AiMesh 2.5Gbps Ethernet backhaul dropping to Gigabit

[ToasterPC]

Hey there, long time no see.

I've moved my router suite over to a Raspberry Pi 4B running OpenWRT, and kept my GT-AX11000 as an access point for the entire floor, then cabled with Cat5e the entire house, and put an RT-AX86U downstairs as another access point using a network switch to connect the Raspberry and both ASUS routers through their 2.5Gbps Ethernet ports using AiMesh.

However for some strange reason, even after testing and confirming the cable runs are alright with a Fluke Cable Tester, after about 48 hours since the installation the 86U drops to a Gigabit link and continues to operate normally.

The run was made with no issues and for about 25 meters, being well below the signal limits for Cat5e, yet I'm unable to sustain a 2.5Gbps link over that particular run.

With the Raspberry Pi I was able to change operation modes to 2.5Gbps for the NIC using ethertool, but I'm not sure how to do the same with Merlin for either diagnosing the problem or forcing the connection.

The 86U is working correctly otherwise at the latest Merlin version, it's just that I'd like to use the full speed available if possible.

If there's anything else I missed I'll gladly provide the required information.

Thanks for the help!

 

[MildlyOffensive]

Unless you were able to test with a network validator like Fluke Networks LIQ-100-IE LINKIQ TESTER that can check signal strength on each wire pair, I would suspect the connection as a whole is not able to sustain 2.5Gbps. Continuity testers like Fluke MT-8200-49A will confirm correct wiring but not the ability to transfer at specified speeds. If your wiring and connectors including patch cables did pass validation, then some kind of problem with the devices.
You could try running a factory Cat6 patch cable between both Asus routers for a while to see if the connection speed is more stable in order to isolate the problem.
I have found that in-wall wiring problems are usually at the connections. Many keystones including Cat6 rated don't actually meet spec. When wiring in the past I have had better luck with signal strength using punch down keystones rather than DIY my own plugs, and thereafter I have quit making my own patch cables.

 

[ToasterPC]

Unless you were able to test with a network validator like Fluke Networks LIQ-100-IE LINKIQ TESTER that can check signal strength on each wire pair, I would suspect the connection as a whole is not able to sustain 2.5Gbps. Continuity testers like Fluke MT-8200-49A will confirm correct wiring but not the ability to transfer at specified speeds. If your wiring and connectors including patch cables did pass validation, then some kind of problem with the devices.
You could try running a factory Cat6 patch cable between both Asus routers for a while to see if the connection speed is more stable in order to isolate the problem.
I have found that in-wall wiring problems are usually at the connections. Many keystones including Cat6 rated don't actually meet spec. When wiring in the past I have had better luck with signal strength using punch down keystones rather than DIY my own plugs, and thereafter I have quit making my own patch cables.

I see, fortunately the link was tested and sustained using Cat8 cabling before going into the keystone jacks, and using weatherproof Cat5e for the intermediate connections of the keystones, and then Cat8 for the keystone to router/switch seemed to work correctly.

I was mostly wondering if there was a way to disable auto-negotiation and try forcing the link to be 2500Mbps Full-Duplex as I'm able to do so with ethertool on OpenWRT.