The answer is A because DAI is rejecting ARP traffic after the manual IP change, as the new IP does not match the trusted DHCP snooping binding database. DAI validates every ARP packet against the snooping table, which only records IP-to-MAC mappings learned from legitimate DHCP transactions; a static IP assignment creates an immediate mismatch, causing DAI to drop the ARP replies and breaking connectivity. On the CCNA 200-301 v2 exam, this question tests your understanding of how DHCP snooping and DAI work together as a security pair—snooping builds the trust anchor, and DAI enforces it. The common trap is blaming Spanning Tree or routing protocols, but remember that DAI operates at Layer 2 on access ports and has nothing to do with STP, OSPF, or PPP. Memory tip: “DAI demands DHCP—no DHCP, no ARP pass.”
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DAI is rejecting ARP traffic because the manual IP change does not match trusted snooping bindings.
The correct answer is A because DAI uses DHCP snooping binding to validate ARP messages; a manual IP change creates a mismatch, causing DAI to block ARP. Option B is incorrect because STP prevents loops and does not block based on MAC address changes. Option C is incorrect because OSPF authentication is a routing protocol feature irrelevant on an access port. Option D is incorrect because PPP authentication applies to serial links, not Ethernet ARP.
Key principle: Dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
DAI is rejecting ARP traffic because the manual IP change does not match trusted snooping bindings.
Why this is correct
This is correct because DAI validates ARP against trusted information, often sourced from DHCP snooping.
STP is blocking the host because its MAC address changed.
Why it's wrong here
This is wrong because STP does not block hosts for changing IP settings.
When this WOULD be correct
In a different scenario where a switch is configured with STP and a host changes its MAC address due to a hardware failure or network interface card (NIC) replacement, the question could state that STP is blocking the port due to a violation of MAC address consistency. This would make option B the correct answer.
✗
OSPF authentication failed on the access port.
Why it's wrong here
This is wrong because OSPF is not the issue in a host ARP validation scenario.
When this WOULD be correct
If the question were about a scenario where OSPF is configured on the switch and the access port requires OSPF authentication, a failure in the authentication process could prevent OSPF routes from being exchanged, leading to connectivity issues. In this case, the question would need to focus on OSPF settings and their impact on host connectivity.
✗
The switch requires PPP authentication before allowing ARP traffic.
Why it's wrong here
This is wrong because PPP authentication is unrelated to switched ARP inspection.
When this WOULD be correct
In a different scenario where a switch is configured to require PPP authentication for all traffic on access ports, a question might ask why ARP packets are being blocked. In that case, if a host attempts to send ARP traffic without completing PPP authentication, this option would be correct.
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.
✓DAI is rejecting ARP traffic because the manual IP change does not match trusted snooping bindings.Correct answer▾
Why this is correct
This is correct because DAI validates ARP against trusted information, often sourced from DHCP snooping.
✗STP is blocking the host because its MAC address changed.Wrong answer — click to see why▾
Why this is wrong here
STP (Spanning Tree Protocol) prevents loops in redundant topologies and does not block hosts based on IP or MAC address changes. It operates at Layer 2 and is unrelated to IP address configuration.
★ When this WOULD be the correct answer
In a different scenario where a switch is configured with STP and a host changes its MAC address due to a hardware failure or network interface card (NIC) replacement, the question could state that STP is blocking the port due to a violation of MAC address consistency. This would make option B the correct answer.
Why candidates choose this
Students may confuse STP's MAC address learning with IP address changes, thinking that a new IP triggers a topology change or port blocking, but STP only reacts to topology changes, not host IP modifications.
✗OSPF authentication failed on the access port.Wrong answer — click to see why▾
Why this is wrong here
OSPF is a Layer 3 routing protocol used between routers, not on access ports connecting hosts. OSPF authentication is configured on router interfaces and does not apply to host ARP traffic on a switch.
★ When this WOULD be the correct answer
If the question were about a scenario where OSPF is configured on the switch and the access port requires OSPF authentication, a failure in the authentication process could prevent OSPF routes from being exchanged, leading to connectivity issues. In this case, the question would need to focus on OSPF settings and their impact on host connectivity.
Why candidates choose this
Test-takers might associate authentication with security features and incorrectly assume OSPF authentication could be involved, but OSPF is not used for host connectivity validation.
✗The switch requires PPP authentication before allowing ARP traffic.Wrong answer — click to see why▾
Why this is wrong here
PPP (Point-to-Point Protocol) authentication is used on serial links or PPPoE connections, not on Ethernet switch ports. It is unrelated to ARP inspection or DHCP snooping in a switched network.
★ When this WOULD be the correct answer
In a different scenario where a switch is configured to require PPP authentication for all traffic on access ports, a question might ask why ARP packets are being blocked. In that case, if a host attempts to send ARP traffic without completing PPP authentication, this option would be correct.
Why candidates choose this
The term 'authentication' may lead students to think of any security mechanism, but PPP authentication is specific to WAN links and not applicable to LAN switching security features.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Be cautious not to confuse DHCP snooping's role with DHCP server functionality or ARP cache operations.
Trap categories for this question
Scenario analysis trap
This is wrong because OSPF is not the issue in a host ARP validation scenario.
Detailed technical explanation
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.
Key takeaway
Dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — 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 correct answer is A because DAI uses DHCP snooping binding to validate ARP messages; a manual IP change creates a mismatch, causing DAI to block ARP. Option B is incorrect because STP prevents loops and does not block based on MAC address changes. Option C is incorrect because OSPF authentication is a routing protocol feature irrelevant on an access port. Option D is incorrect because PPP authentication applies to serial links, not Ethernet ARP.
What should I do if I get this 200-301 question wrong?
Review dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Dynamic ARP Inspection (DAI) uses trusted IP-to-MAC bindings from DHCP snooping to validate ARP packets and prevent ARP spoofing attacks.
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