An internet outage in the middle of the workday isn't just annoying. It halts the ERP, invoicing, the point-of-sale, mail and VoIP phones. In a typical 20-person company, every hour of that downtime costs more than a year's subscription to a second line. Yet a backup line is still treated as a luxury — right up until the first serious outage.
The point isn't to run two parallel fibres from two racked routers — those solutions belong in banks, not at a 15-person furniture maker. The point is that the company doesn't stop for six hours because a digger cut the provider's cable in front of the neighbouring building.
What an hour of downtime actually costs
Before we talk about hardware, it's worth doing the maths on what one hour without internet really costs. Contrary to appearances it's not just the salaries of people "sitting around doing nothing". People will mostly find something to do on paper — the pain sits elsewhere.
In most SMEs, without internet you lose:
- The ERP and invoicing, if the database is in the cloud or hosted.
- VoIP telephony — meaning almost every PBX installed after 2018.
- Mail, calendars and documents in Microsoft 365 or Google Workspace.
- Payment terminals that depend on the office network.
- All customer communication — no answers to inbound leads, no B2B portals, no tracking with your courier.
Even conservatively, for a 20-person service company one hour of blackout is usually a few thousand euros — not in direct losses, but in lost inbound quotes, missed deadlines and customers who got impatient and phoned the competition.
Three levels of protection
You can sort the sensible options into three levels, by rising cost and complexity. The choice doesn't depend on how much you can spend, but on how much downtime actually hurts you.
Level 1 — phone hotspot. Emergency rescue, not protection. Works for two or three key people, provided they know the Wi-Fi password and how to switch their laptop over manually. The absolute minimum. If you have nothing else — at least have that, with the tethering passwords written down somewhere visible.
Level 2 — LTE/5G router with automatic failover. A separate device with a SIM card (usually from a different operator than your fibre) that switches traffic automatically when the main line drops. Users don't even notice. This makes sense for most SMEs from a dozen to several dozen people. Start-up cost: a one-off 500–900 EUR for hardware and setup, then 10–15 EUR a month for the second SIM plan.
Level 3 — two independent fixed lines. Two fibres from different operators taking different routes, plus a BGP or SD-WAN router. This is the expensive path, worth it above 50 people where downtime simply cannot happen. Cost: a few hundred euros a month for the extra line plus a few thousand for hardware. For most SMEs it's overkill — level 2 covers 95% of situations.
A real example — a freight forwarder near Poznań
At one of our clients, an 18-person freight-forwarding company near Poznań mostly handling imports from Germany, a fibre outage at the provider lasted six hours. In that time the TMS, mail, VoIP and the booking platform their customers used all went down. We added up the losses with the owner: eight unattended quote requests (most went to competitors), two customers in Germany could not book their deliveries so the whole chain shifted by a day, three staff sat around shuffling paper. Total cost — real, not hypothetical — around 3 000 EUR.
A year later we installed a Teltonika RUT241 LTE router with two SIM cards from different operators (Play and Orange), configured for automatic failover with a 30-second detection threshold. One-off cost: 600 EUR including installation. Running cost: 10 EUR a month for the extra data plan.
Since it was installed there have been two short outages on the main line (one 40 minutes, one under 2 hours). Users didn't notice — they found out from an IT email that anything had happened at all. The router paid for itself inside the first hour of the first outage.
What to install technically
For most SMEs the sensible choice is an industrial Teltonika router (RUT241, RUT956, RUTX50) or a Mikrotik with an LTE module. Cisco, Fortinet and other enterprise blocks can do this too, but the cost and configuration complexity rarely pay back in an SME.
Some rules worth keeping regardless of hardware:
- A different operator for the SIM. If the fibre comes from operator X, the SIM is from Y. The chance of both failing at once is close to zero.
- Automatic failover, not manual. Detect the outage by pinging an external IP (e.g. 1.1.1.1) every 10–30 seconds. Without that it isn't failover, it's just a second line for when someone manages to react in time.
- Same internal network after failover. Users don't have to switch anything by hand. Addressing, DNS, printer access — everything works as before.
- Traffic priorities. LTE has less bandwidth — during an outage it's worth throttling streaming, Windows updates and cloud backups. It's a 15-minute setting that saves a lot of nerves.
The test — without it, this is just decoration
A backup you never restore doesn't exist. A failover you never test won't fire. Once a quarter, physically unplug the cable from the main router and check the network comes back to life within 30 seconds. If it doesn't — that's a problem to solve now, not in the middle of an outage.
The test should cover: internet access from a random laptop, VoIP working (make a test call), ERP access, Microsoft 365 or Google cloud access. The whole test takes 10 minutes. Booking it into the IT calendar is one of the best-spent minutes of the quarter.
What next
A backup internet line isn't exciting. Nobody notices it when it works. But in that one hour when the provider "has an outage with no ETA", it's the difference between a company that keeps working and one that stops.
If you're not sure whether your business would run tomorrow if the fibre went down for a day — that's a signal to talk about it before you find out in practice. The first conversation is free.
A backup internet line costs less than one hour of downtime. Pay once — use it for years.