Hi,
I like to share my observations and experiences with this router TP-Link Archer C6U v1 EU after a few weeks of testing and trying to get certain functionality to work. What I did to get to this point and hopefully be useful so other don't waste so much time figuring this out. I will try an unbiased balanced report, whenever I mention something is not working well is just stating facts from experience, it is not meant as criticism but meant to help developers and users to achieve success and improvements. I will also report on the good things I've noticed next to the bad things, will refer to issues and problems that are also reported here in the forums.
In general this little router has good potential, is very cheap at the moment and was acquired specifically by me in order to experiment and test mesh, wds , guest networking , interconnect stability with more than 1 unit. The only 'downside' for this router is the small flash size (16Mb) which limits the packages you can install. But fortunately , the USB port functions fine, so the option to add an external flash drive and overlay it would work around this. I do not need Samba but after all the packages I really needed/wanted I could not add this one. Samba is quite a huge packages compared to the rest though. I've had iscsi (server), SQM , openvpn working properly. I chosen to experiment with this router specifically to have a platform that uses Mediatek hardware/wifi chipset.
What I did not test/analysed is throughput performance. From using it daily it seems to do OK, but given the specs of this router it's needless to state that this will not be up to par with more beefy routers, but nevertheless seems to be handling itself quite well.
Setup conditions:
Three units, all named caretaker 1 to 3
- caretaker1 - WAN gateway - WDS gateway - floor 0 - TV connected by wire
- caretaker2 - WDS client station - floor 1 ( concrete floor )
- caretaker3 - WDS client station - floor 0 ( 12 meters from caretaker1 )
Client stations
- Ubuntu 20.04 - Asus Zenbook - very recent hardware
- Ubuntu 20.04 - Asus Zenbook - old machine
- Windows 10 - Asus Vivobook - a few years old
- Windows 10 - Asus ROG - also aged few years
- Oneplus 6T
- Samsung S10 (*2)
- Samsung Tablets ( *3)
- Naim / Samsung TV (cabled connection, less relevant )
Placement: 3 floor apartment, reinforced concrete walls and floors. vertical coverage is the challenge
Setup/ configuration
General observations - stable release
Installing / configuring the routers is trivial and pretty much vanilla OpenWrt installation, Some specific things to know when doing this from the OEM firmware I have documented on the device page. Nothing really earth shattering there. During this process I've also create a device page to record my findings. I would like to invite users to contribute to completing this.
Stability however was not ok. specifically the WIFI part. I could watch hours of netflix through this router without any issues at all, but the WDS connections between stations and also the wifi clients were lost regularly, to the point that it is unworkable.
Setting up a mesh network seems to work initially but after some time the mesh setup gets broken and a kernel WARN is thrown. This doesn't seem to happen when using WDS to interconnect the routers.
But with the stable release, WDS had issues that caretaker2 and caretaker3 often stopped responding and the association of those client stations was lost to caretaker1.
IRQ issues : Users have reported and I could confirm this with 1 router that this was happening. The IRQ problem comes in 2 shapes: You have a ksoftirqd/3 process/thread that is eating up about 25% of the CPU load , and there seems to be an excessive IRQ error counter. But for me it didn't happen on all 3 at the same time.
long lived ssh sessions to three routers become very unresponsive, often just blocking only to recover minutes later, the console 'felt' quite slugish, experiencing latency and unresponsiveness
A forum search will show that users in the past (before the current stable release) have been reporting a number of issues that I will still have to test more . Specifically performance , vlan would be on my list
As a conclusion, I would expect everybody using the stable release to experience these issues and probably be disappointed . But now the good news.
General observations - snapshot release
- OpenWrt SNAPSHOT, r18942-cbfce92367
I decided to install the same snapshot on all three, reconstructed the routers from the package list from stable release. The only package that refused to install was wpad-openssl due to a dependency to hostapd , however making it ignore and force the installation made the WiFi radio work... and work good! Keeping in mind this is still a snapshot.
Although the snapshot hasn't been running quite as long as the time I spent with the stable release to discover problems. It made a huge difference already. Monitoring all three routers for issues overnight showed the disassociation only happened once on caretaker3, it recovered in the same second and was not the farthest router. caretaker2 didn't have any loss of the WDS sid at all. This is a huge contrast with the stable release. all the WIFI sid's work a lot better, the guest network, the WDS network and a third network all keep working fine.
The ksoftirqd load problem seems gone. I do not see it anymore, usually before this change after a bit of uptime, I see it in 1 router atleast. So far, nothing. The IRQ error counters do seem to rise, it rises the most on the gateway (caretaker1), almost none on caretaker2 and caretaker3 has a few 100 (but caretaker2 has been rebooted due to placing it on another floor to test coverage)
uptime 1 and 3 : 13hrs
uptime 2 : 2 hrs at the time I wrote this
root@caretaker1:~# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
7: 0 0 0 0 MIPS 7 timer
8: 4597167 4597149 4597142 4597134 MIPS GIC Local 1 timer
9: 5975055 0 0 0 MIPS GIC 63 IPI call
10: 0 16317548 0 0 MIPS GIC 64 IPI call
11: 0 0 14134460 0 MIPS GIC 65 IPI call
12: 0 0 0 11712736 MIPS GIC 66 IPI call
13: 110962 0 0 0 MIPS GIC 67 IPI resched
14: 0 443040 0 0 MIPS GIC 68 IPI resched
15: 0 0 3499400 0 MIPS GIC 69 IPI resched
16: 0 0 0 1365750 MIPS GIC 70 IPI resched
17: 0 0 0 0 MIPS GIC 19 1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
19: 12 0 0 0 MIPS GIC 33 ttyS0
20: 0 0 0 0 MIPS GIC 29 xhci-hcd:usb1
21: 11140976 0 0 0 MIPS GIC 10 1e100000.ethernet
22: 22 0 0 0 MIPS GIC 11 mt7603e
23: 18 0 0 5298546 MIPS GIC 31 mt7615e
25: 78 0 0 0 MIPS GIC 30 mt7530
26: 5 0 0 0 mt7530 0 mt7530-0:00
27: 21 0 0 0 mt7530 1 mt7530-0:01
28: 43 0 0 0 mt7530 2 mt7530-0:02
29: 9 0 0 0 mt7530 3 mt7530-0:03
30: 0 0 0 0 mt7530 4 mt7530-0:04
31: 0 0 0 0 1e000600.gpio 8 keys
32: 0 0 0 0 1e000600.gpio 10 keys
ERR: 1811
root@caretaker2:~# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
7: 0 0 0 0 MIPS 7 timer
8: 525806 525788 525780 525773 MIPS GIC Local 1 timer
9: 749269 0 0 0 MIPS GIC 63 IPI call
10: 0 1172857 0 0 MIPS GIC 64 IPI call
11: 0 0 1227527 0 MIPS GIC 65 IPI call
12: 0 0 0 773102 MIPS GIC 66 IPI call
13: 95500 0 0 0 MIPS GIC 67 IPI resched
14: 0 66629 0 0 MIPS GIC 68 IPI resched
15: 0 0 161719 0 MIPS GIC 69 IPI resched
16: 0 0 0 101853 MIPS GIC 70 IPI resched
17: 0 0 0 0 MIPS GIC 19 1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
19: 12 0 0 0 MIPS GIC 33 ttyS0
20: 0 0 0 0 MIPS GIC 29 xhci-hcd:usb1
21: 16 0 0 0 MIPS GIC 10 1e100000.ethernet
22: 23 0 0 0 MIPS GIC 11 mt7603e
23: 18 0 0 318070 MIPS GIC 31 mt7615e
25: 0 0 0 0 MIPS GIC 30 mt7530
26: 0 0 0 0 mt7530 0 mt7530-0:00
27: 0 0 0 0 mt7530 1 mt7530-0:01
28: 0 0 0 0 mt7530 2 mt7530-0:02
29: 0 0 0 0 mt7530 3 mt7530-0:03
30: 0 0 0 0 mt7530 4 mt7530-0:04
31: 0 0 0 0 1e000600.gpio 8 keys
32: 0 0 0 0 1e000600.gpio 10 keys
ERR: 5
root@caretaker3:~# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
7: 0 0 0 0 MIPS 7 timer
8: 4368682 4368666 4368658 4368650 MIPS GIC Local 1 timer
9: 6773173 0 0 0 MIPS GIC 63 IPI call
10: 0 10724448 0 0 MIPS GIC 64 IPI call
11: 0 0 10729279 0 MIPS GIC 65 IPI call
12: 0 0 0 6599757 MIPS GIC 66 IPI call
13: 1044898 0 0 0 MIPS GIC 67 IPI resched
14: 0 638509 0 0 MIPS GIC 68 IPI resched
15: 0 0 1788548 0 MIPS GIC 69 IPI resched
16: 0 0 0 919647 MIPS GIC 70 IPI resched
17: 0 0 0 0 MIPS GIC 19 1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
19: 12 0 0 0 MIPS GIC 33 ttyS0
20: 0 0 0 0 MIPS GIC 29 xhci-hcd:usb1
21: 249297 0 0 0 MIPS GIC 10 1e100000.ethernet
22: 21 0 0 0 MIPS GIC 11 mt7603e
23: 16 0 0 3448283 MIPS GIC 31 mt7615e
25: 5 0 0 0 MIPS GIC 30 mt7530
26: 0 0 0 0 mt7530 0 mt7530-0:00
27: 0 0 0 0 mt7530 1 mt7530-0:01
28: 0 0 0 0 mt7530 2 mt7530-0:02
29: 5 0 0 0 mt7530 3 mt7530-0:03
30: 0 0 0 0 mt7530 4 mt7530-0:04
31: 0 0 0 0 1e000600.gpio 8 keys
32: 0 0 0 0 1e000600.gpio 10 keys
ERR: 212
on the point of ssh, all the shells I keep open on the 'old' zenbook (logread -f ) are left open, their response is perfect and I don't experience anymore what I've experienced using the stable release at all.
None of the clients (Oneplus6t in particular as it's my main phone) lost connectivity while walking around the house playing some online poker 
. Which seems to be about the best test I could figure out since this application seems very sensitive to even the smallest hiccup.
Coverage is also a lot better, a room where when I placed one of the routers and where it didn't work before, now associates fine where before I could not get it to connect to the WDS gateway.
My preliminary conclusion would be at the moment that the snapshot of that day works a lot better, it's remarkably more stable and leaves the impression that a lot of the issues users reported in the past have been taken care of by the development efforts so far. Pretty awesome and much appreciated.
general - non firmware version related issues
- SQM seems to not auto-start at boot or restart of the wifi/interface. After some digging , the solution to this issue can be resolved by following instructions here SQM-scripts . I'm not 100% but that seems to be the origin of those scripts and the
make openwrtoption is tailored to fixing any issues with auto-starting this functionality. It's my educated guess that this issue is not really related to the router this subject covers.
As the focus of my research was to try and create a router setup using 3 units to serve a small office (chiropractor) in a private house, where a WiFi network was needed for the guests that are waiting under SQM control, a separated network for the office computers, that was isolated from the WDS network so the private computers where also isolated from the 'main/management' network , it seems that this is starting to become a valid solution. Stability was the main focus, and I will still need to test the following again with the snapshot release : mesh , to see if the kernel warn is still happening, VLAN's seem to also have some issues reported so I'll throw that in as well to confirm/deny. Although the location where I started to design this solution for has cables running to most places, which would be much more superior to running WDS, I wanted to have WDS tested in case a cable wasn't available depending on the placement. It's my brothers house so I wanted this to be a better solution that he currently has using 4 different brands of devices, a repeater mess and a 5GHz network he only activates when he wants to make a copy to his NAS because the 5GHz network he has now is not good.
I only tested 5GHz due to this, but in my experience, 2.4GHz in OpenWrt hardly has issues in any of the routers I own/tested running openwrt. (WRT1200AC *2 , EA8300 , MR8300 )
I hope this helps other users find a working setup and also I hope this is somewhat useful for developers to both signal that they are doing good work and to help focus on the last few bits that could use some love in order to support this little gem of a router.
I like to express my sincere gratitude for all those efforts and I will try and send updates on further tests I perform keeping the feedback loop alive. I would also like to offer my help in testing these out, given the unique opportunity of owning 3 of these routers.
Glenn
