# iptables -A FORWARD -p icmp --icmp-type echo-request -m limit --limit 1/s -j ACCEPT

#>iptables-save >/etc/sysconfig/iptables

进行查看，#iptables -L

ACCEPT     tcp  --  anywhere             anywhere            tcp flags:FIN,SYN,RST,ACK/SYN limit: avg 1/sec burst 5

ACCEPT     tcp  --  anywhere             anywhere            tcp flags:FIN,SYN,RST,ACK/RST limit: avg 1/sec burst 5

ACCEPT     icmp --  anywhere             anywhere            icmp echo-request limit: avg 1/sec burst 5

再次进行查看syn连接：

[root@web ~]# netstat -an | grep SYN | awk \'{print $5}\' | awk -F: \'{print $1}\' | sort | uniq -c | sort -nr | more

     20 10.92.10.220

      1 125.43.36.199

明显SYN连接数已经下来了。