An administrator is adding a QoS policy to a Cisco FTD deployment. When a new rule is added to the policy and QoS is applied on 'Interfaces in Destination Interface Objects", no interface objects are available What is the problem?

Quality of Service (QoS) on Cisco Firepower Threat Defense (FTD) is a feature that is exclusively supported on routed interfaces (Layer 3). When an FTD device is deployed in transparent mode, it functions as a Layer 2 firewall, and its interfaces are not capable of performing the routing functions necessary for QoS policy enforcement. Consequently, when an administrator attempts to apply a QoS policy to destination interfaces on a transparent-mode FTD, no interfaces will appear as available for selection because none meet the prerequisite of being a routed interface.

A. Resource exhaustion would typically manifest as a deployment failure or system performance degradation, not as a complete absence of interfaces in the configuration UI.
B. The IP addressing scheme (contiguous or not) of network segments is irrelevant to an interface's eligibility for a QoS policy.
D. The term "conflict" is too vague; the issue is a fundamental feature incompatibility with the device's operational mode, not a conflict between specific interface types.

1. Cisco Firepower Management Center Configuration Guide, Version 7.0, "Quality of Service" Chapter, "Guidelines and Limitations for QoS" section: "QoS is supported only on routed interfaces. It is not supported on transparent or inline interfaces, nor on passive or ERSPAN interfaces." This statement directly confirms that transparent mode interfaces are ineligible for QoS.

2. Cisco Firepower Threat Defense (FTD) Configuration Guide for Firepower Device Manager, Version 7.2, "Quality of Service" Chapter, "Prerequisites for QoS" section: This guide reiterates the requirement for routed interfaces, stating, "You can apply QoS policies only to the egress traffic on routed interfaces." This explains why no interfaces would be available on a device operating in transparent mode.