D-Link DIR-878 A1 Wan - LAN performance

Sorry people, I just read a pinned topic from 2021 that states I am out of luck with my dated hardware and my fast 1Gbit connection.. Time for an upgrade I think...

Hello fellow Openwrt users.

This is great software and I have been using it for over 3 years without issue. Now that I just upgraded to a 1 Gbit glass fibre connection, I run into a strange performance issue with the D-Link DIR-878 A1 that is connected to the modem through the wan port. If I connect directly to the model with a laptop I get the 1 GB speeds up and down perfectly. When connecting to a lan port of the D-Link DIR-878 A1, I only get up to 450 mbit download and 150 upload. At first I though my connection to the provider was flawed until I connected a wired device directly to the modem.

So, something strange is going on. Is this a hardware limitation of this device? Or could a setting of some sort be culprit? Perhaps there is a known issue I am not aware of.

Running OpenWrt 21.02.0 r16279-5cc0535800 / LuCI openwrt-21.02 branch git-21.231.26241-422c175

(I know, I should upgrade..., but would that solve the issue? )

do try v23 there was patch to at lest not use the lan & wan on the same switch (500M max)

Actually, watching a video from One Marc Fifty on youtube I tried switching on
Software flow offloading and Hardware flow offloading.

That did the trick for me! Full speed behaind the router now. There is a small price. SQM and QOS may not work with this set up, but I don't think I need that.