAfee.com>; Benjamin Kaduk > <kaduk@mit.edu>; Valery Smyslov <valery@smyslov.net> > Cc: dots-chairs@ietf.org; dots@ietf.org > Subject: RE: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed) > > > > Hi Tiru, all, > > Please see inline. > > Cheers, > Med > > > -----Message d'origine----- > > De : Konda, Tirumaleswar Reddy > > [mailto:TirumaleswarReddy_Konda@McAfee.com] > > Envoyé : dimanche 21 juillet 2019 08:52 À : Benjamin Kaduk; Valery > > Smyslov Cc : dots-chairs@ietf.org; BOUCADAIR Mohamed TGI/OLN; > > dots@ietf.org Objet : RE: [Dots] Mirja's DISCUSS: Pending Point (AD > > Help Needed) > > > > Hi Ben, > > > > There seems to several confusions regarding the heartbeat mechanism, I > > will try to address all the comments/Discuss from you, Mirja and > > Valery > > below: > > > > [1] https://tools.ietf.org/html/rfc7252 is specific to UDP transport > > (and does not deal with TCP). Please see the first paragraph in > > https://tools.ietf.org/html/rfc7252#section-3. The message > > transmission parameters (max-retransmit, ack-timeout and > > ack-random-factor) and missing-hb-allowed discussed in DOTS signal > > channel are specific to UDP transport. > > > > [2] CoAP over TCP is discussed in https://tools.ietf.org/html/rfc8323. > > Please see the following differences b/w CoAP-over UDP and > > CoAP-over-TCP relevant to our discussion: > > > > a) CoAP ping/pong defined in RFC7252 (uses Empty confirmable message > > and > > reset) will not work for CoAP-over-TCP. As per > > https://tools.ietf.org/html/rfc8323#section-3.4, Empty messages (Code > > 0.00) can always be sent and MUST be ignored by the recipient. > > CoAP-over- TCP defines its own CoAP ping/pong for connection health > > (see https://tools.ietf.org/html/rfc8323#section-5.4). > > > > b)Confirmable and Non-confirmable message types are specific to UDP, > > and are not supported in CoAP-over-TCP. > > > > [3] For TCP, if no ack is received for CoAP ping for specific > > duration, TCP will close the connection, and the DOTS client will have > > to re- establish the TCP connection. missing-hb-allowed is of no use > > for TCP. We are all in the same page for TCP, and the draft can probably > > be updated for better clarity. > > > > [4] Now coming to UDP, please see my responses below: > > > > a) As you already know, DOTS signal channel uses heartbeat exchange in > > both directions, and hence CoAP ping is sent by both DOTS client and > > server. > > b) CoAP ping is a confirmable message and hence the exponential > > back-off with the default value of MAX_RETRANSMIT is 4 > > (https://tools.ietf.org/html/rfc7252#section-4.8). > > c) CoAP ping is the only confirmable message exchanged during attack > > (all other messages exchanged during an attack are non-confirmable). > > The specification allows distinct values for message transmission > > parameters and missing-hb-allowed to be used during attack and peace > times. > > > > To handle congestion conditions during an attack, the specification > > allows two options: > > > > [Option a] By setting MAX_RETRANSMIT to 1, exponential-back off is > > avoided and missing-hb-allowed set to a very higher value (e.g. 20) to > > handle congestion (high packet loss). The draft can be updated to > > explain [Option a] in more detail. > > [Option b] The CoAP MAX_RETRANSMIT default value of 4 is not modified, > > and for example, missing-hb-allowed can be set to 5 (since 4 transmits > > are not sufficient to detect the peer is not alive during congestion). > > > > [Med] We can add this text to illustrate the configuration flexibility: > > The specification allows for a flexible retry configuration when an > unreliable transport is in use. For example, a server may be tweaked > to return a lower 'missing-hb-allowed' (e.g., 5) value but delegate > the retransmission to the underlying CoAP library by setting 'max- > retransmit' to a high value (e.g., 3). The server may also be > configured to return a 'max-retransmit' set to '1' together with a > higher 'missing-hb-allowed' value (e.g., 15). Looks good, Both these techniques are used by protocols today, I see DTLS heartbeat uses retransmit and exponential back-off (see https://tools.ietf.org/html/rfc6347#section-4.2.4.1) for liveness check and in STUN usage for consent freshness (https://tools.ietf.org/html/rfc7675) STUN binding requests are sent periodically. Cheers, -Tiru > > > > The Discuss from Mirja is not to rely on the CoAP ping/pong but to > > define it in the DOTS layer itself (please see > > https://mailarchive.ietf.org/arch/msg/dots/V6vv28zDpdY5eR_kaB7L- > 60bhkk > > ) and suggested to go with an alternate design using non-confirmable > > messages. The alternate design won't work is our assessment, please > > see my response > > > https://mailarchive.ietf.org/arch/msg/dots/QRMfsmhPTFksN6a_nBBKimVx- > lM > > > > Cheers, > > -Tiru > > > > > -----Original Message----- > > > From: Dots <dots-bounces@ietf.org> On Behalf Of Benjamin Kaduk > > > Sent: Sunday, July 21, 2019 9:35 AM > > > To: Valery Smyslov <valery@smyslov.net> > > > Cc: dots-chairs@ietf.org; mohamed.boucadair@orange.com; > > > dots@ietf.org > > > Subject: Re: [Dots] Mirja's DISCUSS: Pending Point (AD Help Needed) > > > > > > This email originated from outside of the organization. Do not click > > links or > > > open attachments unless you recognize the sender and know the > > > content is safe. > > > > > > Hi Valery, > > > > > > On Fri, Jul 19, 2019 at 02:42:50PM +0300, Valery Smyslov wrote: > > > > 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. > > > > > > Thanks for this crisp summary (and thanks Med for the detailed > > > writeup > > as > > > well)! > > > > > > > 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). > > > > > > My sense is similar; if I could attempt to summarize Mirja's stance, > > it's that > > > we're invoking a transport-level feature that does its own > > > retransmit > > and > > > backoff, but then if the transport comes back and says "the peer is > > gone", we > > > say "but we're under attack, so I don't believe you; try again". > > > This kicks of another independent set of "retransmits" (I know it's > > > not technically the right word) with a fresh exponential backoff. > > > There's > > two > > > complaints about this: (1) we're changing the transport, since if > > > the > > transport > > > concludes the peer is gone then the transport "normally" tears down > > > the connection (*) entirely, and (2) the assembly of (exponential > > > backoff > > 1), > > > (exponential backoff 2), (exponential backoff 2) is strange pacing, > > > and > > might > > > be better served by a similar number of "retransmits" but with > > > different pacing, since the long delay at the end of each backoff > > > period is not > > expected > > > to add a huge amount of value in terms of letting congestion ease > > > during attack time, and we would be just as well served by capping > > > the delay between retransmits and having more retransmits. > > > > > > The asterisk on (1) is of course because, as is noted later in the > > thread, only > > > TCP tears down the association when it concludes the peer is gone > > (assuming > > > I'm reading the right parts of 7252). Quoting 7252: > > > > > > If the > > > retransmission counter reaches MAX_RETRANSMIT on a timeout, or if > the > > > endpoint receives a Reset message, then the attempt to transmit the > > > message is canceled and the application process informed of failure. > > > On the other hand, if the endpoint receives an acknowledgement in > > > time, transmission is considered successful. > > > > > > So all CoAP does is to tell the application "that request didn't > > > work", > > but CoAP > > > is happy to try additional requests on the connection; the teardown > > logic is > > > indeed left up to the application. > > > > > > I'm not sure that we've seen much discussion about (2), though > > > (sorry if > > I > > > missed it) -- why is the repeated backoff-and-restart the right > > > pacing > > for this > > > purpose? > > > > > > -Ben > > > > > > > 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 > > > > > > > > > > _______________________________________________ > > > Dots mailing list > > > Dots@ietf.org > > > https://www.ietf.org/mailman/listinfo/dots
- [Dots] Mirja's DISCUSS: Pending Point (AD Help Ne… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Jon Shallow
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Valery Smyslov
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Valery Smyslov
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Benjamin Kaduk
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… kaname nishizuka
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Benjamin Kaduk
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… Benjamin Kaduk
- Re: [Dots] Mirja's DISCUSS: Pending Point (AD Hel… mohamed.boucadair
- [Dots] FW: Mirja's DISCUSS: Pending Point (AD Hel… Valery Smyslov