Re: [aqm] I-D Action: draft-ietf-aqm-recommendation-04.txt

[Mikael Abrahamsson <[e-mail]>]

On Tue, 12 May 2015, Simon Barber wrote:

> Hi John,
>
> Where would be the best place to see if it would be possible to get agreement 
> on a global low priority DSCP?

Currently the general assumption among ISPs is that DSCP should be zeroed 
between ISPs unless there is a commercial agreement saying that it 
shouldn't. This is generally accepted (there are NANOG mailing list 
threads on several occasions in the past 5-10 years where this was the 
outcome).

The problem is quite complex if you actually want things to act on this 
DSCP value, as there are devices with default behaviour is 4 queue 802.1p, 
with 1 and 2 (which will match AF1x and AF2x) will have lower priority 
than 0 and 3 (BE and AF3x), and people doing DSCP based forwarding, 
usually does things the other way around.

It might be possible to get the last DSCP bits to map into this, because 
for DSCP-ignorant quipment, this would still be standard BE to something 
only looking at CSx (precedence), but that would be lower than 000000. So 
DSCP 000110 (high drop BE) might work, because it's incremental. Possibly 
DSCP 000010 (low drop BE) might be able to get some agreement because it 
doesn't really cause any problems in the existing networks (most likely) 
and it could be enabled incrementally.

I would suggest bringing this kind of proposal to operator organizations 
and the IETF. It needs to get sold to the ISPs mostly, because in this 
aspect the IETF decision will mostly be empty hand-waving unless the 
operators do something.

-- 
Mikael Abrahamsson    email: [e-mail]