350-401 Security Practice Question
A network engineer is implementing Control Plane Policing (CoPP) on a Cisco IOS XE router that runs BGP, SSH, and SNMP. The engineer wants to ensure that BGP keepalives are not dropped during a control plane overload, while still rate-limiting SSH and SNMP. The engineer creates a class-map matching BGP, SSH, and SNMP traffic, then applies a policy-map with a single policer of 1000 pps to that class. After applying the service-policy to the control plane, BGP sessions flap during high CPU utilization. What is the most likely cause?
⚠ Common exam trap
The trap here is assuming that a single policer can adequately protect all control plane protocols, when in fact BGP requires separate treatment to avoid keepalive drops during congestion.
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
✓
The policer rate is too low for BGP keepalives, and all matched traffic is treated equally.
CoPP requires granular classification to protect critical protocols. When BGP, SSH, and SNMP are matched in the same class and policed together, BGP keepalives compete with other traffic and may be dropped during high CPU. BGP should be placed in its own class with a higher rate or priority to prevent flapping. The single policer approach lacks the necessary differentiation.
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 cannot be applied to BGP traffic; it only supports management protocols like SSH and SNMP.
Why it's wrong here
CoPP can match and police any control plane traffic, including BGP. The limitation is not protocol support but the policy design. Claiming CoPP cannot handle BGP is incorrect and would lead the engineer away from the real issue of insufficient classification granularity.
- ✗
The service-policy must be applied to the data plane instead of the control plane for BGP to be protected.
Why it's wrong here
CoPP is specifically applied to the control plane to protect the route processor. Applying it to the data plane would not protect BGP keepalives, which are processed by the control plane. This option misunderstands the purpose and placement of CoPP.
- ✓
The policer rate is too low for BGP keepalives, and all matched traffic is treated equally.
Why this is correct
A single policer applied to a class that matches BGP, SSH, and SNMP treats all three protocols identically. During high CPU, BGP keepalives may exceed the 1000 pps rate along with other traffic, causing drops. BGP requires a separate class with a higher rate or priority to ensure keepalives are not dropped. The design flaw is the lack of granularity.
- ✗
The policer should be configured with 'police cir' instead of 'police pps' to properly rate-limit BGP.
Why it's wrong here
Both pps and cir-based policing can be used in CoPP. The issue is not the unit of measurement but the fact that all three protocols share one policer. Changing to cir would not separate BGP from SSH and SNMP, so BGP could still be dropped during congestion.
Go deeper
Related to this question
Learn chapter
SDN Controllers and Cisco ACI
Key term
Control Plane Policing
Control Plane Policing is a Cisco security feature that protects a router or switch by rate-limiting the traffic that the device's processor must handle, preventing it from being overwhelmed.
Key term
Control Plane Protection
Control Plane Protection (CoPP) is a security feature on Cisco routers and switches that filters traffic destined to the device's control plane to prevent attacks and ensure stability.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 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 350-401 exam.