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Re: Kevin's second byte question

2011-07-28 20:52:04
Brian, I recall some pretty serious agreement almost at the beginning
that it was a diffserv "field", only 6 bits, and that people who were
saying "diffserv byte" were wrong. I also recall some dithering over
whether the other two bits should be declared reserved, but without
conclusion.



On Jul 28, 2011, at 16:58, Brian E Carpenter
<brian(_dot_)e(_dot_)carpenter(_at_)gmail(_dot_)com> wrote:

On 2011-07-28 16:49, Kevin Fall wrote:
Thanks for the quick response.

Here's what my reading revealed, and you can tell me if I'm in error or 
not...

RFC3260 tells us that the first six bits (not 8) are called the DS Field or 
Differentiated Services Field, and the subsequent
two bits are referred to as ECN ("ECN field" according to RFC 3168).  Same 
applies for what was formerly the IPv6 traffic class byte.

That said, RFC 3260 is Informational, yet claims to update standards-track 
RFCs 2474 and 2597.  I'm not quite sure what sort of status that
leaves us with. [?]

It can't. That claim shouldn't have been published IMHO. (And yes, I was 
co-chair
of the diffserv WG at the time). However, it invokes BCP 37 = RFC 2780
which is normative, so probably supersedes RFC 2474. 2780 doesn't answer your
question though, since it refers to the 6-bit DS field and not to the whole
byte or octet except as "superseded".

I think you will need to add a complicated footnote on this.

On 2011-07-29 01:10, Thomson, Martin wrote:

On 2011-07-27 at 18:03:13, Brian E Carpenter wrote:
The second byte in an IPv4 header is called the Differentiated
Services Field.

I believe that this has been obsoleted by RFC 5241.

Good one :-)

   Brian




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