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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?

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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?

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Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Distractor review

Alternate port

Alternate is a backup path role, not the best path to the root.

B

Best answer

Root port

Correct. Lowest-cost path to the root becomes the root port.

C

Distractor review

Designated port

Designated status is elected per segment, not specifically the best uplink on the non-root switch.

D

Distractor review

Disabled port

The lower-cost active path is not disabled.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A common exam trap is confusing the root port with the designated port or alternate port roles. Candidates might incorrectly assume that the lower-cost uplink on a non-root switch becomes a designated port because designated ports forward traffic. However, designated ports are elected per LAN segment, not per switch uplink cost. Another trap is thinking the lower-cost uplink could be an alternate port, which is actually a backup path and remains blocked. Misunderstanding these roles can lead to selecting incorrect answers, especially under time pressure, because the question specifically asks about the role of the lower-cost uplink on a non-root switch toward the root bridge.

Technical deep dive

How to think about this question

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.

KKey Concepts to Remember

  • A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.
  • STP calculates path cost based on link speed to determine the best path toward the root bridge.
  • The root port on a non-root switch is always placed in a forwarding state to send traffic toward the root.
  • Alternate ports on a non-root switch serve as backup paths and are placed in a blocking state to prevent loops.
  • Designated ports are elected per LAN segment and forward traffic away from the root bridge, not based on uplink cost on non-root switches.
  • Disabled ports are administratively shut down or blocked due to errors, not because they have a lower path cost.
  • STP prevents switching loops by blocking redundant paths that do not have the lowest path cost to the root bridge.
  • The root bridge is the reference point for all path cost calculations in the STP topology.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

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More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router has routes for 10.10.0.0/16, 10.10.20.0/24, and a default route. Which route is used for destination 10.10.20.55?

Question 3

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 4

What is the OSPF metric called?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

A non-root switch selects one root port as its lowest-cost path back to the root bridge in STP.

What is the correct answer to this question?

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.

What should I do if I get this 200-301 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

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