At which layer of the OSI model does IPsec work?

Susan sets up a firewall that keeps track of the status of the communication between two systems and allows a remote system to respond to a local system after the local system starts communication. What type of firewall is Susan using?

A. A static packet filtering firewall B. An application-level gateway firewall C. A stateful packet inspection firewall D. A circuit-level gateway firewall

A cell ____________________ is the column and row location of a cell.

Fill in the blank(s) with the appropriate word(s).