Hello John,
Are you migrating from VE to i4000s or from appliance to appliance ?
If you are migrating from physical to physical, follow these steps :
1) Generate an archive file (.ucs) of your old devices in version 11.6
2) Prepare the i4000s appliance:
- Install the same version as your old devices 11.6 + same HF
- Provision the same module LTM & ASM
3) Upload the ucs file created in step 1 to the i4000s appliance
4) Then execute the following command
tmsh load sys ucs "ucs-file-name" no-platform-check no-license
5) Once you have verified that all your configuration is correctly restored on new appliances proceed to the upgrade to 12.1.2
You can follow the following article before upgrading to 12.1.2
https://devcentral.f5.com/codeshare/7-steps-checklist-before-upgrading-your-big-ip-1053
Hope it helps