Recommendations for hardening Linux against DDoS & syn flood attacks

Add the following lines in sysctl.conf....

# Vim /etc/ sysctl.conf
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net.ipv4.tcp_syncookies = 1           [# Prevent the common 'syn flood attack']
net.ipv4.conf.all.rp_filter = 1     [# Prevent the common 'DoS attack']
net.ipv4.conf.default.rp_filter = 1      [# Prevent the common 'DoS attack']
net.ipv4.tcp_max_syn_backlog = 2048
net.ipv4.tcp_synack_retries = 3
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