HP-UX TCP/IP Performance White Paper, March 2008

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Table 1: Summary of TCP/IP Tunables
The following TCP/IP tunables may be queried or set using ndd(1M). All tunables are global, i.e., they
affect all TCP/IP connections. Note that some tunables take effect immediately, while others used to
initialize TCP/IP connection will only affect newly opened connections. See Appendix B for the detailed
description of these tunables.
Tunable Name Description Reference
TCP:
tcp_conn_request_max Max number of outstanding connection requests 4.1.1.2
4.2.4
Appendix A
tcp_cwnd_initial Initial size of the congestion window as a
multiple of the MSS
2.4
tcp_deferred_ack_max Upper limit on the number of bytes of data
(measured in MSS) that can be received without
an ACK.
tcp_delay_final_twh_ack Delay final ack for 3-way handshake connection
establishment
tcp_early_conn_ind Controls when a T_CONN_IND message is sent
upstream
tcp_fin_wait_2_timeout Length of time a TCP connection spends in
FIN_WAIT_2
tcp_frto_enable Enable Forward RTO Recovery 4.3.2
tcp_ip_abort_cinterval R2 during connection establishment 4.3.1
tcp_ip_abort_interval R2 for established connection 4.1.1.4
Appendix A
tcp_ip_notify_cinterval R1 during connection establishment 4.3.1
tcp_ip_notify_interval R1 for established connection
tcp_ip_ttl TTL value inserted into IP header Appendix A
tcp_keepalive_detached_interval Send keepalive probes for detached TCP Appendix A
tcp_keepalive_interval Interval for sending keepalive probes 4.1.1.5
Appendix A
tcp_largest_anon_port Largest anonymous port number to use
tcp_recv_hiwater_def Default receive window size 2.1, 5.3
tcp_recv_hiwater_max Upper bound on TCP receive buffer size 5.3
tcp_recv_hiwater_lfp Default receive window size for fast links 5.3
tcp_recv_hiwater_lnp Default receive window size for slow links 5.3
tcp_rexmit_interval_initial Initial value for round trip time-out 4.3.1
Appendix A
tcp_rexmit_interval_initial_lnp tcp_rexmit_interval_initial for LNP