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350-401 Practice Question: Examine the following configuration snippet on a…
Examine the following configuration snippet on a Cisco IOS switch:
interface GigabitEthernet0/2 switchport mode access switchport access vlan 50 spanning-tree portfast
Which statement is true about this interface?
⚠ Common exam trap
Cisco often tests the misconception that `spanning-tree portfast` only applies to trunk ports or that it still requires the listening/learning states, when in fact it is designed specifically to bypass those states on access ports (or trunk ports with the `spanning-tree portfast trunk` variant).
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interface will immediately forward traffic without any spanning-tree delay.
The `spanning-tree portfast` command on an access port configured with `switchport mode access` and `switchport access vlan 50` causes the interface to bypass the normal spanning-tree listening and learning states. This allows the port to transition directly to the forwarding state, enabling immediate traffic forwarding without the usual 30-second delay (15 seconds for listening, 15 seconds for learning) associated with Rapid Spanning Tree Protocol (RSTP) or the 50-second delay with classic STP (802.1D).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The interface will immediately forward traffic without any spanning-tree delay.
Why this is correct
PortFast is configured on this access port, so the switch immediately moves the interface to the STP forwarding state, bypassing the 15-second listening and 15-second learning states. It still runs Spanning Tree Protocol and can send BPDUs, but it does not wait for the normal 30-second convergence delay before forwarding user traffic. This is intended for end hosts that should not cause a layer-2 loop.
- ✗
The interface will participate in trunking and forward multiple VLANs.
Why it's wrong here
'switchport mode access' explicitly disables trunking on the interface, so DTP will not negotiate or form a trunk regardless of the adjacent switch settings. An access port carries traffic for exactly one VLAN—the access VLAN—and strips or tags each frame accordingly. PortFast changes only the STP timing, not the interface's layer-2 mode, so the interface cannot forward multiple VLANs.
- ✗
The interface will still go through listening and learning states before forwarding.
Why it's wrong here
PortFast eliminates the listening and learning state transitions altogether by making a direct transition from blocking to forwarding once the link is up. The normal STP startup sequence of listening (15 seconds) and learning (15 seconds) is deliberately skipped, so traffic is not delayed by those intermediate states. Saying the interface still goes through them contradicts the very purpose of PortFast, which is to provide immediate connectivity for an attached host.
- ✗
The interface will only forward traffic for VLAN 1.
Why it's wrong here
The access VLAN on this port has been changed to VLAN 50, so the interface forwards frames for VLAN 50, not VLAN 1. On an access port, all untagged frames received or sent are classified to the configured access VLAN; VLAN 1 remains the default only until another access VLAN is assigned. Because the port is not a trunk, it carries a single VLAN, so 'only VLAN 1' is a false statement.
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