hardMultiple Choice
CoPP BGP Police Rate Too Low
A network engineer notices that BGP sessions between two directly connected routers are flapping every few minutes. The routers are running IOS-XE 17.3 and have CoPP enabled. The engineer checks the CoPP policy and sees a class-map matching BGP packets with a police rate of 8000 bps. The BGP session uses MD5 authentication and the routers exchange a full BGP table with 500,000 prefixes. What is the most likely cause of the BGP session flapping?
⚠ Common exam trap
Cisco often tests the misconception that MD5 authentication causes CPU spikes leading to CoPP drops, but the real issue is that CoPP police rates must be sized to accommodate the actual BGP traffic volume, especially during full table exchanges.
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 CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops.
The CoPP police rate of 8000 bps is insufficient for the BGP traffic generated by exchanging a full BGP table of 500,000 prefixes. BGP updates for such a large table can easily exceed 8000 bps, especially when combined with keepalive messages. When the police rate is exceeded, CoPP drops BGP packets, causing the session to flap as the hold timer expires due to missing keepalives or updates.
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 BGP MD5 authentication is causing excessive CPU utilization, triggering CoPP drops.
Why it's wrong here
MD5 authentication adds trivial per-packet hashing overhead and does not saturate CPU on IOS-XE at BGP control-plane rates. Blaming authentication is tempting when sessions flap, but the policer's 8000 bps ceiling is the actual bottleneck: it discards the UPDATE and keepalive traffic needed to sustain the full-table session.
- ✓
The CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops.
Why this is correct
Policing at 8000 bps drops BGP keepalives and update packets once the full 500,000-prefix table and MD5-authenticated exchanges exceed that rate, causing hold-timer expiry and repeated session resets. Raising or exempting the BGP class restores stability.
- ✗
The CoPP class-map is not matching BGP packets correctly because it uses a wrong access-list.
Why it's wrong here
A mismatched access-list would drop all BGP packets consistently, preventing the session from ever establishing rather than flapping every few minutes. The stem states the class-map matches BGP packets, so matching is functioning; the 8000 bps police rate is simply too low for 500,000-prefix updates.
- ✗
The BGP hold timer is set too low, causing the session to reset before CoPP drops are noticed.
Why it's wrong here
Hold timers default to 180 seconds and are unrelated to CoPP policing; drops occur at the control-plane policer, not from timer expiry. Tuning timers is tempting when sessions reset, but the 8000 bps police rate cannot carry 500,000-prefix updates plus keepalives, so BGP packets are dropped and the session tears down.
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JA
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.