The answer is the port security violation mode set to protect. This mode causes the switch to silently drop frames from any unauthorized MAC address without generating a syslog alert or incrementing the violation counter, which explains the one-way traffic symptom where the server can receive but cannot send. When a new server connects, the switch does not learn its MAC address, so it drops the server’s outgoing frames while still forwarding broadcast and unknown unicast frames to the port, allowing inbound traffic. On the Cisco DCCOR / CCNP Data Center Core 350-601 exam, this scenario tests your understanding of how each port security violation mode behaves, with protect mode being the only one that creates a silent, one-way communication failure—a common trap for those who confuse it with restrict or shutdown. Remember the memory tip: “Protect drops in silence, restrict sends an alert, shutdown kills the port.”
350-601 Security Practice Question
This 350-601 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A server team reports that after connecting a new server to a switchport, the server can receive traffic but cannot send traffic. The port is configured with port security. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The port security violation mode is set to protect
When port security violation mode is set to 'protect', the switch drops traffic from unauthorized MAC addresses without generating a syslog message or incrementing the violation counter. In this scenario, the server can receive traffic because the switch still forwards broadcast and unknown unicast frames to the port, but the server's transmitted frames are silently dropped because the switch does not learn the server's MAC address or forward its frames. This matches the symptom of one-way communication where the server can receive but not send.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The port is in errdisable state
Why it's wrong here
In errdisable, no traffic is received or sent.
✓
The port security violation mode is set to protect
Why this is correct
Protect mode drops offending frames silently, allowing the server to receive but not send traffic from an unknown MAC.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The port security maximum is set to 1 and another device is connected
Why it's wrong here
That would cause a violation, but the behavior depends on mode.
✗
The server MAC address is not in the allowed list
Why it's wrong here
If the MAC is not allowed, the violation mode determines action; protect mode would drop as described.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between the three port security violation modes (protect, restrict, shutdown) by presenting a symptom of one-way traffic, which candidates mistakenly attribute to a shutdown or restrict mode rather than the silent dropping behavior of protect.
Detailed technical explanation
How to think about this question
The 'protect' violation mode is unique because it does not increment the violation counter or generate SNMP traps, making it difficult to detect without monitoring traffic flows. Under the hood, when a frame with an unknown source MAC arrives on a protect-mode port, the switch simply drops the frame and does not update the MAC address table, effectively blackholing the server's outgoing traffic while still allowing incoming frames destined to the server's MAC (if already learned). In a real-world scenario, this often happens when a new server is connected to a port that already has learned a different MAC address (e.g., from a previous device), and the protect mode silently prevents the new MAC from being learned.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The port security violation mode is set to protect — When port security violation mode is set to 'protect', the switch drops traffic from unauthorized MAC addresses without generating a syslog message or incrementing the violation counter. In this scenario, the server can receive traffic because the switch still forwards broadcast and unknown unicast frames to the port, but the server's transmitted frames are silently dropped because the switch does not learn the server's MAC address or forward its frames. This matches the symptom of one-way communication where the server can receive but not send.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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