The correct answer is to use the 'show route summary' command to check the routing table size and memory usage. This command is the most efficient way to troubleshoot high memory routing table issues on a Juniper MX router because it provides a concise, non-disruptive snapshot of total route counts and the memory consumed by the routing table, allowing you to quickly confirm if the rpd process is under memory pressure from an overloaded BGP peer. On the JNCIA-Junos exam, this scenario tests your ability to apply operational monitoring commands for performance diagnosis without impacting production traffic—a key skill for service provider engineers. A common trap is jumping to more intrusive commands like 'show route extensive' or restarting the rpd process, which can worsen the problem. Remember the memory tip: "Summary first, surgery last"—always start with the high-level view to isolate the root cause before diving deeper.
JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
You are a network engineer at a service provider. You have a Juniper MX router that serves as a BGP route reflector for a large number of customer routes. Recently, the router has been experiencing high CPU utilization, and the BGP process (rpd) is consuming excessive memory. You suspect that the router is receiving too many routes from a specific BGP peer, causing the routing table to grow beyond the available memory. You need to diagnose the issue without affecting production traffic. Which course of action should you take?
Immediately shut down all BGP peers to stop the influx of routes.
Why wrong: Shutting down all peers is too disruptive and will affect production traffic.
B
Configure a prefix limit on all BGP peers.
Why wrong: This is a preventive measure, not a diagnostic step.
C
Use the 'show route summary' command to check the routing table size and memory usage.
This command provides a high-level view of route counts and memory usage, helping to identify if the routing table is oversized.
D
Use the 'show bgp summary' command to check the number of prefixes per peer.
Why wrong: While this shows prefix counts, it does not show memory usage directly; the summary command is more appropriate for diagnosing memory issues.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the 'show route summary' command to check the routing table size and memory usage.
Option C is correct because the 'show route summary' command provides a high-level overview of the routing table size, including the total number of routes and the memory utilization of the routing table. This allows the engineer to quickly assess whether the routing table has grown beyond available memory without disrupting production traffic, which is the primary goal of the diagnosis.
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.
✗
Immediately shut down all BGP peers to stop the influx of routes.
Why it's wrong here
Shutting down all peers is too disruptive and will affect production traffic.
✗
Configure a prefix limit on all BGP peers.
Why it's wrong here
This is a preventive measure, not a diagnostic step.
✓
Use the 'show route summary' command to check the routing table size and memory usage.
Why this is correct
This command provides a high-level view of route counts and memory usage, helping to identify if the routing table is oversized.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use the 'show bgp summary' command to check the number of prefixes per peer.
Why it's wrong here
While this shows prefix counts, it does not show memory usage directly; the summary command is more appropriate for diagnosing memory issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse 'show bgp summary' (which shows prefix counts per peer) with 'show route summary' (which shows total routing table size and memory usage), and incorrectly assume that checking prefix counts alone is sufficient to diagnose memory exhaustion.
Trap categories for this question
Command / output trap
While this shows prefix counts, it does not show memory usage directly; the summary command is more appropriate for diagnosing memory issues.
Detailed technical explanation
How to think about this question
The 'show route summary' command displays the total number of active routes, the number of routes per protocol (including BGP), and the memory consumed by the routing table (e.g., 'Memory: 1234567K'). In Junos, the routing table is stored in the Routing Engine's memory, and the rpd process manages BGP routes; excessive routes can cause rpd to consume large amounts of memory, leading to high CPU utilization as the process struggles to handle updates. This command is non-disruptive and provides a clear picture of whether the routing table size is the issue, allowing the engineer to then identify the offending peer using 'show bgp summary' or 'show route protocol bgp'.
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 practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Junos OS Fundamentals — This question tests Junos OS Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use the 'show route summary' command to check the routing table size and memory usage. — Option C is correct because the 'show route summary' command provides a high-level overview of the routing table size, including the total number of routes and the memory utilization of the routing table. This allows the engineer to quickly assess whether the routing table has grown beyond available memory without disrupting production traffic, which is the primary goal of the diagnosis.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks 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 JNCIA-JUNOS exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.