Is it possible to make a 5GHz interface to run AP and Client mode at the same time?

Hi, everyone.

I have bought one Linksys E8450 router and flashed it using non-RBI method.
I want to setup the 5GHz interface to run AP and Client mode at the same time like a Wi-Fi extender but I don't know how to achieve it...

Not all radios support it, what's the problem while trying to set it up?

It seems that only one can work at the same time...
I am not sure if my settings are wrong.

Well, your device have two radios, so it shouldn't be impossible to use one as client, 2nd as (re)transmitter.

Neither do we, since we don't know what they are ....

If both devices support, it better go for WDS/4addr:

Both devices can still offer an access point on the radio you're using as WDS client or master.

I found that it is not possible to follow this guide at all as my main router ASUS RT-AC68U is not running in OpenWrt.

I ignore the DHCP part, make the "client" mode to the no WDS one, set the network to wan and configure the wan interface to the "client" wlan1 interface.

With this setting, I can create another AP mode in the same interface and access Internet.

Thank you very much.

Actually I have tried this guide before I posted the question, when I review the procedure, it seems that it does not contain the guide about creating the "AP mode" interface.

Because it's already there, by default, unenabled, with the SSID openwrt.