Solved RT-AX82U Poor LAN transfer speeds fast WAN performance

[piii_man]

Hi All, I upgraded my router from an RT-68U to an RT-AX82U. I mostly did the upgrade for local file transfers but have been disappointed that these are actually slower. Interestingly my WAN speeds i.e. connect via wifi and run an internet speed test are very good. I don't really understand why I can see such good speeds accessing the internet but such poor performance with transfers within my network.

To help diagnose this I did a series of tests with a desktop (wifi card Intel AX210) serving a file to a laptop (wifi card Intel AX211), both in close proximity with the router < 10 feet. The router had a freshly cleared NVRAM and essentially all default settings and the newest firmware (although I have previously played with the firmware and settings to try to diagnose this issue).

The Internet test was done with speedtest.com. The LAN transfers were done using sftp to serve a single 1GB file from one computer in the network to another. The results using SMB for file transfer were similar but not shown. The negotiated bit rates during transfers were approximately 2.4Gb/s and remained steady during tests (unless ac was used then the where 833 Mb/s). While I'm giving the result of single tests here, I tried replicates and used different transfer protocols which looked similar.

RT-AX82U Tests
Internet Speed test from a client connected to router

• Gigabit Wired: 118/114 MB/s (down/up)
• 802.11ax: 117/96 MB/s (down/up)

File Transfer within local network (desktop serving a file to laptop)

• Wired desktop -> Wired Laptop: 40.3 MB/s
• Wired desktop -> 802.11ax laptop: 20.7 MB/s
• 802.11ax desktop -> wired laptop: 22.6 MB/s
• 802.11ax desktop -> 802.11ax laptop: 11.8 MB/s
  • For this one I also did the other way where laptop serves a file to desktop: 11.5 MB/s

RT-68U Tests

• Wired desktop -> wired laptop: 40.3 MB/s
• Wired desktop -> 802.11ac laptop: 38.3 MB/s
• 802.11ac desktop -> wired laptop: 39.8 MB/s
• 802.11ac desktop -> 802.11ac laptop: 19.5 MB/s

So overall I'm seeing much faster file transfers within network using the old ac router as opposed to the new ax. Is there any default configuration of the router that could so significantly hamper local network file transfers? Is there a inherent hardware limitation of the 82U that could cause this?

 

[oldgringo]

The same MIMO setup? The same wifi channels? The same output power? What says the speedtest in wireless mode for both? Is it as in the first part mentioned (100+MB/s) for both? Then it might be also SMB definitions, what samba versions, what setup, what security? Too much questions to say it immediately. Have you seen samba logs? No errors?

 

[oldgringo]

What did you use for a measure, some special application for transfer speed monitoring or some file manager application status?

 

[Volt]

Try playing with OFMDA and MU-MIMO settings. I did a similar test about a year ago on RT-AX56U (which is slower than RT-AX82U) between Galaxy S21 and a Dell laptop with AX211 (over WiFi) and noticed that with the "DL/UL OFDMA + MU MIMO" setting I got the slowest speeds - only about 100-120MBits/s, while with "DL OFDMA Only" or "Disable" - approx. 260-270 MBits/s.

Also try disabling (if they are enabled) TrendMicro-related services, especially AiProtection and QoS, since they make router slower too.

 

[Ripshod]

I'd be concerned with the LAN speeds as well. You can use something like iperf3 to test the true performance of the networks, and if the results are much better (expect total saturation of the connections) then you need to look elsewhere for bottlenecks.

 

[piii_man]

Thanks for the tip about iperf3. I ended up using that. Unfortunately, the speeds were very similar to what I was getting from sftp. Fortunately iperf clued me into something I was noticing during the speed tests: the transfer speeds fluctuated a lot. Iperf was logging a lot of retries and inconsistent window size, which certainly will cause these fluctuations (and kill speed with TCP). I decided I had spent enough time on this and the slow wired speeds in conjunction with lots of retries made me think either I have a bad router or there is some hardware limitation here. I bought an RT-AX86U, and out of the box I am getting over 802.11ax ~63 MBytes/s with sftp, 88 Mbytes/sec (850 mbit) in iperf3 and over wired very nearly gigabit speeds.

I will return the 82U I guess. I am still perplexed about how download and upload speeds were fine with clients to wan endpoints but between networked computers is slow.

Regarding your questions:

I saw what you saw @Volt with MU MIMO, it kills speed (...even more ). I was using the default setting here which was DL OFDMA only.

@oldgringo I wasn't using any of the QoS or AI features, additionally and as a gut check was seeing low CPU load on the router while performing the tests.