Check how many connections an ip has to your server, ordered by the most connections

netstat -anp |grep 'tcp\|udp' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n


#check your tcp timeout time and reduce it to 30s
cat /proc/sys/net/ipv4/tcp_fin_timeout

#added to net.ipv4.tcp_fin_timeout=30:
/etc/sysctl.conf