The Mist platform uses several heuristics to automatically determine a switch's uplink port for topology mapping and network insights. Two primary methods are analyzing Spanning Tree Protocol (STP) roles and traffic volume. The STP root port is, by definition, the port with the best path to the root bridge, making it a logical uplink. Additionally, Mist analyzes traffic statistics; a port with significantly higher transmit (TX) and receive (RX) byte counts compared to other ports is presumed to be an uplink, as it aggregates traffic from access ports.

B. MTU size is a Layer 2 configuration that is not a reliable indicator of a port's topological role; both access and uplink ports can be configured with jumbo frames.

D. Port descriptions are user-configured, arbitrary text strings. Mist's automated discovery algorithms do not parse these descriptions to determine port roles.

1. Juniper Mist Documentation, "View Switch Details": In the section describing the switch topology view, the documentation states, "Mist automatically detects the uplink ports on your switches by using heuristics such as Link Layer Discovery Protocol (LLDP), Spanning Tree Protocol (STP) information, and traffic patterns." This directly supports that STP role (C) and traffic volume (A) are used.

2. Juniper Mist, "Wired Assurance Feature Guide": This guide details the mechanisms for monitoring and managing wired networks. In the chapter on "Network Insights and Topology," it explains that the topology is constructed using data collected from the switches, including STP state and port statistics, to infer relationships between network devices. The port with the STP root role and/or the highest traffic utilization is identified as the uplink.