How Can You Share an Internet Connection Between Buildings?

It sounds easy to share one internet connection between two buildings, but honestly, the hard part is making sure the connection between them is reliable.

That link might be a cable, fiber, or a wireless radio connection. Each has its own weak spots. And if you run a hotspot or an ISP, there are a few extra things to figure out: how to share the bandwidth, who covers the electricity at the other building, and what happens when something breaks.

Choosing the link: cable, fiber, or radio

An Ethernet cable is usually the cheapest and simplest option. Run one from the router in the first building to a switch or access point in the second, and it can work over distances of up to about 100 meters.

The main risk is lightning. The two buildings may be at slightly different electrical potentials, so a nearby strike can send a surge along the metal cable and damage equipment at either end. That’s why many technicians consider copper links between buildings risky. 

If you go this route, use outdoor-rated cable, run it through conduit where possible, install surge protection at both ends, and ask a qualified technician to check the earthing. The general advice is not to connect the two buildings’ grounds through the cable.

Fibre is the safest option. It is made of glass, so it doesn’t conduct electricity, which avoids most lightning and grounding problems. At each end, you will need a media converter or a switch or router with a fiber socket called an SFP port.

Fiber costs more to install and may require someone who can splice or terminate it. But it can cover much longer distances than copper and tends to cause fewer problems over time. Armored fiber can be buried or strung between buildings on a support wire. If you’re going to spend extra on one part of the setup, this is a good place to do it.

A radio link, also known as a point-to-point wireless bridge, uses two outdoor radios aimed at each other. There’s no trench to dig, no cable to run, and no wire for lightning to travel along. Many ISPs use these links to connect sites.

The radios do need a clear line of sight, though. Trees, tall buildings, or even a water tank in the way can weaken the connection or block it altogether. Mount the radios high, keep them level with each other, aim them carefully, and choose a pair designed for a point-to-point link rather than standard Wi-Fi.

So which should you choose?

If the buildings are close together, there is a clear path between them, and you are on a tight budget, a radio link is often the quickest solution. If lightning is common in your area, or you need the most reliable connection you can get, choose fiber. Copper may work if the buildings are very close and you can bury the cable safely, but it needs the most care. And if the route crosses a road or someone else’s land, a radio link may save you the hassle of digging, though you’ll still need permission.

Setting up both ends

There are two ways to set this up. The first is to treat both buildings as one big network. The radio or fiber at the far end connects directly to an access point, so everything works as if it is all in one place. It is simple and works well for a small shop or a nearby room. The downside is that all the network traffic travels across the link. If something goes wrong in one building, it can affect the other too.

The second option is to put another router in the far building. It gets its own address range and runs its own hotspot or PPPoE, while connecting to your billing system just like the first router. It takes a little more work but gives you much more control. You can monitor and limit traffic in each building, troubleshoot one without affecting the other, and add a third building later using the same setup. If you are planning to grow, this is the better choice.

Either way, you will need power at both ends, usually with a PoE injector for the radio. Give each building its own battery or UPS. If the main building loses power, the far building will go down too if its connection runs through it.

Add surge protection to every cable that leaves a building. Keep the link private: encrypt it, change all the default passwords, put radio management on a separate network, and don’t let customers connect to the radio carrying the link. Choose a clear channel away from your customer Wi-Fi. 

Sharing the line fairly

With two buildings on one internet line, both groups are sharing the same connection. If you don’t manage that, the people using the most will get the most, and customers in the quieter building may be the first to notice slowdowns. Decide how you’ll divide the connection before complaints start. 

A router queue can reserve a share for each building, while a fair-sharing queue like PCQ on MikroTik can divide each building’s share evenly among the people using it.

Replace the placeholders with your own network settings and speeds. The link between the buildings should be faster than the internet connection behind it. Otherwise, the link itself becomes a bottleneck and slows everyone down.

Don't sell more speed than the line can handle.

It’s also worth planning for outages. If the line, main router, or power at the first building goes down, the second building will go down with it. Make sure the main building has your strongest backup power, and consider adding a second internet line there. If the link itself fails, the far building will be cut off, so keep a spare radio or fiber converter on hand and know who can replace it.

Billing can stay in one place. If every router sends login requests to the same billing system through RADIUS, customers in both buildings get the same login page, packages, and payment options. You’ll also have one set of records instead of two.