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← 200-301
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mediummultiple choiceObjective-mapped

Exhibit

VLAN 20 clients: 10.20.20.0/24
DHCP server: 10.99.99.10
Clients and server are in different subnets

Exhibit: PCs in VLAN 20 are not receiving addresses from a DHCP server in another subnet. The switch SVI for VLAN 20 is up, and routing is working. Which configuration is most likely missing on the gateway for VLAN 20?

Question 1mediummultiple choice
Full question →

Exhibit: PCs in VLAN 20 are not receiving addresses from a DHCP server in another subnet. The switch SVI for VLAN 20 is up, and routing is working. Which configuration is most likely missing on the gateway for VLAN 20?

Full question →

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

ip default-gateway 10.20.20.1

That is for a Layer 2 switch's own management, not DHCP relay for routed clients.

B

Best answer

ip helper-address 10.99.99.10

That forwards DHCP broadcasts to the remote server.

C

Distractor review

switchport trunk allowed vlan 20

The issue is inter-subnet DHCP, not trunk allowance in the exhibit.

D

Distractor review

spanning-tree portfast default

PortFast is unrelated to relaying DHCP requests to another subnet.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A frequent exam trap is selecting the ip default-gateway command as the solution for DHCP relay issues. This command only applies to Layer 2 switches for their own management traffic and does not forward DHCP broadcasts across routed interfaces. Candidates may also mistakenly focus on VLAN trunking or spanning-tree settings, which do not affect DHCP relay functionality. The key is to recognize that DHCP broadcasts must be explicitly forwarded by the router or Layer 3 switch interface using ip helper-address to reach a DHCP server in another subnet.

Technical deep dive

How to think about this question

DHCP (Dynamic Host Configuration Protocol) uses broadcast messages to discover available DHCP servers and obtain IP addresses. When clients reside in a different subnet than the DHCP server, broadcasts do not cross router boundaries by default. To enable clients in remote VLANs or subnets to receive DHCP addresses, the router interface acting as the default gateway must relay these DHCP broadcast requests to the DHCP server using a helper function. The Cisco IOS command ip helper-address is configured on the Layer 3 interface (SVI or routed port) serving as the gateway for the client VLAN. This command specifies the IP address of the DHCP server to which the router forwards DHCP broadcast messages as unicast packets. Without this configuration, DHCP Discover messages from clients in VLAN 20 will not reach the DHCP server in another subnet, causing clients to fail to obtain IP addresses. A common exam trap is confusing the ip default-gateway command with DHCP relay functionality. The ip default-gateway command is used only on Layer 2 switches for management traffic and does not relay DHCP requests. Understanding the role of ip helper-address in forwarding UDP broadcasts such as DHCP is critical for inter-VLAN DHCP operations and avoiding misconfigurations that block client IP assignment.

KKey Concepts to Remember

  • DHCP clients send broadcast messages that do not cross router boundaries without relay configuration.
  • The ip helper-address command on a Layer 3 interface forwards DHCP broadcasts to a specified remote DHCP server.
  • A switch virtual interface (SVI) for a VLAN acts as the default gateway and must have ip helper-address for DHCP relay.
  • The ip default-gateway command configures a management gateway on Layer 2 switches and does not relay DHCP requests.
  • Routing must be operational between VLANs for DHCP relay to function correctly across subnets.
  • Without ip helper-address, DHCP Discover messages from clients in remote VLANs will not reach the DHCP server.
  • The ip helper-address command forwards several UDP services, including DHCP, to the specified server IP address.
  • DHCP relay enables centralized DHCP servers to serve multiple VLANs or subnets without local DHCP servers.

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.

Related practice questions

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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 clients send broadcast messages that do not cross router boundaries without relay configuration.

What is the correct answer to this question?

The correct answer is: ip helper-address 10.99.99.10 — DHCP Discover messages are broadcasts and do not cross routers by default. An ip helper-address on the client gateway interface relays those requests to a remote DHCP server.

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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