So, I have been able to implement the proxy server,
but not "exactly" the same way as the author has implemented.
This is for anyone who has the usb mode set to
14db or
1f01 in lsusb.
My setting
operator : ubuntu
machine : rasbarry pi 3 b+
lte usb modem : huawei E353/E3131
if you are stuck on 12d1:1f01, you can call
sudo usb_modeswitch -v 12d1 -p 1f01 -M '55534243123456780000000000000a11062000000000000100000000000000'
to change your usb modem state to 1f01 -> 14db.
lsusb results
14db means that the usb is in huawei HiLink state.
in HiLink state, we can go to the base ip of the device in order to connect to the lte and settings of this modem
my huawei settings home page is 192.168.1.1,
ifconfig shows : inet 192.168.1.100 netmask 0xffffff00 broadcast 192.168.1.255
so 192.168.1.100 -> 192.168.1.1 (home page)
the internal ip might differ, but the last number changes, 100 -> 1
When you click connect on this page and inspect this page and check the network

you will see a endpoint here called dial.
So what the homepage has done is send this website a POST request,
in order to manipulate this request you can call in your cmd
curl -X POST
http://192.168.1.1/api/dialup/dial -d "<?xml version="1.0" encoding="UTF-8"?><request><Action>1</Action></request>"
I have tested methods to change the ip address of the modem,

In Settings -> network settings
change the settings to HSPA + \ UMTS only.
And change it back to LTE only.
Reconnect.
You can manipulate this by sending curl of the network.
And also, the author has implemented by usb0, but mine showed up on eth1.
You can just change the settings
Code:
sudo echo "Let's setup the IP"
sudo ifconfig eth1 192.168.1.100
sleep 2
sudo echo "Let's setup the routes for the proxy"
sudo ip route add 192.168.1.0/24 dev eth1 src 192.168.1.100 table gw1
sudo ip route add default via 192.168.1.1 dev eth1 table gw1
sudo ip rule add from 192.168.1.100/32 table gw1
sudo ip rule add to 192.168.1.100/32 table gw1
sleep 5
sudo echo "Let's start the proxy "
sudo 3proxy /home/ubuntu/3proxy.cfg
See that the
usb0 is replaced with
eth1.
I have also changed 192.168.
0.0 into 192.168.
1.0
because, when the modem changed its internal ip, the internet connection was lost.
This thread is very old, but I cannot thank more to this awesome chad author.
SUCCESS!!!!
