diff --git a/How-to-upgrade-flash-4G-ext-firmware.md b/How-to-upgrade-flash-4G-ext-firmware.md
index 1607986..8f6e6cc 100644
--- a/How-to-upgrade-flash-4G-ext-firmware.md
+++ b/How-to-upgrade-flash-4G-ext-firmware.md
@@ -159,6 +159,16 @@ So, the appearance of usb0 indicates success.
 
 In fact, at this point, if the SIM card is inserted correctly, the 4G network should already be connected.
 
+to test if the 4G connection is ok by
+```
+cpi@raspberrypi:~/LE20B04SIM7600G22_cpi $ ping -I usb0 8.8.8.8
+PING 8.8.8.8 (8.8.8.8) from 192.168.225.25 usb0: 56(84) bytes of data.
+64 bytes from 8.8.8.8: icmp_seq=1 ttl=109 time=331 ms
+64 bytes from 8.8.8.8: icmp_seq=2 ttl=109 time=98.8 ms
+64 bytes from 8.8.8.8: icmp_seq=3 ttl=109 time=84.3 ms
+64 bytes from 8.8.8.8: icmp_seq=4 ttl=109 time=89.0 ms
+```
+
 # Precautions
 The above-mentioned flashing operation requires your familiarity with Linux and firmware flashing. Please do not attempt it without sufficient experience, as we will not be held responsible for any consequences. Thank you for your understanding.