You can connect two routers to a single fiber optic supply by configuring the primary router as the main gateway for broadband and telephony, while setting the secondary Fritzbox 7590AX to operate in bridge mode or as an access point. This setup allows you to leverage the advanced features of the replacement router without creating double NAT issues or conflicting DHCP servers on your local network.
Understanding the Fiber Optic Connection Architecture
When an Internet Service Provider (ISP) installs fiber optics, they typically provide a Network Termination Unit (NTU) or Optical Network Terminal (ONT). This device converts the optical signal into Ethernet data that standard routers can process. In many cases, the ISP provides a pre-configured router that handles both internet connectivity and Voice over IP (VoIP) telephone services. However, if the ISP does not supply the router, you are free to use your own hardware, such as the AVM Fritzbox 7590AX, which offers robust parental controls, mesh networking capabilities, and superior Wi-Fi 6 performance.
The challenge lies in integrating a second router into this chain without disrupting the telephone service or causing network conflicts. The key is to ensure that only one device manages the public IP address assignment and the VoIP registration with the ISP’s server. The other router must be configured to extend the network locally rather than act as an independent gateway.
Configuring the Primary Router for Broadband and Telephone
The first step is to identify which router will serve as the primary gateway. Usually, this should be the device most compatible with the ISP’s specific requirements for VoIP. Connect the primary router directly to the ONT’s Ethernet port. Access the router’s administration interface, often found at
192.168.1.1 or via the manufacturer’s dedicated app.
Configure the WAN settings to match the ISP’s connection type. For fiber connections, this is typically PPPoE or DHCP depending on the provider. If your ISP requires specific VLAN tagging for voice traffic, ensure this is enabled in the router’s advanced network settings. Register your telephone numbers with the ISP using the SIP credentials provided. Test the voice service by making a call to confirm that audio quality is clear and registration is successful.
Once the primary router is stable, verify that it has obtained a public IP address and that all devices connected to it have internet access. This router now acts as the sole manager of your external network resources.
Setting Up the Secondary Fritzbox 7590AX
To integrate the Fritzbox 7590AX effectively, you must prevent it from acting as a second router. The most common error users make is leaving the secondary device in its default routing mode, which creates a separate subnet and breaks communication between devices on different routers. Instead, configure the Fritzbox in "Access Point" or "Bridge" mode.
In the Fritzbox interface, navigate to the network settings and look for the option to disable the DHCP server. Set the LAN IP address of the Fritzbox to a static IP within the same subnet as the primary router but outside the DHCP range. For example, if the primary router uses
192.168.1.1 and hands out addresses from
.100 to
.200, set the Fritzbox to
192.168.1.2.
Connect an Ethernet cable from a LAN port on the primary router to a LAN port on the Fritzbox. Do not use the WAN port on the Fritzbox when operating in this mode. This physical connection ensures that the Fritzbox simply extends the existing network, allowing devices connected to it to communicate seamlessly with those on the primary router.
For more details on managing multiple subnets, see our guide on
Enabling Communication Between Two Subnets in a Home Office.
Optimizing Wi-Fi and Network Features
With the network topology established, you can now utilize the extra features of the Fritzbox. Since it is part of the same local network, you can enable Mesh Wi-Fi functions if supported by your primary router, or simply use the Fritzbox to cover dead zones in your home. Ensure that both routers broadcast on non-overlapping channels to minimize interference.
If you require specific features like Quality of Service (QoS) for gaming or video calls, configure these on the primary router since it handles the traffic routing. The secondary Fritzbox can still manage local device settings, such as restricting internet access for children’s devices connected to its ports, thanks to its user-friendly interface.
It is also advisable to update the firmware on both devices to ensure compatibility and security. Regular updates protect against vulnerabilities and may improve stability with newer fiber optic standards.
Troubleshooting Common Issues
If internet connectivity drops after connecting the second router, check the physical links. Ensure that the cable from the primary router to the Fritzbox is functioning correctly. Restart both devices to refresh the network lease. If telephone service fails, verify that the primary router is still registered with the ISP and that no firewall rules are blocking SIP traffic.
In some cases, ISPs may restrict the number of devices allowed on their network. Contact your provider if you experience intermittent disconnections, as they may need to whitelist your MAC addresses. For older hardware setups, consider using a managed switch to handle traffic distribution more efficiently, as discussed in
Is it Possible to Use a Fast Switch for a Network of Older Routers?.
Frequently Asked Questions
Can I use the WAN port on the secondary router?
No, using the WAN port will create a double NAT situation, which can break online gaming and VoIP services. Always connect the secondary router via a LAN port when configuring it as an access point or bridge.
Will this setup affect my telephone service quality?
As long as the primary router handles the VoIP registration and the secondary router is in bridge mode, the telephone service will remain unaffected. The secondary router simply passes through the data without interfering with voice packets.
How do I assign IP addresses to avoid conflicts?
Set the primary router’s DHCP range to exclude the IP address you manually assign to the secondary router. This prevents the primary router from trying to assign the same IP to another device, which would cause an IP conflict.
What happens if I want to change the Wi-Fi password?
You should change the Wi-Fi password on both routers if you want them to share the same network name (SSID) for seamless roaming. If you prefer separate networks, you can set different passwords for each router’s SSID.
Is it possible to use a third router in this setup?
Yes, you can add more access points following the same principle. Each additional router must be connected via LAN-to-LAN and have its DHCP server disabled to maintain a single, cohesive network.