Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Exhibit
interface Vlan20 ip address 10.20.20.1 255.255.255.0 ip helper-address 10.50.0.100 interface Vlan30 ip address 10.30.30.1 255.255.255.0 ip helper-address 10.50.0.10 DHCP server address: 10.50.0.10
Users on VLAN 20 are not receiving IPv4 addresses from the centralized DHCP server at 10.50.0.10. Users in other VLANs are working normally. Based on the exhibit, which change should fix the issue for VLAN 20 clients?
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
Change the helper address on interface Vlan20 to 10.50.0.10.
That points DHCP relay to the actual DHCP server.
B
Distractor review
Convert the VLAN 20 user ports to trunk mode.
User access ports should stay in access mode.
C
Distractor review
Configure a default gateway on the user PCs manually.
That does not solve the DHCP relay problem.
D
Distractor review
Disable DHCP snooping on VLAN 20.
Nothing in the exhibit suggests DHCP snooping is the cause.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that user ports must be trunks or that disabling DHCP snooping will fix DHCP address assignment issues. In reality, user ports should remain in access mode to maintain VLAN membership, and DHCP snooping is unrelated to forwarding DHCP requests. Another common mistake is thinking that manually configuring a default gateway on clients solves DHCP problems, but DHCP discovery requires proper relay configuration on the Layer 3 interface. Misconfiguring or omitting the ip helper-address on the VLAN interface causes DHCP requests to fail, which is the core issue here.
Technical deep dive
How to think about this question
DHCP relay is a critical function in multi-VLAN networks where a centralized DHCP server provides IP addresses to clients across different subnets. Since DHCP clients initially send broadcast messages to discover a DHCP server, these broadcasts cannot cross Layer 3 boundaries by default. To solve this, Cisco devices use the ip helper-address command on the VLAN interface (SVI) to forward DHCP broadcasts as unicast packets to the DHCP server’s IP address. This mechanism ensures clients in remote VLANs receive IP addresses without requiring a DHCP server in each VLAN. The decision process for DHCP relay involves verifying that each VLAN’s SVI has the correct helper address configured. If the helper address is missing or incorrect, DHCP requests from clients in that VLAN will not reach the DHCP server, causing address assignment failures. In this question, VLAN 20 clients fail to get addresses because the helper address on interface Vlan20 does not point to the DHCP server at 10.50.0.10. Correcting this configuration directs DHCP requests properly, restoring service. A common exam trap is confusing port modes or unrelated features with DHCP relay issues. For example, converting user ports to trunk mode or disabling DHCP snooping does not fix DHCP relay problems. DHCP snooping controls DHCP message security but does not forward requests. Similarly, manually setting a default gateway on clients does not influence DHCP relay. Understanding the role of the ip helper-address command on SVIs is essential to avoid these pitfalls and ensure DHCP functions correctly in routed VLAN environments.
KKey Concepts to Remember
- DHCP relay uses the ip helper-address command on a Layer 3 interface to forward client DHCP broadcasts to a centralized DHCP server.
- Each VLAN’s switched virtual interface (SVI) must have the correct helper address configured to ensure DHCP requests reach the DHCP server.
- DHCP broadcasts are not routed by default, so the helper address enables forwarding of DHCP requests across different IP subnets.
- Access ports connected to end devices should remain in access mode to maintain proper VLAN membership and avoid DHCP issues.
- Manually configuring a default gateway on clients does not resolve DHCP relay problems because DHCP discovery relies on broadcast forwarding.
- DHCP snooping is a security feature that filters DHCP messages but is unrelated to DHCP relay configuration on SVIs.
- Incorrect or missing helper addresses on SVIs cause DHCP requests from clients in that VLAN to fail reaching the DHCP server.
- The ip helper-address command points the router or Layer 3 switch to the correct DHCP server IP, enabling address assignment.
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?
DHCP relay uses the ip helper-address command on a Layer 3 interface to forward client DHCP broadcasts to a centralized DHCP server.
What is the correct answer to this question?
The correct answer is: Change the helper address on interface Vlan20 to 10.50.0.10. — The SVI for VLAN 20 is forwarding DHCP requests to the wrong helper address. DHCP relay depends on the Layer 3 interface for that VLAN sending client broadcasts to the correct server. Trunks, access ports, and the DHCP pool name on the server are not the first issue shown here.
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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