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300-410 Practice Question: Examine the following DHCP configuration on…

Examine the following DHCP configuration on router R1:

ip dhcp excluded-address 192.168.1.1 192.168.1.10

!

ip dhcp pool POOL1
 network 192.168.1.0 255.255.255.0

default-router 192.168.1.1 dns-server 8.8.8.8 lease 0 2 30 !

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 ip helper-address 192.168.2.2
 no shutdown

What is the effect of this configuration?

⚠ Common exam trap

Cisco often tests the misconception that a router acting as a DHCP server on an interface will automatically suppress the ip helper-address relay function, but in reality, both processes operate independently, leading to duplicate offers.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

Clients on the 192.168.1.0/24 subnet will receive IP addresses from the local DHCP pool, and the ip helper-address will forward DHCP requests to 192.168.2.2, causing duplicate offers.

The router R1 is configured as a DHCP server for the 192.168.1.0/24 subnet via the local pool POOL1, and the ip helper-address 192.168.2.2 on the same interface will forward broadcast DHCP requests from clients to the remote DHCP server at 192.168.2.2. This results in both the local pool and the remote server offering IP addresses, leading to duplicate offers on the subnet.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Clients on the 192.168.1.0/24 subnet will receive IP addresses from the local DHCP pool, and the ip helper-address will forward DHCP requests to 192.168.2.2, causing duplicate offers.

    Why this is correct

    The local DHCP server will respond to requests, but the helper address will also forward broadcasts to the remote server, leading to duplicate DHCP offers and potential address conflicts.

  • The ip helper-address command will be ignored because the router is the DHCP server for that subnet.

    Why it's wrong here

    The ip helper-address is not ignored; it still forwards broadcasts to the specified server, as the router does not automatically disable it when acting as a DHCP server.

  • The excluded-address range is misconfigured because it includes the router's own interface IP, which will prevent the router from functioning.

    Why it's wrong here

    Excluding the router's own IP is a best practice to avoid conflicts; the router will still function normally.

  • The DHCP pool will not assign addresses because the network statement does not match the interface subnet exactly.

    Why it's wrong here

    The network 192.168.1.0 255.255.255.0 matches the interface subnet exactly, so it is valid.

Visual reference

Client DHCP Server 1 Discover (broadcast) 2 Offer (IP: 192.168.1.10) 3 Request (I accept) 4 Acknowledge (lease confirmed) DORA — the four-step DHCP lease process

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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