How to share USB modem internet connection with router connected to Ubuntu box?

by Bruce   Last Updated March 13, 2018 07:02 AM

I am trying to share a USB modem internet connection over a standard broadband router using the method described here:

How do I share my Ubuntu's Internet connection with a LAN (via hardware router)

No matter what I try I cannot ping the router from the computer. Here is information on the hardware and network settings:

PC running Ubuntu v.16.04.3 LTS

ZTE Falcon 4G USB cellular modem
IP Address:        192.168.0.2 (set by me in ZTE Falcon web UI)
WAN IP Address:    10.42.0.1 (from T-Mobile)
connected by USB cable to Ubuntu box

Technicolor C2000T broadband modem/router
IP Address:        192.168.0.1
WAN Settiings:
ISP Protocol:      IPoE via Static IP
Single Static IP:  192.168.0.3
Subnet Mask:       255.255.255.0
Gateway Address:   192.168.0.2
WAN port connected via ethernet cable to standard network card in Ubuntu box

Here is more detail on the Ubuntu configuration:

Contents of /etc/network/interfaces:

auto lo
iface lo inet loopback

Output of ifconfig -a:

enp0s25   Link encap:Ethernet  HWaddr 00:1a:a0:9f:be:9e 
          inet6 addr: fe80::21a:a0ff:fe9f:be9e/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2230 errors:0 dropped:16 overruns:0 frame:0
          TX packets:731 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:146536 (146.5 KB)  TX bytes:103987 (103.9 KB)
          Interrupt:20 Memory:fdfc0000-fdfe0000 

enp0s26f7u4 Link encap:Ethernet  HWaddr 3a:bc:d5:40:d6:f9  
          inet addr:192.168.0.81  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::9261:413f:d13:b6de/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6027 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7123 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3392446 (3.3 MB)  TX bytes:1610722 (1.6 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:14205 errors:0 dropped:0 overruns:0 frame:0
          TX packets:14205 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:948763 (948.7 KB)  TX bytes:948763 (948.7 KB)

The above IP address of 192.168.0.81 was assigned by DHCP running on the ZTE Falcon USB modem. While testing I tried disabling DHCP on the modem but it seems that doing so prevents Ubuntu from being able to set up a connection with the modem.

Using Ubuntu's Network Connections application and starting with no network connections defined, when I first connect the ZTE Falcon modem, Ubuntu automatically creates "Wired connection 1" with the interface name of enp0s29f7u4 and the MAC address 00:1a:a0:9f:be:9e from the modem. At that point I have internet connectivity from the Ubuntu box.

Next I used Network Connections to create a new Ethernet connection using the other available device (besides enp0s29f7u4). This connection has the interface name enp0s25 and is presumably the network card. Curiously, I have run through these steps a few times and the MAC address for enp0s25 appears to be different each time. On enp0s25 I changed the IPV4 Settings | Method to "Shared to other computers". I also tried creating a new shared connection for enp0s29f7u4.

After connecting an ethernet cable from a Windows laptop to a port on the C2000T modem/switch I used the web UI to set the following under DHCP Settings:

Modem IP Address:       192.168.0.1
Beginning DHCP Address: 192.168.0.200
Ending DHCP Address:    192.168.0.250
Subnet Mask:            255.255.255.0

and the following under WAN settings:

ISP Protocol:     IPoE via Static IP
Single Static IP: 192.168.0.3
Subnet Mask:      255.255.255.0
Gateway Address:  192.168.0.2

After making these changes on the router, the WAN light glows a steady green but the internet light is a flashing red. I tried various things such as power-cycling the router and running "service network-manager restart" I was hoping to be able to ping 192.168.0.1 from the Ubuntu box and get a reply from the router. Unfortunately, ping replies with "Destination Host Unreachable". Pinging the Ubuntu box from the Windows laptop yields the same. I have tried running "ufw disable" to temporarily disable the firewall but it does not change anything.

The ultimate goal is to be able to plug a couple computers into the router and have them connect to the internet via the USB modem. If there is any other information about my setup that would be helpful for troubleshooting please let me know. Is there anything obviously wrong with my configuration or anything else I should try? Thanks for your help.



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