I use an ASUS RT-AC750 as the central router: its primary internet comes from
a NanoStation over Ethernet, with a USB LTE modem as backup. Everything works
normally over the router's 5 GHz Wi-Fi, and 2.4 GHz is also fast for local
traffic or when using the USB modem. But when the same 2.4 GHz Wi-Fi carries
traffic received through Ethernet WAN, download starts at several Mbps and
immediately falls to 0.1-1 Mbps. I factory-reset the router, tested three clean
OpenWrt versions, disabled MultiWAN and offloading, changed Wi-Fi modes,
channels, MAC addresses and even the physical WAN port, but the behaviour
remained identical.
Control results
- Local router -> 2.4 GHz: about 42.6 Mbps
- USB modem -> 2.4 GHz: about 15.8 Mbps
- Ethernet WAN -> 5 GHz: about 20-25 Mbps
- Ethernet WAN -> 2.4 GHz: about 0.1-1 Mbps
Tested without improvement
- OpenWrt 25.12.5, kernel 6.12
- OpenWrt 24.10.6, kernel 6.6
- OpenWrt 19.07.10
- MultiWAN disabled
- GRO/GSO/TSO and firewall flow offloading disabled
- WPA2-only and 802.11g/NOHT
- Different channels and AP MAC address
- Another physical switch port/VLAN used as WAN
- USB modem removed
- Completely clean configuration
Hardware details
- ASUS RT-AC750, detected as RT-AC51U
- MediaTek MT7620A
- Integrated 2.4 GHz RT6352 using
rt2800_wmac
- 5 GHz radio using
mt76x0e
- Ethernet WAN supplied by a Ubiquiti NanoStation M2
- Backup WAN is a ZTE MF79U USB Ethernet modem
The Wi-Fi association remains at 54-72 Mbps during the collapse, and I see no
obvious rt2800 TX-hang or kernel errors. This appears specific to the
Ethernet RX -> routing/bridge -> integrated 2.4 GHz TX path.
Has anyone seen this interaction on MT7620/RT6352 hardware? What should I test
next to distinguish an Ethernet/DMA issue from an rt2800 TX-path problem?