Kernel message “possible SYN flooding on port 41121. Sending cookies”

This problem is related with having a lot of TIME_WAIT connections:

netstat -an | grep TIME_WAIT | wc -l > 20000

A solution is to tune your kernel Linux up inputting the following parameters:

echo 32000> /proc/sys/net/ipv4/tcp_max_syn_backlog
echo 30> /proc/sys/net/ipv4/tcp_fin_timeout

This is not meant to be used with load balancing/clustering environments:

echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle

Was this article helpful?