Hi Amr_Ali  ,

To Add LTMs to the GTMs you have to follow the following process:

Have you created the LTMs server objects in F5 GTMs.

First run this on LTMs and GTMs to get the internal and external Self IP, you have to use the local self IP of both the LTMs ,

list net self one-line

Use this link to go thrugh all the necessary details for adding LTMs to GTMs:

K43300744: Adding BIG-IP LTM to a network with BIG-IP DNS (13.x - 17.x)

https://my.f5.com/manage/s/article/K43300744

Without regards to the fact that they are combined into an Active/Standby HA Pair ... can you define the two separately, each one with its own non-floating self-IP ... then define the two of them as a Prober Pool -- choosing to load balance between the two LTMs via the Global Availability load balancing method.

Use Iquery for validation:

show gtm iquery EXT_Self_IP_of_LTM1

show gtm iquery EXT_Self_IP_of_LTM2

you have to add the LTMs in GTMs using bigip_add