Re: [tcpinc] TCP's treatment of data in SYN packets

[Jeremy Harris <[e-mail]>]

On 29/07/16 20:41, Kyle Rose wrote:
> Right, I get that for interoperability with ENO-unaware stacks there is no
> way to change data presented in the SYN. In the case where both ends
> understand ENO but the server is not negotiating it, we can define TCP SYN
> payload semantics differently: essentially, when there is an ENO option in
> the SYN, an ENO-aware server will do one of two things:
[...]
> (2) If it is not negotiating ENO, it will not ACK the data, and will in
> fact throw it away and explicitly permit transmission of *different* data
> for the same sequence number range.

I don't think so.  Whatever the client is, if the server is not showing
support for different behaviour then the client must assume a standards
TCP-implementing server, meaning that any data sent cannot be altered
in a retransmission.  That applies whether or not the _initial_ ack for
a SYN-with-data acks that data; even if it did not, a later one might.

Unless you're dividing signalling of ENO-aware from ENO-negotiating?
-- 
Jeremy