interface g0/1 ip address 172.16.1.1 255.255.255.0 ip helper-address 10.20.20.10
A router is configured as follows:
interface g0/1 ip address 172.16.1.1 255.255.255.0 ip helper-address 10.20.20.10
Hosts on 172.16.1.0/24 are not receiving addresses from the DHCP server at 10.20.20.10. The server is reachable by ping from the router.
What is the purpose of the ip helper-address command in this scenario?
Answer choices
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
It converts DHCP unicast replies into broadcasts on the client segment
The key problem is not taking DHCP replies and turning them into broadcasts. The real challenge is that the client starts with a broadcast that cannot cross the router by default. The helper-address command solves that by relaying the request toward the server. So this option focuses on the wrong direction of the process.
It forwards certain UDP broadcasts, including DHCP requests, to a remote server
Correct. This is correct. The command relays certain UDP broadcasts, including DHCP client requests, to a server on another subnet. That is why DHCP can work even when the server is not local to the client VLAN.
It provides DNS resolution for DHCP clients before they receive an address
DNS resolution is a different service entirely. A DHCP client does not need the router to resolve hostnames before it can request an IP address. In many cases DHCP later tells the client which DNS server to use, but that is separate from the helper-address relay function.
It creates a static route to the DHCP server
The command does not create a static route. Basic IP reachability may already exist, as the question states by mentioning successful pings. The missing function is broadcast relay for DHCP-related traffic, not path creation in the routing table.
Common exam trap
A frequent exam trap is confusing the ip helper-address command as a feature that converts DHCP unicast replies into broadcasts on the client segment. In reality, the router forwards DHCP client broadcasts as unicast to the server, not the other way around. Another mistake is assuming the command creates static routes or provides DNS resolution, which it does not. Misunderstanding these functions leads to incorrect troubleshooting and answer choices, especially when the DHCP server is reachable by ping but clients still fail to get addresses due to missing broadcast relay.
Technical deep dive
The ip helper-address command is a critical feature in Cisco routers that enables the forwarding of certain UDP broadcasts, including DHCP requests, from one subnet to a DHCP server located on a different subnet. Normally, routers do not forward broadcast traffic between interfaces to prevent broadcast storms and maintain network segmentation. However, DHCP clients initially send broadcast messages to discover available DHCP servers because they lack an IP address and cannot communicate via unicast. When a router interface is configured with the ip helper-address command, it listens for specific UDP broadcasts such as DHCP (ports 67 and 68), TFTP, DNS, and others. Upon receiving these broadcasts, the router converts them into unicast packets and forwards them to the specified helper address, which is typically the IP address of a DHCP server on a remote subnet. This relay mechanism allows DHCP clients to obtain IP addresses even when the DHCP server is not on the same local network segment. A common exam trap is misunderstanding the direction and purpose of the ip helper-address command. It does not convert DHCP replies into broadcasts; instead, it relays client broadcast requests as unicast to the server. Additionally, it is not a routing command or a DNS feature. Practically, this command is essential in multi-VLAN environments where DHCP servers reside centrally, enabling seamless IP address assignment across VLAN boundaries without requiring DHCP servers on every subnet.
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practise DHCP scopes, relay, leases and troubleshooting.
Practise routing-table output, longest-prefix match, AD and route selection.
Practise trunk verification and VLAN forwarding across switches.
Practise WLAN security, authentication and wireless architecture concepts.
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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FAQ
The ip helper-address command enables a router to forward specific UDP broadcasts, including DHCP requests, from clients to a remote server on a different subnet.
The correct answer is: It forwards certain UDP broadcasts, including DHCP requests, to a remote server — The ip helper-address command exists to solve a broadcast-boundary problem. DHCP clients begin by sending broadcast traffic because they do not yet have a valid IP configuration. Routers normally do not forward broadcasts between subnets, so if the DHCP server lives on a different network, the client request would stop at the router. The helper-address function listens for that local broadcast and relays it as unicast traffic to the remote DHCP server. In plain language, it lets a client on one VLAN ask a DHCP server on another VLAN for an address. The command is not a routing statement and it is not a DNS feature. It is a relay mechanism for broadcast-based UDP services such as DHCP.
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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