WLAN Master and Client simultaneously? (Archer C6 as repeater)


I have bought a TP-Link Archer C6 (v2 EU), today installed OpenWRT 19.7.04, then upgraded to 19.07.06.
Configured and started two wireless networks, 5GHz and 2.4Ghz.

This OpenWRT-Archer-C6 is needed to bring Wireless into a building without network cables. So I need it to work as a repeater.
To do this, I configured a second device in 5GHz, as a client. I now have:


  • SSID: OpenWrt_C6_5GHz | Mode: Master | Encryption: WPA2 PSK (CCMP)
  • SSID: Church-guest-5GHz | Mode: Client | Encryption: WPA2 PSK (TKIP, CCMP)


  • SSID:** OpenWrt_C6_2.4GHz | Mode: Master | Encryption: WPA2 PSK (CCMP)

I can connect my laptop to the 2.4GHz network, and the Archer C6 is using it's 5Ghz client connection to another AP to reach the internet. This is working great!
But why is the OpenWrt_C6_5Ghz not available anymore? Is it not possible to use radio0 simultaneously for a master and a client connection?
The Archer C6 is advertised with MU-MIMO, so I expected it to be able to use more than one connection per frequency?

Sorry, I am still a beginner with using and configuring modern wifi-technology.


If this ^^^ is down, your "OpenWrt_C6_5GHz" won't come up. I'm guessing your STA link is down.

No, it's the other way around: The client-connection to the SSID "Church-guest-5GHz" on another AP is working, but the master "OpenWRT_C6_5GHz" is down.
I can connect to the master on radio1 "OpenWRT_C6_2.4GHz", and the Archer C6 uses the client connection to "Church-guest-5GHz" to reach the internet. This is working.

But I can't see "OpenWRT_C6_5GHz" anymore (the master), and I wonder why.
Already tried to disable and re-enable it. (in LuCI)

If your STA link is up, your other SSID should come up as well. I'd use iwinfo on the router to see what's what.

root@OpenWrt_Archer_C6:~# iwinfo
wlan0     ESSID: "Church-guest-5GHz"
          Access Point: CC:32:E5:B3:41:84
          Mode: Client  Channel: 100 (5.500 GHz)
          Tx-Power: 26 dBm  Link Quality: 36/70
          Signal: -74 dBm  Noise: -105 dBm
          Bit Rate: 6.0 MBit/s
          Encryption: WPA2 PSK (TKIP, CCMP)
          Type: nl80211  HW Mode(s): 802.11nac
          Hardware: 168C:0056 0000:0000 [Qualcomm Atheros QCA9886]
          TX power offset: none
          Frequency offset: none
          Supports VAPs: yes  PHY name: phy0

wlan0-1   ESSID: "OpenWrt_C6_5GHz"
          Access Point: CE:32:E5:B3:41:84
          Mode: Master  Channel: unknown (5.000 GHz)
          Tx-Power: 0 dBm  Link Quality: unknown/70
          Signal: unknown  Noise: -105 dBm
          Bit Rate: unknown
          Encryption: WPA2 PSK (CCMP)
          Type: nl80211  HW Mode(s): 802.11nac
          Hardware: 168C:0056 0000:0000 [Qualcomm Atheros QCA9886]
          TX power offset: none
          Frequency offset: none
          Supports VAPs: yes  PHY name: phy0

wlan1     ESSID: "OpenWrt_C6_2.4GHz"
          Access Point: CC:32:E5:B3:41:85
          Mode: Master  Channel: 11 (2.462 GHz)
          Tx-Power: 20 dBm  Link Quality: 55/70
          Signal: -55 dBm  Noise: -95 dBm
          Bit Rate: 110.5 MBit/s
          Encryption: WPA2 PSK (CCMP)
          Type: nl80211  HW Mode(s): 802.11bgn
          Hardware: unknown [Generic MAC80211]
          TX power offset: unknown
          Frequency offset: unknown
          Supports VAPs: yes  PHY name: phy1


Internet (DSL) --> "Fritzbox 7490" --ethernet--> "TP-Link EAP225 Outdoor (stock firmware)" --5GHz--> "OpenWRT Archer C6 (19.07.6)" --2.4GHz--> Laptop

In most countries(*) DFS rules apply to channel 100. And the ath10k driver won't do AP and STA at the same time on a DFS channel.

Unless you can get the church to change channel, it isn't going to be possible to run the AP.

  • Make sure the wifi config is set to your country.

Since I am currently the admin of the network, I can change everything. I installed the EAP225 Outdoor, and I configured it.

I have read a geman article about outdoor wlan: https://www.heise.de/select/ct/2019/15/1563266137704674

Since the EAP225 is placed on the outside of a building, I am only allowed to use channels 100-140, if I understood it correctly. So in the EAP225 configuration (no OpenWRT yet) I checked "channel limit". The manual says: "With this function enabled, the wireless frequency 5150MHz~5350MHz will be disabled."
DFS should also be activated.

Question: if the EAP225 uses channel 100, and the OpenWRT-archer-c6 as a client of course also talks on channel 100 with the EAP225, isn't it possible to simultaneously work as master for 5GHz clients on a different channel? Can radio0 use two different channels simultaneously?

In the OpenWRT-Archer-C6 device configuration, I have set "channel" to "auto". And in Wireless - "Advanced Settings", I have set "Country Code=DE Germany", in hope to fulfill all regulations.

Right now I tried to use a guest network for testing, but the goal is to have several wireless networks, for example the normal one that is used in the office and a second one for guests. Maybe even a third one for wireless switches, sensors, zigbee gateways.
Currently every router/AP has its own SSIDs. But of course we would prefer it, if users only have to use one SSID/passphrase everywhere, so I will bee looking into mesh-networking, too.

But as I said, I consider myself still a beginner. In the past I have only used what stock firmware offered, especially the AVM Fritzboxes...

The radio can only work on one channel. In STA mode it scans the channels to find it's AP then operates there. It takes separate radio hardware to work on two channels at once.

Try setting the client to channel 100 and htmode to exactly match the AP. At one time that was important for ath9k.

I am not sure, if I understand you correctly.
STA mode means station mode, is this the same as the client mode that I am using right now to connect through the EAP225 to the internet? Or are there subtle differences?
In LuCI, in "Interface Configuration" - "General Setup", "Mode" offers several options, and for example there is "Client" as well as "Client (WDS)" and other options. (Yes, I have heard "Wireless Distribution System" before, but I don't know the differences yet.)

You write "try setting the client to Channel 100 [...]".
With "client" you mean the wireless network in client mode on the OpenWRT-Archer-C6 that is connected to the EAP225, right?
It is on channel 100, because the EAP225 it connects to is on this channel. But I don't have a problem with this client network. The problem is, that the second 5 GHz network in master mode doesn't seem to come up. I have set this master to channel 100, too.

In an earlier posting you wrote "the ath10k driver won't do AP and STA at the same time on a DFS channel."
Ok, this would be an explanation. As far as I know, I am not allowed to use non-DFS channels outdoor. This would mean, that it's not possible to do what I tried to do. But maybe it would work with different mode settings? I will read more about WDS and about mesh, but this might take some time.

And I still don't understand about all this MU-MIMO and channel thing. The claim is, that a router with MU-MIMO can provide several streams through several antennas to several clients. But they do all this on only one channel!?
I know, that MU-MIMO and Wireless Repeater functionality are completely different things, but I figured, that it should be easy for a router that is capable to communicate with different users independently, to provide a client and a master network simultaneously.
I am missing some basic information, I know. Back to reading...

for explanation: AP = Access point ( = server), STA = station ( = client), these abreviations are used in hostapd...

I can imagine that because the client wifi channel and frequency is not stable due to DFS, you cannot at the same time run a Wifi as access point, as they might interfere.

What you could do is to use 2 different devices, one as client for your church guest wifi, and one as server for your additional wifi and connect the 2 devices by cable.

I will try a second device, but would still like to know what is possible with one router. Electricity is expensive here, 5W over 365days would cost almost 15 Euro per year, and those devices tend to multiply like rabbits...

Maybe we don't even need the 5GHz master. Everything seems to work alright, right now. But as I said, I would like to learn and to know what's possible. And there are other electronics in this building like wireless microphone working on the 2.4GHz frequency. Those microphones have their own problems, so I would like to be able to switch the Wlan to 5GHz completely, if necessary.

Mike, I think you were right: it's probably the DFS channel.
I tested a similiar setup with my WLR755ac Repeater/Router (Mediatek-chip), connected as client to my (indoor) Fritzbox Wlan router. Initially it was the same problem: no master and client simultaneously. But after I changed the 5 GHz channel on the Fritzbox to channel 36, everything was fine.
Still have to test it with the EAP255 Outdoor and the OpenWrt-Archer-C6.

Thank you.

I still don't want to close the topic yet, since I would like to know: how do repeaters/range extenders work normally? My (AVM stock firmare) Fritz!Repeater 1200 did repeat on channel 100. How do they do it?
Do people who put a normal (stock firmware) repeater outside violate the regulations? (because channel 36 is not allowed outdoors, and channel 100+ are WDS)
And do commercial outdoor repeaters have two separate radios?
Or would everything be different, if I used different modes, for example "client (WDS)" instead of "client"? Or...?