Junos OS Upgrade on EX4200 Virtual Chassis We have couple of EX4200s switches in Virtual Chassis mode running in the network. Each Virtual chassis has only 2 member switches. We are required to upgrade the Junos OS on each member switch in the virtual chassis. There are two approaches to perform Junos OS upgrade. 1) Perform the Junos OS upgrade on all members of the virtual chassis at the same time. This will be bring complete outage for period of time till all member switches come back after reboot. 2) Perform Junos OS upgrade on each member switch individually instead of whole virtual chassis. This however will avoid complete service outage. Which option is considered to be the best practice / recommended approach that has a high probability of success and less prone to instabilities / abnormal behavior post upgrade situation. If some one could help on this , would highly appreciate that. Many Thanks.

As per discussion on various forums and with Juniper networks , recommendation will be upgrading the whole virtual chassis as it has less probabilities to fail and it is simpler. The process should take around 10-15mins.

Doing it one by one will take longer, and it has more chances to fail when the units are split. Please keep in mind that while they are split only one of them will be forwarding traffic.