Each ExtremeXOS image comes bundled with an I/O module image and contains a unique upgrade compatibility version number, known as the I/O version number.
This number determines the relationship between the I/O module image and the ExtremeXOS image and their support for hitless upgrade. The I/O version number contains build information for each version of ExtremeXOS, including the major and minor version numbers, and the I/O version number.
Extreme Networks generates the I/O version number, and this number increases over time. Any modifications to the I/O module image after a major software release changes the I/O version number. For example, if Extreme Networks delivers a patch or service release that modifies the I/O module image, the I/O version number increases.
When you initiate a hitless upgrade by using the run msm-failover {force} command on the backup MSM, it checks the I/O version number to determine if a hitless upgrade is possible.
Depending on the currently running software, the switch performs, allows, or denies a hitless upgrade. The following describes the switch behavior:
To prevent a loss in functionality, schedule time to take the switch offline to perform the upgrade; do not upgrade the software using hitless upgrade.
The switch warns you that the upgrade may not be hitless. You can either continue the upgrade or cancel the action. If you continue the upgrade, the primary MSM downloads the new image to the I/O module and reboots.
The following is a sample of the warning message displayed by the switch:
WARNING: Failover will not be hitless due to incompatible images. Traffic will be interrupted. Are you sure you want to failover? (y/n)
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