easyMultiple Choice
350-401 Practice Question: Runs the following command on Switch SW7: SW7#…
A network engineer runs the following command on Switch SW7:
SW7# show spanning-tree vlan 70
VLAN0070 Spanning tree enabled protocol ieee Root ID Priority 24646 Address aabb.cc00.0c00 Cost 4 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768 (priority 32768 sys-id-ext 70) Address aabb.cc00.0d00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Altn BLK 4 128.3 P2p
Based on this output, which port is the alternate port?
⚠ Common exam trap
Cisco often tests the distinction between alternate and backup ports; the trap here is that candidates may confuse 'Altn' (alternate, which provides a backup to the root port) with 'Backup' (which provides a backup to the designated port on the same segment), or assume that only root and designated ports exist in a stable topology.
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
✓
GigabitEthernet0/3
The alternate port is GigabitEthernet0/3 because it is in the 'Altn' role with a 'BLK' (blocking) state. In Rapid Spanning Tree Protocol (RSTP) and Per-VLAN Spanning Tree Plus (PVST+), an alternate port provides an alternative path to the root bridge and remains blocked unless the current root port fails. The output clearly shows Gi0/3 as 'Altn BLK', making it the alternate port.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
GigabitEthernet0/1
Why it's wrong here
GigabitEthernet0/1 is the root port, which is the port on this switch with the lowest cost to the root bridge. A root port is placed in the forwarding state, so it cannot be an alternate port. The alternate port must be one that is administratively blocked while still receiving BPDUs.
- ✗
GigabitEthernet0/2
Why it's wrong here
GigabitEthernet0/2 is a designated port, meaning it is the single forwarding port responsible for the attached LAN segment and sends BPDUs to downstream switches. Designated ports are not blocked and do not provide redundant backup paths, so Gi0/2 cannot be the alternate port requested in the question.
- ✓
GigabitEthernet0/3
Why this is correct
GigabitEthernet0/3 is the correct alternate port because its port state is shown as Altn BLK, indicating it is blocked but has received a superior BPDU from another switch. This gives a different path to the root bridge than the root port, so it will transition to forwarding if Gi0/1 fails.
- ✗
There is no alternate port.
Why it's wrong here
There is no alternate port is incorrect because the spanning-tree output explicitly lists GigabitEthernet0/3 as an alternate port in the Altn BLK state. Alternate ports exist specifically to maintain a backup path to the root bridge on redundant links, and Gi0/3 fulfills that role in this topology.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.