sysctl(配置优化参数)

net.ipv4.tcp_keepalive_time = 300 #意思是如果某个TCP连接在idle 2个小时后,内核才发起probe.如果probe 9次(每次75秒)不成功,内核才彻底放弃,认为该连接已失效

net.ipv4.tcp_syncookies = 1  #当出现SYN等待队列溢出时，启用cookies来处理，可防范少量SYN攻击，默认为0，表示关闭。

net.ipv4.tcp_timestamps = 1 #该文件表示是否启用以一种比超时重发更精确的方法来启用对 RTT 的计算；为了实现更好的性能应该启用这个选项。

net.ipv4.tcp_fin_timeout = 15 #减少处于FIN-WAIT-2连接状态的时间，使系统可以处理更多的连接

net.ipv4.tcp_tw_recycle = 1 #表示开启TCP连接中TIME-WAIT sockets的快速回收，默认为0，表示关闭。

net.ipv4.tcp_tw_reuse = 1 #表示开启重用,允许将TIME-WAIT sockets重新用于新的TCP连接,默认为0,表示关闭

net.ipv4.tcp_synack_retries = 1 #这个是三次握手中，服务器回应ACK给客户端里，重试的次数。默认是5。显然攻击者是不会完成整个三次握手的，因此服务器在发出的ACK包在没有回应的情况下，会重试发送。当发送者是伪造IP时，服务器的ACK回应自然是无效的。

#为了防止服务器做这种无用功，可以把tcp_synack_retries设置为0或者1。因为对于正常的客户端，如果它接收不到服务器回应的ACK包，它会再次发送SYN包，客户端还是能正常连接的，只是可能在某些情况下建立连接的速度变慢了一点。

net.ipv4.tcp_syn_retries = 1 #该文件表示本机向外发起TCP SYN连接超时重传的次数，不应该高于255；该值仅仅针对外出的连接，对于进来的连接由tcp_retries1控制。

net.ipv4.ip_local_port_range = 1024 65535

net.ipv4.tcp_max_syn_backlog = 8192

net.ipv4.tcp_max_tw_buckets = 5000

net.ipv4.tcp_mem = 94500000 915000000 927000000

net.ipv4.tcp_max_orphans = 3276800

net.core.wmem_default = 8388608

net.core.wmem_max = 16777216

net.core.rmem_default = 8388608

net.core.rmem_max = 16777216

# see details in https://help.aliyun.com/knowledge_detail/39428.html
net.ipv4.conf.all.rp_filter=0

net.ipv4.conf.default.rp_filter=0

net.ipv4.conf.default.arp_announce = 2

net.ipv4.conf.lo.arp_announce=2

net.ipv4.conf.all.arp_announce=2

# see details in https://help.aliyun.com/knowledge_detail/41334.html
net.ipv4.tcp_max_tw_buckets = 5000

net.ipv4.tcp_syncookies = 1

net.ipv4.tcp_max_syn_backlog = 1024

net.ipv4.tcp_synack_retries = 2

net.ipv6.conf.all.disable_ipv6 = 1

net.ipv6.conf.default.disable_ipv6 = 1

net.ipv6.conf.lo.disable_ipv6 = 1

#############################

net.ipv4.tcp_fin_timeout = 2

net.ipv4.tcp_tw_reuse = 1

net.ipv4.tcp_tw_recycle = 1

net.ipv4.tcp_keepalive_time = 1

net.ipv4.ip_local_port_range = 4000 65000

net.ipv4.tcp_max_syn_backlog = 16384

net.ipv4.tcp_max_tw_buckets = 36000

net.ipv4.route.gc_timeout = 100

net.ipv4.tcp_syn_retries = 1

net.ipv4.tcp_synack_retries = 1

net.core.somaxconn = 16384

net.core.netdev_max_backlog = 16384

net.ipv4.tcp_max_orphans = 16384

#Tcp SYN flood洪水攻击

增大 tcp_max_syn_backlog

减小 tcp_synack_retries

启用 tcp_syncookies

net.ipv4.tcp_syn_retries = 2

net.ipv4.tcp_keepalive_time = 300

net.ipv4.tcp_orphan_retries = 3

net.ipv4.tcp_max_syn_backlog = 8192

net.ipv4.tcp_tw_reuse = 1

net.ipv4.tcp_fin_timeout = 30

net.ipv4.tcp_keepalive_probes = 5

net.core.netdev_max_backlog = 3000

tcp_max_tw_buckets 

* soft nproc 131072

* hard nproc 131072

* soft nofile 655350

* hard nofile 655350