[TP-LINK XDR6088] Not able to set MTU > 2022 in TP-LINK XDR6088

Installing and Using OpenWrt Network and Wireless Configuration
1

Hi everyone,

I recently purchased a TP-LINK XDR6088 and flashed it to the latest OpenWRT 23.05.5 using the firmware from OpenWRT Firmware Selector.

My goal is to use the XDR6088 as an AP + managed switch with jumbo frame support. After uploading the firmware via the recovery firmware, I began exploring the DSA settings. In the Interface -> Device -> br-lan section, I was able to set Bridge VLAN Filtering and successfully tested the tag/untag function. However, when I tried to configure jumbo frames by increasing the MTU, I found that it doesn’t work if the MTU is set above 2022 (e.g., MTU = 9000).

I came across this issue on GitHub https://github.com/openwrt/openwrt/issues/7159, where one developer mentioned that this hack broke the system because DSA includes the CPU port, and the GMAC in the old MT7621 only supports a 2K MTU. Therefore, it’s not possible to set an MTU greater than 2022.

If this is true, is there any method to disable DSA and use the legacy swconfig? Alternatively, can I just use this fix in my case?

2

Try snapshot, though no signs in the thread the "hack" was ever submitted or included.
Probably OK that you submit it after testing thanking the original author.