Primary or secondary Nexus switch

 If we have a Primary or secondary Nexus switch, which switches do we need to start the first iOS upgrade or reload?

In a network with a Primary and Secondary Nexus switch (typically part of a redundant setup like a VPC - Virtual Port Channel or Stack), the general approach to performing an iOS upgrade or reload involves the following steps:
1. Reloading or Upgrading the Primary Switch First:
Reason:
The Primary switch handles the control plane and usually the management plane for the system. Reloading or upgrading the Primary Switch first ensures that the configuration and management functions remain intact as you perform the upgrade or reload on the Secondary.
It minimizes the risk of losing connectivity or disrupting the overall system's stability because the Primary Switch will maintain its role as the main controller during the process.
2. Steps to Follow:
Step 1: Perform the IOS Upgrade or Reload on the Primary Switch
Upgrade or reload the Primary switch first. This step ensures that the main system continues to function with minimal disruption. If it's a non-disruptive upgrade (like a non-disruptive in-service software upgrade), the upgrade can be done with minimal service impact, but you still want to prioritize the Primary for any major updates.
Step 2: Verify Stability and Functionality of the Primary Switch
After upgrading or reloading the Primary switch, make sure it comes up correctly, and its configuration is intact.
Step 3: Perform the IOS Upgrade or Reload on the Secondary Switch
Once the Primary switch is successfully upgraded/reloaded, perform the same process on the Secondary Switch. This ensures that both switches run on the same software version for consistency and stability.
Step 4: Verify Both Switches
After the reload/upgrade process on both switches, verify the system to ensure that both the Primary and Secondary switches are functioning correctly, and all interfaces are up and connected.
3. Important Considerations:
Redundancy and High Availability:
If you're running a setup with high availability (such as VPC), make sure that the Secondary switch will still be able to take over in the event of failure during the upgrade process, so the network remains functional.
Software Compatibility:
Before upgrading, ensure that both the Primary and Secondary switches are running compatible versions of IOS to avoid issues related to feature mismatches.
Backup Configuration:
Always back up your configuration before starting the upgrade or reload process, so you can easily restore it if something goes wrong.
4. Non-Disruptive Upgrade
If you have a Cisco Nexus with support for ISSU (In-Service Software Upgrade) or a similar non-disruptive upgrade method, you can perform the upgrade with minimal impact on traffic. However, it's still best practice to upgrade the Primary switch first.
Summary:
Start with the Primary Nexus Switch for either an IOS upgrade or reload.
After the Primary is verified, proceed with the Secondary switch.