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TCP_RACK(4) Kernel Interfaces Manual TCP_RACK(4) NAME tcp_rack -- TCP RACK-TLP Loss Detection Algorithm for TCP SYNOPSIS To use this TCP stack, place the following line in the kernel configu- ration file: options TCPHPTS To load the TCP stack as a module at boot time, place the following line in loader.conf(5): tcp_rack_load="YES" To enable the TCP stack, place the following line in the sysctl.conf(5): net.inet.tcp.functions_default=rack DESCRIPTION RACK-TLP uses per-segment transmit timestamps and selective acknowledg- ments (SACKs) and has two parts. Recent Acknowledgment (RACK) starts fast recovery quickly using time-based inferences derived from acknowl- edgment (ACK) feedback, and Tail Loss Probe (TLP) leverages RACK and sends a probe packet to trigger ACK feedback to avoid retransmission timeout (RTO) events. Compared to the widely used duplicate acknowledgment (DupAck) threshold approach, RACK-TLP detects losses more efficiently when there are ap- plication-limited flights of data, lost retransmissions, or data packet reordering events. It is intended to be an alternative to the DupAck threshold approach. MIB Variables The algorithm exposes the following scopes in the net.inet.tcp.rack branch of the sysctl(3) MIB: net.inet.tcp.rack.misc Misc related controls net.inet.tcp.rack.features Feature controls net.inet.tcp.rack.measure Measure related controls net.inet.tcp.rack.timers Timer related controls net.inet.tcp.rack.tlp TLP and Rack related Controls net.inet.tcp.rack.timely Rack Timely RTT Controls net.inet.tcp.rack.hdwr_pacing Pacing related Controls net.inet.tcp.rack.pacing Pacing related Controls net.inet.tcp.rack.tp Rack tracepoint facility net.inet.tcp.rack.probertt ProbeRTT related Controls net.inet.tcp.rack.stats Rack Counters net.inet.tcp.rack.sack_attack Rack Sack Attack Counters and Controls Besides the variables within the above scopes the following variables are also exposed in the net.inet.tcp.rack branch: net.inet.tcp.rack.clear Clear counters net.inet.tcp.rack.opts RACK Option Stats net.inet.tcp.rack.outsize MSS send sizes net.inet.tcp.rack.req_measure_cnt If doing dynamic pacing, how many measurements must be in be- fore we start pacing? net.inet.tcp.rack.use_pacing If set we use pacing, if clear we use only the original burst mitigation net.inet.tcp.rack.rate_sample_method What method should we use for rate sampling 0=high, 1=low SEE ALSO cc_chd(4), cc_cubic(4), cc_hd(4), cc_htcp(4), cc_newreno(4), cc_vegas(4), h_ertt(4), mod_cc(4), tcp(4), tcp_bbr(4), mod_cc(9) Neal Cardwell, Yuchung Cheng, Nandita Dukkipat, and Priyaranjan Jha, The RACK-TLP Loss Detection Algorithm for TCP, February 2021, RFC 8985. Ahmed M. Abdelmoniem and Brahim Bensaou, T-RACKs: A Faster Recovery Mechanism for TCP in Data Center Networks, February 2021, https://arxiv.org/abs/2102.07477. HISTORY The tcp_rack congestion control module first appeared in FreeBSD 13.0. AUTHORS The tcp_rack congestion control module was written by Randall Stewart <rrs@FreeBSD.org> and sponsored by Netflix, Inc. This manual page was written by Gordon Bergling <gbe@FreeBSD.org>. FreeBSD 14.0 March 19, 2023 TCP_RACK(4)
NAME | SYNOPSIS | DESCRIPTION | MIB Variables | SEE ALSO | HISTORY | AUTHORS
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