DHCP Relay on Router Interface for Branch Hosts

300-410 By islever Editorial Last updated

Troubleshoot IPv4 and IPv6 DHCP (DHCP client, IOS DHCP server, DHCP relay, DHCP options)

Short answer

D Configure the ip helper command on the interface GigabitEthernet 0/2 of the R2 router.

Question

Refer to the exhibit. Branch 2 hosts cannot receive dynamic IP addresses. Which action resolves the issue? - Exhibit: DHCP Relay on Router Interface for Branch Hosts - Exhibit: DHCP Relay on Router Interface for Branch Hosts - Exhibit: DHCP Relay on Router Interface for Branch Hosts
  1. Configure the ip helper command on the Layer 2 switch SW2 interfaces.
  2. Configure the ip helper command on the Interface GigabltEthernet 0/0 of the DHCP router.
  3. Configure the ip helper command on the Interface GigabltEthernet 0/2 of the DHCP router.
  4. Configure the ip helper command on the interface GigabltEthernet 0/2 of the R2 router. Correct Answer

Key Takeaways

The core trap is identifying which router interface faces the client subnet versus the server subnet; applying the helper address on the wrong interface fails to forward DHCP broadcasts.

This question tests the configuration of DHCP relay (ip helper-address) to enable dynamic IP assignment across subnets. It establishes that the command must be applied to the router interface receiving the broadcast requests.

Common mistake: Learners often select Option A, incorrectly assuming a Layer 2 switch handles DHCP relaying, or choose B/C by misidentifying the interface connected to the client VLAN.

Expert Analysis

Why the Answer Is Correct

The correct action is to configure the ip helper command on the Interface GigabitEthernet 0/2 of the R2 router (Option D). DHCP requests are broadcast packets that do not cross routers by default. The router interface connecting to the branch network (where the clients reside) must have the 'ip helper-address' configured to convert these broadcasts into unicast messages directed at the DHCP server.

Why the Other Options Are Wrong

Option A is incorrect because Layer 2 switches generally do not perform DHCP relay functions natively without specific L3 features or proxy configurations, and the topology implies an L3 boundary. Options B and C suggest configuring the command on the DHCP router itself, which is illogical since the DHCP server receives unicast requests directly from the relay agent; it does not need to forward them anywhere.

Community Comment Notes

The community consensus strongly supports Option D. As one user noted, "D is correct The command is given on the wrong interface" in other scenarios, emphasizing the criticality of interface selection. Another commenter confirmed, "because the G0/2 recieve the DHCP quiries," highlighting that this is the ingress interface for the client traffic.

Exam Strategy

Always identify the router interface that is part of the same subnet as the DHCP clients. This is the only interface that needs the ip helper-address command to forward broadcasts to the remote DHCP server.

Frequently Asked Questions

Why can't we use a Layer 2 switch for DHCP relay?

Standard Layer 2 switches do not route broadcasts. While some managed switches support DHCP relay, the exam scenario typically relies on the router interface for this function.

Does the DHCP server need an ip helper command?

No. The DHCP server listens for incoming unicast requests. The relay agent (router) is responsible for forwarding the initial broadcast request to the server.

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Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. [Removed] 👍 2 Answered D
    D is correct The command is given on the wrong interface.
  2. aa4a63c 👍 1 Answered D
    D because the G0/2 recieve the DHCP quiries
  3. Br2 👍 2 Answered D
    D is correct

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