Packet filtering firewall exists what problem so stateful firewall is proposed? (Multiple choice)
A . Unable to detect certain attack behaviors from the transport layer and application layer (such as TCP SYN, Java Applets, etc.)
B . For multi-channel application layer protocols (such as FTP, SIP, etc.), some security policy configurations are unpredictable.
C . For the TCP connection, the first packet is required to be SYN packet, and the first TCP packet of the non-SYN packet is discarded.
D . Unrecognized ICMP error packets from the network, so ICMP malicious attacks cannot be avoided
Answer: AB