I've read a lot of threads here and on reddit regarding RB5009 2,5Gbe port related issues, but most of them got resolved around ROS7.9 and I haven't found anyone with setup similar to mine.
I have a dumb 2,5Gbe switch connected to RB5009's 2,5Gbe port. Apart from RB5009, NAS and PC are connected to this switch which allows me to transfer files between PC and NAS quickly as well as to uzilize 2Gbe downlink from my ISP which is provided using SFP module. That portion of the network works flawlessly and I can utilize full internet speed on both NAS and PC as well as transfer files at >1Gbe speeds between them (HDDs in NAS are limiting factor).
Problem starts with two Xiaomis AX3600 which are flashed with openWRT and wired directly to 1Gbe ports of my RB5009. And this one is really strange. If I connect anything to AX3600 using ethernet cable - no problems there. I can see 1gig troughput from NAS and internet downlink. But as soon as I switch to WiFi that no longer is the case - I still can do speedtest @ 1Gig speed (AX3600's are capable of 1,3-1,7Gbe wireless while copying from two sources to overcome 1Gbe link limit), but transfer from NAS is limited to ~400Mbps. As soon as I remove 2,5Gbe advertisement on RB5009's eth1 port, transfer speed goes up to 1Gbe, which can be observed on this screen recording:
The only clue I got is that 400Mbps is the value I get while running iperf3 between my wirelessly connected laptop and NAS with 1 thread. Increasing thread count with 1Gbe enforced increases troughput to 1Gbe gradually, but when 2,5Gbe is enabled it does close to nothing when it comes to transfer speed. Do note that I have SMB Multichannel enabled on my NAS which also uses multiple threads to copy files. It's like having 2,5Gbe enabled on eth1 somehow breaks the ability to use multithreaded transfers and that would explain why only wifi is affected as using the cable I can saturate 1Gbe / 2,5Gbe links using just one thread.
To me it looks like I discovered some bug in ROS, but I cannot figure out how to troubleshoot it further. I used two 2,5Gbe switches based on different platforms (Realtek and Broadcom): TP-Link TL-SH1005 and QNAP QSW-1105T-5T. I have RB5009UPR+S+IN running latest ROS stable - 7.11.2. I also attached simple diagram to help visualize my network setup. If some configuration files are needed, I will happily provide them.
You do not have the required permissions to view the files attached to this post.