Linux下如何防御SYN Flood工具

SYN Flood (SYN洪水) 是种典型的DoS (Denial of Service，拒绝服务) 攻击。效果就是服务器TCP连接资源耗尽，停止响应正常的TCP连接请求。

如果您遭受SYN洪水攻击下的Linux服务器，您可以设置以下:

减少SYN-超时时间:

iptables -A FORWARD -p tcp –syn -m limit –limit 1/s -j ACCEPTiptables -A INPUT -i eth0 -m limit –limit 1/sec –limit-burst 5 -j ACCEPT

每秒最多3个syn数据包

iptables -N syn-floodiptables -A INPUT -p tcp –syn -j syn-floodiptables -A syn-flood -p tcp –syn -m limit –limit 1/s –limit-burst 3 -j RETURNiptables -A syn-flood -j REJECT

设置syncookies

sysctl -w net.ipv4.tcp_syncookies=1sysctl -w net.ipv4.tcp_max_syn_backlog=3072sysctl -w net.ipv4.tcp_synack_retries=0sysctl -w net.ipv4.tcp_syn_retries=0sysctl -w net.ipv4.conf.all.send_redirects=0sysctl -w net.ipv4.conf.all.accept_redirects=0sysctl -w net.ipv4.conf.all.forwarding=0sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1

防止ping命令

sysctl -w net.ipv4.icmp_echo_ignore_all=1

阻止特定的IP范围

iptables -A INPUT -s 192.168.5.1/8 -i eth0 -j Drop