The answer is to apply a prefix-limit on each BGP session to restrict the number of prefixes received. This immediately reduces high CPU due to BGP prefix processing because the Routing Protocol Daemon (rpd) no longer has to handle an overwhelming flood of incoming routes; by capping the prefix count per peer, you stop the router from accepting more updates than it can safely process, which directly lowers CPU load while preserving existing sessions and network stability. On the JNCIA-Junos exam, this scenario tests your understanding of BGP route management and the `prefix-limit` configuration under `protocols bgp group` or `neighbor`—a common trap is to mistakenly reset sessions or filter routes after they are learned, which disrupts stability. Remember the memory tip: “Limit the load, keep the code” — set a prefix-limit to cap the route count and avoid rpd meltdown.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
A network administrator notices that the CPU utilization on an MX240 router has been consistently above 90% for the past hour. Users are reporting intermittent connectivity issues. The administrator logs in and runs 'show system processes extensive' which shows the Routing Protocol Daemon (rpd) consuming 70% of the CPU. Further investigation reveals that the router has over 5000 BGP prefixes from multiple peers. The administrator suspects that the high CPU is due to continuous route processing. What should the administrator do to immediately reduce CPU load while maintaining network stability?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply a prefix-limit on each BGP session to restrict the number of prefixes received
Applying a prefix-limit on each BGP session immediately restricts the number of prefixes the router will accept from peers. This prevents the Routing Protocol Daemon (rpd) from processing excessive BGP updates, reducing CPU load while maintaining network stability by keeping existing sessions and routes intact. The prefix-limit action (e.g., with a teardown threshold) ensures the router does not accept more prefixes than it can handle, directly addressing the root cause of high CPU usage.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Perform a 'show log messages' to check for errors before taking action
Why it's wrong here
This is diagnostic but does not immediately reduce CPU load.
✓
Apply a prefix-limit on each BGP session to restrict the number of prefixes received
Why this is correct
Prefix limits reduce the number of routes rpd must process, directly lowering CPU usage.
Clue confirmation
The clue word "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Bounce all BGP sessions by clearing them with 'clear bgp neighbor *'
Why it's wrong here
Clearing all BGP sessions causes network disruption and may temporarily increase CPU due to re-establishment.
✗
Disable BGP multipath to reduce route processing
Why it's wrong here
Multipath helps load-balance; disabling it may reduce processing slightly but not significantly, and could affect traffic distribution.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse diagnostic actions (like checking logs) or disruptive resets (like clearing all BGP sessions) with immediate corrective measures, overlooking the targeted, non-disruptive solution of applying prefix limits to control route processing load.
Detailed technical explanation
How to think about this question
BGP prefix limits are configured under the 'family inet' or 'family inet6' hierarchy using the 'prefix-limit' statement, which allows setting a maximum number of prefixes and an optional teardown threshold (e.g., 'maximum 5000 teardown 95'). When the limit is exceeded, the session is automatically torn down, preventing the router from processing further updates. In real-world scenarios, ISPs often use prefix limits to protect against route leaks or misconfigurations that could overwhelm the control plane, and the 'idle-timeout' option can be set to automatically re-establish the session after a specified period.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply a prefix-limit on each BGP session to restrict the number of prefixes received — Applying a prefix-limit on each BGP session immediately restricts the number of prefixes the router will accept from peers. This prevents the Routing Protocol Daemon (rpd) from processing excessive BGP updates, reducing CPU load while maintaining network stability by keeping existing sessions and routes intact. The prefix-limit action (e.g., with a teardown threshold) ensures the router does not accept more prefixes than it can handle, directly addressing the root cause of high CPU usage.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "immediately / without restart". Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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