Grading Checklist

• Uses iptables -L -v -n (with -n for numeric output) to inspect all chains.
• Identifies the specific DROP rule in the OUTPUT chain blocking traffic to the payment gateway IP range.
• Understands iptables rule evaluation order: rules are matched top-to-bottom, first match wins.
• Recognizes that a broad DROP rule placed before a more specific ACCEPT rule causes the block.
• Uses iptables -L -v -n --line-numbers to identify the exact rule number.
• Demonstrates how to delete or reorder the offending rule.
• Tests the fix with curl or telnet to the payment gateway.
• Suggests using strace -e trace=network to confirm the connection failure at the syscall level.
• Mentions checking the packet/byte counters on the DROP rule to confirm it is matching traffic.
• Recommends persisting the fix with iptables-save or the appropriate persistence mechanism.
• Notes that iptables rules are lost on reboot unless persisted.
• Suggests implementing a change management process for firewall rules.