sudo nano /etc/sysctl.conf
Add or modify the following.

# IP Spoofing protection
​net.ipv4.conf.all.rp_filter = 1
​net.ipv4.conf.default.rp_filter = 1
​
​# Ignore ICMP broadcast requests
​net.ipv4.icmp_echo_ignore_broadcasts = 1
​
​# Disable source packet routing
​net.ipv4.conf.all.accept_source_route = 0
​net.ipv6.conf.all.accept_source_route = 0
​net.ipv4.conf.default.accept_source_route = 0
​net.ipv6.conf.default.accept_source_route = 0
​
​# Ignore send redirects
​net.ipv4.conf.all.send_redirects = 0
​net.ipv4.conf.default.send_redirects = 0
​
​# Block SYN attacks
​net.ipv4.tcp_syncookies = 1
​net.ipv4.tcp_max_syn_backlog = 2048
​net.ipv4.tcp_synack_retries = 2
​net.ipv4.tcp_syn_retries = 5
​
​# Log Martians
​net.ipv4.conf.all.log_martians = 1
​net.ipv4.icmp_ignore_bogus_error_responses = 1
​
​# Ignore ICMP redirects
​net.ipv4.conf.all.accept_redirects = 0
​net.ipv6.conf.all.accept_redirects = 0
​net.ipv4.conf.default.accept_redirects = 0
​net.ipv6.conf.default.accept_redirects = 0
​
​# Ignore Directed pings
​net.ipv4.icmp_echo_ignore_all = 1

# Accept Redirects? No, this is not router
net.ipv4.conf.all.secure_redirects = 0

# Log packets with impossible addresses to kernel log? yes
net.ipv4.conf.default.secure_redirects = 0

#Enable ExecShield protection
kernel.exec-shield = 1
kernel.randomize_va_space = 1

########## IPv6 networking start ##############
# Number of Router Solicitations to send until assuming no routers are present.
# This is host and not router
net.ipv6.conf.default.router_solicitations = 0

# Accept Router Preference in RA?
net.ipv6.conf.default.accept_ra_rtr_pref = 0

# Learn Prefix Information in Router Advertisement
net.ipv6.conf.default.accept_ra_pinfo = 0

# Setting controls whether the system will accept Hop Limit settings from a router advertisement
net.ipv6.conf.default.accept_ra_defrtr = 0

#router advertisements can cause the system to assign a global unicast address to an interface
net.ipv6.conf.default.autoconf = 0

#how many neighbor solicitations to send out per address?
net.ipv6.conf.default.dad_transmits = 0

# How many global unicast IPv6 addresses can be assigned to each interface?
net.ipv6.conf.default.max_addresses = 1