Re: [tsvwg] David Black (individual) on safety of L4S for the Internet

[Gorry Fairhurst <[e-mail]>]

See in-line

On 15/05/2020 01:03, Black, David wrote:
> Bob,
> [still posting as an individual, not as WG chair]
>
>> Firstly an appeal to everyone to stop talking about wiping the ECN field
>> as if it is acceptable. Bleaching ECN is not a safety mechanism, except
>> as a last resort. Treating ECT(1)/as if/  it is Not-ECT is far
>> preferable to wiping it so it/is/  Not-ECT.
> I concur with that appeal ... but ...
>
> ... We've been through an analogous adventure with DSCP bleaching, as RFC 2474 recommends that behavior for DSCPs (treat unknown DSCPs as best effort without changing the DSCP) but the network operators went ahead and bleached DSCPs at network boundaries, as described in Section 1 of RFC 8100 (https://www.rfc-editor.org/rfc/rfc8100.html#section-1).  I strongly suggest reviewing that history towards understanding why things turned out that way.
>
Well, some operators have chosen a model that does that, I can't resist 
self-citing some research that shows this might not be the full story 
..."Exploring DSCP modification pathologies in the Internet" (2018).

https://www.sciencedirect.com/science/article/pii/S0140366417312835

The reasons for field bleaching seem to vary, (and, alas, a significant 
proportion still seems to be due to configured ToS semantics).

Gorry