CCNA Network Services and Security Practice Question

Answer analysis

Option-by-option breakdown

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

• ✗

  ip dhcp excluded-address 10.40.40.1 10.40.40.10

  Why it's wrong here

  The ip dhcp excluded-address command is a server-side configuration used by the DHCP server to reserve a pool of addresses (10.40.40.1 to 10.40.40.10) so those IPs are never leased to clients. It does not relay or forward DHCP broadcasts across subnets, nor does it enable a client to discover a server. Even if it were present, it would not solve the problem of clients not receiving addresses; it would only restrict which addresses could be handed out.

  When this WOULD be correct

  In a different scenario where the question involves configuring DHCP settings for a specific range of IP addresses on a DHCP server, such as preventing certain addresses from being assigned to clients, this option would be correct. For example, if the question asked how to prevent the DHCP server from assigning addresses within a specific range to avoid conflicts, this would apply.

• ✓

  ip helper-address 172.16.1.10

  Why this is correct

  The ip helper-address command must be applied to the VLAN 40 SVI (interface vlan 40). DHCP clients broadcast DHCPDISCOVER packets, and routers do not forward broadcasts by default; this command converts those broadcasts into unicasts and relays them to the DHCP server at 172.16.1.10. The server then replies with an address appropriate for VLAN 40's subnet, which is why this is the correct fix.

• ✗

  service dhcp

  Why it's wrong here

  The service dhcp command globally enables the DHCP server and relay agent processes on the device. While it is required for the relay agent to function, it is typically enabled by default, and merely having it enabled does not cause any forwarding of DHCP broadcasts. Without the ip helper-address on the VLAN 40 interface, the relay agent has no destination to forward the client's DHCPDISCOVER to, so the clients remain without addresses.

  When this WOULD be correct

  If the question were about configuring a router to act as a DHCP server for VLAN 40, then 'service dhcp' would be the correct answer. This would imply that the router is intended to provide IP addresses directly to clients in that VLAN.

• ✗

  ip default-gateway 172.16.1.10

  Why it's wrong here

  The ip default-gateway command is a global command used on a Layer 2 switch to give the management interface a gateway when IP routing is disabled. It does not affect DHCP operations on the VLAN 40 SVI or allow broadcasts to reach a remote DHCP server. Hosts in VLAN 40 would still be unable to get an address because this command only impacts the switch's own management traffic, not the client traffic.

  When this WOULD be correct

  In a different scenario where a question asks for the configuration of a standalone device, such as a router or switch that is not acting as a DHCP relay, specifying 'ip default-gateway 172.16.1.10' would be correct to ensure that the device can route packets to the DHCP server for itself.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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