Operating Fritz!Box with ONT: Models, Connection Options, Performance & Setup

Operating Fritz!Box with ONT: the clean solution for FTTH

Many fiber households receive an ONT (Optical Network Terminal) from their provider – often also called a fiber modem. Instead of buying a Fritz!Box with integrated SFP module, almost any current Fritz!Box with WAN port can be operated directly behind the ONT. From my tests, this is the most flexible option: free router choice, quick commissioning, full control over the home network.

What does operating the Fritz!Box with ONT mean?

The ONT works as a fiber-to-Ethernet converter. So you connect a normal network cable between ONT and Fritz!Box. Requirements are an active FTTH connection and a free Ethernet port on the ONT. The ONT remains the property of the provider and is usually already correctly provisioned.

• Requirements: FTTH active, ONT with Ethernet (1G or 2.5G), provider's access type known (PPPoE or DHCP), possibly VLAN-ID.
• Advantages: Router of choice, quick setup, provider-side fiber configuration not needed, clean separation between modem and router.
• Control: You determine QoS, firewall, port forwarding, VPN, mesh and telephony – without provider firmware.

"ONT = Modem. Fritz!Box = Router." This separation is often the most robust and future-proof solution in fiber everyday life.

Suitable Fritz!Box models and ports

The good news: Many Fritz!Boxes come with a WAN mode, usually via LAN 1. This is sufficient for gigabit tariffs. Those who book more than 1 Gbit/s should pay attention to 2.5G-WAN/LAN to avoid creating a bottleneck.

• LAN 1 as WAN (up to ~1 Gbit/s): Fritz!Box 7530 AX, 7590 AX, 4040 (pure router), 5490/5491 in router mode, various cable models in WAN operation.
• 2.5G-WAN for >1 Gbit/s: Fritz!Box 4060 (2.5G-WAN), 5590 Fiber (2.5G-LAN), 5530 Fiber (2.5G-LAN). These models are predestined for 1–2.5 Gbit/s tariffs.
• Fiber models with ONT: 5530/5590 can alternatively also be operated via Ethernet with the ONT – practical when the provider mandates their own ONT.

Comparison: recommended models for ONT operation

Torn between integrated modem and ONT solution? The detailed comparison helps with the selection: [url="https://www.siio.de/quack/4718/fritzbox-5590-vs-7590ax-mit-modem—was-ist-besser/",name="Fritz!Box 5590 vs. 7590 AX – Which is better?",title="This link leads to siio.de"]

Connection options with ONT

The physical connection is simple: ONT-Ethernet to WAN/LAN 1 of the Fritz!Box. The access data is crucial:

1. Access type: Depending on provider PPPoE (often with Telekom) or DHCP (with many municipal utilities). IPv6 should be activated if dual-stack is available.
2. VLAN tagging: Some providers require a VLAN-ID (e.g. Telekom: VLAN 7 for internet). You activate tagging in the internet assistant.
3. Telephony/TV: IPTV and VoIP sometimes use separate VLANs or profiles. This is mapped in the Fritz!Box via provider profiles or manual settings.

Performance and throughput

ONT operation is performant – as long as ports and configuration match. My experience values:

• Up to 1 Gbit/s: 7530/7590 AX achieve in PPPoE scenario in practice usually ~0.9–0.95 Gbit/s net. This is sufficient for common gigabit tariffs.
• > 1 Gbit/s: For 1.5 or 2.5 Gbit/s, 2.5G-WAN/LAN and hardware acceleration are advisable (e.g. 4060, 5590/5530 in Ethernet operation).
• Influencing factors: QoS/traffic shaping, VPN (IPSec/WireGuard), intrusion features and IPv6 firewall can noticeably reduce throughput. For maximum speed tests, temporarily deactivate critical features.

Also important is the end-to-end 2.5G chain (ONT port, router WAN, LAN backbone, switch/NAS/PC). A 1G switch immediately limits.

Step-by-step setup in the Fritz!Box

1. Cabling: ONT-LAN to Fritz!Box-WAN (LAN 1). For >1 Gbit/s use a 2.5G-capable cable (Cat 6/6a).
2. Start assistant: In the Fritz!Box interface under Internet, call up the assistant and select "Internet access via external modem/ONT".
3. Select access type: PPPoE or DHCP according to provider. Enter PPPoE username/password.
4. Set VLAN-ID: If required (e.g. 7 with Telekom). With DHCP connections often no VLAN needed – check provider specifications.
5. Save & test: Establish connection, check status, activate IPv6 (dual-stack, if available).
6. Set up telephony: Store provider's SIP access data in Fritz!Box, assign phone numbers, check dialing rules.
7. WLAN/Mesh: Set WLAN name/key, activate band steering, connect repeaters as mesh nodes. Configure guest network separately.

Still unsure? The model comparison provides additional decision support – including practical evaluation of WLAN performance: [url="https://www.siio.de/quack/4718/fritzbox-5590-vs-7590ax-mit-modem—was-ist-besser/",name="To comparison article",title="This link leads to siio.de"]

Provider specifics and pitfalls

• VLAN-IDs: Different depending on provider (e.g. Telekom: Internet VLAN 7; IPTV often own VLAN). Without correct tagging, the connection remains empty.
• MTU: PPPoE typically works with MTU 1492. With DHCP, 1500 is common. A wrong MTU manifests in fragmented or hanging connections.
• Dual-Stack vs. DS-Lite: Some providers deliver IPv4 only via DS-Lite. For port forwarding/VPN, better book real dual-stack.
• IPTV/VoIP: Sometimes separate VLANs or IGMP requirements. In the Fritz!Box select the appropriate provider profile.
• Router-in-front-of-ONT scenarios: If a provider router is upstream, use bridge mode or exposed host to avoid double NAT.

Testing, optimization and troubleshooting

This is how I check stability and throughput after setup:

• Speed tests via LAN: Measure directly at the router with a 2.5G or 1G capable PC. WLAN distorts results.
• Check link rate: Fritz!Box shows 1G/2.5G link. If only 1G, check cable/port.
• High-quality cables: At least Cat 5e (1G), better Cat 6/6a for 2.5G routes.
• PPPoE error codes: Often indicate wrong access data or VLAN mismatch.
• MAC/port binding: Some ONTs are bound to the first MAC. Disconnect Fritz!Box from power briefly or ask provider for resynchronization.
• Optimize WLAN separately: Choose channels manually or automatically, prioritize 5 GHz, activate band steering, place mesh nodes sensibly.

• help

  Can I also operate a Fritz!Box 5530/5590 with ONT?

  Yes. Both fiber models can alternatively be operated via Ethernet behind the ONT. This is practical when the provider insists on their own ONT or doesn't release SFP modules.

• help

  Do I always need VLAN tagging?

  No. Many municipal utilities deliver DHCP without VLAN. Others, like Telekom, require VLAN 7 for internet (PPPoE). The correct parameters are in the provider documents.

• help

  What limits my gigabit tariff?

  Often PPPoE overhead, router SoC, enabled features (QoS/VPN), 1G ports or unsuitable cables. For >1 Gbit/s you need 2.5G on the entire route.

Conclusion and recommendation

Operating a Fritz!Box with ONT is uncomplicated, powerful and above all flexible in practice. For gigabit models like 7530/7590 AX are sufficient. For 1.5–2.5 Gbit/s I recommend routers with 2.5G-WAN/LAN like the 4060 or the 5590/5530 as Ethernet routers. Check your provider's requirements (PPPoE/DHCP, VLAN, MTU) carefully – then nothing stands in the way of stable bandwidths.

My recommendation: Compare integrated modem vs. ONT operation before purchase and check which setup fits your tariff: [url="https://www.siio.de/quack/4718/fritzbox-5590-vs-7590ax-mit-modem—was-ist-besser/",name="To detailed router comparison",title="This link leads to siio.de"]. For a quick, proven ONT combo you can also find suitable Fritz!Box models here:

Briefly summarized – Implement now:

• Connect ONT via Ethernet to Fritz!Box-WAN (LAN 1 or 2.5G-WAN).
• In assistant select PPPoE/DHCP, set VLAN/MTU if necessary, add telephony.
• Optimize WLAN/mesh, perform speed tests via LAN.
• Further details and model recommendations: [url="https://www.siio.de/quack/4718/fritzbox-5590-vs-7590ax-mit-modem—was-ist-besser/",name="Read router comparison",title="This link leads to siio.de"]