The DiffServ specifies that how many bits in the modified IP ToS field are used to designate the packet's PHB?

The correct answer is based on the Differentiated Services (DiffServ) architecture, which uses the Differentiated Services Code Point (DSCP) to classify packets. Within this framework, the IP Type of Service (ToS) field was extended to enable packet classification based on the desired level of service.

Specifically, in the modified IP ToS field, 6 bits are allocated for the DSCP, which designates the Per-Hop Behavior (PHB) for the packet. This allows network devices to determine how to handle the packet based on its assigned service level, enabling Quality of Service (QoS) mechanisms to prioritize traffic efficiently.

The remaining bits in the ToS field are used for other purposes, such as the Explicit Congestion Notification (ECN). Thus, knowing that 6 bits are specifically used for defining the packet's PHB is crucial for understanding how traffic is managed and prioritized in a network utilizing DiffServ.