Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A switch receives superior BPDUs on a port where the design requires that no downstream device ever become the root path for that segment. Which feature is the best fit for that requirement?
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
Best answer
Root guard
This is correct because root guard prevents the port from becoming a root path when superior BPDUs appear.
B
Distractor review
BPDU Guard
This is wrong because BPDU Guard is typically used on edge ports to disable them when BPDUs appear unexpectedly.
C
Distractor review
Port security
This is wrong because port security controls MAC address behavior, not STP root-path conditions.
D
Distractor review
DHCP Snooping
This is wrong because DHCP Snooping is unrelated to STP root-role protection.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting BPDU guard instead of root guard because both involve BPDU handling. BPDU guard disables a port immediately upon receiving any BPDU, which is suitable for edge ports but not for ports where topology control is required. Root guard, on the other hand, only blocks ports that receive superior BPDUs, allowing normal BPDUs from the current root bridge. Confusing these features can lead to incorrect answers, as BPDU guard does not protect the root path role but rather protects against unauthorized devices on edge ports.
Technical deep dive
How to think about this question
Spanning Tree Protocol (STP) is a Layer 2 network protocol that prevents loops by electing a root bridge and calculating the best paths to it. Switch ports are assigned roles such as root port, designated port, or blocked port based on BPDU (Bridge Protocol Data Unit) information. When a switch receives a superior BPDU (one indicating a better path to the root bridge), it may change its port roles and topology accordingly to maintain a loop-free environment. Root guard is a Cisco feature designed to enforce the network topology by preventing a port from becoming a root port if it receives superior BPDUs. When root guard is enabled on a port, if that port receives a superior BPDU, the port is placed into a root-inconsistent state, effectively blocking it from forwarding traffic and preventing the downstream device from becoming the root bridge or influencing the root path. This preserves the intended STP topology and prevents topology changes caused by unauthorized or misconfigured switches. A common exam trap is confusing root guard with BPDU guard. BPDU guard disables a port if any BPDU is received, typically used on edge ports to protect against accidental switches or loops. Root guard, however, only blocks ports receiving superior BPDUs, allowing normal BPDUs from the current root bridge. Understanding this distinction is critical for correctly applying STP protection features and answering related CCNA questions accurately.
KKey Concepts to Remember
- Root guard prevents a switch port from becoming a root port by blocking the port if it receives superior BPDUs.
- Superior BPDUs indicate a better path to the root bridge and can cause topology changes if not controlled.
- BPDU guard disables a port entirely when any BPDU is received, protecting edge ports from unexpected switches.
- Port security controls MAC address access on a port and does not influence STP root path decisions.
- DHCP snooping protects against rogue DHCP servers and does not affect STP or root bridge election.
- STP uses BPDUs to elect the root bridge and determine port roles to maintain a loop-free topology.
- Root guard places a port into a root-inconsistent state to block forwarding when superior BPDUs are detected.
- Proper use of root guard maintains the intended STP topology by preventing downstream devices from becoming the root.
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 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 3
What is the OSPF metric called?
Question 4
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?
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?
Root guard prevents a switch port from becoming a root port by blocking the port if it receives superior BPDUs.
What is the correct answer to this question?
The correct answer is: Root guard — Root guard is the best fit because it is designed to prevent a port from becoming the path toward a new root bridge when superior BPDUs are received. In practical terms, it protects the intended STP topology by keeping that port from taking on a root-related forwarding role when the design says it should not. This is different from BPDU Guard, which is more commonly used on edge ports to disable them entirely if BPDUs appear. Root guard is about protecting topology roles, not just edge-port assumptions.
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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