300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. 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.
CoPP is rate-limiting legitimate routing traffic. Router R1 has: class-map match-any ROUTING, match protocol bgp, match protocol ospf, policy-map COPP, class ROUTING, police 10000 conform-action transmit exceed-action drop. BGP sessions flap. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The police rate is too low, causing drops of BGP packets.
B is correct because the police rate of 10,000 bps (10 kbps) is too low for BGP traffic. BGP uses TCP port 179 and can generate bursts of packets during keepalive and update exchanges; if the policer drops BGP packets, the TCP session times out and flaps. The class-map correctly matches both BGP and OSPF, but the rate limit is insufficient for the combined control-plane traffic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The class-map should match only BGP, not OSPF.
Why it's wrong here
Both are routing protocols; the issue is the rate limit.
✓
The police rate is too low, causing drops of BGP packets.
Why this is correct
10 kbps is insufficient for BGP keepalives and updates, leading to flaps.
Related concept
Read the scenario before looking for a memorised answer.
✗
CoPP should be applied to the control plane, not the data plane.
Why it's wrong here
CoPP is applied to control plane; the configuration is correct.
✗
BGP sessions flap due to MTU mismatch, not CoPP.
Why it's wrong here
MTU issues cause different symptoms; CoPP directly drops packets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that CoPP class-map matching must be exclusive, when in fact the root cause is an overly restrictive police rate that drops essential control-plane packets like BGP keepalives.
Detailed technical explanation
How to think about this question
BGP uses TCP with a default keepalive timer of 60 seconds and hold timer of 180 seconds; if the policer drops even a few keepalive packets, the hold timer expires and the session resets. CoPP polices traffic before it reaches the route processor, so a rate of 10 kbps may be insufficient for a single BGP session that can burst to several kbps during updates, especially with multiple peers. In real-world deployments, Cisco recommends at least 200 kbps for BGP keepalives and updates, and the police rate should be based on measured control-plane traffic.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The police rate is too low, causing drops of BGP packets. — B is correct because the police rate of 10,000 bps (10 kbps) is too low for BGP traffic. BGP uses TCP port 179 and can generate bursts of packets during keepalive and update exchanges; if the policer drops BGP packets, the TCP session times out and flaps. The class-map correctly matches both BGP and OSPF, but the rate limit is insufficient for the combined control-plane traffic.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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