Subject: [nvo3] Geneve & ECN: MUST not SHOULD

From: Bob Briscoe <[email-masked]>
Date: Fri, 8 Jul 2016 17:02:46 +0100

Jesse, Ilango,

Just checked 
https://tools.ietf.org/html/draft-ietf-nvo3-geneve-01#section-4.1.2

It currently says:
    [RFC6040] describes the mechanism for exposing ECN capabilities on IP
    tunnels and propagating congestion markers to the inner packets.
    This behavior SHOULD be followed for IP packets encapsulated in
    Geneve.

I'm afraid this has to be a MUST. Otherwise, if you don't follow 
RFC6040, what do you implement instead?
The whole point of RFC6040 was to specify one single consistent 
behaviour for all types of tunnel endpoints, with zero options, zero 
config, zero management (unlike Diffserv).
So this statement a little earlier is also a bit wrong:

    there are several options for propagating DSCP and ECN bits

ECN is now becoming popular in private DCs to keep buffer occupancy v 
shallow (e.g. with DCTCP).
If a decapsulator doesn't propagate congestion notification at all, it 
black-holes it. Admittedly you have loss to fall back on... eventually. 
However, while ECN is black-holed sources carry on increasing their 
rate, until they overflow the buffer. Particularly with pooled memory 
for buffering that can introduce a huge amount of delay before 
black-holed ECN turns into loss. Even if ECN isn't being used at the 
moment, it must be implemented in case it starts to be used.

Cheers

Bob

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/

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From: Jesse Gross <[email-masked]>
Date: Fri, 8 Jul 2016 23:00:17 +0000

Bob,

Thanks for reviewing the draft and your comments. I agree with what you said and have changed the SHOULD to MUST and also the statement about there being “several options” for DSCP and ECN to “several considerations”. I just uploaded a new version of the draft (great timing by the way as I was in the process of updating it today) that reflects this.

Jesse

On 7/8/16, 9:02 AM, "Bob Briscoe" <[email-masked]<mailto:[email-masked]>> wrote:

Jesse, Ilango,

Just checked

It currently says:

Cheers

Bob

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From: Bob Briscoe <[email-masked]>
Date: Sun, 10 Jul 2016 11:47:25 +0100

Jesse, I agree with your changes (of course).
Thx, Bob

On 09/07/16 00:00, Jesse Gross wrote:
>
> Bob,
>
> Thanks for reviewing the draft and your comments. I agree with what 
> you said and have changed the SHOULD to MUST and also the statement 
> about there being “several options” for DSCP and ECN to “several 
> considerations”. I just uploaded a new version of the draft (great 
> timing by the way as I was in the process of updating it today) that 
> reflects this.
>
> Jesse
>
>     Bob Briscoe http://bobbriscoe.net/ <http://bobbriscoe.net/>
>