Re: [tsvwg] operational feedback regarding draft-ietf-tsvwg-le-phb-04

["Bless, Roland (TM)" <[e-mail]>]

Hi Mikael,

see inline.

Am 06.04.2018 um 09:06 schrieb Mikael Abrahamsson:

> I have asked people in the operational community what they think about
> this proposal, and the little feedback I have received so far has been
> that one person thought CS1 should be used instead, others have said
> that 000001 seems fine. In the process of this there have been patches
> proposed for ssh which historically has been using TOS:
> 
> https://marc.info/?l=openbsd-tech&m=152251266032032&w=2

Wow, this recommends CS1 for LE which isn't good. It should use the
new LE codepoint then. I'm also not sure that scp always belongs to
the LE class...

> So it seems to me that there are applications out there that are using
> IPTOS_THROUGHPUT and IPTOS_LOWDELAY, in use today.
> 
> I found this in a header file:
> 
> /*
>  * Definitions for IP type of service (ip_tos)
>  */
> #define    IPTOS_LOWDELAY        0x10
> #define    IPTOS_THROUGHPUT    0x08
> #define    IPTOS_RELIABILITY    0x04
> 
> So trying to figure out what bits go where, right-shifting two times and
> trying to not get this wrong (I frequently have gotten it wrong, but
> let's try again):
> 
> IPTOS_LOWDELAY      DSCP 000100
> IPTOS_THROUGHPUT    DSCP 000010
> IPTOS_RELIABILITY   DSCP 000001
> 
> So does this mean that the new LE DSCP CP maps to IPTOS_RELIABILITY?

I would put it the other way round: if only the
IPTOS_RELIABILITY is set, it will be mapped to the LE DSCP.
So you are right here. However, RFC2474 already obsoleted the IP ToS
semantics:
   A replacement header field, called the DS field, is defined, which is
   intended to supersede the existing definitions of the IPv4 TOS octet
   [RFC791] and the IPv6 Traffic Class octet [IPv6].
...
   The structure of the DS field shown above is incompatible with the
   existing definition of the IPv4 TOS octet in [RFC791].
...
   No attempt is made to maintain backwards compatibility with the "DTR"
   or TOS bits of the IPv4 TOS octet, as defined in [RFC791].

RFC2474 only preserved the IP precedence semantics by defining the
class selector codepoints CSx. So, I don't see any problems here.

> Anyhow, I have also asked the RIPE Atlas team if they can do some
> measurement about bleaching in todays networks, seeing if there is any
> difference in bleaching for 000001 (LE) and 001000 (CS1).

I also asked them, but right now Atlas isn't supporting this type
of measurement.

> I will also ask around and see if there is anyone with sFlow dumping
> from a major IX that can tell me what DSCP code points they see in the
> wild, and if I can get a summary. Or has this work already been done so
> I don't need to?

More measurements are always good!
I think that the neat project and Gorry's group did some work, see:
https://www.ietf.org/proceedings/96/slides/slides-96-maprg-6.pdf
https://datatracker.ietf.org/meeting/99/materials/slides-99-tsvwg-sessb-31measurements-concerning-the-dscp-for-a-le-phb-00

Regards,
 Roland