How to Add a Second ISP to Your WatchGuard Firewall

A reliable internet connection is critical for any business, even a short outage can interrupt operations, affect customers and impact productivity. Your WatchGuard Firewall makes it easy to add a secondary ISP so your network stays online when your primary connection fails.

In this guide, you’ll learn how to set up a backup internet connection, configure failover, and choose the right type of ISP for true redundancy.

image showing how to add second isp for internet backup

Step 1: Connect Your Primary ISP (Main Internet Line)

Your primary ISP is the main connection your business uses every day. This is typically:

Fiber

Cable

High-speed broadband

This connection feeds into the WAN port of your WatchGuard Firewall and handles most of your network’s traffic.Once your primary ISP is connected and stable, you’re ready to add a backup connection.

Step 2: Add a Secondary (Backup) Internet Connection

In the diagram, the secondary ISP is shown on the left in grey. This second modem connects to an available WAN port on your WatchGuard Firewall and acts as your backup internet line.

When a secondary ISP is added, the firewall can:

Fail over automatically if primary (red) connection goes down

Load balance by sharing traffic between the two internet lines

A backup ISP is extremely helpful for:

Businesses that can’t afford downtime

Teams working from the cloud

VoIP phones and POS systems

Remote or hybrid staff who rely on consistent connectivity

Step 3: Connect Your Devices

Your secure network—also known as the business network—is shown in blue in the diagram.

Connect your wired devices such as:

Desktop PCs

Office printers

Laptops that use Ethernet

Even though these devices plug in with a cable, they are still part of the MSFW protected zone (Make Safe for Work). This zone keeps your internal systems safe, encrypted, and monitored by WatchGuard’s security services.

The blue dotted line in the diagram represents the secure wireless connections for approved business devices.

Your firewall also broadcasts a secure Wi-Fi network for employee laptops, tablets, and mobile devices. This network is part of the same blue business network, giving your team encrypted and filtered access. This is the network your staff should use every day

Step 4: Choose the Right Backup Internet Type

When it comes to internet redundancy, diversity is key. It’s not just about having a second connection, it’s about having the right kind.

Using different types of connections or providers ensures true reliability. For example, AT&T owns most of the copper lines, so using two copper-based connections (even from different providers) doesn’t offer real redundancy.

Instead, combine different delivery types for better protection:

Fiber + Copper: Great for areas with limited fiber coverage but stable DSL lines.
Fiber + Cellular: One of the most effective setups fiber for speed, cellular for backup when the physical line is down.
Copper + Cellular: A strong option when fiber isn’t available.

Best Practice:

Use a different provider whenever possible.

Even if two ISPs advertise differently, they might use the same backbone. Choosing two truly independent routes ensures real redundancy

Step 5: Test Your Secondary ISP Setup

Once both connections are active:

Disconnect your primary ISP

WatchGuard should switch to the backup connection

Test basic apps (email, web, VoIP)

Reconnect your primary ISP

Ensure the firewall returns to normal operation

Testing ensures your business won’t experience surprises during a real outage.

Why Adding a Second ISP Matters

Downtime can cost a business money, productivity, and reputation. By configuring your WatchGuard Firewall with multiple internet connections and using different providers or connection types, you’re building a network designed for resilience.

A well-planned failover strategy keeps your team connected, your customers served, and your operations running smoothly even when the unexpected happens.

Next Step: If you haven’t already set up your WatchGuard with your primary ISP and secure networks, start with our first guide:

How to Set Up Your WatchGuard Firewall (Primary Internet Only)