What is preserved by enabling graceful Routing Engine switchover (GRES)?

Enabling graceful Routing Engine switchover (GRES) is designed to maintain various states and information during a routing engine failure or upgrade. The primary aspect preserved by GRES is the interface and kernel information. This preservation is crucial because it allows the device to maintain its operational status without interruption. When GRES is implemented, it ensures that the routing platform can quickly transition from one routing engine to another while keeping the necessary interface configurations, configurations associated with the kernel, and other processed packets intact, thus minimizing downtime and maintaining network stability.

While control-plane state, link-state protocol adjacencies, and BGP peering relationships are important features, GRES's main focus is on preserving interface and kernel information to enable a seamless transition. This capability is particularly valuable in ensuring continuous operation of network services without the interruption that might otherwise occur during a failover event.