Firewalls operate at the:Group of answer choicesNetwork and application layerInterface between LANs and WANsIP layer of a computer networkNetwork layer

To determine where firewalls operate, it’s essential to understand the different layers of the OSI model.

1. Firewalls and OSI Model: Firewalls primarily operate at two specific layers of the OSI model—Network and Transport layers (sometimes also at the Application layer).

2. Examination of Options:

   • Network and application layer: This option is accurate as many firewalls manage traffic based on network layer IP addresses and routing, as well as filtering based on application layer protocols.
   • Interface between LANs and WANs: While firewalls can be used in this context, they are not defined solely by their physical placement.
   • IP layer of a computer network: This can be misleading because while firewalls do inspect IP packets, it's more about the network layer functionality than being solely IP-layer-based.
   • Network layer: This is correct but does not encompass the full functionality which can extend to the application layer.

Conclusion

The best answer is Network and application layer, as firewalls commonly operate across these layers to filter traffic based on both network-level rules and application-level criteria.