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Re: Kevin's second byte question

2011-07-28 12:05:40
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. [?]

(normally this wouldn't really concern me all that much, but I'm writing some 
introductory material and want to ensure the proper current terminology is 
being used.  The thing that caused me to really notice this was RFC 6145... esp 
section 5.1).

thx,
- K


On Jul 27, 2011, at Jul 273:03 PMPDT, Brian E Carpenter wrote:

The second byte in an IPv4 header is called the Differentiated Services Field.

Quoting RFC 2474:

2.  Terminology Used in This Document
...
  Differentiated Services Field: the IPv4 header TOS octet or the IPv6
  Traffic Class octet when interpreted in conformance with the
  definition given in this document.  Also DS field.

It's a historical accident that the ECN bits were shoehorned into this octet.

-- 
Regards
  Brian Carpenter



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