Stayin' alive...
OS config
Linux proc
echo 600 > /proc/sys/net/ipv4/tcp_keepalive_time
echo 60 > /proc/sys/net/ipv4/tcp_keepalive_intvl
echo 20 > /proc/sys/net/ipv4/tcp_keepalive_probes
Registry keys
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters
TCP_KEEPCNT: overrides tcp_keepalive_probes
TCP_KEEPIDLE: overrides tcp_keepalive_time
TCP_KEEPINTVL: overrides tcp_keepalive_intvl
Peek data to check socket is open.
recv(sock, &buf, 1, MSG_PEEK | MSG_DONTWAIT);
Linux only
MSG_DONTWAIT: set blocking per recv call
Windows PowerShell script
while (1) {clear; echo hello; netstat -n -a | select-string 2300; sleep 1}
C
Set extra params using SOL_TCP.
optval = 1;
optlen = sizeof(optval);
if(setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
perror("setsockopt()");
close(s);
exit(EXIT_FAILURE);
}
Nagle's algorithm
"Congestion Control in IP/TCP Internetworks"