Junos High Availability Design Guide
High availability is one of the important consideration during network design and deployment stage and all most all the network vendors support various high availability features.
The objective of this article is to describe Junos best practices required to achieve minimum downtime in case of fail-over scenarios.
The Routing Engine or Control Plan is the brain in Junos based devices to run and execute all the management functions. Most of the Junos based devices offers redundant routing engines (either through default configuration or through explicit configuration virtual chassis ). At one time only one Routing engine can be active (exception of Active-Active MC-LAG which is beyond the scope of this blog). The mere presence of 2nd routing engine in the Junos device will not add any advantage with respect to high availability until certain features are not configured.
- Grace-full Routing Engine Switch Over (GRES). GRES enables synchronization of kernel and chassis demon between mater routing engine and backup routing engines and in case of failure of master routing Packet Forwarding Engine (PFE) will simply join to new master routing engine (which was backup routing before fail-over).


GRES can be configured by following configuration command:-
set chassis redundancy graceful-switchover
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Packet competes with the likes of AWS and Azure.
Another step toward infrastructure-as-code.