A network administrator is optimizing a Cisco Catalyst switch that connects desktop computers and IP phones across access ports. The administrator enables Cisco STP PortFast on these access interfaces. Which two operational behaviors or benefits occur on a PortFast-enabled access interface when a device connects to it? (Select two.)
- The interface transitions immediately from the Blocking state to the Forwarding state, bypassing the Listening and Learning states.Answer
- The switch suppresses Spanning Tree Topology Change Notification (TCN) messages when the interface state changes.Answer
- CThe interface disables Spanning Tree loop detection so that it can be safely used on inter-switch trunk links without risk of transient loops.
- DThe switch lowers its STP bridge priority by a standard increment of 4096 whenever the port becomes active to protect root bridge status.
Answer
PortFast immediately transitions an access port to the Forwarding state by bypassing the Listening and Learning states, and it prevents the switch from issuing Topology Change Notifications (TCNs) when edge interfaces flap.
Enabling Cisco STP PortFast on edge ports provides two primary operational behaviors: first, it bypasses the 802.1D Listening and Learning states so the port enters the Forwarding state immediately upon link up. Second, it prevents the switch from generating Topology Change Notifications (TCNs) when the link toggles, protecting the network from frequent, unnecessary MAC table flushes.
Step-by-Step Solution
Key Concept
STP PortFast Benefits and Operational Behavior