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Sistro Networks
Sistro Networks

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High Availability Is Not Just Two Firewalls

A common infrastructure mistake is assuming that deploying two firewalls automatically creates high availability.

It doesn't.

Consider:

ISP

Firewall A / Firewall B

Single Core Switch

Servers

The firewall layer is redundant.

The network is not.

The core switch is now the single point of failure.

A proper HA assessment should identify failure domains across:

WAN connectivity
firewalls
heartbeat links
switching
power
routing
applications
monitoring

FortiGate FGCP is a good practical example.

It supports HA clustering and synchronization between members, while session pickup can help preserve TCP sessions after failover.

But the broader engineering principle is vendor-neutral:

Availability is an end-to-end property.

Do not ask only whether a component is redundant.

Ask:

What happens to the service when this component fails?

Spanish FortiGate HA architecture example:

https://sistro.net/fortigate-high-availability-ha-cuando-conviene

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