Which statement about QoS trust boundaries or domains is true?
- The trust boundary is always a router.
- The IP phone is a common trust boundary.
- The service provider and the enterprise network need to be one single trust domain or else routing will not work.
- PCs, printers, and tablets are usually part of a trusted domain.
Explanation: In network design, a trust boundary is the specific point where a device identifies and marks traffic, determining whether the existing QoS markings on a packet should be accepted or rewritten before it enters the trusted domain. An IP phone is a classic example of a common trust boundary because it can classify its own voice traffic as high priority while treating data from an attached PC as untrusted, ensuring that only legitimate markings are propagated through the network. By contrast, end-user devices such as PCs, printers, and tablets are typically categorized as part of an untrusted domain because their traffic markings cannot be verified and could be manipulated by users to seek unfair priority. While trust boundaries are frequently established at the edge switch in campus environments, they are not strictly limited to routers, and it is common for enterprise and service provider networks to maintain distinct trust domains rather than a single shared one. Establishing these boundaries allows administrators to protect network resources by only acting upon markings from devices they manage, thereby preventing congestion caused by unauthorized or malicious traffic prioritization.
Related exam: Modules 1 – 7: Checkpoint Exam: Network Switching Answers (CCNP ENCOR v9)
