Tethering a Ubiquity Network to a Mobile Hotspot

Tethering a Ubiquity Network to a Mobile Hotspot

I saw it happen.
The cable-chewing device
The contractor in the neighbor’s back yard with the Ditch Witch trencher burying a cable.
I was working outside at the patio table and just about to go into a Zoom meeting.
Then the internet dropped out.
Suddenly, and with a wrenching feeling in my gut, I remembered where the feed line was buried between the house and the cable company’s pedestal in the right-of-way between the properties.
Yup, he had just cut it.
To be fair, the utility locator service did not mark the my cable’s location, and he was working for a different cable provider than the one we use.
(There are three providers in our neighborhood.)
It did mean, though, that our broadband internet would be out until my provider could come and run another line.
It took an hour of moping about the situation to figure out a solution, then another couple of hours to put it in place: an iPhone tethered to a Raspberry Pi that acted as a network bridge to my home network’s UniFi Security Gateway 3P.
Network diagram with tethered iPhone
A few years ago I was tired of dealing with spotty consumer internet routers and upgraded the house to
UniFi
gear from Ubiquity.
Rob Pickering, a college comrade, had
written about his experience with the gear
and I was impressed.
It wasn’t a cheap upgrade, but it was well worth it.
(Especially now with four people in the household working and schooling from home during the
COVID-19 outbreak
.)
The UniFi Security Gateway has three network ports, and I was using two: one for the uplink to my cable internet provider (WAN) and one for the local area network (LAN) in the house.
The third port can be configured as another WAN uplink or as another LAN port.
And you can tell the Security Gateway to use the second WAN as a failover for the first WAN (or as load balancing the first WAN).
So that is straight forward enough, but do I get the Personal Hotspot on the iPhone to the second WAN port?
That is where the Raspberry Pi comes in.
The
Raspberry Pi
is a small computer with USB, ethernet, HDMI, and audio ports.
The version I had laying around is a Raspberry Pi 2—an older model, but plenty powerful enough to be the network bridge between the iPhone and the home network.
The toughest part was bootstrapping the operating system packages onto the Pi with only the iPhone Personal Hotspot as the network.
That is what I’m documenting here for future reference.
Bootstrapping the Raspberry Pi
The Raspberry Pi runs
its own operating system called Raspbian
(a Debian/Linux derivative) as well as more mainstream operating systems.
I chose to use the
Ubuntu Server for Raspberry Pi
instead of Raspbian because I’m more familiar with Ubuntu.
I tethered my MacBook Pro to the iPhone to download the Ubuntu 18.04.4 LTS image and follow the
instructions for copying that disk image to the Pi’s microSD card
.
That allows me to boot the Pi with Ubuntu and a basic set of operatin…