1. Delete all existing rules

iptables -F

2. Set default chain policies

iptables -P INPUT DROP

iptables -P FORWARD DROP

iptables -P OUTPUT DROP

3. Block a specific ip-address

BLOCK_THIS_IP="x.x.x.x"

iptables -A INPUT -s "$BLOCK_THIS_IP" -j DROP

4. Allow ALL incoming SSH

iptables -...

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