Question 1mediummulti select
Full question →mediummulti selectObjective-mapped
Which two actions help protect access-layer switch ports from rogue DHCP servers?
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
Enable DHCP snooping globally and for the needed VLANs
That turns on the feature and applies it to selected VLANs.
B
Best answer
Trust the uplink toward the legitimate DHCP server path
The real DHCP responses must be allowed on trusted interfaces.
C
Distractor review
Enable PortFast on all trunks to block rogue servers
PortFast is not the control for rogue DHCP service.
D
Distractor review
Disable ARP on access ports
ARP is needed and unrelated to DHCP snooping in this way.
E
Distractor review
Set every access port as trusted
That would defeat the protection.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting options that trust every access port or enable unrelated features like PortFast to prevent rogue DHCP servers. Trusting all access ports disables DHCP snooping’s filtering, allowing rogue DHCP servers to operate on user-facing ports, which defeats the security purpose. PortFast only accelerates port forwarding states and does not filter DHCP messages, so it does not protect against rogue DHCP servers. Another trap is disabling ARP on access ports, which is unrelated to DHCP snooping and would break normal IP communication. Candidates must focus on enabling DHCP snooping correctly and trusting only uplink ports toward legitimate DHCP servers.
Technical deep dive
How to think about this question
DHCP snooping is a Layer 2 security feature implemented on Cisco switches to protect the network from rogue DHCP servers that can assign incorrect IP addresses to clients. It works by classifying switch ports as trusted or untrusted. Trusted ports are uplinks toward legitimate DHCP servers or DHCP relay agents, while untrusted ports are typically user-facing access ports. DHCP messages from untrusted ports that claim to be from a DHCP server are blocked, preventing unauthorized DHCP servers from distributing IP addresses. When DHCP snooping is enabled globally and on specific VLANs, the switch inspects DHCP traffic only on those VLANs, filtering DHCP server messages on untrusted ports. This selective application ensures that only authorized DHCP servers can respond to client requests. The trusted uplink ports allow legitimate DHCP server responses to pass through, maintaining proper IP address assignment. This setup also enables the switch to build a DHCP snooping binding table, which maps MAC addresses, IP addresses, VLANs, and lease times, helping prevent IP spoofing and other attacks. A common exam trap is to mistakenly trust all access ports or enable unrelated features like PortFast to block rogue DHCP servers. Trusting all access ports disables DHCP snooping’s filtering, allowing rogue DHCP servers to operate freely. PortFast only affects Spanning Tree Protocol port states and does not filter DHCP messages. Disabling ARP is unrelated and would disrupt normal network communication. Understanding the correct use of DHCP snooping and trusted ports is critical for securing access-layer switch ports against rogue DHCP servers in Cisco networks.
KKey Concepts to Remember
- DHCP snooping is a security feature that filters DHCP messages and prevents rogue DHCP servers by classifying switch ports as trusted or untrusted.
- Enabling DHCP snooping globally and on specific VLANs activates the filtering mechanism only where needed, protecting those VLANs from unauthorized DHCP servers.
- Trusted ports are typically uplinks toward legitimate DHCP servers or DHCP relay agents, allowing DHCP server messages to pass through without restriction.
- Untrusted ports are user-facing access-layer switch ports where DHCP server messages are blocked to prevent rogue DHCP server attacks.
- DHCP snooping builds and maintains a binding table that tracks legitimate DHCP clients and their assigned IP addresses to prevent IP address spoofing.
- Incorrectly trusting all access ports defeats DHCP snooping’s purpose by allowing rogue DHCP servers to operate on user-facing ports.
- PortFast does not affect DHCP snooping or DHCP server filtering; it is designed to speed up port transition to forwarding state and is unrelated to DHCP security.
- Disabling ARP on access ports is not a valid method to prevent rogue DHCP servers because ARP is essential for normal IP communication and unrelated to DHCP snooping.
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.
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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 snooping is a security feature that filters DHCP messages and prevents rogue DHCP servers by classifying switch ports as trusted or untrusted.
What is the correct answer to this question?
The correct answer is: Enable DHCP snooping globally and for the needed VLANs — DHCP snooping marks trusted and untrusted interfaces and filters server-type DHCP messages on untrusted ports. Uplink ports toward the real DHCP server or relay are typically trusted, while user-facing ports stay untrusted.
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.
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