DEC740 Slow upload speeds on ax1

[Tjh3]

 First off, my internet speed is 4Gbps both ways and i have a DEC740 (the older model)

For a start here's what my network diagram looks like:

XGSPON <---Cat5/5e cable (yea i know)---> QNAP QSW308-1c <---10Gtek DAC cable --> ax1 port on DEC740

ax0 port on DEC740 <---10gtek SFP+ module---- fs.com OM3 cable--- 10gtek sfp+ module---> miktrotik crs305 <--- Intel x520 card  on desktop.

I upgraded to multi-gig and thus connected ax1 for the first time yesterday. Once I had everything connected, in fact I can get 3800/3800 or more, and have gotten it more than once. However, the issue is, more often than not, the upload speed for speedtest goes down to 200Mbps or even lower. If i do 10 tests 1 or 2 will give 3500+ each way the other will give like 3700/150. I initally had RSS enabled which was causing other issues so I have since removed that.

As for settings, except for an extra vlans on LAN side and adguard, both of which i've been using from the get go without any issues: everything else is standard DEC740 config.

Some notes:

• prior to upgrading to 4Gbps i had a 1Gbps plan, at that point i was using the cat5 cable directly connected to a 1Gbe port on the DEC740 and could consistently get 950+ both ways. This all started yesterday when I connected the ax1 port for the first time (prior to this I had never used that port).
  
• i have tested with iperf3 from the router to my desktop and I do in fact get 9Gbps one way and 6Gbps the other way - I suspect the issue with that latter is because the router isn't able to write to disk fast enough to download over 6Gbps to the disk, which is fine and both are over the 4Gb i'm expecting, at any rate
• I had tested a 10Gbase-T module on ax1, and ended up having the same issues, without changing anything else my upload speeds were suddenly very slow.
• i have connected cable directly from XGSPON to my computer, entirely  bypassing the DEC740 with absolutely no issues.

 so far I've settled on ax1 being broken, possibly. Because everything else seems to work, and I have no other explanation.

ETA: I finally figured out how to physically  connect the router directly to my PC via the problematic ax1 port, and assign it to LAN. I did an iperf test to the router (router is iperf server), I generally don't expect to see more than 6Gbps. The big issue was traffic coming out of ax1 rather than going in, which should be the reverse option (ie my computer recving data) right? i was able to get 6Gbit, or more, which is far more than the <200Mbps i see in that direction to the internet.

So, i have no idea what's going on.

[ou1]

Although I don't really have any suggestions on how to solve your issue, do you mind if I ask what kind of issues you ran into by enabling RSS? I'm playing with it now and it would be nice to know what to watch out for, not just assume it's working.

thanks

[mooh]

I don't have a diagnosis or solution but I want to mention that iperf3 doesn't write to disk. If you observe high disk activity during performance testing, I could be excessive logging. When connecting the computer directly to the XGSPON you're also bypassing the Mikrotik and QNAP switches.

If I was looking for the cause of low throughput, I'd check if there's high CPU load during upload testing? And if so, check where all the power is going. What about MTU size? Is fragmentation involved? What about retransmissions or other low level errors? Mikrotik switches have decent diagnostic features and statistics, at least in their SwitchOS. Is there any kind of flow control or flooding control active on the switch? Same for the QNAP.

[Greg_E]

Do you have IDS/IPS, Crowdsec, Zenarmor enabled?

I doubt the cat5e is the problem, but worth an upgrade when you have time and money, I'd probably go cat6a shielded for "future proof" or just run some OM4 or OM5 fiber if you are running new cable anyway, not too expensive if you are short enough to buy a premade jumper and just be careful with it.