USG FLEX H Series – WAN Interface Configuration with Static IP and DNS Settings

This article explains how to configure a static IP address and DNS settings on a Zyxel USG FLEX H Series firewall.

First, we will show how to configure a static IP address during the Initial Setup Wizard when deploying the firewall for the first time. We will then review WAN interface and DNS configuration through the local Web GUI for existing deployments. Use this guide when your Internet Service Provider (ISP) has assigned a static IP address and requires manual configuration of the WAN connection parameters, including the IP address, subnet mask, default gateway, and DNS servers.

Configure the WAN Connection During Initial Setup

During the Initial Setup Wizard, you can configure the WAN connection using either DHCP or a Static IP address, depending on the requirements provided by your Internet Service Provider (ISP).

If a static IP address is assigned by the ISP, select Static as the Interface Type and enter the required WAN IP address, subnet mask, default gateway, and DNS server information. Use the Connection Test option to verify connectivity before proceeding to the next step.

The WAN and DNS settings configured during the Initial Setup Wizard can be modified later at any time through the local Web GUI.

Configure a Static IP Address and DNS Settings via the Local Web GUI

Navigate to Network > Interface > External, select the WAN interface, and configure the connection using either DHCP or Static IP. When using a static IP address, enter the WAN IP address, subnet mask, default gateway, and DNS server information provided by your ISP.

After configuring the WAN interface, navigate to Network > Interface > Trunk and verify that Default Trunk is selected. This ensures that the configured WAN interface is used for outbound Internet connectivity according to the system's default routing behavior.

Configure DNS Resolution

To specify the DNS server used for domain name resolution, navigate to System > DNS & DDNS > DNS.

Enable Global Zone Forwarder and click Add to create a new entry. Configure the following settings:

• Domain: *
• DNS Server: 8.8.8.8 (or a DNS server provided by your ISP)
• Query Via: auto

Click Apply to save the configuration.

A user-defined Global Zone Forwarder entry takes precedence over the default system DNS configuration and allows the firewall to forward DNS queries to the specified DNS server.

Configure MAC Address Cloning

If your Internet Service Provider (ISP) requires a specific MAC address to authorize Internet access, you can configure MAC address cloning on the WAN interface.

Navigate to Network > Interface > Interface and edit the WAN interface.

In the MAC Address section, select Overwrite Default MAC Address and enter the MAC address provided by your ISP.

Click Apply to save the configuration.

After applying the changes, verify Internet connectivity from a client connected to the LAN network. Test connectivity by pinging a public IP address, such as 8.8.8.8, and a domain name, such as google.com, to confirm that both Internet access and DNS resolution are functioning correctly.