Firewalls generally work at layer 3, 4 & 7. First generation firewalls provided PACKET filtering and operate at layer 3 (Network Layer). Second generation firewalls can operate up to the Transport layer (layer 4) and record all connectivity passing through it and decides whether a packet is the start of a NEW connection or a part of an existing connection, or without any part of the connection.

Second generation firewalls are fundamentally USED for Stateful Inspection.

Third generation firewalls can operate at layer 7. The key benefit of this application layer filtering is that it can “UNDERSTAND” certain applications and protocols (such as File Transfer Protocol (FTP), Domain Name SYSTEM (DNS), or Hypertext Transfer Protocol (HTTP)) on its own

Firewalls generally work at layer 3, 4 & 7. First generation firewalls provided packet filtering and operate at layer 3 (Network Layer). Second generation firewalls can operate up to the Transport layer (layer 4) and record all connectivity passing through it and decides whether a packet is the start of a new connection or a part of an existing connection, or without any part of the connection.

Second generation firewalls are fundamentally used for Stateful Inspection.

Third generation firewalls can operate at layer 7. The key benefit of this application layer filtering is that it can “understand” certain applications and protocols (such as File Transfer Protocol (FTP), Domain Name System (DNS), or Hypertext Transfer Protocol (HTTP)) on its own