Normally, the port used by the FTP active mode server for data transmission is the TCP ( ) port.

Use the Ping command on the firewall to test the reachability of the server (the security zone where the server is located is the DMZ). If the security policy is configured to allow the test traffic, the source security zone is ______.

Which of the following attacks is not a special message attack?

IPv6 supports configuring the router authorization function on the device, verifying the identity of the peer through a digital certificate, and selecting a legal device.

In the Linux system, if the user wants to enter the tmp folder in the root directory, the command that needs to be entered is ________/tmp. [Fill in the blanks]