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Rolling Stack Upgrade (RSU) with 3750X (IOS 15.0.1-SE3)

Level 1
Level 1


We have some issues with the RSU functionality.

We made a quick draw of our network to explain what we are trying to do. It’s attached to this discussion.

Switch 2 has an interface configured in RSU Standby.

Switch 3 has an interface configured in RSU active.

The upgrading sequence is : Switch 2, Switch 1, Switch3.

The aim of the test is to prove that there is no loss of IP connectivity throught the RSU process.

During the RSU process, there are ping between all the computers.

IOS starting version : 15.0-1.SE3

IOS upgrading version (with OVERWRITE) : 15.0-1.SE3 (same version)

1rst step : Switch 2 reboot and come back master but isolated from original stack (switch 1 and 3)

2nd step : Switch 1 reboot, and come back with switch 2 into the upgrading stack.

Issue : at this step :

-  Switch 1 put its interface (IP up :

Switch 3 has not reboot and still has its interface (IP up

=> we have some OSPF adjencies and mac flapping issues : switch 1 and 3 are trying to mount there OSPF adjencies on the same IP. We loss our IP connectivity since step 3 is not over.

3rd step : Switch 3 reboot and come back up in the upgrading stack. The IP connectivity is back, and the RSU process is done.

Is that a normal behaviour ?

How can we avoid to loose IP connectivity during RSU process ?

Best regards,

2 Replies 2

Level 1
Level 1


I think this behavior is expected.  There would be a minimun downtime when using RSU.  This has been designed to have the minimum of network disruption as possible but that network disruption will be always shown.

"hosts with connectivity (either wireless or wired)  to two different switches in the same stack would experience minimal  traffic loss when switching from one uplink path to the redundant one  while the rolling upgrade is being performed."

I hope that helps.

Level 1
Level 1

I decided to document the steps as I couldn't find the exact process on the interwebs.  It's posted on my blog @

Hope this helps.


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