Introduction

One of the main selling points of incorporating pfSense into our networks is that it facilitates reliability. This is often expressed in terms of two components: redundancy and high availability. Redundancy is defined as the duplication of critical components. This can mean either passive or active redundancy—with passive redundancy, we incorporate excess capacity into a network, so that when a component fails, resources are still available. Active redundancy involves monitoring components and performing an automatic reconfiguration if a component fails. High availability means ensuring a specified level of operational performance over a period of time, for example, 99.9% uptime.

pfSense incorporates redundancy and high availability via multi-WAN setups, server load balancing, and Common Address Redundancy Protocol (CARP). Multi-WAN configurations allow you to have more than one outbound interface, either to aggregate multiple internet connections, or to guarantee that if one...