- A
A root port is the port on a non-root bridge that provides the best path to the root bridge.
Correct. The root port is selected based on the lowest root path cost to the root bridge.
- B
A designated port is the port on a segment that has the lowest path cost to the root bridge, and there can be multiple designated ports on the same segment.
Why wrong: Incorrect. There is exactly one designated port per segment; multiple would cause a loop.
- C
In classic STP, a port in the blocking state can still send and receive BPDUs.
Correct. In blocking state, the port does not forward user traffic but can still process BPDUs to maintain the spanning tree.
- D
An alternate port is a port that provides a backup path to the root bridge and is in the forwarding state when the root port is active.
Why wrong: Incorrect. Alternate port is an RSTP concept and is in discarding state when the root port is active; it only becomes forwarding after root port failure.
- E
A backup port is a port that provides a redundant connection to the same segment and is in the learning state when the designated port is active.
Why wrong: Incorrect. Backup port is also an RSTP role and is in discarding state when the designated port is active; it does not learn.
Quick Answer
The correct answer is that in classic STP, a port in the blocking state can still send and receive BPDUs. This is true because the blocking state, defined in IEEE 802.1D, prevents user data from being forwarded to avoid loops, but the port must remain active in the STP topology by listening for and processing incoming BPDUs to potentially transition to a listening or learning state. The root port is the single port on a non-root bridge with the best path to the root bridge, while a designated port is the one port per segment that offers the best path to the root; both are active forwarding roles. On the ENCOR 350-401 exam, this concept tests your ability to distinguish between STP port roles and states, with a common trap being the assumption that a blocking port is completely silent—it is not, as it still receives BPDUs to maintain loop-free convergence. A helpful memory tip: "Blocked but not deaf—BPDUs still received."
350-401 Spanning Tree Protocol Practice Question
This 350-401 practice question tests your understanding of spanning tree protocol. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
Which two statements about STP port roles and states are true? (Choose two.)
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
A root port is the port on a non-root bridge that provides the best path to the root bridge.
In classic STP (802.1D), a port can be in blocking, listening, learning, forwarding, or disabled state. The root port is the port on a non-root bridge that has the best path to the root bridge. A designated port is the port on a segment that has the best path to the root bridge; there is exactly one designated port per segment. Alternate and backup ports are roles defined in RSTP, not classic STP. A port in blocking state does not send or receive user data but can still receive BPDUs.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A root port is the port on a non-root bridge that provides the best path to the root bridge.
Why this is correct
Correct. The root port is selected based on the lowest root path cost to the root bridge.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
A designated port is the port on a segment that has the lowest path cost to the root bridge, and there can be multiple designated ports on the same segment.
Why it's wrong here
Incorrect. There is exactly one designated port per segment; multiple would cause a loop.
- ✓
In classic STP, a port in the blocking state can still send and receive BPDUs.
Why this is correct
Correct. In blocking state, the port does not forward user traffic but can still process BPDUs to maintain the spanning tree.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
An alternate port is a port that provides a backup path to the root bridge and is in the forwarding state when the root port is active.
Why it's wrong here
Incorrect. Alternate port is an RSTP concept and is in discarding state when the root port is active; it only becomes forwarding after root port failure.
- ✗
A backup port is a port that provides a redundant connection to the same segment and is in the learning state when the designated port is active.
Why it's wrong here
Incorrect. Backup port is also an RSTP role and is in discarding state when the designated port is active; it does not learn.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
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Spanning Tree Protocol — study guide chapter
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FAQ
Questions learners often ask
What does this 350-401 question test?
Spanning Tree Protocol — This question tests Spanning Tree Protocol — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: A root port is the port on a non-root bridge that provides the best path to the root bridge. — In classic STP (802.1D), a port can be in blocking, listening, learning, forwarding, or disabled state. The root port is the port on a non-root bridge that has the best path to the root bridge. A designated port is the port on a segment that has the best path to the root bridge; there is exactly one designated port per segment. Alternate and backup ports are roles defined in RSTP, not classic STP. A port in blocking state does not send or receive user data but can still receive BPDUs.
What should I do if I get this 350-401 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 18, 2026
This 350-401 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 350-401 exam.
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