Not getting an error if static IP i gave was not allocated to device

[arihantdaga]

I am making a low power sensor device and connecting to the internet quickly is a must for the device. I am using static IP config to speed up the connection, (it helps by reducing 2 seconds in my case). I plan to deploy multiple devices with different routers. I am doing it this way, on first connection the device would connect using dhcp and then store the IP, Gateway, subnet etc in non volatile storage. On subsequent connection, it can use this saved data.
However if the device is waking up later, that IP may be allocated to another device and device would not get this IP.
But on esp side, i am not able to detect this failure of allocation of IP, instead i get connection successful, but later the device does not connect with router. Is there any method/way to check whether we have an issue with IP address, so that we can retry using DHCP.

My sketch -
https://gist.github.com/arihantdaga/68b78139ed403a6082c178898a3d6209

I expected that if i give an IP out of the range of subnet it would throw error in connection. But it's not.

Is there any way to detect this ?

[JAndrassy]

this is how TCP/IP network works.
use DHCP or use IPs outside of the DHCP range. don't mix it
on some routers you can reserve the DHCP assigned address for a specific MAC address

[arihantdaga]

Hmm. I was just wondering. Since sometimes in laptop, we get a conflicting IP address error. Is it possible to get the same sort of error in esp as well ?