It's time for our company to upgrade our Core switches (2x 6509 Sup720 in VSS).

My question is if we should care about choosing a IOS image which has the certification "Safe Harbor" or not since the newest IOS image for Sup720 with "Safe Harbor" is from 15-MAR-2014 (12.2.33-SXI13), which is quite old.

We are currently running 12.2.33-SXI7 which is rather old now.

What are your experiences with IOS stability when not choosing a "Safe Harbor" certified IOS for a VSS configuration?

We would prefer to jump right into the newest one available: 15.1.2-SY6, do anyone have any good or bad experience with this version in a VSS config that they could share?

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    Jan 5, 2021 at 19:43

1 Answer 1


You should never want to update to the latest version just because it is the latest version. In business networks, stability is paramount. The reason for going with a newer version is that it has one or more features which you need which you can't get on the older, more stable version. You need to weigh the the required feature(s) with the possibility of needing to back out of the newer version.

This is why so many companies have labs to thoroughly test something like this. Also, you should ask Cisco for a bug scrub of any new IOS version which you are interested in. There are many time we have looked at newer IOS versions because Cisco added something we want to use, but based on the bug scrub or lab testing, we have decided to wait because there is a bug in the code which causes something we already need to not function properly. Cisco may also have workarounds for such bugs.

Also, a lot of 6500 parts are EoS/EoL. You may want to investigate waiting until you can replace the equipment with newer equipment (e.g., 4500 switches).

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