Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A client on VLAN 20 must obtain an IPv4 lease from a DHCP server located on VLAN 100. Which feature is required on the Layer 3 interface for VLAN 20?
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
Distractor review
NAT overload
NAT is not required just to relay DHCP across VLANs.
B
Best answer
DHCP relay
Correct. The SVI or routed interface needs DHCP relay.
C
Distractor review
Port security
Port security does not forward DHCP broadcasts between VLANs.
D
Distractor review
Private VLAN
Private VLAN is unrelated to DHCP relay functionality.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting NAT overload or port security as the required feature for DHCP communication across VLANs. NAT overload is used for IP address translation and does not forward DHCP broadcasts, while port security restricts MAC addresses on switch ports but does not relay DHCP messages. Another trap is confusing private VLANs with DHCP relay; private VLANs isolate Layer 2 domains but do not forward DHCP requests between VLANs. The key is understanding that DHCP relay is the only feature that forwards DHCP broadcasts as unicast messages across Layer 3 boundaries, enabling clients on VLAN 20 to obtain leases from a DHCP server on VLAN 100.
Technical deep dive
How to think about this question
DHCP relay is a critical feature in Layer 3 devices that enables clients on one VLAN to obtain IP addresses from a DHCP server located on a different VLAN or subnet. Normally, DHCP clients send broadcast messages to discover DHCP servers, but broadcasts do not cross Layer 3 boundaries. A DHCP relay agent listens for these broadcasts on the client VLAN interface and forwards them as unicast messages to the DHCP server's IP address, typically configured with the ip helper-address command on Cisco devices. In the context of VLANs, each VLAN is a separate broadcast domain with its own subnet. When a client on VLAN 20 requests an IP address, the Layer 3 interface for VLAN 20 must be configured to relay DHCP requests to the DHCP server on VLAN 100. Without DHCP relay, the DHCP broadcast messages would not reach the server, and the client would fail to obtain an IP lease. This relay functionality is essential in routed VLAN interfaces (SVIs) or routed physical interfaces that serve multiple VLANs. A common exam trap is confusing DHCP relay with other Layer 2 or security features like port security or private VLANs, which do not forward DHCP broadcasts across VLANs. Also, NAT overload is unrelated to DHCP forwarding and only translates IP addresses for outbound traffic. Understanding the role of DHCP relay in forwarding DHCP messages across Layer 3 boundaries is crucial for correctly answering questions about inter-VLAN DHCP communication in Cisco networks.
KKey Concepts to Remember
- A DHCP relay agent forwards DHCP client broadcast messages as unicast to a remote DHCP server across different VLANs or subnets.
- Layer 3 interfaces configured as SVIs require DHCP relay to enable clients on one VLAN to obtain IP addresses from a DHCP server on another VLAN.
- Broadcast DHCP requests do not cross Layer 3 boundaries, so DHCP relay is necessary to forward these requests between VLANs.
- The ip helper-address command on Cisco Layer 3 interfaces configures the DHCP relay agent to forward DHCP requests to the server's IP address.
- NAT overload does not facilitate DHCP message forwarding and is unrelated to DHCP relay functionality in inter-VLAN communication.
- Port security controls MAC address access on switch ports but does not forward DHCP broadcasts between VLANs.
- Private VLANs segment Layer 2 domains for security but do not provide DHCP relay capabilities across VLANs.
- Without DHCP relay, clients on VLANs without a local DHCP server cannot obtain IP addresses from servers on other VLANs.
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
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Question 2
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Question 3
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Question 4
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Question 5
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Question 6
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FAQ
Questions learners often ask
What does this 200-301 question test?
A DHCP relay agent forwards DHCP client broadcast messages as unicast to a remote DHCP server across different VLANs or subnets.
What is the correct answer to this question?
The correct answer is: DHCP relay — A DHCP relay agent forwards client broadcasts as unicast to the remote server, typically using ip helper-address.
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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