Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
interface Vlan30 ip address 10.30.30.1 255.255.255.0 no shutdown interface Vlan99 ip address 10.99.99.1 255.255.255.0 no shutdown Remote DHCP server: 10.99.99.20
Based on the exhibit, which configuration should be added to restore DHCP service for clients in VLAN 30?
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
ip helper-address 10.99.99.20 under interface Vlan30
This is correct because the VLAN 30 SVI must relay DHCP requests toward the remote server.
B
Distractor review
switchport mode trunk under interface Vlan30
This is wrong because an SVI is not a Layer 2 switchport.
C
Distractor review
ip default-gateway 10.99.99.20 under interface Vlan30
This is wrong because that is not how DHCP relay is configured.
D
Distractor review
spanning-tree portfast under interface Vlan30
This is wrong because PortFast is unrelated to DHCP relay on an SVI.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is confusing the ip helper-address command with ip default-gateway or Layer 2 commands like switchport mode trunk. Candidates might incorrectly apply switchport commands to an SVI, which is a Layer 3 interface, or think setting ip default-gateway will relay DHCP requests. These mistakes cause DHCP broadcasts to fail reaching the remote server, leading to no IP address assignment for clients. Understanding that ip helper-address is the DHCP relay mechanism on Layer 3 interfaces is critical to avoid this trap.
Technical deep dive
How to think about this question
DHCP relay is essential in multi-VLAN environments where the DHCP server resides on a different subnet than the clients. Clients send DHCPDISCOVER messages as broadcasts, which routers do not forward by default. To enable DHCP communication across subnets, the router’s VLAN interface (SVI) must be configured with the ip helper-address command, which forwards these broadcasts as unicast packets to the DHCP server’s IP address. This process allows clients to obtain IP addresses even when the DHCP server is remote. The ip helper-address command acts as a relay agent on the Layer 3 interface associated with the VLAN. When a DHCP broadcast is received on the SVI, the router converts it into a unicast message directed at the DHCP server. This relay function is critical because routers block broadcasts between subnets to reduce unnecessary traffic. Without this configuration, clients in VLAN 30 cannot reach the DHCP server on a different subnet, resulting in failed IP address assignment. A frequent source of confusion is treating the SVI like a Layer 2 interface and applying commands such as switchport mode trunk or spanning-tree portfast, which are invalid on SVIs. Another mistake is using ip default-gateway, which only sets the management gateway on Layer 2 devices and does not relay DHCP requests. Understanding the SVI’s role as a Layer 3 gateway and the necessity of ip helper-address for DHCP relay is crucial for both exam success and practical network troubleshooting.
KKey Concepts to Remember
- A VLAN interface (SVI) must have an ip helper-address configured to relay DHCP broadcasts to a DHCP server on a different subnet.
- DHCP clients send broadcast messages that cannot cross Layer 3 boundaries without a relay agent like the ip helper-address feature on an SVI.
- The ip helper-address command forwards UDP broadcasts for DHCP and other services from clients to a specified remote server IP address.
- An SVI is a Layer 3 interface and does not support Layer 2 commands such as switchport mode trunk or spanning-tree portfast.
- The ip default-gateway command is used on Layer 2 devices to specify a gateway for management traffic and does not relay DHCP requests.
- Without the ip helper-address on the VLAN interface, DHCP requests from clients in that VLAN will not reach the DHCP server on another subnet.
- The local gateway interface (SVI) acts as the DHCP relay agent, forwarding client broadcasts to the DHCP server using the ip helper-address.
- Configuring ip helper-address on the correct VLAN interface ensures proper DHCP service restoration for clients in that VLAN.
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
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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?
A VLAN interface (SVI) must have an ip helper-address configured to relay DHCP broadcasts to a DHCP server on a different subnet.
What is the correct answer to this question?
The correct answer is: ip helper-address 10.99.99.20 under interface Vlan30 — The correct fix is to add an IP helper address pointing to the remote DHCP server on the Layer 3 interface for VLAN 30. In practical terms, the clients are sending DHCP discovery as a broadcast, and the server is on another subnet. The SVI for VLAN 30 is the local gateway that must relay those requests toward the server. This is one of the most exam-realistic campus troubleshooting scenarios because it tests both subnet boundaries and the role of the local gateway interface.
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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