There are two pertinent kernel variables that are settable via ndd
tcp_conn_req_max - which sets the maximum number of connections queued
per listener (default 32). It has a maximum allowed value of 1024.
tcp_ip_abort_cinterval - sets the number of milliseconds to hold the
queued connections before dropping them (default 180 seconds). It has a
minimum allowed value of 1 second and a max of 4294967 seconds or about
50 days.
I've written (and now testing) a program (synsave) that dynamically
adjusts the tcp_ip_abort_cinterval value depending on the number of half
open connections (hocs) queued on the system. When the number of hocs
exceeds a threshold value the program adjusts the value downward to more
agressively drop these connections. When the number of hocs drops to a
sane level the program will adjust tcp_ip_abort_cinterval back to its
preset value.
geoff
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