Final answer:
The default CoS value for traffic received on an access port is usually 0, meaning the traffic is treated as 'best effort' with no special priority.
Step-by-step explanation:
The default Class of Service (CoS) value for traffic received from a host on an access port is typically 0. This value is used in Quality of Service (QoS) to prioritize different types of network traffic. When a frame reaches an access port on a switch without any CoS value set, the switch generally assumes the default CoS value, which, according to the most common standard, is 0. This means that this traffic is considered 'best effort' with no special prioritization over other traffic.