I need to migrate F5 8900 to i7800, IOS is different as well interfaces are different. I have already tried with UCS file and bypassed platform and licence but still got error. please help to get shorter way to copy all config from existing device to new device.
This is a loaded question and the easy answer would be it depends :)
Here's a good reference for the activity your are trying to achieve, different options exists so you can pick the one that's best for your environment.
Migration to iSeries
Hope this helps