AVM’s latest FritzOS 8.21 firmware delivers more than 70 improvements for the Fritz!Box 6670 Cable, 5690 Fiber and 7690 DSL routers. The update adds a modernised web UI, fixes IPv6 stability, introduces cable‑specific DOCSIS enhancements, strengthens security, and provides fail‑over protection and extended monitoring for fiber and DSL models, ensuring faster, more reliable home networking.
Key Features in FritzOS 8.21 for Fritz!Box 6670 Cable
- Modernised web interface – refreshed UI with responsive design for tablets and smartphones, simplifying configuration.
- IPv6 stability fixes – patches that eliminate intermittent IPv6 connectivity issues reported by cable users.
- Cable‑specific bug corrections – DOCSIS‑3.1 stack adjustments that improve upstream stability and reduce link drops.
- Enhanced security hardening – updated OpenSSL libraries and stricter default firewall rules to protect against emerging threats.
FritzOS 8.20 Enhancements for Fritz!Box 5690 Fiber and 7690 DSL
- Fail‑over protection (Ausfallschutz) – watchdog mechanism that automatically reboots the device after critical failures, minimizing downtime.
- Extended online monitor – expanded telemetry that logs connection quality metrics over longer periods for deeper insight.
- General stability and performance tweaks – refinements to the routing engine and Wi‑Fi radio management that boost throughput and reduce latency spikes.
Why These Updates Matter
The modernised web UI reduces the learning curve for new users and speeds up routine tasks such as guest‑network setup or parental‑control adjustments. Improved IPv6 reliability is crucial as more ISPs transition to native IPv6, preventing disruptions to streaming and VoIP services.
Fail‑over protection adds a safety net for fiber and DSL customers who depend on uninterrupted connectivity for remote work or smart‑home automation. By automatically rebooting after a fault, the router minimizes manual intervention and aligns with AVM’s “set‑and‑forget” reliability promise.
Security enhancements, including updated cryptographic libraries and hardened firewall defaults, raise the baseline protection across all three models, addressing vulnerabilities in the underlying Linux kernel and networking stacks.
How to Install the Firmware
Owners can apply the updates directly through the router’s web interface or via the AVM “Fritz!Box Firmware Update” app. The process is fully automated, requires no manual flashing, and completes without interrupting normal network operation.
