A UNIX Parameter $cat tcp_sack 1 $ Parameter Definition tcp_sack – BOOLEAN Enable select acknowledgments (SACKS). SACK is defined by RFCs 2018, 2883, and 3517 (see Resources for links to these RFCs). Plain TCP (in other words, non-SACK) acknowledgments are strictly cumulative-an acknowledgment of N means that byte N and all previous bytes have been …