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

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 <David.Black@dell.com> 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 <detnet-bounces@ietf.org> On Behalf Of Stewart Bryant
>> Sent: Thursday, October 1, 2020 11:12 AM
>> To: Grossman, Ethan A.
>> Cc: secdir@ietf.org; last-call@ietf.org; Stewart Bryant; detnet@ietf.org; draft-
>> ietf-detnet-mpls-over-udp-ip.all@ietf.org; 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. <eagros@dolby.com> 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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