Re: [secdir] [Detnet] Secdir last call review of draft-ietf-detnet-mpls-over-udp-ip-06

["Black, David" <[e-mail]>]

Stewart,

Going back to my earlier note to identify the design choice:

> > ... IF the DetNet service defines packet loss as a failure case, i.e., something
> > that can't happen unless something in the network has actually failed and the
> > preferred failure behavior is late delivery rather than non-delivery of impacted
> > data, THEN TCP may be useful/appropriate.  

I read your note as advocating that the preferred failure behavior is non-delivery of impacted data, in which case, I would agree that TCP is not a good choice of protocol.

Thanks, --David

> -----Original Message-----
> From: Stewart Bryant <[e-mail]>
> Sent: Friday, October 2, 2020 8:21 AM
> To: Black, David
> Cc: Stewart Bryant; Grossman, Ethan A.; [e-mail]; [e-mail];
> [e-mail]; [e-mail]; Stephen
> Farrell
> Subject: Re: [Detnet] Secdir last call review of draft-ietf-detnet-mpls-over-udp-
> ip-06
> 
> 
> [EXTERNAL EMAIL]
> 
> David
> 
> The way that I look at it, TCP will deliver a given byte fed into its transmission
> stream in its own good time, delaying that byte until all previous bytes are
> delivered. It will also keep trying to deliver that byte as long as there is
> connectivity between source and sink. That is a contrast with DetNet which is
> looking for fast delivery with possibly some mitigation for packet loss. In such
> circumstances TCP is a liability to the service that wanted deterministic
> characteristics. I cannot therefore think of any good reason to pay the price of
> DetNet to deliver TCP. If you do want to use a transport protocol that is more
> sophisticated than UDP, then SCTP-PR is probably a better choice.
> 
> - Stewart
> 
> 
> 
> > On 1 Oct 2020, at 20:35, Black, David <[e-mail]> wrote:
> >
> > Playing devil's advocate for a moment ...
> >
> >> I would be rather surprised if anyone tried to run a deterministic
> >> application over TCP.
> >>
> >> TCP would undo all the temporal determinism and or course it looks
> >> after packet loss.
> >
> > ... IF the DetNet service defines packet loss as a failure case, i.e., something
> that can't happen unless something in the network has actually failed and the
> preferred failure behavior is late delivery rather than non-delivery of impacted
> data, THEN TCP may be useful/appropriate.  OTOH, use of TCP increases the
> DetNet attack surface, as (in contrast to UDP), causing a drop or otherwise
> triggering retransmission becomes a way to attack the DetNet service by
> increasing the amount of traffic sent into limited reserved network capacity and
> also by delaying delivery of received data to the deterministic application.
> >
> > I've lost track of the original context, so I'm not able to suggest specific text and
> where to add it or make changes.
> >
> > Thanks, --David
> >
> >> -----Original Message-----
> >> From: detnet <[e-mail]> On Behalf Of Stewart Bryant
> >> Sent: Thursday, October 1, 2020 11:12 AM
> >> To: Grossman, Ethan A.
> >> Cc: [e-mail]; [e-mail]; Stewart Bryant;
> >> [e-mail]; draft- [e-mail];
> >> Stephen Farrell
> >> Subject: Re: [Detnet] Secdir last call review of
> >> draft-ietf-detnet-mpls-over-udp-
> >> ip-06
> >>
> >>
> >> [EXTERNAL EMAIL]
> >>
> >>
> >>
> >>> On 24 Sep 2020, at 21:28, Grossman, Ethan A. <[e-mail]> wrote:
> >>>
> >>> Thanks Stephen. FWIW it isn't too late to add some text to the
> >>> DetNet Security
> >> draft regarding DetNet over UDP, if someone can think up something
> >> useful to say. I suppose one could simply mention UDP in the same
> >> breath as TCP (implying that the same general security guidelines apply, if
> that's our stance).
> >>> Any thoughts (from anyone)?
> >>
> >> Ethan
> >>
> >> I would be rather surprised if anyone tried to run a deterministic
> >> application over TCP.
> >>
> >> TCP would undo all the temporal determinism and or course it looks
> >> after packet loss.
> >>
> >> - Stewart
> >>
> >>
> >>
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