1D0-571 · Question #47
Which of the following describes the practice of stateful multi-layer inspection?
The correct answer is C. Inspecting packets in all layers of the OSI/RM with a packet filter. See the full explanation below for the reasoning.
Question
Which of the following describes the practice of stateful multi-layer inspection?
Options
- AUsing a VLAN on a firewall to enable masquerading of private IP addresses
- BPrioritizing voice and video data to reduce congestion
- CInspecting packets in all layers of the OSI/RM with a packet filter
- DUsing Quality of Service (QoS) on a proxy-oriented firewall
How the community answered
(13 responses)- A8% (1)
- B8% (1)
- C77% (10)
- D8% (1)
Community Discussion
5
Dervla O.Jan 23, 2026C is your answer. Stateful multi-layer inspection means the firewall is tracking connection state AND examining packet contents across all OSI layers, not just checking headers at layer 3 the way a basic packet filter does, so the phrase "inspecting packets in all layers of the OSI/RM with a packet filter" captures the core mechanism being tested here.
Viktor S.Feb 11, 2026Look, I went back and forth on this one and I keep landing on B. Think about what "multi-layer" actually means in practice, it means the system is not just sitting at layer 3 dropping packets by IP, it is actively involved in managing what goes through at higher layers, and QoS traffic shaping for voice and video is exactly that kind of cross-layer awareness. The "stateful" part fits too because QoS has to track flows over time to know which streams get priority, it is not a one-packet-at-a-time judgment, it maintains session context. C sounds tempting but "packet filter" is specifically the dumb stateless kind that reads a header and either passes or drops, calling that multi-layer inspection is a stretch when it has no memory of the conversation. B describes a system that understands the nature of the traffic across layers and makes ongoing decisions based on session state, which is the whole point of the term.
Dervla O.Feb 12, 2026Viktor, the key distinction the stem is testing is that "stateful multi-layer inspection" refers to a firewall that tracks connection state and inspects across OSI layers for security enforcement, which is answer C. QoS traffic shaping in B is about prioritization and bandwidth management, not security inspection, so it doesn't fit the definition the question is driving at regardless of how much cross-layer awareness it requires.
Ola B.Feb 7, 2026Spin up a pfSense lab and you will see it firsthand, when you tag a VLAN on the firewall interface and enable masquerading, the device is tracking the internal state of each private address as it maps outbound, which is exactly the stateful part of multi-layer inspection. A is the one.
Dervla O.Feb 10, 2026Ola, the stateful piece you are describing is NAT session tracking, which is a Layer 4 behavior, but the question is asking specifically about the inspection mechanism that correlates packets across the session to enforce policy, and that is stateful packet inspection as its own distinct function, making C the stronger answer.