About this interactive
From the lesson:
- **Blocking:** receives BPDUs only. **Listening:** sends and receives BPDUs. **Learning:** also adds source MAC addresses to the table. **Forwarding:** also forwards frames. **Disabled:** shut down by an admin, no part in spanning tree.
- **Timers:** hello 2 seconds (how often BPDUs go out); forward delay 15 seconds, spent once in listening and again in learning; max age 20 seconds, how long a switch keeps the last BPDU it heard before it acts. Together they are the 50-second wait the lesson describes.
- **PortFast** puts an end-device port straight into forwarding. Never use it on a link to another switch: a loop could form. **BPDU guard** shuts a PortFast port down if a BPDU arrives.
- Two slips in the video: max age is not "time spent in blocking", and a blocked alternate port is in blocking, not disabled.
What you'll learn
- Predict what a port does in each 802.1D state, blocking, listening, learning and forwarding, and what the default hello and forward delay timers mean for how long it takes
- Explain why PortFast belongs on end-device ports and not on links between switches
Aligned to
Cisco CCNA
2.5
Interpret basic operations of Rapid PVST+ Spanning Tree Protocol
Key terms
- Spanning Tree Protocol
STP
- A network protocol that prevents loops in Ethernet networks by creating a loop-free logical topology.
- Blocking State
- An STP port state in which a port does not forward frames but still receives BPDUs, preventing network loops in redundant topologies.
- PortFast
- A Cisco Spanning Tree Protocol feature applied to access-layer ports connected to end devices that allows the port to transition immediately to the forwarding state, bypassing the normal STP listening and learning phases that would otherwise delay connectivity by up to 30 seconds. PortFast should only be used on ports that connect to end devices, not to other switches.
- Forward Delay
- An STP timer that defines the time a port spends in each of the listening and learning states; the default is 15 seconds per state for a total of 30 seconds.
- Hello Timer
- An STP timer that defines the interval between BPDU transmissions; the default is 2 seconds with a range of 1 to 10 seconds.
- BPDU Guard
- A Cisco STP security feature applied to PortFast-enabled ports that immediately shuts down the port if a BPDU is received, preventing an unauthorized switch from being connected and disrupting the spanning tree topology. It protects access-layer ports that should only connect to end devices, not other switches.
Topics
Stp
Port States
Stp Timers
Portfast
Interactive
Predict
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