User identification by IP + Port?

Question

Computer networks

Hello everyone

There is some protocol over UDP (encryption is also used).
Connections are identified by IP + Port.
Protection against IP + Port Spoofing consists in checking the packet's mac(message authentication code) using the hmac key associated with the packet's current IP + Port.

Problem: Since users may be mobile clients, their IP may change as they move. So identification by IP + Port is not suitable.
There is an idea instead of a bunch of port and ip to identify the user by UUID.
What are the downsides to this approach? (except that the packet size will grow by 16 bytes)
Well, or maybe this problem can be solved somehow differently, without UUID?