To turn on TCP SYN cookie protection in Linux, you need to modify the kernel parameters.
You can do this by adding the following line to the /etc/sysctl.conf file:
net.ipv4.tcp_syncookies = 1
After adding this line, run the following command to apply the changes:
sysctl -p
This will activate TCP SYN cookie protection, which helps prevent certain types of denial of service (DoS) attacks by tracking incoming connection requests and sending back a special cookie in response to each request.
Note: The availability of TCP SYN cookie protection depends on the specific version and configuration of your Linux distribution.