The only switch on a LAN that has all designated interfaces is which type of switch?

In a Local Area Network (LAN), the switch that maintains a state where all its interfaces are designated is a root switch. This specific role is defined by the Spanning Tree Protocol (STP), which is utilized to prevent loops in network topologies.

When a switch is elected as the root bridge in a spanning tree topology, it assumes the responsibility of managing the paths in the network. All interfaces on this root switch are designated ports because they are responsible for forwarding traffic towards the root and to other devices on the network. This setup facilitates optimal performance and efficient data transmission, ensuring the root switch handles the primary traffic flow without any loops.

Other types of switches, such as access, distribution, and core switches, serve distinct functions in the network hierarchy. Access switches typically connect end-user devices and may have a mix of designated and blocking ports depending on their role in the network and the overall topology. Distribution switches aggregate traffic from access switches, while core switches handle high-speed data transfer between distribution switches. However, they do not inherently have all interfaces in the designated state like the root switch does.

Understanding the role of each switch helps in network design and troubleshooting, highlighting why the root switch is unique in its configuration among LAN switches.