Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A DHCP server is located on a different VLAN from the clients. Which feature is required so the clients can still receive addresses?
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
DHCP snooping
DHCP snooping is a security feature, not the relay mechanism.
B
Best answer
DHCP relay
Correct. DHCP relay enables cross-VLAN DHCP service.
C
Distractor review
Port security
Port security is unrelated to relaying DHCP requests.
D
Distractor review
NAT overload
NAT overload does not solve this broadcast-forwarding issue.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting DHCP snooping as the solution for clients on different VLANs to receive DHCP addresses. DHCP snooping is a security mechanism that filters DHCP messages to prevent rogue servers but does not forward DHCP broadcasts across VLANs. Another tempting but incorrect choice is port security, which controls MAC address access on switch ports but does not affect DHCP broadcast forwarding. NAT overload is unrelated to DHCP address assignment and only translates IP addresses for outbound traffic. The key misunderstanding is confusing DHCP relay’s role in forwarding broadcasts with security or address translation features.
Technical deep dive
How to think about this question
DHCP relay is a critical feature in networks where DHCP clients and servers reside on different VLANs or subnets. Normally, DHCP clients broadcast requests to find a DHCP server, but broadcasts do not cross router interfaces by default. DHCP relay agents, typically configured on Layer 3 interfaces, intercept these broadcasts and forward them as unicast packets to the DHCP server's IP address. This mechanism ensures that clients on separate VLANs can still obtain IP addresses and configuration parameters from a centralized DHCP server. In Cisco networks, the DHCP relay function is implemented using the 'ip helper-address' command on the router or Layer 3 switch interface connected to the client VLAN. This command specifies the DHCP server's IP address to which the relay agent forwards DHCP requests. The relay agent listens for DHCP broadcast messages, encapsulates them into unicast packets, and sends them to the server. When the server replies, the relay agent forwards the response back to the client VLAN, enabling seamless IP address assignment across VLAN boundaries. A common exam trap involves confusing DHCP relay with DHCP snooping or other security features. DHCP snooping is designed to prevent rogue DHCP servers and does not facilitate cross-VLAN DHCP communication. Similarly, port security and NAT overload do not address the broadcast forwarding issue inherent in DHCP requests across VLANs. Understanding the specific role of DHCP relay in forwarding DHCP broadcasts as unicasts to remote servers is essential for correctly answering related CCNA questions and for practical network design.
KKey Concepts to Remember
- DHCP relay forwards DHCP client broadcast requests as unicast packets to a DHCP server located on a different VLAN or subnet.
- The 'ip helper-address' command on a Layer 3 interface configures DHCP relay by specifying the DHCP server's IP address.
- Routers and Layer 3 switches do not forward broadcast packets between VLANs by default, requiring DHCP relay for cross-VLAN DHCP service.
- DHCP snooping is a security feature that prevents unauthorized DHCP servers and does not enable DHCP requests to cross VLAN boundaries.
- Port security restricts MAC addresses on switch ports and does not influence DHCP request forwarding or relay.
- NAT overload translates multiple private IP addresses to a single public IP and does not facilitate DHCP broadcast forwarding.
- DHCP relay agents listen for client broadcasts and convert them into unicasts directed at the DHCP server to enable IP address assignment across VLANs.
- Without DHCP relay, clients on VLANs separate from the DHCP server cannot receive IP addresses because broadcasts are not routed.
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
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
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 relay forwards DHCP client broadcast requests as unicast packets to a DHCP server located on a different VLAN or subnet.
What is the correct answer to this question?
The correct answer is: DHCP relay — DHCP relay forwards client broadcasts to a remote server as unicast, typically using ip helper-address on the Layer 3 interface.
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.
Discussion
Loading comments…
Sign in to join the discussion.