Which statement is correct about graceful Routing Engine switchover (GRES)?

Which statement is correct about graceful Routing Engine switchover (GRES)?
A . The PFE restarts and the kernel and interface information is lost.
B . GRES has a helper mode and a restarting mode.
C . When combined with NSR, routing is preserved and the new master RE does not restart rpd.
D . With no other high availability features enabled, routing is preserved and the new master RE does not restart rpd.

View Answer

Answer: C

Explanation:

The Graceful Routing Engine Switchover (GRES) feature in Junos OS enables a router with redundant Routing Engines to continue forwarding packets, even if one Routing Engine fails1. GRES preserves interface and kernel information, ensuring that traffic is not interrupted1. However, GRES does not preserve the control plane1.

To preserve routing during a switchover, GRES must be combined with either Graceful Restart protocol extensions or Nonstop Active Routing (NSR)1. When GRES is combined with NSR, nearly 75 percent of line rate worth of traffic per Packet Forwarding Engine remains uninterrupted during GRES1. Any updates to the primary Routing Engine are replicated to the backup Routing Engine as soon as they occur1.

Therefore, when GRES is combined with NSR, routing is preserved and the new master RE does not restart rpd1.