200-301 Practice Questions: Which Port Role Is Assigned To The Switch Port That Has The Lowest Cost To Reach The Root Bridge?

In the intricate world of networking, ensuring a loop-free topology is paramount for maintaining efficient and reliable communication. The question “Which port role is assigned to the switch port that has the lowest cost to reach the root bridge?” is a cornerstone for professionals pursuing the Cisco Certified Network Associate (CCNA) 200-301 Certification, as it delves into the heart of the Spanning Tree Protocol (STP). The answer—root port—highlights a critical component of STP’s mechanism for preventing network loops while optimizing traffic flow.

This article explores STP, the role of the root bridge, path cost calculations, and the significance of the root port, all within the context of the CCNA 200-301 exam. By showcasing how Study4Pass’s comprehensive study materials empower candidates to master these concepts, we’ll demonstrate why Study4Pass is the ultimate resource for achieving CCNA certification success.

Introduction to Spanning Tree Protocol (STP) in the CCNA Context

The Spanning Tree Protocol (STP), standardized as IEEE 802.1D, is a foundational Layer 2 protocol designed to prevent loops in Ethernet networks with redundant paths. Loops can cause broadcast storms, MAC address table instability, and network outages, making STP indispensable for stable network operations. In 2025, with enterprises managing complex LANs and data centers, STP remains a critical skill for network professionals, especially those preparing for the CCNA 200-301 exam.

The Cisco CCNA 200-301 certification, updated in 2020, validates a broad range of networking skills, including network fundamentals, IP connectivity, and security. STP is a key topic within the Network Fundamentals and Network Access domains, as it ensures loop-free topologies in switched networks. Questions like the one above test a candidate’s ability to understand STP’s mechanics, including port roles, path costs, and topology optimization. Study4Pass’s 200-301 study materials provide a clear, exam-focused introduction to STP, with detailed explanations, diagrams, and practice scenarios that prepare candidates for both the exam and real-world network management.

STP operates by electing a root bridge as the central reference point in the network topology, then assigning port roles to switch ports to create a loop-free path. The root port, designated port, and non-designated port roles determine which ports forward traffic and which are blocked, ensuring efficient data flow. Understanding these roles, particularly the root port, is essential for CCNA candidates, and Study4Pass’s resources make this complex topic accessible through interactive labs and practice questions.

The Root Bridge: The Foundation of the STP Topology (CCNA Perspective)

The root bridge is the cornerstone of an STP topology, serving as the reference point for all path calculations. In a switched network, STP elects one switch as the root bridge based on the Bridge ID (BID), which comprises:

• Bridge Priority: A configurable value (default 32768), adjustable in increments of 4096.
• MAC Address: The switch’s lowest MAC address serves as a tiebreaker if priorities are equal.

The switch with the lowest BID becomes the root bridge, acting as the “root” of the spanning tree. All other switches (non-root bridges) calculate the shortest path to the root bridge, determining their port roles based on these paths.

Root Bridge Election Process

1. BID Comparison: Switches exchange Bridge Protocol Data Units (BPDUs) containing their BIDs. The switch with the lowest BID is elected root.
2. Tiebreaker: If bridge priorities are equal, the switch with the lowest MAC address wins.
3. Configuration: Administrators can influence the election by setting a lower priority (e.g., spanning-tree vlan 1 priority 4096) on a preferred switch.

Importance for CCNA

For CCNA candidates, understanding the root bridge election is critical, as it affects port role assignments and network performance. Misconfigured priorities can lead to suboptimal topologies, where a less capable switch becomes the root, causing inefficiencies. Study4Pass’s 200-301 labs simulate root bridge elections, allowing candidates to configure priorities, analyze BPDUs, and verify the root using commands like show spanning-tree, ensuring hands-on mastery of this concept.

Practical Example

In a network with three switches (SW1, SW2, SW3), SW1 has a priority of 32768 and the lowest MAC address, making it the root bridge. SW2 and SW3 adjust their port roles to optimize paths to SW1. This election ensures a centralized reference point, simplifying path calculations and preventing loops. Study4Pass’s video tutorials illustrate this process with visual topology diagrams, helping candidates grasp the root bridge’s role in STP.

Path Cost: The Metric for Root Bridge Reachability (Critical for CCNA Calculations)

Path cost is the metric STP uses to determine the shortest path from a non-root switch to the root bridge. Each switch port is assigned a cost based on its speed, as defined by IEEE 802.1D (or updated standards like 802.1w for Rapid STP). The total path cost is the sum of costs along the path to the root bridge, and the port with the lowest path cost becomes the root port.

Calculating Path Cost

For a non-root switch, STP evaluates all possible paths to the root bridge, summing the costs of each link. The path with the lowest total cost determines the root port. If costs are equal, STP uses tiebreakers:

1. Lowest Sender BID: Prefer the path through the switch with the lowest BID.
2. Lowest Sender Port ID: Prefer the path through the port with the lowest ID (combination of port priority and number).

Example Calculation

Consider a network where SW2 connects to the root bridge (SW1) via two paths:

• Path 1: SW2’s Gi0/1 (1 Gbps, cost 4) directly to SW1.
• Path 2: SW2’s Gi0/2 (100 Mbps, cost 19) to SW3, then SW3’s Gi0/1 (1 Gbps, cost 4) to SW1 (total cost: 19 + 4 = 23).

SW2 selects Gi0/1 as its root port, as it has the lowest path cost (4 vs. 23). Study4Pass’s 200-301 practice exams include path cost calculation questions, guiding candidates through scenarios with multiple paths and tiebreakers, ensuring exam readiness.

CCNA Relevance

Path cost calculations are a frequent topic in the 200-301 exam, testing candidates’ ability to analyze topologies and assign port roles. Errors in cost calculations can lead to incorrect root port selections, causing suboptimal traffic paths. Study4Pass’s Practice Tests provide topology-based exercises, allowing candidates to calculate costs, configure port priorities, and verify results with show spanning-tree, bridging theory and practice.

The Root Port: The Optimal Path to the Root Bridge (Direct Answer to the Question)

The port role assigned to the switch port with the lowest cost to reach the root bridge is the root port. Each non-root switch designates one root port, which is the port providing the shortest (lowest-cost) path to the root bridge. The root port forwards traffic toward the root bridge, forming part of the active spanning tree topology.

Characteristics of the Root Port

• One per Non-Root Switch: Every non-root switch has exactly one root port, except the root bridge, which has no root ports (all its ports are designated).
• Forwarding State: Root ports are in the Forwarding state, actively sending and receiving traffic.
• Path Cost-Based: Selected based on the lowest cumulative path cost to the root bridge, with tiebreakers as needed.

Root Port Selection Process

1. Calculate Path Costs: For each port, sum the costs of all links to the root bridge.
2. Select Lowest Cost: The port with the lowest path cost is designated the root port.
3. Apply Tiebreakers: If costs are equal, use the lowest sender BID, then lowest sender port ID.

Example Scenario

In a network with SW1 as the root bridge, SW2 has two connections:

• Gi0/1 to SW1 (1 Gbps, cost 4).
• Gi0/2 to SW3, then to SW1 (100 Mbps + 1 Gbps, cost 19 + 4 = 23).

SW2 assigns Gi0/1 as its root port due to the lower cost (4). If SW3 advertises a better path, SW2 recalculates, ensuring dynamic adaptation. Study4Pass’s 200-301 labs simulate this process, allowing candidates to configure STP, adjust port costs, and verify root port assignments with show spanning-tree vlan 1.

CCNA Exam Focus

The root port is a core STP concept tested in the 200-301 exam, often through topology-based questions requiring candidates to identify port roles or troubleshoot misconfigurations. Study4Pass’s practice questions mirror these scenarios, providing detailed explanations of root port selection and common errors, such as overlooking tiebreakers.

Practical Implications and Troubleshooting for CCNA 200-301

Practical Implications

Understanding the root port’s role has significant implications for network design and performance:

• Optimized Traffic Flow: Root ports ensure traffic takes the shortest path to the root bridge, minimizing latency.
• Redundancy Management: By selecting one root port, STP eliminates loops while maintaining failover paths via alternate ports.
• Scalability: Proper root port assignments support large LANs with multiple switches, ensuring efficient topologies.

For example, in a campus network, a well-placed root bridge and correctly assigned root ports reduce congestion, enhancing user experience for applications like VoIP or video streaming. Study4Pass’s video tutorials demonstrate these implications with real-world case studies, helping candidates connect STP theory to practical applications.

Troubleshooting STP Issues

Common STP issues related to root ports include:

• Incorrect Root Port Selection: Caused by misconfigured port costs or priorities, leading to suboptimal paths. Use show spanning-tree to verify costs and adjust with spanning-tree cost .
• Root Bridge Misplacement: A low-capacity switch as root can bottleneck traffic. Set a preferred root with spanning-tree vlan 1 priority 4096.
• BPDU Issues: Missing BPDUs can disrupt root port assignments. Check interface status with show interfaces.
• Topology Changes: Frequent changes can cause instability. Monitor with show spanning-tree detail.

Study4Pass’s 200-301 labs include troubleshooting exercises, guiding candidates through diagnosing root port issues, analyzing BPDUs, and optimizing STP configurations, ensuring exam and job readiness.

CCNA Exam Scenarios

The 200-301 exam often presents simulation questions where candidates must identify the root port in a given topology or troubleshoot a misconfigured network. Study4Pass’s practice exams replicate these scenarios, offering interactive topologies and command-line simulations to build confidence in STP troubleshooting.

Conclusion: Mastering STP Port Roles for the CCNA 200-301 Exam

The root port, assigned to the switch port with the lowest cost to reach the root bridge, is a pivotal component of the Spanning Tree Protocol, ensuring a loop-free and efficient network topology. By understanding the root bridge election, path cost calculations, and root port selection, CCNA 200-301 candidates can design and troubleshoot robust networks, a skill critical for both the exam and professional networking roles.

Study4Pass is the premier resource for 200-301 preparation, offering comprehensive study guides, interactive labs, and practice exams that align with Cisco’s objectives. Unlike unreliable exam dumps, Study4Pass fosters deep understanding through expertly curated content, ensuring you’re ready for the exam and your career. Whether you’re calculating path costs or troubleshooting STP issues, Study4Pass provides the tools you need to succeed.

Start your CCNA journey with Study4Pass today. With their user-friendly platform and exam-focused resources, you’ll not only pass the 200-301 exam but also gain the expertise to build and maintain efficient, loop-free networks in a connected world.

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Actual Exam Questions From Cisco 200-301 Certification

Below are five exam-style questions designed to reflect the Cisco CCNA (200-301) exam objectives, focusing on STP and root port concepts. These questions help you test your knowledge and prepare effectively with Study4Pass.

Which port role is assigned to the switch port that has the lowest cost to reach the root bridge?

A. Designated port

B. Root port

C. Non-designated port

D. Alternate port

A switch has two paths to the root bridge: Path A with a cost of 19 and Path B with a cost of 4. Which port will be selected as the root port?

A. The port on Path A

B. The port on Path B

C. Both ports

D. Neither port

Which Cisco IOS command displays the root port and path cost for a specific VLAN?

A. show running-config

B. show spanning-tree vlan 1

C. show ip route

D. show interfaces

A network administrator notices that a switch’s root port is connected to a suboptimal path. What should they do to correct this?

A. Reboot the switch

B. Adjust the port cost using spanning-tree cost

C. Disable STP on the port

D. Change the switch’s MAC address

What is the default STP path cost for a 1 Gbps Ethernet link?

A. 2

B. 4

C. 19

D. 100