firewalld is the default firewall daemon on RHEL 10. It's a user-space management layer that programs kernel packet-filter rules (nftables on RHEL 10) based on a zone-based model: every network interface is assigned to a zone, and each zone has its own list of allowed services, ports, and rich rules. You interact with it via firewall-cmd — almost never by writing nftables rules directly. On the exam, you'll configure which services and ports are open on one or more zones, remember to use --permanent plus --reload, and occasionally add a source-based rule for a specific subnet.
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