What is the minimum number of network connections in a multi homed firewall?

A multi-homed firewall, in common secure architectural designs, requires a minimum of three network connections to effectively segment traffic: one for the internal (trusted) network, one for the external (untrusted) network like the Internet, and crucially, a third for a Demilitarized Zone (DMZ) to host public-facing servers with controlled access.

While a firewall can have five network connections for more complex segmentation, this number is not the minimum required to define a multi-homed firewall incorporating standard security zone separation.

Four network connections are possible for specific, more granular network segmentation scenarios but exceed the minimum of three interfaces typically considered for a secure multi-homed firewall architecture including a DMZ.

Although a firewall with two network connections (e.g., internal and external) is technically multi-homed, a more robust and secure 'multi-homed firewall' design typically implies at least three interfaces to adequately separate internal, external, and DMZ traffic.