Internet - Prioritise Wifi connection over 3G Modem

Question

I have:

1. A Raspberry Pi 3B SBC
2. I have a Huawei E5330 3G Wifi router connected to the Pi via USB
3. I have a Wireless router connected to my internet line (fibre)
4. I have set a static IP address for my Pi's connection to the internet Wifi router
5. I can connect to the Pi using SSH using that static IP

I have the challenge that when the Pi tries to access the internet (e.g, when running sudo apt-get update), it uses the Huawei modem's connection.

I want it to use the fibre's Wifi router connection(not connect through the Huawei 3G one).

What I have tried:

1. Ran $ sudo route add default gw 192.168.1.1 wlan0 based on this answer

Ran netstat -rn, and got the following result, where 192.168.1.1 is my fibre line's Wifi router and 192.168.8.1 is my 3G router

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 wlan0
0.0.0.0         192.168.8.1     0.0.0.0         UG        0 0          0 enx001e101f0000
0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 wlan0
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 wlan0
192.168.8.0     0.0.0.0         255.255.255.0   U         0 0          0 enx001e101f0000

Then Ran rote

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.1.1     0.0.0.0         UG    0      0        0 wlan0
default         www.huaweimobil 0.0.0.0         UG    204    0        0 enx001e101f0000
default         192.168.1.1     0.0.0.0         UG    303    0        0 wlan0
192.168.1.0     0.0.0.0         255.255.255.0   U     303    0        0 wlan0
192.168.8.0     0.0.0.0         255.255.255.0   U     204    0        0 enx001e101f0000

I don't want to mess up the configs, if I haven't already, so any help would be appreciated on how I can make all internet requests to go through my fibre's Wifi router (192.168.1.1)

Answer 1

You have three default routes. Only one default route can be used. Which one is determined by the metric. The route with the lowest metric wins. You have used deprecated command route that sets a metric of 0 if not specified. Now it is somewhat unclear what a metric of 0 means. Does it have the highest priority? It seems not to be in all cases. I have found a discussion about this at In Linux, what metric has a route with no metric?. You should better use more up to date command ip route.

The best is you omit using metric 0 to avoid confusing. But with your problem you do not have to care about metric at all. You add a default route but instead you should delete one. There is already a default route to the internet router:

default         192.168.1.1     0.0.0.0         UG    303    0        0 wlan0

It has only a lower metric than the one to the USB 3G router so it isn't used. You should just delete the default route to the 3G router with:

rpi ~$ sudo ip route del default via 192.168.8.1 dev enx001e101f000

Then you only have one default route to the internet router.

To make this persistent you have to modify /etc/dhcpcd.conf (I suppose you are using default network setup). Just add this two lines:

interface enx001e101f000
nogateway

Here are some details about this Can I prevent a default route being added when bringing up an interface?.

Answer 2

In addition to the comments by Ingo you should list how you set a static IP address (many people do this incorrectly) - or better still don’t set one.

This may prevent routing from working properly.

In general Ethernet interfaces are preferentially used.