Upgrading and Replacing aged GTMs in multiple data centers

It is going to be a challenge for you to do this without knowing DNS protocol, and only with LTM knowledge. As GTM functions totally different than LTM.

The zone transfer is done automatically by the GTMs, as long as you have the checkbox to synchronize the DNS zone files. In v13 the option is:

DNS > Settings > GSLB > General

GTM itself is always standalone but can be in a sync group with other GTMs. However, they are all standalone and active.

If a new GTM, configure the base config, create the GTM server object in the existing GTM to represent this new GTM, do a gtm_add after. Very import, gtm_add from the new GTM to point to the OLD GTM.

If you are replacing a GTM with the same IPs, configure the base config, do a gtm_add after. Very import, gtm_add from the new GTM to point to the OLD GTM. Don't forget to configure the replacement GTM out of the network, and then shutdown the old one and connect the new one.

I hope this gives you some ideas. Better you try this in a lab environment before.

gtm_add solution:

https://support.f5.com/csp/article/K13312