The answer is that CoPP drops BGP update packets from specific clients due to rate limiting, so those prefixes are not learned. This occurs because the Control Plane Policing policy matches BGP traffic in a class-map and polices it to 500 pps, which can throttle incoming BGP updates from a route reflector client without affecting the session itself. Keepalive packets are smaller and less frequent, so they pass the policer, maintaining the BGP session state, but the larger update packets carrying new prefixes are dropped, leaving the route reflector’s table incomplete. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how CoPP interacts with BGP route reflector operations—a common trap is assuming a missing prefix implies a session reset, when in fact the session stays up because keepalives are not policed. Remember the memory tip: “Keepalives keep the session, but updates update the table—if updates are dropped, prefixes are stopped.”
300-410 Control Plane Policing (CoPP) Practice Question
This 300-410 practice question tests your understanding of control plane policing (copp). This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An engineer configures CoPP on a router that is a route reflector for iBGP. The policy includes a class-map matching BGP traffic and polices it to 500 pps. After deployment, some iBGP prefixes are missing from the route reflector's table, but the BGP sessions are up. Which is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
CoPP drops BGP update packets from specific clients due to rate limiting, so those prefixes are not learned.
Route reflectors propagate BGP updates. If CoPP drops incoming BGP updates from a client, the route reflector may not have those prefixes. The session stays up because keepalives are not dropped, but updates are lost.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 keepalive packets, causing the session to reset.
Why it's wrong here
Sessions are up, so keepalives are not dropped.
✓
CoPP drops BGP update packets from specific clients due to rate limiting, so those prefixes are not learned.
Why this is correct
Update packets are larger and more frequent; they may exceed the police rate.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The route reflector is configured to ignore certain prefixes.
Why it's wrong here
No such configuration is mentioned.
✗
CoPP only affects eBGP, not iBGP.
Why it's wrong here
CoPP matches on TCP port 179, which includes both eBGP and iBGP.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: CoPP drops BGP update packets from specific clients due to rate limiting, so those prefixes are not learned. — Route reflectors propagate BGP updates. If CoPP drops incoming BGP updates from a client, the route reflector may not have those prefixes. The session stays up because keepalives are not dropped, but updates are lost.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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