- A
It blocks DHCP server messages received on untrusted ports.
DHCP snooping classifies ports as trusted or untrusted. Untrusted ports are not permitted to send DHCP server-side messages (e.g., DHCPOFFER, DHCPACK), thereby preventing rogue DHCP servers.
- B
It generates a Cisco Discovery Protocol packet for each DHCP request.
Why wrong: DHCP snooping does not generate CDP packets. CDP is a separate Cisco-proprietary neighbor discovery protocol unrelated to DHCP.
- C
It builds a DHCP binding table.
DHCP snooping dynamically creates a binding table that records the IP address, MAC address, VLAN, and interface associated with each successful DHCP lease.
- D
It relays DHCP requests across VLANs.
Why wrong: Relaying DHCP requests across different subnets is the role of a DHCP relay agent, typically configured using the `ip helper-address` command on the gateway interface.
- E
It converts DHCP broadcasts into unicasts.
Why wrong: The conversion of DHCP client broadcast messages (DISCOVER, REQUEST) into unicast packets is performed by a DHCP relay agent, not by DHCP snooping.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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 actions does DHCP snooping perform by default on a Cisco switch?
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
It blocks DHCP server messages received on untrusted ports.
DHCP snooping is a Layer 2 security feature that filters DHCP messages and builds a binding table. By default, it blocks DHCP server messages on untrusted ports and dynamically creates a binding table mapping IP addresses to MAC addresses. It does not relay requests across VLANs or convert broadcasts to unicasts (those are relay agent functions).
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It blocks DHCP server messages received on untrusted ports.
Why this is correct
DHCP snooping classifies ports as trusted or untrusted. Untrusted ports are not permitted to send DHCP server-side messages (e.g., DHCPOFFER, DHCPACK), thereby preventing rogue DHCP servers.
Related concept
Access ports place end devices into a single VLAN.
- ✗
It generates a Cisco Discovery Protocol packet for each DHCP request.
Why it's wrong here
DHCP snooping does not generate CDP packets. CDP is a separate Cisco-proprietary neighbor discovery protocol unrelated to DHCP.
- ✓
It builds a DHCP binding table.
Why this is correct
DHCP snooping dynamically creates a binding table that records the IP address, MAC address, VLAN, and interface associated with each successful DHCP lease.
Related concept
Access ports place end devices into a single VLAN.
- ✗
It relays DHCP requests across VLANs.
- ✗
It converts DHCP broadcasts into unicasts.
Why it's wrong here
The conversion of DHCP client broadcast messages (DISCOVER, REQUEST) into unicast packets is performed by a DHCP relay agent, not by DHCP snooping.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓It blocks DHCP server messages received on untrusted ports.Correct answer▾
Why this is correct
DHCP snooping classifies ports as trusted or untrusted. Untrusted ports are not permitted to send DHCP server-side messages (e.g., DHCPOFFER, DHCPACK), thereby preventing rogue DHCP servers.
✗It generates a Cisco Discovery Protocol packet for each DHCP request.Wrong answer — click to see why▾
Why this is wrong here
This statement incorrectly associates two separate features; DHCP snooping operates at Layer 2 for DHCP security, not for CDP.
✗It relays DHCP requests across VLANs.Wrong answer — click to see why▾
Why this is wrong here
This function belongs to the relay agent, not to DHCP snooping, which operates within a single VLAN to enforce security policies.
✗It converts DHCP broadcasts into unicasts.Wrong answer — click to see why▾
Why this is wrong here
This is a relay agent feature; DHCP snooping does not alter the broadcast nature of DHCP packets, it only filters them.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
Relaying DHCP requests across different subnets is the role of a DHCP relay agent, typically configured using the `ip helper-address` command on the gateway interface.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: It blocks DHCP server messages received on untrusted ports. — DHCP snooping is a Layer 2 security feature that filters DHCP messages and builds a binding table. By default, it blocks DHCP server messages on untrusted ports and dynamically creates a binding table mapping IP addresses to MAC addresses. It does not relay requests across VLANs or convert broadcasts to unicasts (those are relay agent functions).
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
About these practice questions
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Last reviewed: Jun 14, 2026
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