CCNA Network Services and Security Practice Question
Which STP role identifies the port on a non-root switch that has the best path back to the root bridge?
⚠ Common exam trap
A frequent exam trap is mistaking the designated port for the root port. While both forward traffic, the designated port is selected per LAN segment to forward frames away from the root bridge, not necessarily providing the best path back to the root. Another trap is confusing the alternate port with the root port; alternate ports are backup paths kept in blocking state and do not forward traffic unless the root port fails. Candidates often overlook that the root port is unique per non-root switch and always represents the lowest-cost path to the root bridge, which is the key to answering this question correctly.
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
✓
Root port
The root port is the single port on a non-root switch that provides the lowest-cost path toward the root bridge. Designated ports forward away from the root for a segment, and alternate ports are backup paths.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Designated port
Why it's wrong here
A designated port is the forwarding port on a LAN segment that is responsible for sending BPDUs to that segment, and it represents the best path from that segment toward the root bridge. However, on a non-root switch, a designated port is selected for downstream segments, not for the switch's own uplink to the root bridge. The root port specifically identifies the best path on the non-root switch itself, whereas a designated port belongs to the segment's viewpoint.
When this WOULD be correct
In a question asking for the port role on a switch that connects to the root bridge and is responsible for forwarding traffic towards it, the designated port would be the correct answer. For example, if the question stated, 'Which port role on a switch connects to the root bridge and forwards traffic towards it?' then the designated port would be correct.
- ✓
Root port
Why this is correct
The root port is the single port on a non-root switch that has the lowest root path cost to the root bridge, making it the switch's best path toward the root. It is determined by examining received BPDUs, comparing root path cost, then sender bridge ID, then sender port ID. This port is placed in the forwarding state and is the only port that actively forwards traffic toward the root, ensuring a loop-free topology.
- ✗
Alternate port
Why it's wrong here
An alternate port is a blocked port that provides a secondary path to the root bridge, but it is not the best path. It receives a superior BPDU from another switch on the same segment, indicating that another port has a lower root path cost. In STP, it serves as a backup to the root port and remains in discarding state unless the root port fails, so it does not meet the role of the best path.
When this WOULD be correct
In a question asking about the role of ports in a Rapid Spanning Tree Protocol (RSTP) environment, the alternate port could be identified correctly if the question specifies a scenario where a switch has multiple paths to the root bridge and is asked to identify ports that can be activated if the primary path fails.
- ✗
Disabled port
Why it's wrong here
A disabled port is an interface that is administratively shut down or has failed, so it does not participate in spanning tree elections. Since STP only assigns roles to active ports that send and receive BPDUs, a disabled port cannot be considered for any best-path selection. This option is incorrect because the root port role is a dynamic result of the spanning tree algorithm on a functioning, enabled port.
When this WOULD be correct
In a different question asking which port state is used for troubleshooting or configuration purposes, a scenario might involve a network administrator needing to identify ports that are intentionally disabled for security reasons. In that context, 'disabled port' could be the correct answer.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Root portCorrect answer▾
Why this is correct
The root port is the single port on a non-root switch that has the lowest root path cost to the root bridge, making it the switch's best path toward the root. It is determined by examining received BPDUs, comparing root path cost, then sender bridge ID, then sender port ID. This port is placed in the forwarding state and is the only port that actively forwards traffic toward the root, ensuring a loop-free topology.
✗Designated portWrong answer — click to see why▾
Why this is wrong here
The designated port is the port on a switch that has the best path to the root bridge, but it is not specific to non-root switches. The question specifically asks for the port role on a non-root switch that identifies the best path back to the root bridge, which is the root port.
★ When this WOULD be the correct answer
In a question asking for the port role on a switch that connects to the root bridge and is responsible for forwarding traffic towards it, the designated port would be the correct answer. For example, if the question stated, 'Which port role on a switch connects to the root bridge and forwards traffic towards it?' then the designated port would be correct.
Why candidates choose this
Candidates may confuse the designated port with the root port due to their roles in STP, as both are involved in determining the best path for traffic. Additionally, the term 'designated' may sound authoritative, leading candidates to believe it is the correct choice.
✗Alternate portWrong answer — click to see why▾
Why this is wrong here
The alternate port is a port on a switch that has a backup path to the root bridge but is not currently in use for forwarding traffic. It does not represent the best path back to the root bridge, which is the role of the root port.
★ When this WOULD be the correct answer
In a question asking about the role of ports in a Rapid Spanning Tree Protocol (RSTP) environment, the alternate port could be identified correctly if the question specifies a scenario where a switch has multiple paths to the root bridge and is asked to identify ports that can be activated if the primary path fails.
Why candidates choose this
Candidates may confuse the alternate port with the root port due to their similar roles in providing redundancy and may mistakenly believe that any port that provides an alternative path qualifies as the best path.
✗Disabled portWrong answer — click to see why▾
Why this is wrong here
A disabled port is not operational and does not participate in STP, making it irrelevant for identifying the best path to the root bridge. Therefore, it cannot be the correct answer for this question regarding STP roles.
★ When this WOULD be the correct answer
In a different question asking which port state is used for troubleshooting or configuration purposes, a scenario might involve a network administrator needing to identify ports that are intentionally disabled for security reasons. In that context, 'disabled port' could be the correct answer.
Why candidates choose this
Candidates may confuse 'disabled port' with other port roles due to a lack of understanding of STP states, thinking that any non-operational port might still have relevance in the context of network topology.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Key term
Segment
A segment is a division of a larger network, such as a collision domain, broadcast domain, or a portion of a TCP data stream, used to organize traffic and improve performance.
Key term
Root port
A root port is the port on a non-root switch in a Spanning Tree Protocol network that has the lowest cost path to the root bridge.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.