Hi Deepu While GTMs are different versions, you cannot sync them. Which is fine, but you'll need to either freeze DNS updates for the duration of your overall maintenance window (getting both sets of Viprion guests upgraded), OR you'll need to make updates to each GTM since they are not synced. Just make sure to designate one or the other of each your internal/external to be the source of truth in your upgrade plan, and add the other back into sync. Specific steps around the GTM sync process are here in this very thorough MyF5 knowledge article. Hope this helps!