nanog mailing list archives

Re: followup on TCP stuff.

From: Bill Manning <bmanning () ISI EDU>
Date: Wed, 9 Jun 1999 15:06:47 -0700 (PDT)

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

Current thread:

Re: followup on TCP stuff. Bill Manning (Jun 09)