Business Internet Failover: 6 Proven SD-WAN Lessons

By Claudia Sterling · 27 October 2026

When the internet drops, most offices simply stop: no email, no Teams calls, no cloud accounting, no online banking. Business internet failover means having a second connection that takes over automatically, so staff barely notice. This month we at ZSI set this up for a professional services firm moving into a new Georgetown office, using two providers, GTT and E-Networks, and a Fortinet firewall running SD-WAN. Here’s what we learned.

What is SD-WAN, in plain English?

SD-WAN (software-defined wide-area networking) lets one firewall manage several internet connections as a team. It keeps testing each line and sends traffic down whichever ones are healthy.

Business internet failover diagram: one firewall sharing GTT and E-Networks connections

That gives you three things:

  • Failover. If one provider goes down, traffic moves to the other within seconds.
  • Load sharing. When both lines are up, both are used, so you get the benefit of the second line every day, not only during an outage.
  • Smart routing. You can send important traffic, such as Teams calls, down whichever line is performing best at that moment.

Older failover setups kept the second line sitting idle, waiting for a problem. SD-WAN puts it to work.

Why business internet failover matters in Guyana

Almost every business system has moved online: Microsoft 365, cloud accounting and ERP, internet phone systems, card terminals. One internet connection is now a single point of failure for the whole office.

Using two different providers is the key. GTT and E-Networks run separate networks, so a fault or maintenance on one shouldn’t affect the other. When you order, ask each provider how their line reaches your building. Two services sharing the same pole or duct are less independent than they look.

6 lessons from a real business internet failover install

1. Order the second line early

Internet installation can take weeks. On this project the office moved on temporary wireless while the lines were being installed, and the second provider was connected after the move. Order both lines as soon as the move date or project is confirmed.

2. Check the cables, not just the contracts

After the firewall was built, both connections were stuck at about 95 Mbps, a fraction of what the lines should deliver. The cause wasn’t the providers. The firewall ports had connected at only 100 Mbps over temporary cables. Once the equipment was moved into the switch room with proper patch cables, both ports connected at 1 Gbps and speeds jumped. We later found the same problem on two Wi-Fi access point cable runs.

Tip: your firewall shows the speed each port has connected at. It should say 1000 Mbps, not 100.

It’s also worth knowing that, with full security scanning switched on (antivirus, web filtering and intrusion prevention), this small FortiGate still delivered over 600 Mbps in our speed test. Security doesn’t have to slow you down.

3. Make sure your firewall has enough internet ports

Some smaller firewalls have only one port labelled “WAN” (internet). On most models, including the one we used, a spare network port can be reassigned as a second internet port. Check this before you buy, especially if you might add a third connection later.

4. Set a health check and a rule for calls

SD-WAN needs to know when a line is “bad”, not just “unplugged”. A health check regularly tests each connection against a reliable internet address and measures delay and lost packets. We then added a rule sending Teams calls down the line with the lowest delay. Everything else is shared between the two lines by computer, so each PC stays on one line and websites such as online banking don’t log you out halfway through.

5. Turn off the Wi-Fi on the providers’ routers

Internet providers’ routers usually broadcast their own Wi-Fi. If staff join that network, they bypass your firewall and all its security. It also crowds the airwaves for your real Wi-Fi. At this office both providers’ devices were broadcasting. Turn this Wi-Fi off, or ask the provider to, so everyone goes through the firewall.

6. Test failover before you rely on it

At a quiet time, unplug one line, then the other. Check that browsing, Teams calls and VPN connections carry on. Also make sure each provider’s router always gives your firewall the same address, so a router restart doesn’t quietly break that line.

Is business internet failover worth the cost?

A second line is a monthly cost. Compare it with what one lost working day costs your business in staff time, missed calls and delayed payments. For most offices that rely on cloud services, the second line pays for itself the first time the main provider has a bad day.

Your business internet failover checklist

  • ✅ Two lines from two different providers, ordered early
  • ✅ Firewall with SD-WAN and enough internet ports
  • ✅ Proper patch cables; every port connected at 1000 Mbps
  • ✅ Health checks on both lines; priority rule for calls
  • ✅ Wi-Fi on the providers’ routers switched off
  • ✅ Fixed address for the firewall on each provider’s router
  • ✅ Failover tested by unplugging each line
  • ✅ Firewall firmware kept up to date (see our Fortinet firewall update checklist)

How ZSI helps

Zenith Services Inc. designs, installs and manages business internet failover for offices in Georgetown and across Guyana, using Fortinet firewalls with SD-WAN, FortiSwitches and FortiAP Wi-Fi. We coordinate with your internet providers, test everything before go-live, and watch your connections afterwards as part of our managed IT services. Learn more about our cybersecurity and data protection services, or read how we moved our email from GoDaddy to Microsoft 365.

Want business internet failover for your office? Talk to our team and we’ll plan it with you.