Heather has been tasked with setting up and implementing VPN tunnels to remote offices. She will most likely be implementing IPsec VPN tunnels to connect the offices. At what layer of the OSI model

does an IPsec tunnel function on$?$

A$.$ They function on the data link layer.

B$.$ They work on the network layer.

C$.$ They function on either the application or the physical layer.

D$.$ They work on the session layer.