SIM820X RNDIS Dail-up

Check the connection between the SIM820X and the Raspberry Pi through the following commands, if the connection is OK, you can view the Qualcomm device and ttyUSB0-USB4.
```
 lsusb
 ls /dev/ttyUSB*
```

Open the ttyUSB2 port via minicom:

ls /dev/ttyUSB*
sudo apt-get install minicom
sudo minicom -D /dev/ttyUSB2

Send the following command via minicom and wait for the module to reboot.
```
at+cusbcfg=usbid,1e0e,9011
```

Test Networking

After dialing, the Raspberry Pi can see that usb0 has obtained the ip through the following command:
```
ifconfig -a
```
Test usb0 networking status:
```
ping -I usb0 www.baidu.com
```

If failed to obtain IP or to connect successfully, you can use the following command to obtain IP and connect:

sudo dhclient -v usb0
sudo apt-get install udhcpc
sudo udhcpc -i usb0
sudo route add -net 0.0.0.0 usb0
auto usb0
iface usb0 inet dhcp

Some systems may not be able to obtain the usb0 network card, please use the following command to obtain the usb0 network card:
```
sudo ifconfig usb0 up
```
If you need to switch to the Windows system, or restore the default settings of the module, you can send the following command to restore through the serial port:
```
at+cusbcfg=usbid,1e0e,9001
```

Config DNS (Optional)

If you can ping the IP, but cannot ping the URL, it is a DNS server problem, you can configure it according to the following steps:
After restarting the Raspberry Pi, you can see that the DNS setting is successful through the following command.
```
sudo nano /etc/resolvconf.conf
```
Add the following command at the end of the file:
```
name_servers=8.8.8.8 114.114.114.114
```
Save the file and reboot the Raspberry Pi.
After restarting the Raspberry Pi, you can see that the DNS setting is successful through the following command.
```
sudo nano /etc/resolv.conf
```
Save the file, exit, and ping test again.

If you use Jetson Nano, you can use the following commands to configure:

sudo cp /etc/systemd/resolved.conf /etc/systemd/resolved.conf.bak
sudo vi /etc/systemd/resolved.conf
DNS=114.114.114.114 8.8.8.8 8.8.4.4
sudo systemctl restart systemd-resolved.service
sudo systemctl enable systemd-resolved.service
sudo mv /etc/resolv.conf /etc/resolv.conf.bak
sudo ln -s /run/systemd/resolve/resolv.conf /etc/

Select A Network Card (Optional)

Edit the network configuration file dhcpcd.conf:
```
sudo nano /etc/dhcpcd.conf
```

Add the following statement at the end:

interface usb0
metric 200
interface eth0
metric 300

Load USB Device Descriptor

After the SIM7600X is changed to 9011 mode, some Linxu systems cannot recognize ttyUSB*, and you can load the USB device descriptor through the following command:

ubuntu system

sudo su
sudo echo 1e0e 9011 > /sys/bus/usb-serial/drivers/generic/new_id

raspbian and centos systems

sudo su
sudo modprobe option
sudo sh -c 'echo "1e0e 9011" > /sys/bus/usb-serial/drivers/option1/new_id'
sudo sh -c 'echo "1e0e 9018" > /sys/bus/usb-serial/drivers/option1/new_id'
sudo sh -c 'echo "1e0e 901E" > /sys/bus/usb-serial/drivers/option1/new_id'

Auto-start usb0 On Boot

To set auto-start usb0 on boot, open Raspberry Pi boot configuration script.
```
sudo nano /etc/rc.local
```
Add the startup command to the penultimate line, noting that it is the absolute path of your internet-running file, which is the line above exit 0.
```
sudo dhclient -v usb0
```
Note that you must add "&" to run in the background, otherwise the system may not start.

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