Connect a Zyxel USG20 Firewall to ISP Modem (Router Mode) for Internet

Hello Everyone, i have a Zyxel USG 20 VPN Firewall. The ISP Modem is a Fiber ONT device which is setup with a static public ip & can only be set in Router mode. (Bridge mode isnt working). The eth0 port of the ISP modem is connected to the USG WAN port. The LAN port of the firewall is connected to a network switch which is then connected to clients. DHCP in Firewall & ISP Modem is disabled, as we have a windows DHCP Server running in Active Directory Server. Please suggest a proper way to configure the Firewall to route traffic through/from the ISP modem for internet access and also to maintain a secure internal network. Let me know if you need more information. Thanks in advance.


  • lalaland
    lalaland Posts: 90  Ally Member
    First Anniversary 10 Comments Friend Collector First Answer
    Can you draw a brief network topology with each device role and interface IP assignment.
    It would be easily to understand network topology  for community users.=)

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