Thank you very much for your exhausting answer. Only one thing is strange to me. I was not aware, that you could ACK some data, and somehow un-ACK the data in the IP Options.
Would not it be safer if one could only ACK data using concatenation, not substraction ? Like the only valid way would be to: ACK what an ACK packet normally ACKs and ACK some more data using SACK. Oh my, quite a poem i wrote :) Best Regards, Maciej Soltysiak
