Router port facing to Core switch is running trunk mode allowed vlan 200 & 300. I am placing a firewall between the trunk connection. Can I set the firewall as L2 transparent mode or I need to configure the firewall as trunk mode for both ports? The setup i was wondering whether firewall normal switchport interface can it talk to the router port trunk mode? It is like connecting a PC/L2 switch to the router trunk port. I was wondering whether it works and concept behind. Thanks guys! I need help!

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    What kind of firewall? (Manufacturer, OS?) – grawity Nov 3 '17 at 6:55
  • Is it a non-famous brand. Howveer the same concept shld applies for all firewall. The question is does the firewall need to set as transparent or trunk mode in order for traffic to pass through from core sw to router without any interruption – jack peterson Nov 3 '17 at 9:26

A firewall can be L2 transparent (depending on configuration), but that's not quite enough.

For full functionality, the firewall needs to recognize VLAN tagged frames and look inside them for IP. It's possible that some types might do this automatically. But others might require a separate virtual "VLAN interface" to be configured on the firewall for each and every VLAN ID.

If the firewall is merely L2 transparent but doesn't understand VLANs, then it won't protect them: either it'll drop the frames as unknown, or bypass them as unknown.

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