Bill,

Can you forward my reply here, and tell Nanog'ers to check TCPIMPL for more info?

Thanks,

Joe

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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

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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.

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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