Let’s look at the modes Firewall can be deployed in.
1. Bridge mode, also known as transparent mode, puts Firewall inline so that it can monitor and scan all of the traffic and protect the network, it does this by transparently passing the traffic through. Note that some functions cannot be used in bridge mode and require either gateway mode or mixed mode; these include using the Firewall as a VPN concentrator and support for multiple WAN links.
Network Setup: Internet < Router /Other Firewall < Firewall < LAN systems.
Refer Below Diagram for Understanding.
2. In gateway mode, Firewall provides zone-based filtering and scanning and acts as the entry and exit point for other networks and subnets. In most cases the Firewall is the default gateway for the computers on the internal networks that it is protecting.
Network Setup: Internet < Firewall < LAN systems.
Refer Below Diagram for Understanding.
3. Mixed mode is a combination of bridge mode and gateway mode where two or more interfaces are bridged together transparently, but Firewall still acts as the gateway using ports which are not part of a bridge.
Refer Below Diagram for Understanding
