Netgear XCM8806 - 8800 SERIES 6-SLOT CHASSIS SWITCH ユーザーズマニュアル

If you download an image to the backup MSM, the image passes 

through the primary MSM before the image is downloaded to the 
backup MSM.

This section describes the following topics:

•     Understanding the I/O Version Number 

•     Performing a Hitless Upgrade 

•     Hitless Upgrade Examples 

Understanding the I/O Version Number

Each XCM8800 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 XCM8800 image and 
their support for hitless upgrade. The I/O version number contains build information for each 
version of XCM8800, including the major and minor version numbers, and the I/O version 
number. 

NETGEAR 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 NETGEAR 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:

If the new XCM8800 image supports hitless upgrade and is compatible with the current 

running I/O module image, you can perform a hitless upgrade.

If the new XCM8800 image supports hitless upgrade, is compatible with the current 

running I/O image but with a degradation of functionality, you can perform a hitless 
upgrade with caveats. The switch warns you that the upgrade is hitless; however, the 
downloaded software may result in a loss of new functionality. You can either continue the 
upgrade with the modified functionality or cancel the action.

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. 

If the new XCM8800 image supports hitless upgrade but is not compatible with the 

current running I/O module image (the I/O version numbers do not match), you cannot 
perform a 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.