BCP regarding TOS transparancy for internet traffic

Thu May 26 05:54:57 UTC 2005

  Back in 1999 or early 2000, at GBLX we decided to implement DSCP settings 
  on transit network traffic.

  We found that a remotely small % of TCP traffic abended when the DSCP
  were changed within the stream.  Understandably, we were concerned.

  Given the incompatibility with intended TOS/DSCPs behavior, and the 
  TCP spec, we 'fixed' TCP in RFC 2873, June, 2000.

  Another 'fix' to interpretations of the TCP spec was authored by S. Floyd,
  RFC 3360, August, 2002.

  -alan

Thus spake Fred Baker (fred at cisco.com)
 on or about Wed, May 25, 2005 at 11:18:42AM -0700:
> 
> 
> On May 25, 2005, at 10:39 AM, Sam Stickland wrote:
> 
> >While it's true that IP is end-to-end, are fields such as TOS and DSCP 
> >meant to be end to end? A case could be argued that they are used by 
> >the actual forwarding devices on route in order to make QoS or even 
> >routing decisions, and that the end devices shouldn't actually rely on 
> >the values of these fields?
> 
> It used to be that TCP would reset a session if the TOS byte changed in 
> mid-session. That certainly sounds like an end-to-end expectation.