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

"Bless, Roland (TM)" <roland.bless@kit.edu> Tue, 01 August 2017 08:52 UTC

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To: Ruediger.Geib@telekom.de, gorry@erg.abdn.ac.uk
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From: "Bless, Roland (TM)" <roland.bless@kit.edu>
Organization: Institute of Telematics, Karlsruhe Institute of Technology
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Subject: Re: [tsvwg] COMMENT PLEASE: Which DSCP value should we use for LE PHB?
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Hi,

Am 01.08.2017 um 10:22 schrieb Ruediger.Geib@telekom.de:> 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

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