JNCIS-SP: Juniper Networks Certified Specialist – Service Provider Routing — Question 57

Which statement correctly describes unified in-service software upgrades (ISSU)?

Answer options

• A. Unified ISSU is built upon graceful-restart extensions to allow upgrades with no impact to the data plane.
• B. Unified ISSU is supported on systems with single or dual Routing Engines.
• C. Unified ISSU permits both upgrades and downgrades with no control plane disruption and is based on the graceful Routing Engine switchover (GRES) feature.
• D. Unified ISSU is based on nonstop-routing (NSR) and graceful Routing Engine switchover (GRES), and permits software upgrades only.

Correct answer: D

Explanation

The correct answer is D because unified ISSU indeed allows software upgrades based on nonstop-routing (NSR) and graceful Routing Engine switchover (GRES). Options A and B provide partial insights but do not fully capture the nature of unified ISSU. Option C incorrectly states that ISSU also allows downgrades, which is not true.