Thanks! There's no packet firewall at all, no iptables/nftables. On macOS the VM's NIC is a Virtualization.framework file-handle device. The daemon runs gvproxy, which terminates the guest's connections and re-dials them as host sockets, so I filter with an allow-list right before the dial. One caveat, since you asked about root specifically: that's the macOS path, and it only works thanks to the fd NIC. Firecracker on Linux only speaks a TAP, which needs root, so there I do shell out to sudo, but just for the device. The filtering is still the same userspace allow-list.