Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A switch is configured with DHCP snooping and Dynamic ARP Inspection. Hosts suddenly lose connectivity after changing IP settings manually. Which explanation is strongest?
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
Best answer
DAI is rejecting ARP traffic because the manual IP change does not match trusted snooping bindings.
This is correct because DAI validates ARP against trusted information, often sourced from DHCP snooping.
B
Distractor review
STP is blocking the host because its MAC address changed.
This is wrong because STP does not block hosts for changing IP settings.
C
Distractor review
OSPF authentication failed on the access port.
This is wrong because OSPF is not the issue in a host ARP validation scenario.
D
Distractor review
The switch requires PPP authentication before allowing ARP traffic.
This is wrong because PPP authentication is unrelated to switched ARP inspection.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting STP or OSPF-related options as the cause of connectivity loss after manual IP changes. Candidates might incorrectly believe STP blocks hosts for IP changes or that OSPF authentication affects ARP traffic. However, STP only blocks ports based on Layer 2 topology loops, not IP changes, and OSPF authentication operates at Layer 3 routing, unrelated to ARP validation. The real cause is DAI rejecting ARP packets because the manual IP does not match the trusted DHCP snooping bindings, which is a Layer 2 security mechanism.
Technical deep dive
How to think about this question
Dynamic ARP Inspection (DAI) is a security feature that validates ARP packets on a network to prevent ARP spoofing attacks. It relies on trusted IP-to-MAC address bindings, which are typically learned from DHCP snooping. DHCP snooping builds a binding table by monitoring DHCP transactions and recording the allocated IP addresses and corresponding MAC addresses. This binding table is then used by DAI to verify that ARP requests and replies match the expected IP-MAC pairs. When a host manually changes its IP address without going through DHCP, the new IP-to-MAC mapping is not present in the DHCP snooping binding table. As a result, DAI considers ARP packets from this host as invalid or suspicious and blocks them to protect the network from potential ARP spoofing. This interaction between DHCP snooping and DAI enforces strict validation, ensuring only legitimate ARP traffic is forwarded. A common exam trap is to assume that other protocols or features like STP or OSPF authentication are responsible for connectivity loss after manual IP changes. However, STP does not block hosts based on IP changes, and OSPF authentication is unrelated to ARP validation on access ports. Understanding the dependency of DAI on DHCP snooping bindings is crucial for correctly diagnosing connectivity issues in this scenario.
KKey Concepts to Remember
- Dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.
- DHCP snooping builds a binding table by monitoring DHCP transactions and recording IP and MAC address pairs for security validation.
- DAI blocks ARP packets that do not match the trusted DHCP snooping binding table, causing connectivity loss if IP addresses are manually changed.
- Spanning Tree Protocol (STP) does not block hosts based on IP address changes; it only prevents Layer 2 loops by blocking redundant links.
- OSPF authentication is unrelated to ARP validation and does not affect host connectivity at the access switch port level.
- Manual IP configuration bypasses DHCP snooping, leading to missing or outdated bindings that cause DAI to reject ARP traffic.
- DAI and DHCP snooping work together as complementary security features to enforce trusted Layer 2 address mappings on Cisco switches.
- Understanding the interaction between DHCP snooping and DAI is essential for diagnosing connectivity issues caused by manual IP address changes.
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?
Dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.
What is the correct answer to this question?
The correct answer is: DAI is rejecting ARP traffic because the manual IP change does not match trusted snooping bindings. — The strongest explanation is that the manually configured IP information no longer matches trusted DHCP snooping binding data, so DAI rejects the ARP traffic. In practical terms, DAI uses trusted information to validate ARP behavior. If a host starts claiming an IP-to-MAC mapping that does not match the expected binding, the switch treats that as suspicious and blocks it. This is a good example of security features interacting. DHCP snooping provides the trusted binding information, and DAI uses it to validate ARP messages.
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.