Device: Banana Pi BPI-R4 Firmware: OpenWrt 24.10.2 Interface tested: eth1 Test method:
for mtu in $(seq 9500 -100 1500); do
echo -n "Testing MTU $mtu … "
if ip link set dev eth1 mtu $mtu 2>/dev/null; then
echo “
supported”
else
echo “
unsupported”
fi
done
Test Results:
Testing MTU 9500 … unsupported
Testing MTU 9400 … unsupported
Testing MTU 9300 … unsupported
…
Testing MTU 2100 … unsupported
Testing MTU 2000 … supported
Testing MTU 1900 … supported
Testing MTU 1800 … supported
Testing MTU 1700 … supported
Testing MTU 1600 … supported
Testing MTU 1500 … supported
Summary:
MTU values above 2000 are not supported on eth1.
Maximum supported MTU: 2000 bytes
All standard and slightly extended MTU values (1500–2000) are working as expected.
Jumbo frames (MTU > 2000) are currently not supported on this interface with OpenWrt 24.10.2.
If anyone knows whether this is a hardware limitation of the MT7988 SoC, or a driver/configuration limitation (e.g., DSA or MTK HNAT driver), further insights would be appreciated.