- A
Enable MPLS traffic engineering to reroute ICMP
Why wrong: MPLS TE is for traffic engineering, not control plane protection.
- B
Use BGP prefix filtering to block ICMP routes
Why wrong: BGP prefix filtering is for routing updates, not for ICMP traffic.
- C
Implement CoPP by creating a class-map for ICMP and applying a police rate under a control-plane policy-map
CoPP allows granular classification and rate-limiting of control plane traffic.
- D
Configure an ACL to deny ICMP on all interfaces
Why wrong: This would block all ICMP, which is too restrictive and not a recommended practice.
Question 787 of 1,000
350-501 Security and Services Practice Question
This 350-501 practice question tests your understanding of security and services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 protect its core routers from CPU exhaustion caused by excessive ICMP traffic. Which control plane protection mechanism on IOS XR would be most appropriate to rate-limit ICMP packets destined to the router?
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
✓
Implement CoPP by creating a class-map for ICMP and applying a police rate under a control-plane policy-map
CoPP (Control Plane Policing) on IOS XR uses class maps and policy maps to classify and rate-limit control plane traffic, including ICMP. ACL-based policing is less granular, and MPLS TE or BGP prefix filtering do not apply.
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.
- ✗
Enable MPLS traffic engineering to reroute ICMP
Why it's wrong here
MPLS TE is for traffic engineering, not control plane protection.
- ✗
Use BGP prefix filtering to block ICMP routes
- ✓
Implement CoPP by creating a class-map for ICMP and applying a police rate under a control-plane policy-map
Why this is correct
CoPP allows granular classification and rate-limiting of control plane traffic.
Related concept
Standard ACLs match source addresses.
- ✗
Configure an ACL to deny ICMP on all interfaces
Why it's wrong here
This would block all ICMP, which is too restrictive and not a recommended practice.
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: Implement CoPP by creating a class-map for ICMP and applying a police rate under a control-plane policy-map — CoPP (Control Plane Policing) on IOS XR uses class maps and policy maps to classify and rate-limit control plane traffic, including ICMP. ACL-based policing is less granular, and MPLS TE or BGP prefix filtering do not apply.
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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