What is the trust boundary in QoS?

• A. The network point where QoS markings are accepted as trustworthy.
• B. The boundary between two subnets inside a campus.
• C. The boundary where firewall rules are updated.
• D. The boundary for NAT translation.

Answer: (A)

In QoS, the trust boundary is the point in the network where QoS markings (such as DSCP or CoS) are considered trustworthy and are used to guide classification, policing, and queuing. Within this boundary, devices accept the markings from upstream devices and apply the corresponding QoS policies. Outside it, markings are not trusted and may be stripped, ignored, or re-marked to enforce local policies. In practice, you place trusted boundaries at the edge where you want to preserve markings from an upstream device (like a WAN edge), while ports connected to end users are often untrusted to prevent users from falsifying priority.