Re: [tsvwg] COMMENT PLEASE: Which DSCP value should we use for LE PHB?

[<[e-mail]>]

Hi Roland,

AF classes are structured sets of DSCP. Their definition starts with a bit-mask based on DSCP bits 0-2, resulting in AFnx notation. This notation also corresponds to CSn definitions, resulting in up to 4 standard DSCPs sharing the same bits 0-2. 

To configure re-marking of an AF class or of eight DSCPs I need _per DSCP_ :

- a class definition
- an assignment of a received DSCP to a class
- a re-mark order of the class to my internal DSCP

If a provider operates MPLS, the number of Treatment Aggregates/PHBs offered at interconnection is often 3 or 4. The options that I am aware of are:
- a bit-mask based re-mark allows to transport and maintain up to 8 DSCP by a "3 line configuration"
- a DSCP based re-mark combined with a bit-mask based classification allows to transport up to n 
   DSCP by a "3 line configuration" and they are all re-marked to a single DSCP.
- a DSCP based re-mark aiming on maintaining different requires "n*3 lines of configuration" for n DSCP.
- There's no binding standard on Diffserv class/codepoint assignment at interconnection. Setting up 
  a per carrier per DSCP to DSCP and class mapping scheme is requiring some effort (negotiation, 
  configuration, operation). I'm trying to avoid that.

To me, two choices to make operational sense:
- either bit-mask based DSCP re-mark with up to 8 DSCP per MPLS Treatment Aggregate
- or DSCP based re-mark with a single DSCP per MPLS Treatment Aggregate.

Regards, 

Ruediger


-----Ursprüngliche Nachricht-----
Von: Bless, Roland (TM) [mailto:[e-mail]] 
Gesendet: Dienstag, 1. August 2017 10:53
An: Geib, Rüdiger <[e-mail]>; [e-mail]
Cc: [e-mail]
Betreff: Re: [tsvwg] COMMENT PLEASE: Which DSCP value should we use for LE PHB?

Hi,

Am 01.08.2017 um 10:22 schrieb [e-mail]:> GF> There seems evidence that there are still even now deployed routers
> that have not adjusted their remarking behaviour after the IETF 
> deprecated ToS Precedence bleaching.
> 
> [RG2] True. I prefer a core-router to be able to re-mark DSCPs by 
> bit-mask at interconnection interfaces rather than DSCP by DSCP. The 
> config effort to customize re-marking on a DSCP by DSCP basis is high. 
> An easy to configure alternative is to classify by bit-mask and re-mark to a single DSCP. Gorry, do you have any preference here?

Hmm, RFC2474 states that the DSCP is unstructured:
  "The DSCP field is defined as an
   unstructured field to facilitate the definition of future per-hop
   behaviors.

   With some exceptions noted below, the mapping of codepoints to PHBs
   MUST be configurable.  A DS-compliant node MUST support the logical
   equivalent of a configurable mapping table from codepoints to PHBs"

IMHO it shouldn't be difficult to have a mapping table from each DSCP to a PHB. The mapping table should initially only contain mappings to the default PHB (no need to remark anything then).
Configuring DSCP remarking by using bitmasks is IMHO not RFC2474 compliant and a broken concept causing the trouble we just ran into.

Regards,
 Roland