- A
Strict mode
Strict mode verifies source IP reachability via the same interface.
- B
ACL-based filtering
Why wrong: ACLs are static and not as dynamic as uRPF.
- C
Reverse path filtering disabled
Why wrong: Disabling allows spoofing.
- D
Loose mode
Why wrong: Loose mode only checks if source IP exists in FIB, not the interface.
Question 720 of 1,000
350-501 Security and Services Practice Question
This 350-501 practice question tests your understanding of security and services. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 service provider wants to prevent IP spoofing at the customer edge by verifying that the source IP address of incoming packets is reachable via the interface they arrive on. Which uRPF mode should be used?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Strict mode
Strict mode checks that the source IP is in the FIB and that the best return route is through the same interface. Loose mode only checks that the source IP is in the FIB. Strict mode is used at customer edges where traffic should come from a specific interface.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Strict mode
Why this is correct
Strict mode verifies source IP reachability via the same interface.
Related concept
Standard ACLs match source addresses.
- ✗
ACL-based filtering
Why it's wrong here
ACLs are static and not as dynamic as uRPF.
- ✗
Reverse path filtering disabled
Why it's wrong here
Disabling allows spoofing.
- ✗
Loose mode
Why it's wrong here
Loose mode only checks if source IP exists in FIB, not the interface.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-501 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 350-501 question test?
Security and Services — This question tests Security and Services — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Strict mode — Strict mode checks that the source IP is in the FIB and that the best return route is through the same interface. Loose mode only checks that the source IP is in the FIB. Strict mode is used at customer edges where traffic should come from a specific interface.
What should I do if I get this 350-501 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-501 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jul 4, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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