Immediately behind the organization's external firewall is the correct option.

The DMZ hosts public facing services and it must be reachable from the Internet while still being isolated from the internal network. Placing the DMZ immediately behind the organization's external firewall lets that firewall enforce access controls and logging for traffic to the DMZ and prevents direct, unfiltered Internet access to internal systems.

Directly in front of the organization's external firewall on the Internet side is wrong because putting the DMZ on the public side would expose those systems without the protection of the external firewall. That placement defeats the purpose of isolating and filtering traffic to public services.

Behind the first internal active network firewall is wrong because locating the DMZ inside the internal firewall mixes public facing services with internal resources and reduces isolation. The DMZ must sit outside the internal network so that a compromise of DMZ hosts does not directly threaten internal systems.

Behind a passive HTTP only perimeter filter is wrong because a passive filter does not actively enforce access controls and an HTTP only filter only covers one protocol. A proper DMZ requires active firewalling and controls for all protocols used by the hosted services to provide adequate protection.

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