hardMultiple ChoiceObjective-mapped
300-410 Practice Question: A router has CoPP configured with a class-map…
A router has CoPP configured with a class-map that matches BGP traffic (TCP port 179) and polices it to 500 pps. The router has multiple iBGP peers. After applying the policy, some BGP sessions flap, but others remain stable. The flapping peers are those with higher latency. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that CoPP drops packets based on source IP or that BGP uses UDP for keepalives, leading candidates to overlook the impact of TCP retransmissions from high-latency peers on policer thresholds.
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
✓
High-latency peers generate more TCP retransmissions, which are more likely to be dropped by the police rate, causing session flaps.
B is correct because high-latency BGP peers experience more TCP retransmissions due to delayed acknowledgments. The CoPP policer drops packets exceeding 500 pps, and these retransmissions increase the packet rate for those sessions, making them more likely to exceed the policer and be dropped. Dropping BGP TCP segments (including keepalives) causes the BGP hold timer to expire, leading to session flaps.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
CoPP drops BGP packets based on source IP, and high-latency peers have different source IPs.
Why it's wrong here
CoPP matches on protocol, not source IP, unless specifically configured.
- ✓
High-latency peers generate more TCP retransmissions, which are more likely to be dropped by the police rate, causing session flaps.
Why this is correct
TCP retransmissions increase with latency, and CoPP may drop them, leading to BGP session failure.
- ✗
BGP uses UDP for keepalives, and CoPP only polices TCP.
Why it's wrong here
BGP uses TCP for all communications.
- ✗
The CoPP policy is applied to the wrong control plane; it should be applied to the forwarding plane.
Why it's wrong here
CoPP is applied to the control plane.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.