350-501 Networking Practice Question
A service provider is experiencing high CPU usage on a router running BGP. Which action should be taken first to mitigate the issue without disrupting traffic?
⚠ Common exam trap
Cisco often tests the misconception that route dampening is a first-line CPU mitigation tool, when in fact it is a stability mechanism for flapping routes and can itself be CPU-intensive; the correct first step is to filter unwanted routes at the point of entry.
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
✓
Apply inbound route filtering using prefix lists.
High CPU usage on a BGP-speaking router is often caused by processing a large number of BGP updates. Applying inbound route filtering using prefix lists (option C) reduces the number of routes the router must process and store, directly lowering CPU load without disrupting existing traffic flows. This is a non-disruptive, targeted mitigation that addresses the root cause of excessive route processing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable BGP on the router.
Why it's wrong here
Disabling BGP would disrupt all BGP traffic, causing an outage.
- ✗
Increase the BGP keepalive timer.
Why it's wrong here
Keepalive timer affects session keepalives, not the processing load of route updates.
- ✓
Apply inbound route filtering using prefix lists.
Why this is correct
Filtering unnecessary inbound routes reduces the number of prefixes the router must process, lowering CPU utilization.
- ✗
Implement BGP route dampening.
Why it's wrong here
Route dampening addresses flapping routes, not high CPU usage from many BGP prefixes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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