What command would be BEST to use if iptables is dropping all connections and needs to remove existing rules?

The most appropriate command to use when iptables is dropping all connections and you need to remove existing rules is the command that clears all the current rules in the filter table. This command effectively flushes the existing rules, allowing for a clean slate for future rule configuration.

The command that achieves this is the one that uses the flush option, which clears all the rules from the selected tables. By doing this, it allows all incoming connections to be handled based on the default policies rather than any restrictive current rules.

The other options serve different purposes. The command that sets the policy to DROP will block all incoming packets unless explicitly allowed by other rules. While it is important for security configuration, it does not clear existing rules and instead enforces a policy based on them, which is not helpful in a scenario where existing restrictive rules are causing connectivity issues.

Using the flush command allows you to start fresh, making it easier to troubleshoot and configure the firewall settings appropriately.