MISSION BRIEFING
The company's edge firewall was reset during a maintenance window. You have 0 rules protecting a production web server, database, and SSH management interface. Build the firewall from scratch before attackers discover the gap.
iptables Reference
iptables -L -n -v
List all rules (numeric, verbose)
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
Allow SSH
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Allow established connections
iptables -A INPUT -s 10.0.0.0/24 -j ACCEPT
Allow subnet
iptables -P INPUT DROP
Default deny policy
iptables -A INPUT -i lo -j ACCEPT
Allow loopback
iptables-save > /etc/iptables.rules
Save rules to file
iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
Allow ping
Why This Matters
iptables is the kernel-level packet filter in Linux. Every packet that enters, leaves, or traverses the system passes through these chains. A misconfigured firewall can lock you out or leave you wide open. This is CompTIA Security+ domain 3.3 material.
