JNCIS-ENT High Availability Practice Question
An engineer is preparing to perform an In-Service Software Upgrade (ISSU) on a pair of dual-RE MX240 routers. Which condition must be met to ensure the ISSU succeeds without dropping traffic?
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
✓
Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.
ISSU requires specific hardware compatibility (matching RE models, line card types), GRES and NSR configured and operating, and a supported Junos image path.
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 backup Routing Engine must be physically removed from the chassis during the upgrade.
Why it's wrong here
Removing the backup RE would break redundancy and abort the ISSU process.
- ✗
All physical interfaces must be manually disabled prior to issuing the request system software in-service command.
Why it's wrong here
Disabling physical interfaces would cause an outage, contradicting the purpose of ISSU.
- ✓
Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.
Why this is correct
ISSU relies heavily on GRES and NSR to maintain routing states across the routing engine reboot during the upgrade process.
- ✗
All routing protocols must be migrated from OSPF to IS-IS before starting ISSU.
Why it's wrong here
Protocol choice does not dictate ISSU eligibility as long as graceful restart / NSR is supported.
About these practice questions
This JNCIS-ENT question is part of Courseiva's 519-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.