huawei e8231 usb modeswitch

By default, device work in Mass Storage mode

root@fwhlin:~ # lsusb | grep Huawei
Bus 009 Device 007: ID 12d1:1f01 Huawei Technologies Co., Ltd. E353/E3131 (Mass storage mode)
root@fwhlin:~ # 

Create file

vi /etc/usb_modeswitch.d/12d1:1f01

With following content

root@fwhlin:~ # cat /etc/usb_modeswitch.d/12d1:1f01
# Huawei E3531s-2 - switch to modem mode instead of HiLink CDC-Ether mode
TargetVendor=0x12d1
TargetProduct=0x1f01

# switch to 12d1:1001 (modem mode, 3 virtual serial ports)
#MessageContent="55534243123456780000000000000011062000000100000000000000000000"

# switch to 12d1:14dc (default HiLink CDC-Ether mode)
MessageContent="55534243123456780000000000000a11062000000000000100000000000000"

# switch to 12d1:1442 (debug mode with 2 virtual serial ports)
# MessageContent="55534243000000000000000000000011060000000000000000000000000000"

root@fwhlin:~ # 

To switch to Modem Mode, run

usb_modeswitch -I -W -c /etc/usb_modeswitch.d/12d1\:1f01

If it worked, device will change to modem mode

root@fwhlin:~ # lsusb | grep Hu
Bus 009 Device 003: ID 12d1:14dc Huawei Technologies Co., Ltd. 
root@fwhlin:~ # 

Notice it changed name, also device ID changed to 14dc.

ifconfig will list a new network interface usb0

usb0      Link encap:Ethernet  HWaddr 9a:82:a1:91:20:32  
          inet6 addr: fe80::9882:a1ff:fe91:2032/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:236 errors:0 dropped:0 overruns:0 frame:0
          TX packets:98 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:111083 (111.0 KB)  TX bytes:15412 (15.4 KB)