> Also, how does a device keep an address when it switches between cellular data and WiFi? How does IPv6 make this and similar issues go away? It doesn't (unl

> Also, how does a device keep an address when it switches between cellular data and WiFi? How does IPv6 make this and similar issues go away? It doesn't (unless people use Mobile IPv6, which seems unlikely). However, changing IP address is a small potato problem compared to the problems caused by keepalives and NATs. A device will know when its IPv6 address changes and can re-initiate its TCP connections. Right now, a device doesn't know when a NAT/stateful firewall has timed out one of its connections or decided to start NAT'ing to a new public IP address, which is why constant battery-draining keepalives are needed.