Upload speed reduction when using gigabit LAN connection on TL-WR1043ND v1

Initial data:

  1. Gigabit LAN
  2. 100 megabit WAN
  3. OpenWrt any version (15.05.1, 17.01.7, 18.06.9, 19.07.10, 21.02.7, 22.03.5), software flow offloading on/off
  4. Speedtest host with 190 ping
  5. Speed 41/18

The speed increases to 39/85 if I add a 100 megabit switch to the LAN.

In the original firmware, the problem is not observed. It looks like there is a buffer overflow due to high ping.

Any thoughts on how this can be fixed? (Hardware is too weak for SQM, and it seems that this can not be a solution, so 100 megabit WAN works without problems)

There are recent reports about problems when mixing 100 Mbps interface speeds with 1000Mbps on the same switch... since your router's wan port seems to be part of the same switch you might be able to get away with disabling flow control for the switch's WAN port?

I haven't found a way to turn off flow control on the WAN port. And I don't think it will help.

I found another way that solves the problem by limiting the speed on the internal port:

uci add network switch_port
uci set network.@switch_port[-1].device='switch0'
uci set network.@switch_port[-1].port=5
uci set network.@switch_port[-1].rate_in=100000
uci set network.@switch_port[-1].rate_out=100000
uci commit

This method has some minor disadvantages:

  1. Reduced maximum speed to WAN: 93 -> 87 megabits
  2. Reduced maximum speed to the router: ~150 -> ~100 megabits

The speed between gigabit devices shouldn't be limited, but I can't verify that.

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