STP Port Cost vs Bandwidth Relationship

H12-811 By islever Editorial Last updated

Spanning Tree Principles and Configuration

Short answer

A In STP, port cost is inversely proportional to bandwidth, so higher bandwidth results in a lower cost.

Question

During STP calculation, the port cost is associated with the port bandwidth by default. Which of the following statements about the relationship between port cost and port bandwidth is true?
  1. A higher port bandwidth indicates a smaller port cost. Correct Answer
  2. A higher port bandwidth indicates a larger port cost.
  3. The port bandwidth is equal to the port cost.
  4. The port cost varies randomly according to port bandwidth.

Key Takeaways

STP port cost is inversely related to bandwidth; faster links get lower costs to be preferred paths.

Learn how STP calculates port cost based on bandwidth. Higher bandwidth links receive lower costs to ensure optimal path selection in network topology.

Common mistake: Choosing B (higher bandwidth = larger cost) by mistakenly assuming that better performance should incur a higher penalty rather than being favored.

Expert Analysis

The question tests the fundamental relationship between port cost and bandwidth in Spanning Tree Protocol (STP) calculations. According to IEEE standards, STP assigns a cost value to each port to determine the best path to the root bridge. This cost is inversely proportional to the link's bandwidth: higher bandwidth links are assigned lower costs because they can transmit data more efficiently and quickly than lower bandwidth links.

Option A states that higher bandwidth indicates smaller port cost, which aligns with the inverse relationship principle. For example, a 10 Gbps link will have a significantly lower cost value than a 1 Mbps link, making it the preferred path for traffic. Option B suggests a direct relationship, which contradicts STP logic. Option C implies equality, which is incorrect as cost is a derived metric, not identical to bandwidth. Option D suggests randomness, which is false since STP uses deterministic algorithms based on standardized or configured cost values. The community comments overwhelmingly support Option A, correctly identifying that 'higher bandwidth means smaller port cost'.

Official Reference

https://standards.ieee.org/standard/802_3-2018.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

Memorize the inverse relationship between STP port cost and bandwidth. When evaluating path selection questions, always look for the link with the highest bandwidth (lowest cost) as the preferred active path unless blocked by other factors like priority.

Frequently Asked Questions

Why does STP assign lower costs to higher bandwidth links?

To ensure the most efficient paths are selected. Lower cost links are preferred, so high-speed links become the primary forwarding paths.

Can I manually change the STP port cost?

Yes, administrators can manually configure port costs on switches if the default auto-calculated values do not meet design requirements.

More H12-811 FAQ →

Discussion 16 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 16

  1. miftah_rahman 👍 6
    higher bandwidth means smaller port cost, answer is A
  2. Ja10m 👍 4 Answered A
    A higher bandwidth means smaller port cost, answer is A
  3. ekirira22 👍 3 Answered A
    Answer is A. https://vceguide.com/which-of-the-following-statements-about-the-relation-between-port-cost-and-port-bandwidth-is-true/
  4. izzraihan 👍 3
    A is make sense, so because if the bandwidth is higher on the port, the resulting cost is small
  5. NickENG 👍 3 Answered A
    Correct answer is A, the cost will be less if the bandwidth is higher.
Show 11 more comments
  1. Silveira 👍 3 Answered A
    maior largura de banda, menor custo de porta, a resposta é A
  2. UZUKO 👍 2 Answered A
    ANSWER IS A
  3. Ibgentle 👍 1
    I don't know who is upvoting B here, but it's so wrong! If I have a bigger pipe, more water will flow in less time to fill my tanks! You see, cost is about time and completeness of the delivery of anything - whether in networking or any other area of life. Don't get it twisted.
  4. FerioSiqueira 👍 1 Answered A
    Higher bandwidth always means smaller port cost. The answer is A.
  5. 4c4da48 👍 1 Answered A
    A. a higher port bandwidth indicates smaller cost (page 380)
  6. Pheaktra168 👍 1 Answered A
    higher port bandwidth indicates smaller cost
  7. ahmedhellopacket 👍 1
    did you take the exam ?
  8. Mamusfregene 👍 1 Answered A
    Hope am correct?
  9. Dafuerre 👍 1 Answered A
    Correct one is A
  10. TIConstecoin 👍 1 Answered A
    A is correct
  11. hafizhou 👍 1
    AAAAAA

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