Full form: Spanning Tree Protocol
Also known as: Spanning Tree Protocol, IEEE 802.1D
Quick Definition
A Layer 2 loop-prevention protocol that blocks redundant paths in a switched network.
STP (IEEE 802.1D) prevents switching loops in networks with redundant links by placing some ports in a blocking state. STP elects a Root Bridge (the switch with the lowest Bridge ID), then each non-root switch selects a Root Port (best path to the Root Bridge) and each network segment elects a Designated Port. All other ports are placed in a blocking state. STP convergence can take 30–50 seconds with default timers.
show spanning-tree show spanning-tree vlan 10
Lower Bridge Priority wins the Root Bridge election (default priority is 32768, VLAN ID is added). If priorities are equal, the switch with the lowest MAC address wins. Without configuration, the switch with the lowest MAC becomes root — this is usually not optimal.
An enhanced version of STP that converges in seconds instead of 30–50 seconds.
A Cisco enhancement of STP that runs a separate spanning tree instance for each VLAN.
The STP control frames that switches exchange to elect the Root Bridge and maintain the spanning tree.
An STP feature that bypasses the Listening and Learning states on access ports, putting them immediately into Forwarding.
Shuts down a PortFast-enabled port if it receives a BPDU, protecting the spanning tree.
Prevents a port from becoming the Root Port, protecting the Root Bridge position.
STP (IEEE 802.1D) prevents switching loops in networks with redundant links by placing some ports in a blocking state. STP elects a Root Bridge (the switch with the lowest Bridge ID), then each non-root switch selects a Root Port (best path to the Root Bridge) and each network segment elects a Designated Port. All other ports are placed in a blocking state. STP convergence can take 30–50 seconds with default timers.
Lower Bridge Priority wins the Root Bridge election (default priority is 32768, VLAN ID is added). If priorities are equal, the switch with the lowest MAC address wins. Without configuration, the switch with the lowest MAC becomes root — this is usually not optimal.
STP falls under the Spanning Tree domain of the 200-301 exam. Understanding it in context with related terms like rstp and pvst-plus is essential for answering scenario-based questions correctly.