Which type of traffic can’t be filtered by a network layer firewall?

Network layer firewalls, also called packet filters, operate at a relatively low level of the TCP/IP
protocol stack, not allowing packets to pass through the firewall unless they match the
established rule set. Which type of traffic can’t be filtered by a network layer firewall?

A.
SMTP traffic

B.
ICMP messages

C.
HTTP traffic

D.
Email sender verification