JNCIS-ENT High Availability Practice Question
When planning an In-Service Software Upgrade (ISSU) on a Juniper routing platform, what is the behavior of the Routing Engines during the execution of the upgrade command?
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 backup Routing Engine is upgraded, a graceful switchover takes place, and then the newly elected backup Routing Engine is upgraded.
During ISSU, the backup RE is upgraded first, then a switchover occurs, and then the former primary RE is upgraded, maintaining control plane availability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Both Routing Engines are rebooted simultaneously, relying entirely on OSPF Graceful Restart helper mode.
Why it's wrong here
Rebooting both REs simultaneously would cause a total control plane outage; ISSU specifically avoids this.
- ✗
The forwarding plane is restarted first, followed by a simultaneous upgrade of the dual REs.
Why it's wrong here
The forwarding plane remains operational throughout an ISSU.
- ✗
The primary Routing Engine is wiped and reloaded while data traffic is redirected through the console port.
Why it's wrong here
Console ports are management interfaces and cannot carry production data traffic.
- ✓
The backup Routing Engine is upgraded, a graceful switchover takes place, and then the newly elected backup Routing Engine is upgraded.
Why this is correct
ISSU upgrades the backup RE, performs a GRES switchover, and then upgrades the second RE, all while data forwarding continues.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Juniper Networks exam blueprint
This JNCIS-ENT 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 JNCIS-ENT exam.