The simplest form of a firewall is a packet filtering firewall. Typically a router works as a packetfiltering firewall and has the capability to filter on some of the contents of packets. On which of the
following layers of the OSI reference model do these routers filter information? Each correct
answer represents a complete solution. Choose all that apply.

A.
Transport layer

B.
Physical layer

C.
Data Link layer

D.
Network layer