Even more basic, ONTAP uses a broadcast domain (not to be confused with subnetting, by the same name) to segment storage spaces. For example if you have two clients who you sell storage for, they could both have the same IP 10.1.2.3 for storage, but one client could be on e0a, one client on e1a. That's separated by a broadcast domain.
Your ports must be in the same broadcast domain space to be able to assign LIFs to.