SYN flood attack how to deal with?

Question

DDoS Protection

Found a SYN flood attack on one of the servers using netstat -n --tcp | grep SYN_RECV | wc -l gives out 200+ connections, htop gives out loading of kernels under 100% tell me please, how can they be blocked?
And would adding net.ipv4.tcp_syncookies = 1 to /etc/sysctl.conf help?
The file is currently empty