Firewall
network firewall · NGFW · next-generation firewall · packet filtering · network filtering · pare-feu
A device or piece of software that filters communications between networks according to rules: anything not explicitly allowed is blocked.
In practice
A firewall separates the internet from the internal network, but also internal zones from each other (office, servers, production, guests). “Next-generation” models recognise applications and users, not just addresses and ports. Its value lies in its filtering policy: “allow everything” rules added as a quick fix and never removed defeat its purpose. ANSSI recommends documenting every rule, reviewing them regularly and filtering outbound traffic too.
Fictional case: an audit reveals that an SME’s firewall holds 412 rules, 60 of which allow “any to any” for old projects. After a clean-up, 95 remain, all documented: the network is both safer and easier to understand.
