Quick Answer
The answer is root port. On any non-root switch in a Spanning Tree Protocol topology, the port with the lowest total STP path cost to the root bridge is elected as the root port, while the higher-cost uplink becomes an alternate (blocked) port to prevent loops. This election is based solely on cumulative cost along the path, not on speed alone, making the STP root port election based on lowest path cost to root bridge a fundamental concept for loop-free Layer 2 design. On the CCNA 200-301 v2 exam, this often appears in scenario-based questions where you must identify port roles after a topology change, with a common trap being confusion between root port and designated port—remember, a designated port exists on the downstream side of a link, not on the switch itself. A simple memory tip: “Root port is the cheapest ticket home to the root bridge.”
This 200-301 practice question tests your understanding of switching and network access. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: a non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Alternate port
Why wrong: Alternate is a backup path role, not the best path to the root.
Root port
Correct. Lowest-cost path to the root becomes the root port.
Designated port
Why wrong: Designated status is elected per segment, not specifically the best uplink on the non-root switch.
Disabled port
Why wrong: The lower-cost active path is not disabled.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Root port
On a non-root switch, the port with the lowest path cost toward the root bridge becomes the root port. The higher-cost uplink would become an alternate (blocked) port. A designated port is found on the upstream switch toward this switch, not on the non-root switch itself. A disabled port is administratively shut down, which does not apply here.
Key principle: A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Alternate port
Why it's wrong here
Alternate is a backup path role, not the best path to the root.
When this WOULD be correct
In a different scenario where a switch has multiple uplinks and one link fails, the remaining uplink with a higher cost could be designated as an alternate port, providing a backup path to the root bridge while the primary path is down.
Root port
Why this is correct
Correct. Lowest-cost path to the root becomes the root port.
Related concept
A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.
Designated port
Why it's wrong here
Designated status is elected per segment, not specifically the best uplink on the non-root switch.
When this WOULD be correct
In a different scenario, if the question stated that a switch has multiple segments and one of the uplinks is the only connection to a segment with multiple switches, then that uplink could be designated if it has the lowest cost to the root bridge for that segment.
Disabled port
Why it's wrong here
The lower-cost active path is not disabled.
When this WOULD be correct
In a different scenario, if a switch is configured with a specific port that has been administratively shut down or if the STP has determined that the port should not be used due to a loop or misconfiguration, the question might ask about the status of that port, making 'disabled port' the correct answer.
Option-by-option analysis
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.
Why this is correct
Correct. Lowest-cost path to the root becomes the root port.
Why this is wrong here
An alternate port is a backup path to the root bridge that is not currently in use. In this scenario, the lower-cost uplink is actively forwarding traffic as the root port, making 'alternate port' an incorrect designation.
★ When this WOULD be the correct answer
In a different scenario where a switch has multiple uplinks and one link fails, the remaining uplink with a higher cost could be designated as an alternate port, providing a backup path to the root bridge while the primary path is down.
Why candidates choose this
Candidates may confuse the roles of ports in STP, especially if they focus on the presence of multiple uplinks and mistakenly associate lower-cost paths with alternate roles instead of recognizing the active forwarding role of the root port.
Why this is wrong here
The designated port is the port on a network segment that has the lowest cost to the root bridge and is responsible for forwarding traffic towards the root. In this case, the question specifies a non-root switch with two uplinks, where the lower-cost uplink is the root port, not a designated port.
★ When this WOULD be the correct answer
In a different scenario, if the question stated that a switch has multiple segments and one of the uplinks is the only connection to a segment with multiple switches, then that uplink could be designated if it has the lowest cost to the root bridge for that segment.
Why candidates choose this
Candidates might confuse the roles of ports in STP, thinking that any port involved in forwarding traffic could be designated, especially if they overlook the specific context of uplinks and cost comparisons.
Why this is wrong here
A disabled port is not actively participating in the Spanning Tree Protocol (STP) and cannot forward traffic. In the context of the question, the lower-cost uplink would be actively used as the root port, not disabled.
★ When this WOULD be the correct answer
In a different scenario, if a switch is configured with a specific port that has been administratively shut down or if the STP has determined that the port should not be used due to a loop or misconfiguration, the question might ask about the status of that port, making 'disabled port' the correct answer.
Why candidates choose this
Candidates may confuse the concept of port states in STP and mistakenly think that a lower-cost path could be disabled due to misconfigurations or administrative actions, leading them to choose this option.
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?”
Common exam traps
Remember, the root port is determined by the lowest path cost to the root bridge, not by any other criteria.
Detailed technical explanation
Spanning Tree Protocol (STP) is a Layer 2 protocol designed to prevent switching loops in Ethernet networks by creating a loop-free logical topology. Each switch in the STP domain elects a root bridge, which serves as the reference point for all path cost calculations. Non-root switches determine their best path to the root bridge by selecting the port with the lowest cumulative path cost, known as the root port. The root port on a non-root switch is the single port that provides the lowest cost path back to the root bridge. STP calculates path cost based on the speed of each link, with lower costs assigned to faster links. When a non-root switch has multiple uplinks toward the root bridge, it compares the total path cost of each uplink and selects the one with the lowest cost as the root port. This port is placed in a forwarding state to ensure traffic flows efficiently toward the root. Other uplinks that do not provide the lowest cost path become alternate ports. Alternate ports serve as backup paths and are placed in a blocking state to prevent loops. Designated ports are elected per network segment to forward traffic away from the root bridge, but they are not chosen based on the uplink cost on a non-root switch. Disabled ports are administratively shut down or blocked due to errors or configuration, not because of path cost. Understanding the root port role is critical for CCNA candidates because it directly affects network stability and performance. The root port ensures that each switch forwards traffic along the most efficient path to the root bridge, maintaining a loop-free topology and optimal data flow in switched networks.
Key takeaway
A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review a non-root switch selects one root port as its lowest-cost path back to the root bridge in STP., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Switching and Network Access — This question tests Switching and Network Access — A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP..
The correct answer is: Root port — On a non-root switch, the port with the lowest path cost toward the root bridge becomes the root port. The higher-cost uplink would become an alternate (blocked) port. A designated port is found on the upstream switch toward this switch, not on the non-root switch itself. A disabled port is administratively shut down, which does not apply here.
Review a non-root switch selects one root port as its lowest-cost path back to the root bridge in STP., then practise related 200-301 questions on the same topic to reinforce the concept.
A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.
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Last reviewed: May 17, 2026
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