Why use the shun command?

Why use the shun command?

A.
PIX Firewall does not support shunning

B.
to enable the PIX Firewall to detect and block intrusion attempts

C.
you know the IP address of an attacking host and want the PIX Firewall to drop packets
containing its destination address

D.
you know the IP address of an attacking host and want the PIX Firewall to drop packets
containing its source address