Can't find "bt0" on Raspberry Pi 4

Question

Hello, Everyone I am going to develop an IoT project with nRF52840 and Raspberry Pi 4 My idea is exactly the same as this link https://visualgdb.com/tutorials/arm/nrf51/6lowpan/ I have followed the below links to build BLE 6LoWPAN environment on my Rpi4 
 
 https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v14.2.0%2Fiot_ug_border_router.html 
 https://devzone.nordicsemi.com/f/nordic-q-a/26003/rpi3-6lowpan_control-permission-denied 
 
 All commands were working fine until echo "connect <mac address of other device> 1" > /sys/kernel/debug/bluetooth/6lowpan_control. As seen from the websites, after this command execution, there should be bt0 interface created. But it is not visible in ifconfig -a. 
 Also the 6lowpan_control file is empty. But when I try to connect the other device using the command hcitool con after executing the above command, I am able to see the desired connections in the terminal, still no bt0 device available. I have even tried with the command ifconfig bt0 add 2001:db8::1/64 but resulted in the error SIOGIFINDEX: No such device . 
 How to resolve this problem?

Lin Bencheng · Answer

Thanks for your reply 
 I am using Raspberry pi OS full (2021.1.21 released). I tried the old version of Raspberrian OS, But if I install the old version, My RPi 4 doesn't start OS. Yes, This new OS support 6LowPAN as default. I can find my nRF52 DK board with this command on RPi 4 hcitool lescan Then also this command works echo "connect 00:AA:BB:XX:YY:ZZ 1" > /sys/kernel/debug/bluetooth/6lowpan_control After this when I tri this command ifconfig I couldn't find the bt0. Of course, I created the RAVID configuration file on the etc folder 
 interface bt0 
 { 
 AdvSendAdvert on; 
 prefix 2001:db8::/64 
 { 
 AdvOnLink off; 
 AdvAutonomous on; 
 AdvRouterAddr on; 
 }; 
 }; 
 
 As you can see, I couldn't connect to nRF DK but can't find bt0 interface I hope your news Thanks