You are running through a series of tests on your network to check for any security vulnerabilities. After normal working hours, you initiate a DoS attack against your external firewall. The firewall quickly freezes up and becomes unusable. You then initiate an FTP connection from an external IP into your internal network. The connection is successful even though you have FTP blocked at the external firewall. What has happened?

A.
The firewall failed-open

B.
The firewall failed-bypass

C.
The firewall failed-closed

D.
The firewall ACL has been purged