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Re: followup on TCP stuff.

  • From: Bill Manning
  • Date: Wed Jun 09 18:08:57 1999

> Bill,
> 
> Can you forward my reply here, and
> tell Nanog'ers to check TCPIMPL for
> more info?
> 
> Thanks,
> 
> Joe
> 
> 
> > >To: alan@globalcenter.net, nanog@merit.edu, tcp-impl@lerc.nasa.gov
> > >Subject: Re: TOS issues with non RFC compliant TCP stacks
> > >Cc: touch@ISI.EDU
> > >
> > >> From owner-tcp-impl@lerc.nasa.gov Tue Jun  8 23:27:07 1999
> > >> Date: Tue, 8 Jun 1999 22:45:11 -0700
> > >> From: Alan Hannan <alan@globalcenter.net>
> > >> To: nanog@merit.edu, tcp-impl@lerc.nasa.gov
> > >> Subject: TOS issues with non RFC compliant TCP stacks
> > >...
> > >>   It has come to our attention that a notable fraction of the
> > >>   internet client community uses a TCP stack which is not RFC
> > >>   compliant, as far as we can determine.
> > >> 
> > >>   Certain versions of MacTCP send a RST when they receive SYN ACK
> > >>   packets of TOS!=0.
> > >
> > >Far as I have found, the spec (STD7) says that TOS is a TCP 
> > >per-connection property (page 12). 
> > >
> > >On page 36 it appears to clearly state that (case 2):
> > >
> > >    terminated then).  If our SYN has been acknowledged (perhaps in this
> > >    incoming segment) the precedence level of the incoming segment must
> > >    match the local precedence level exactly, if it does not a reset
> > >    must be sent.
> > >
> > >>   So, the empirical part:  We implemented TOS bit-setting for the
> > >>   purpose of tracking traffic flows and traffic levels.  For an
> > >>   entirely arbitrary reason, we chose TOS=5 for the default of
> > >>   traffic.  We found that MacTCP ceased functioning.  The MacTCP
> > >>   stack would initiate an RST when receiving SYN ACK packets with
> > >>   a TOS=5, as the SYN packets had a TOS=0.  Therefore, all TCP
> > >>   sessions would fail.
> > >
> > >Granted, this is a first cut read, but wouldn't this appear
> > >to indicate that NOT sending the RST is the violation of the 
> > >spec?
> > >
> > >Can you clarify?
> > >
> > >Joe 
> > >


--bill





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