Regarding protection against IP/ICMP attacks, which of the following statements is correct?
A. The principle of defending against IP/ICMP attacks on the user side is to discard the packets whose source IP from the user side is the system IP of the access device
B. The principle of defending against IP/ICMP attacks on the user side is to discard the messages from the user side whose destination IP is the system IP of the access device
C. The principle of defending against user-side IP/ICMP attacks is to discard all packets whose source IP is the system IP of the access device
D. The principle of defending against user-side IP/ICMP attacks is to discard all packets whose destination IP is the system IP of the access device