This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: dHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet.. 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 PC in VLAN 30 must obtain an address from a DHCP server in VLAN 99. Which feature is required on the Layer 3 interface for VLAN 30?
Port security
Why wrong: Port security limits MAC behavior on a switchport; it does not forward DHCP broadcasts across VLANs.
DHCP snooping
Why wrong: DHCP snooping validates DHCP exchanges but does not replace relay across subnets.
DHCP relay
Correct. DHCP relay is what allows a client to reach a server on another subnet.
Dynamic ARP inspection
Why wrong: DAI inspects ARP traffic, not DHCP forwarding between networks.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DHCP relay
DHCP Discover messages are broadcasts and do not cross Layer 3 boundaries on their own. DHCP relay, commonly configured with ip helper-address, forwards the requests to a server on another subnet.
Key principle: DHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Port security
Why it's wrong here
Port security limits MAC behavior on a switchport; it does not forward DHCP broadcasts across VLANs.
When this WOULD be correct
In a scenario where the question asks about securing access to a specific port on a switch to prevent unauthorized devices from connecting, port security would be the correct answer. For example, if the question specifies that only certain MAC addresses are allowed on a port, port security would be necessary.
DHCP snooping
Why it's wrong here
DHCP snooping validates DHCP exchanges but does not replace relay across subnets.
When this WOULD be correct
In a scenario where a network administrator is asked to secure a network by preventing rogue DHCP servers while allowing legitimate DHCP traffic, a question might specify that DHCP snooping should be enabled on all access ports to ensure only trusted servers can provide IP addresses. This would make DHCP snooping the correct answer.
DHCP relay
Dynamic ARP inspection
When this WOULD be correct
In a different exam question, if the scenario involved ensuring the integrity of ARP requests and responses in a network where multiple VLANs are present, and the focus was on preventing ARP spoofing, then Dynamic ARP inspection would be the correct answer.
Option-by-option analysis
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.
Why this is correct
Correct. DHCP relay is what allows a client to reach a server on another subnet.
Why this is wrong here
Port security is used to restrict access to a switch port based on MAC addresses and does not facilitate communication between VLANs or enable DHCP services. Therefore, it does not address the requirement for a PC in VLAN 30 to obtain an IP address from a DHCP server in VLAN 99.
★ When this WOULD be the correct answer
In a scenario where the question asks about securing access to a specific port on a switch to prevent unauthorized devices from connecting, port security would be the correct answer. For example, if the question specifies that only certain MAC addresses are allowed on a port, port security would be necessary.
Why candidates choose this
Candidates may choose this option because they associate VLANs with security measures, thinking that controlling access to ports is relevant to managing DHCP traffic across VLANs.
Why this is wrong here
DHCP snooping is used to prevent unauthorized DHCP servers from providing IP addresses to clients, but it does not facilitate the relay of DHCP requests between different VLANs. Therefore, it is not the required feature for a PC in VLAN 30 to obtain an address from a DHCP server in VLAN 99.
★ When this WOULD be the correct answer
In a scenario where a network administrator is asked to secure a network by preventing rogue DHCP servers while allowing legitimate DHCP traffic, a question might specify that DHCP snooping should be enabled on all access ports to ensure only trusted servers can provide IP addresses. This would make DHCP snooping the correct answer.
Why candidates choose this
Candidates might choose this option because they associate DHCP snooping with DHCP operations and security, leading them to mistakenly believe it is relevant to the process of obtaining an IP address across VLANs.
Why this is wrong here
Dynamic ARP inspection is used to prevent ARP spoofing attacks by validating ARP packets in a network. It does not facilitate the process of obtaining an IP address from a DHCP server across different VLANs, which is required in this scenario.
★ When this WOULD be the correct answer
In a different exam question, if the scenario involved ensuring the integrity of ARP requests and responses in a network where multiple VLANs are present, and the focus was on preventing ARP spoofing, then Dynamic ARP inspection would be the correct answer.
Why candidates choose this
Candidates may confuse the need for security features in a network with the requirements for DHCP communication, leading them to select Dynamic ARP inspection due to its relevance in VLAN environments.
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
A frequent exam trap is selecting DHCP snooping or port security as the solution for inter-VLAN DHCP communication. DHCP snooping is often misunderstood as a relay mechanism, but it only validates DHCP messages to prevent unauthorized servers and does not forward broadcasts between VLANs. Similarly, port security controls MAC address access on switchports but does not affect DHCP message forwarding. Candidates may also confuse Dynamic ARP Inspection with DHCP relay, but DAI only inspects ARP traffic for security purposes. The key mistake is overlooking that DHCP broadcasts are Layer 2 broadcasts and require DHCP relay on the Layer 3 interface to reach servers in other VLANs.
Detailed technical explanation
DHCP relay is a critical feature in multi-VLAN networks where DHCP clients and servers reside in different IP subnets. DHCP clients initially send DHCP Discover messages as broadcasts, which are limited to their local VLAN and do not cross Layer 3 boundaries. To enable clients in VLAN 30 to obtain IP addresses from a DHCP server in VLAN 99, the Layer 3 interface serving VLAN 30 must be configured to forward these broadcasts as unicast messages to the DHCP server. This forwarding is accomplished using the DHCP relay agent functionality, typically configured with the ip helper-address command on Cisco devices. The DHCP relay agent listens for DHCP broadcast requests on the local VLAN interface and then forwards those requests as unicast packets to the specified DHCP server IP address in another VLAN or subnet. This mechanism allows centralized DHCP servers to serve multiple VLANs without requiring a DHCP server in each VLAN. The relay agent also forwards DHCP replies back to the requesting client, ensuring seamless IP address assignment across VLAN boundaries. This behavior is essential in routed networks where VLANs segment broadcast domains. A common exam trap is confusing DHCP relay with DHCP snooping or port security. DHCP snooping is a security feature that filters DHCP messages to prevent rogue servers but does not forward DHCP requests across VLANs. Port security restricts MAC addresses on switchports but does not enable DHCP broadcast forwarding. Understanding that DHCP relay is the mechanism that bridges DHCP communication across Layer 3 boundaries is crucial for correctly answering questions about inter-VLAN DHCP address assignment.
Key takeaway
DHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet.
Real-world example
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
Review dHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Network Services and Security — This question tests Network Services and Security — DHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet..
The correct answer is: DHCP relay — DHCP Discover messages are broadcasts and do not cross Layer 3 boundaries on their own. DHCP relay, commonly configured with ip helper-address, forwards the requests to a server on another subnet.
Review dHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet., then practise related 200-301 questions on the same topic to reinforce the concept.
DHCP relay forwards DHCP client broadcast messages from one VLAN to a DHCP server located in a different VLAN or subnet.
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Last reviewed: May 17, 2026
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