Retired Techie
Getting older, not necessarily wiser!
Using Multiple ISP’s
Published on April 29, 2022 at 7:38 pm by LEWIntroduction
Recently I experienced an outage from my Internet Service Provider (ISP). This in itself is not unusual. I have experienced outages from my ISP in most every place I have ever lived (and actually had an ISP). What made this particularly interesting is that I had just switched to a new ISP, and was able to setup a temporary Internet connection through the old ISP.
Obviously the above statement is leaving a lot of information out, of which I will go into more detail below. However, for me this was a unique situation in that my previous ISP connection was prepaid. This made it possible to quickly setup a temporary Internet connection with almost no haste.
Now the temporary Internet connection is not screaming fast, but it does work for those situations when my main ISP provider has an issue. The one thing I would like would be more options for the temporary connection.
The Switch Over
I was using a cellular ISP for years at the current residence. The speeds were dependent on the time of day, but on average where 5 Mbps. Though late night and early morning could see speeds around 15 Mbps.
This was also what is referred to as a prepaid plan. You buy a chunk of data good for a number of days. When the data is exhausted or the time period passes, you need to load up again. Loading can be done from your cell phone or at most local convenience stores.
The down side is you do have to keep an eye on your data (from your cell phone or computer). Also cellular internet tends to have some high lag times. For some applications this may not be acceptable.
Having extended family over with kids and lots of devices, the cellular Internet was not cutting it. I found that there was a real need for a faster and more reliable Internet connection. So I decided to upgrade to Fiber, which I found had become available in my area.
With multiple people streaming I was chewing through cellular data pretty fast, so it turned out that the fiber was only slightly moire expensive. Plus I started getting download speeds of around 300 to 400 Mbps and upload speeds of around 75 to 150 Mbps. My latency dropped to under 5 ms also.
The Down Times
So it turns out my fiber ISP is doing some upgrading in our area. This is a generally a good thing. I am hoping they implement IPv6 at some point, because I really would like to not have to deal with CGNAT (but that is a different post here). Some of the upgrades do have the side effect of dropping my Internet connection, sometimes for several days.
Plus there are other reasons for down time (car hits a junction box or a Typhoon for example). As I stated, I have never not had a ISP that did not experience some form of downtime. It happens.
In my current situation, however, I had an unused cellular modem sitting there. So I figured, why not put it to use. Depending on your network setup this is not quite as straight forward as it might seem.
So I am going to walk though my initial Simple Stupid method of connecting both modems to my LAN. This method is crude but it works. I am going to be setting up a more eloquent solution, which I will touch on in this post.
The Issue
Basically you cannot have two of the same IP addresses on your LAN, which means each modem would need a separate default gateway (different IP address). This could become confusing to some of your network enabled devices, causing them to loose connectivity. In many cases, the default gateway is also the default DNS server (the router is not the DNS server, but it forwards to the ISP DNS server).
The eloquent way of setting this up is to have a separate router that both modems plug into. The router would need to have three separate networks, and be able to load share between ISP’s. This is not a feature found on most consumer grade routers (though it can be found on the more expensive top of the line routers).
If you have a spare computer with three NIC cards (and don’t mind getting your hands dirty) you can achieve the same results with programs like PFSense, IPFire, Openwrt, or any number of others (check here).
My Simple Stupid Solution
What I have done temperately, while I work on the eloquent solution (I will be using PFSesne, just need to get another NIC setup on a spare PC) is as follows.
- Connect each modem solely to my laptop, and log in.
- Set up each modems LAN side identically, including default IP address, and DHCP range.
- While both modems are off, connect both to a small four port switch, which I in turn connect to my LAN
- Turn on each modem separately and test it to confirm Internet Connectivity and that it works with all devices on my LAN.
- Now leave the fiber modem on and the cellular modem off.
The Way It Works
- Since the cellular modem requires a load to work, it is left off.
- When the fiber modem looses connectivity (for whatever reason), it gets turned off.
- Then the cellular modem gets turned on and a load applied.
- Once fiber service is restored, turn off the cellular modem and turn on the fiber modem.
Like I said, simple stupid. Generally when the fiber goes down it is an hour or two, though sometimes it can be a day.
The smallest load I can put on the cellular modem is 5 GB of data for three days (this costs about $1 US). I generally do not keep a load on the cellular modem unless it is needed.
Conclusion
This post basically covers how I initially integrated a cellular modem into my LAN to be used when the main fiber modem looses connectivity. The method is simple and straight forward. Once I get the appropriate hardware I will be setting up the more eloquent solution, using a router, so both modems could be on at the same time.
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