What are two types of BPDUs in the Spanning Tree Protocol? (Choose two.)
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The Spanning Tree Protocol (STP) is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network (LAN). One of the mechanisms used by STP is the exchange of Bridge Protocol Data Units (BPDUs) between switches to elect the root bridge and create a loop-free topology.
There are two types of BPDUs in the Spanning Tree Protocol: Configuration BPDUs and Topology Change Notification (TCN) BPDUs.
Configuration BPDUs: Configuration BPDUs are sent by each switch during the initial phase of the STP to elect the root bridge. The root bridge is the switch with the lowest Bridge ID, which is a combination of the bridge priority and the MAC address. The root bridge is responsible for calculating the shortest path to each network segment in the network. Configuration BPDUs are also sent periodically to ensure that the root bridge is still functional.
Topology Change Notification (TCN) BPDUs: TCN BPDUs are sent by a switch when a change in the network topology is detected. For example, when a port goes up or down or when a switch is added or removed from the network. When a switch sends a TCN BPDU, it triggers all switches in the network to re-calculate their Spanning Tree topology, which helps to prevent network loops and ensure network stability.
Note: Hello BPDU and Link State BPDU are not types of BPDUs used in the Spanning Tree Protocol. The Hello BPDU is used in other protocols like OSPF to detect neighbors, while the Link State BPDU is used in IS-IS to exchange link state information.