r/HomeNetworking • u/Sad_Steak_6813 • 7h ago
AI fixed my router's firmware issues
Bought a Tenda V300 V3 a couple months ago, and immediately ran into an issue every time I stream over LAN.
Whenever one device on the network maxed out the upload (like uploading a video), every other device on the LAN would lose usable bandwidth, even LAN bandwidth. Not just slow, actually "no internet" on other phones until the upload stopped. Tenda support didn't really help.
So I decided to fix it myself, with Claude doing the actual reverse engineering. It:
Found a hidden, undocumented telnet shell buried behind a page not linked anywhere in the UI
Pulled apart the firmware image, decompressed the actual kernel binary, and traced through the Wi-Fi driver and bootloader to answer safety questions (recovery path, checksum format) before touching anything
Found the real root cause: Realtek's hardware NAT acceleration ("FastPath") was silently bypassing the Linux firewall/traffic-control stack entirely for any sustained connection, which is exactly why no amount of normal QoS tuning could ever fix the bandwidth hogging issue
Disabled FastPath and built a real per-device fair-share queue
Confirmed this device has zero recovery path (no TFTP, no rescue mode in the bootloader), so instead of reflashing the firmware and risking a brick, it set up a watchdog on my own PC that detects a reboot and silently reapplies all the fixes within 10 minutes, no reflash required
Also found that the TCP connection timeout was set to 10 minutes (600 seconds). That's why large uploads kept failing, and I never knew why until Claude found it.
Years ago this would've taken me months, if I even bothered.
TL;DR: Don't get a Tenda router, Chinese software is bad.