Disable IPV6 on Debian 10

Three (3) steps to completely eliminate IPV6 on your system. Step 3 applies only if you are using SSH in daemon mode (on a server). The following should work for all Debian.

Step 1

sudo vi /etc/sysctl.conf

# to disable IPv6 on all interfaces system wide
net.ipv6.conf.all.disable_ipv6 = 1

# Uncomment the next two lines to enable Spoof protection (reverse-path filter)
# Turn on Source Address Verification in all interfaces to prevent some spoofing attacks

# Do not accept ICMP redirects (prevent MITM attacks)
net.ipv4.conf.all.accept_redirects = 0
net.ipv6.conf.all.accept_redirects = 0

# Do not send ICMP redirects (we are not a router)
net.ipv4.conf.all.send_redirects = 0

# Do not accept IP source route packets (we are not a router)
net.ipv4.conf.all.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0

# a helpful addition I use to avoid excess swapping

sudo sysctl -p /etc/sysctl.conf

Step 2

sudo echo 'net.ipv6.conf.all.disable_ipv6 = 1' > /etc/sysctl.d/90-disable-ipv6.conf

sudo sysctl -p -f /etc/sysctl.d/90-disable-ipv6.conf

Step 3

sudo vi /etc/ssh/sshd_config

addressFamily inet

sudo service ssh restart

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