- A
uRPF
Why wrong: uRPF prevents spoofing but not dynamic filtering.
- B
S/RTBH
Why wrong: S/RTBH only blackholes traffic to a destination IP, not filtering rules.
- C
BGP FlowSpec
FlowSpec distributes fine-grained filtering rules via BGP.
- D
ACLs
Why wrong: ACLs are static and not distributed via BGP.
Question 168 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 network operator wants to distribute traffic filtering rules to multiple routers dynamically during a DDoS attack. Which technology 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
✓
BGP FlowSpec
BGP FlowSpec (RFC 8955) allows encoding of flow specifications (e.g., source/dest IP, ports, protocol) and distributing them via BGP to routers, which then apply traffic filtering actions (e.g., drop, rate-limit) dynamically.
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.
- ✗
uRPF
Why it's wrong here
uRPF prevents spoofing but not dynamic filtering.
- ✗
S/RTBH
Why it's wrong here
S/RTBH only blackholes traffic to a destination IP, not filtering rules.
- ✓
BGP FlowSpec
Why this is correct
FlowSpec distributes fine-grained filtering rules via BGP.
Related concept
Standard ACLs match source addresses.
- ✗
ACLs
Why it's wrong here
ACLs are static and not distributed via BGP.
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.
Visual reference
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: BGP FlowSpec — BGP FlowSpec (RFC 8955) allows encoding of flow specifications (e.g., source/dest IP, ports, protocol) and distributing them via BGP to routers, which then apply traffic filtering actions (e.g., drop, rate-limit) dynamically.
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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